Non-tolerances and the science of prescribing spectacles

Optometry in Practice 2015 Volume 16 Issue 4 131 144 Non-tolerances and the science of prescribing spectacles David B Elliott 1 PhD MCOptom FAAO and Christopher Howell-Duffy 2 BSc(Hons) MSc PhD MCOptom 1 Bradford School of Optometry and Vision Science, University of Bradford, West Yorkshire 2 Faculty of Life Sciences, University of Manchester EV-30782 C-43096 1 CET point for UK optometrists Abstract This review paper summarises the scientific evidence that supports partial prescribing of spectacles. This is the prescribing of a refractive correction that differs from the subjective refraction and typically involves prescribing a correction that is in between the subjective refraction result and the refractive correction in the patient s habitually worn spectacles. It is commonly used by very experienced clinicians, but not by those newly qualified. Partial prescribing is likely to reduce cases of patient dissatisfaction with spectacles (non-tolerance cases or non-tols ) and reduce the risk of inducing both dizziness and falls in frail, older patients. The review includes a discussion of the validity and variability of subjective refraction, the degree of tolerance to small changes from the subjective refraction and causes of spectacle adaptation difficulties in the elderly. The latter includes a brief discussion of the vestibulo-ocular reflex, which should be considered when making large changes in refractive correction. A list of 11 prescribing guidelines is provided for inexperienced clinicians: (1) Check the prescription I: over the patient s spectacles; (2) Check the prescription II: outside the exam room; (3) If it ain t broke, don t fix it; (4) If it ain t broke, don t fix it (distance-specific); (5) If it ain t broke, don t fix it much; (6) Be careful when reducing the minus power in a happy myope; (7) Cut the plus ; (8) Prescribe conservatively in older patients (0.75D or less); (9) Partial prescribing for astigmatic change; (10) Be careful when making large power changes in the near prescription; (11) Warn the patient of potential adaptation problems. Art or science? Walsh (2009) suggested that although many practitioners may wish it to be a science, prescribing spectacles is essentially an art. In this context, art is assumed to mean clinical experiential wisdom and an attempt can be made to summarise this in scientific form. Note that evidence-based practice means integrating the best available clinical research evidence with individual clinical expertise (Greenhalgh 2006). Here we provide a summary of the science (both experiential and from research reports) behind determining the appropriate refractive correction to provide to a patient. This will include a review of when things go wrong (non-tolerance cases or non-tols ), the validity and variability of subjective refraction, the degree of tolerance to small changes from the subjective refraction, clinical guidelines for prescribing based on limitations of subjective refraction, the possible causes of difficulties adapting to new spectacles and, finally, clinical guidelines for prescribing. As some of this discussion involves describing things learned by clinical experiential wisdom (Howell-Duffy et al. 2011), please be aware that some of this discussion will be like teaching grandmother to suck eggs to the more experienced clinician. Non-tols : do they matter? Spectacle non-tolerance has tended to be used by optometrists and dispensing opticians to describe spectacle problems that could not be rectified by addressing dispensing difficulties or errors. Freeman and Evans (2010) reported an average spectacle non-tolerance rate in a community optometric practice in England of 1.8% (59 of 3091 eye examinations, range for seven optometrists of 1.3 3.0%), and Hrynchak (2006) reported a 1.6% prevalence from a Canadian university teaching clinic. Other reported prevalence data from ophthalmology clinic studies include 2.8% of 432 patients (Mwanza and Kabasele 1998), 2.3% of 5467 patients (Riffenburgh et al. 1983) and 6% of 2000 patients (Milder 1962). A survey by a US optical laboratory reported by Sims (1982) found that 5% of 6000 prescriptions were doctor remakes. However, details of the methodology in the latter papers were limited. These data suggest non-tolerance prevalence rates in the range of 1.0 3.0%. Using an average figure of 2% would suggest that about 290 000 patients each year in the UK (based on an estimate of 14.5 million dispensings in the UK in 2012 1 ) return to a practice dissatisfied with their spectacles due to refraction 1 21.6 million is the approximate number of eye examinations in 2012: http://www.aop.org.uk/uploads/regulatory/gos/optics_at_a_glance_2012.pdf. If 67% is a typical dispensing rate, this suggests an estimated 14.5 million dispensings in the UK in 2012. Date of acceptance: 9 September 2015. Address for correspondence: Dr DB Elliott, Bradford School of Optometry and Vision Science, University of Bradford, Bradford, West Yorkshire BD71DP, UK. d.elliott1@bradford.ac.uk 2015 The College of Optometrists 131

D B Elliott and C Howell-Duffy errors or adaptation problems. In addition, the figures above are highly likely to underestimate the prevalence of patients dissatisfied with their spectacles, as some patients may simply revert to their habitual spectacles or alternatively seek remediation with a different clinician. Non-tols not only reduce practitioner productivity by taking up an additional eye examination appointment and incur associated reglazing costs, but they can also tarnish a practitioner s professional reputation (Cockburn 1987; Gordon and Amos 1987). Conventional marketing research would suggest that generating such consumer negative word-of-mouth opinion exhibits a much more powerful impact than positive word-of-mouth communication (Arndt 1967) and dissatisfied customers are likely to tell at least twice as many people as satisfied customers and also tell their story to at least nine other people (Buttle 1998). Thus, spectacle dissatisfaction appears to be a significant problem in terms of both reduced practitioner productivity and loss of patient goodwill. How to deal with non-tolerance cases There are many possible potential reasons to explain why patients may be unhappy with their new spectacles, and these are summarised in Table 1. When patients return to report problems with their new spectacles, a full history is required and should include the onset, frequency, severity and duration of symptoms and whether these were present when wearing the habitual spectacles (Gordon and Amos 1987). As can be seen from Table 1, poor adaptation and incorrect refractive error assessment represent only a small subset of the possible reasons for spectacle dissatisfaction. Other issues which could be termed dispensing issues should not be underestimated, as Brooks and Borish (1979) suggest that the majority of complaints in clinical practice are related to the physical fit of the spectacle frame. This may be simply due to poor frame adjustment or more complex psychological issues such as the patient reporting discomfort but the underlying reason for dissatisfaction is that the patient changed his/her mind regarding the cosmetic appearance of the chosen frame. Clearly, in this latter situation no amount of frame adjustment is likely to pacify the patient. A further category of patients expressing problems with their new spectacles could be derived from lens issues. These problems stem from changes made to the lens design of the new spectacles when compared to the patient s habitual spectacles and may be relatively simple issues such as the placing of the bifocal segment. Other differences may include the positioning of optical centres, presence of an antireflective coating or changes in lens base curve or lens form (Table 1). Non-tol : a misnomer Although widely used within optometric practice, the validity of the term non-tol or spectacle non-tolerance is questionable. The label appears to be a misnomer as it attributes blame to the patient for not being able to tolerate what was by implication a perfectly correct pair of spectacles and refractive correction. Patients view things differently and believe that any problem is a failure by the optometrist (Gordon and Amos 1987). The truth is somewhere in the middle, of course, with the literature indicating that non-tols can be caused by both dispensing or prescription errors made by the clinician and by lack of adaptation to a correct prescription by the patient (Cockburn 1987; Freeman and Evans 2010; Hrynchak 2006; Mwanza and Kabasele 1998). Perhaps a more appropriate term than Table 1. Potential causes of patient dissatisfaction with new spectacles Refractive correction Lens Frame Other issues Refraction error Poor cosmesis (eg thick edges, power rings, poor coatings or tints) Improper fit or adjustment Financial Error in determining near working distance(s) Poor-quality lenses (eg pits, chips, scratches, distortions) Improper alignment: Pantoscopic tilt Vertex distance Patient not properly educated: How to use spectacles When to use spectacles Adaptation issues Adaptation problems (too big a change in correction, especially for elderly patients) Poor glazing (eg lens loose, gaps between lens and frame) Laboratory error Variable refraction: Contact lens-induced Systemic disease (eg diabetes) Ocular disease (eg cataract, macular oedema) Induced prismatic effects: Horizontal and/or vertical Induced magnification effects: Base curve Centre thickness Vertex distance Cylinder form Segment type and position Reflections Lens materials or weight Inappropriate frame selected: Poor fit Poor cosmesis Excessive size or weight Psychosocial: Concerns regarding appearance Concerns regarding convenience Adapted from Gordon and Amos (1987). 132

Non-tolerances and the science of prescribing spectacles non-tolerance for any patient who is unhappy with new spectacles is spectacle dissatisfaction. Subjective refraction: the gold standard The misnomer of the non-tol suggests we have great faith in the subjective refraction result. Similarly, in the research setting, the subjective refraction result is taken as the gold standard when assessing other forms of refraction, such as retinoscopy and autorefraction. The suggestion is that, if retinoscopy and autorefraction are not the same as the subjective refraction, they must be incorrect. Gold standards can become almost unquestionable (other examples of gold standards include Goldmann applanation tonometry and a consultant ophthalmologist s diagnosis of glaucoma. These may be the best available assessment, but are similarly by no means perfect). The use of subjective refraction as a gold-standard assessment of refractive error has meant that there has been little or no comparison of the various methods used in subjective refraction. Previous studies have tended to compare the various tests against each other. For example, West and Somers (1984) compared the various binocular balancing tests and found that they all gave similar results and concluded that they were therefore all equally useful. Johnson and colleagues (1996) reported a similar finding when comparing subjective tests for astigmatism. These are not surprising findings and are limited by an unhelpful study design. Is the faith in subjective refraction justified? A very good but underutilised approach to assess the validity of subjective refraction is to use some measure of patient satisfaction as the gold standard. In a double-masked, randomised, cross-over design study, 195 patients wore two spectacle prescriptions (determined by subjective refraction or autorefractor) for at least 3 weeks (Bullimore 2000). A majority (115, 59%) of patients considered both pairs acceptable, 43 (22%) accepted the optometrist s prescription only, 21 (11%) accepted the autorefractor prescription only and the remaining 16 (8%) rejected both pairs. The subjective refraction result was acceptable in 81% of cases and was certainly preferred, but was far from perfect. A similar result was found by Strang and colleagues (1998). The repeatability of subjective refraction is also imperfect. Although the repeatability for an individual clinician is often within 0.25D (80% of cases), it can vary by ±0.50D in 15% of cases (Goss and Grosvenor 1996) and variation between clinicians can vary by ±0.75D (MacKenzie 2008; Shah et al. 2009). It is also likely that patients with poor visual acuity will exhibit even greater refractive variability due to greater tolerance of defocus (Leinonen et al. 2006). This variability is not surprising given the subjective nature of the task and the difficulty (and worry) that many patients associate with it (eg Shickle et al. 2014). Are spectacle dissatisfaction cases inevitable? The refractive correction determined in recheck examinations is within 0.50D of the initial (unsatisfactory) correction in 84% of cases (Freeman and Evans 2010). In addition, patients can experience symptoms such as mild headache, distortion or depth perception problems when the spectacle prescription is asymmetrically ±0.25DS in error (Atchison et al. 2001), and a binocular +0.25DS addition can make spectacles unacceptable to a substantial number of patients (Miller et al. 1997). The complexity of the issue is further compounded by both the personality traits and demographic status of the patient. Anecdotally, many optometrists would be wary of the archetypal physics lecturer who is intelligent, fastidious with detail (Constantine-Smith 2002) and this clinical wisdom has been supported by research evidence, as Woods and colleagues (2010) have shown an association between blur tolerance and personality type. Comparing these findings with the repeatability of subjective refraction results discussed earlier suggests that some low level of spectacle dissatisfaction may be inevitable. The question is whether there are any evidence-based clinical guidelines or clinical pearls (of wisdom) that can be used to keep spectacle dissatisfaction to a minimum. Do you have to prescribe the subjective refraction result? In the majority of cases, newly qualified optometrists in particular prescribe the subjective refraction result (Howell-Duffy et al. 2011). However this may not always be appropriate. First and foremost, the subjective refraction may be incorrect and this should be considered. Does it make sense in terms of changes in visual acuity from the habitual correction? As the typical astigmatic changes with age occur slowly (Leung et al. 2012), many changes in refractive correction are mainly spherical. Consider the example from a 23-year-old patient in Table 2. Table 2. Subjective refraction results and the visual acuity (VA) obtained should always be compared to the patient s spectacle correction and VA to ensure any differences make sense. In the examples in the table, refraction 1 is likely over-minused, refraction 2 seems incorrect and needs rechecking and, although refraction 3 may be accurate, it still might not be the most appropriate correction to prescribe Habitual Rx 3.00 / 1.00 175 2.75 / 0.50 10 Subjective refraction 1 3.50 / 1.00 180 3.25 / 0.50 10 Subjective refraction 2 3.00 / 1.00 20 3.00 DS Subjective refraction 3 2.75 / 1.00 180 2.50 / 0.50 5 6/4 6/4 6/4 6/4 6/4-2 6/4-3 6/4 6/4 133

D B Elliott and C Howell-Duffy The patient reports no problems with his current spectacles, is very happy with his distance and near vision and has visual acuity that is normal for age (Elliott et al. 1995) in both eyes. Refraction 1 includes a minor change in the cylindrical correction in the right eye, but has 0.50DS extra in both eyes. Despite this, there is no increase in visual acuity (assuming this was possible on the chart used) and this suggests that the subjective refraction result has been over-minused and is incorrect. Refraction 2 has some small changes in the cylindrical corrections in both eyes. As the visual acuities are worse with the subjective refraction result than with the spectacles, this suggests that they are incorrect (assuming that true visual acuity thresholds were recorded by pushing the patient to read as many letters as possible). Refraction 3 shows a reduction in the myopic correction compared to the patient s current spectacles and there is no loss of visual acuity. The subjective refraction is the gold standard approach might suggest that you need to prescribe this. The patient happiness in a correction is the gold standard approach would suggest that the subjective refraction was performed at 6m (+0.17D) and not the far distance, and is a somewhat variable value so that the patient could be unhappy if you prescribed this reduced correction as he might complain of distance vision blur. Adaptation problems In addition to recognising that the subjective refraction result might not be perfect, sometimes a perfect correction cannot be tolerated by a patient as it is too large a change in prescription and the patient is unable to adapt to it. The main reason for difficulties in adapting to new spectacles is probably changes in magnification, which can be attributed to altering spectacle lens form and/or spectacle type (eg varifocals) as well as changes in prescription. Magnification differences cause changes to the appearance of objects, which can become distorted or appear larger or smaller, closer or further away. They can also affect the vestibuloocular reflex (VOR) gain, which is described below. The small magnification changes associated with 1.00D or more of myopic or hyperopic shift may seem trivial, but are not when considered against the accuracy required for some fine motor skills such as pouring hot water from a kettle into a cup or ascending or descending stairs. Negotiating stairs uses a large amount of energy (Hamel et al. 2005; Startzell et al. 2000) and foot clearance is reduced as stairs are ascended or descended to conserve energy. This means that some foot clearances can be very small and a matter of a mere few millimetres (Hamel et al. 2005; Startzell et al. 2000), such that slight magnification changes can make a difference. Myopic shifts cause stairs to look smaller and further away and reduce foot clearance, while hyperopic shifts cause stairs to look bigger and closer so that subjects can land just on the edge of the step (Elliott and Chapman 2010). Astigmatic magnification, particularly when oblique (Johnson et al. 2013), modifies the perceived shape of objects, including stairs, so that they are even more difficult to negotiate until patients have adapted to the change. The effect of altered stereoacuity due to different magnification changes (including astigmatic ones) in the two eyes (Adams et al. 2001) is unknown, but would seem to offer large potential for accidents in older patients. The vestibulo-ocular reflex (VOR) The VOR connects the inner ear (the semicircular canals and the otolith organs, which determine the head s position and movement) to the eye s extraocular muscles and ensures that any changes in head position are linked with changes in eye movement in the opposite direction of the same size and speed (Figure 1). Without this reflex, the visual world would move when the head is moved. However, new spectacles change magnification and alter the amount of eye movement gain that is needed to match head movement: myopes tend to have lower VOR gains and hyperopes higher VOR gains (Cannon et al. 1985). For example, a myopic shift in prescription minifies the visual world so that a head movement of, say, 20 leads to a much larger eye movement than is now needed (the patient should use a lower VOR gain) and the visual world will move or, as described by patients, it will swim. The adaptation with astigmatic changes is complicated further as different amounts of magnification occur in different meridians. Other changes to the lens type can also require VOR adaptation and these include variation of base curves, lens thickness and frame/lens shape. Similarly, adaptation to progressive addition lenses is complicated by variation in magnification across the lens requiring variable VOR gain across the visual field (Michaelides and Schutt 2014). Large changes in both spherical and astigmatic refractive correction together with a modification of progressive addition lens type (even if this was a new and improved lens) would represent the greatest of adaptation challenges for an elderly patient. Figure 1. The vestibulo-ocular reflex that links the semicircular canals and otolith organs of the inner ear to the extraocular eye muscles (from https://commons. wikimedia.org/wiki/main_page). 134

Non-tolerances and the science of prescribing spectacles Surely patients can adapt to new spectacles easily enough? Younger patients may well be able to adapt quickly and easily to new spectacle prescriptions and may also be able to avoid accidents or falls due to quick reactions to trips, for example. However, older patients seem to have greater difficulties adapting to spectacles if the amount of refractive correction or the change in correction is relatively large. For example, Fylan and Grunfeld (2005) reported that nearly a half (49%) of 158 presbyopic patients were concerned about whether they would adapt to their new spectacles. This appears to be worse with elderly patients and with larger prescriptions. Häkinnen (1984) reported the spectacle-wearing habits of 600 elderly people and found that 18% could not wear their aphakic correction and one-third could not wear their moderately powered spectacles when travelling and over a third blamed adaptation difficulties. Elderly patients with mobility problems and dizziness were particularly reluctant to wear glasses when moving about. A recent study has also shown that large changes in oblique astigmatism can cause dizziness (Supuk et al. in press). Moderate changes in refractive correction can also cause problems in elderly patients. The optometric intervention randomised controlled trial by Cumming and colleagues (2007) intended to determine whether new spectacles reduced falls. It is well known that visual impairment causes falls, so it seems reasonable to expect new spectacles to reduce falls. The authors included about 300 participants aged 70+ and living in the community in each arm of a randomised controlled trial with an intervention of an optometric examination, treatment and referral and a control group who were left to their usual care. Of the intervention group, 92 received new spectacles. Very surprisingly, falls occurred more often in the year follow-up period in the intervention group than in the control group (65% vs 50% falls rate, 758 vs 516 total falls, P < 0.001) and there was a trend towards more fractures in the intervention group (31 vs 18, P = 0.06). The most likely cause of this surprising result was poor spectacle adaptation in some of these older frail patients. The authors reported that 74% of the intervention group who had major changes in refractive correction fell, compared with 53% (at the pre-intervention and control group level of falls rate) of those who had minor changes. A major change in refraction was defined as ±0.75DS or DC, axis changes of 10 up to 0.75DC and 5 for 0.75DC+, any prism change or an introduced anisometropia of 0.75DS. Clinical guidelines for prescribing In the context of partial prescribing to facilitate spectacle adaptation and comfort and avoid spectacle dissatisfaction, many texts provide a section or chapter on when and how practitioners should make adjustments to the prescribed refractive correction (eg Ball 1982; Carlson and Kurtz 2004; Elliott 2014a; Eperjesi et al. 2007; Fletcher et al. 1998; Lee and Tahran 2007; Newman 2006; Obstfeld 1988; Polasky 1991). Furthermore, there are three textbooks that focus almost exclusively on this topic: Clinical Pearls in Refractive Care by US optometrists Werner and Press (2002), Refractive Management of Ametropia, edited by Brookman (1996), another US optometrist, and The Fine Art of Prescribing Glasses Without Making a Spectacle of Yourself by US ophthalmologists Milder and Rubin (2004). These chapters and textbooks typically provide clinical guidelines or rules (or clinical pearls, in the US literature) that are based on clinical experience. That is, clinicians examine patients dissatisfied with their spectacles, they change the spectacle correction based on the recheck examination and the new spectacles work and the patient is happy with them. At this juncture, it should be noted that the principles of partial prescribing referred to throughout this article are only intended to apply to adult patients. The prescribing of spectacles for infants and children will not be discussed further, as other factors, such as emmetropisation and the treatment or prevention of amblyopia and strabismus, predominate in the prescribing decision (Farbrother 2008). In addition, we are not covering the avoidance of binocular vision anomalies as part of prescribing, such as inducing a decompensated esophoria by too much increased minus prescription or inducing differential vertical phoria by prescribing round segment bifocals in both lenses to a patient made newly anisometropic. Although some texts suggest that the following partial prescribing guidelines should only be implemented in patients who do not adapt to the full subjective refraction result (Milder and Rubin 2004), a more pre-emptive approach would seem desirable (and/or logical?). From a pragmatic viewpoint, partial prescribing could be employed with patients who report problems such as spatial distortion or mobility issues when wearing the full prescription in the trial frame (Brookman 1996). Alternatively, significant refractive change in the older patient could be viewed by the practitioner as sufficient reason to employ a partial prescribing approach (Elliott 2014a; Fletcher et al. 1998; Werner and Press 2002). 1. Check the prescription I: over the patient s spectacles Changes in prescription can often be shown to the patient by adding appropriate trial case spherical lenses over the top of the patient s current spectacles. This provides a comparison with the current spectacles, which tends to be appreciated by the patient and is much simpler than swapping between the current spectacles and the prescription in a trial frame. Do the extra lenses improve distance or near visual acuity or not? For near vision, you should use real-world tasks (particularly any that the patient mentioned were a problem in the case history), such as mobile phones, newspapers, sewing needles, music sheets. Also show the patient what might be lost: for example, extra plus at near may improve reading at 40cm, but slightly blur vision for the computer, which is often further away. Although astigmatism normally changes with age from with the rule to against the rule (Leung et al. 2012), this change is slow and the typical change in astigmatism between eye exams is negligible compared to spherical changes of 0.50DS or more. 135

D B Elliott and C Howell-Duffy Table 3. Example of a patient whose non-tol or spectacle dissatisfaction could have been avoided with the use of the clinical guideline if it ain t broke, don t fix it Patient age Chief complaint 65 years Routine eye examination. No symptoms or visual problems Habitual correction R +2.25 / 1.75 165 Add +2.50 L +1.75 / 1.25 20 Add +2.50 Prescribed correction (ie the subjective refraction result) Recheck complaint R +2.50/ 1.50 170 Add +2.50 L +2.25/ 1.00 15 Add +2.50 Distance blur in both eyes with new spectacles Recheck correction R +2.25/ 1.75 170 Add +2.50 L +1.75/ 1.25 25 Add +2.50 Adapted from Howell-Duffy et al. (2012). VA, visual acuity. 2. Check the prescription II: outside the exam room It is good practice to check the distance prescription that you are thinking of prescribing outside the exam room. Take the patient outside the exam room and show the change in far distance vision ( down the hall or outside the window etc.) with and without the extra spherical lenses over the top of the patient s own spectacles, particularly when thinking of reducing a myopic prescription (see guideline 6). It can also be useful to ask the patient to walk about with the correction in a trial frame (Werner and Press 2002). 3. If it ain t broke, don t fix it In its various guises, this is the most common prescribing guideline pervading the literature (Brookman 1996; Constantine-Smith 2002; Elliott 2014a; Gordon and Amos 1987; Milder and Rubin 2004; Werner and Press 2002). It is also known as don t rock the boat and in medical circles as primum non nocere or above all, do no harm. The rationale underpinning this guideline is that patient happiness with a pair of spectacles is the best indicator of the validity of a refractive correction: if a patient is happy with the current refractive correction and can attain a satisfactory level of vision, any prescription changes implemented by the prescriber have the possibility of making that patient unhappy. Ideally, other parameters of the patient s spectacles should also be the same: base curves, distance between optical centres, lens material, vertex distance, segment style and height (Gordon and Amos 1987). In reviews of the non-tols or patient dissatisfaction cases from the UK (Elliott 2008) and Canada (Howell-Duffy et al. 2012), approximately 25% of cases could have been avoided by use of this clinical guideline. Some examples are given in Tables 3 and 4. In the example in Table 3, the habitual prescription provided excellent visual acuity in both eyes, yet the practitioner had prescribed the subjective refraction result and increased the power of the hyperopic correction by +0.38D mean spherical equivalent in the right and +0.63D mean spherical equivalent in the left. The patient returned after 25 days to complain of distance blur with the new spectacles. However, if the practitioner had followed the if it ain t broke, don t fix it guideline in the first instance, then it seems very unlikely that patient dissatisfaction would have occurred. 4. If it ain t broke, don t fix it (distance-specific) This is a simple variant of the guideline, in which the patient Table 4. Example of a patient whose non-tol or dissatisfaction with spectacles could have been avoided with the use of the clinical guideline if it ain t broke, don t fix it distance-specific Chief complaint Patient age 46 years. Near blur both eyes. No problems with distance vision with spectacles Habitual correction R 1.50/ 0.25 65 L 2.00/ 0.50 75 VA 6/6 Prescribed correction (the subjective refraction) Recheck complaint R 1.00/ 0.25 65 Add +1.50 L 1.75/ 1.00 90 Add +1.50 Distance blur in both eyes with new spectacles Recheck correction R 1.50/ 0.25 65 Add +1.50 L 2.00/ 0.75 90 Add +1.50 Adapted from Howell-Duffy et al. (2012). VA, visual acuity. 136

Non-tolerances and the science of prescribing spectacles does not have symptoms for distance tasks, but does have symptoms for near tasks. In this case, the near correction can typically be appropriately changed by increasing the near or reading addition, but the distance correction is not changed. Table 4 provides an example of a spectacle dissatisfaction case that could have been avoided using this guideline. It is interesting to note that the near correction (as opposed to the near addition) was also changed after the recheck examination. 5. If it ain t broke, don t fix it much A limitation of the clinical guideline if it ain t broke, don t fix it is the scenario where the patient has a real change in refractive correction (ie the subjective refraction result is correct and is different to the spectacle correction, typically by 0.50D or more, and this is appreciated during trial frame comparison), but currently no symptoms and little, if any, loss of visual acuity in the spectacles. If the guideline was pedantically followed and no change in correction prescribed, the patient could return with symptoms after 1 2 months (or even 1 2 weeks!). In this case, the guideline can be amended to: If it ain t broke, don t fix it much prescribe approximately half of any change, particularly in spherical correction. 6. Be careful when reducing the minus power in a happy myope This is a subset of the guideline if it ain t broke, don t fix it, but refers to myopic patients whose refractive correction has plateaued and is now starting to decrease. Many myopes undergo a small reduction in power (a hyperopic shift) from around age 30 until cataractous refractive changes occur or cataract surgery intervenes (eg Lee et al. 2002; Saunders 1986). These patients are used to accommodating slightly in their spectacles when looking in the distance and obtaining very clear distance vision. Remember that a maximum-plus refractive correction (eg on the red using duochrome) obtained in the exam room provides a perfect correction for 6m so that fine detail beyond 6m will appear slightly blurred, particularly when a patient is used to accommodating slightly to focus in the far distance. 7. Cut the plus Once the requirements of a subjective refraction using the push the plus or maximum plus for maximum visual acuity approach has been learned, it can be useful to reduce the plus correction prescribed if changes of 0.75DS or more are found. This is for the same reasons as previously discussed: the 1/6D blur due to the 6m chart distance and the variability in the subjective refraction result. Furthermore, a truncated visual acuity chart/measurement does not help. Many old charts have a bottom line of 6/5 and there is a general assumption that 6/6 ( 20/20 ) is normal visual acuity, yet the majority of younger patients with normal, healthy eyes have acuity better than 6/6 (Table 5). Pushing the plus to an acuity of 6/6 or even a bottom line of 6/5 will blur patients who can actually see 6/4.5, 6/4 and even 6/3. Hrynchak (2006) reported that over-plussing the distance vision prescription was the most common reason for spectacle non-tolerance and Werner and Press (2002) provide examples of recheck exam cases where the cutting the plus rule has been successfully applied. There are two subtly different approaches to cutting the plus. Milder and Rubin (2004) suggest undercorrecting large increases in hyperopia by 0.25DS (ie prescribing +2.00DS if the prescription has increased from +1.25DS to +2.25DS). A slightly different approach which would typically involve cutting slightly more than +0.25DS, as suggested by Werner and Press (2002), Newman (2006) and Elliott (2014a), is to prescribe a hyperopic prescription or change in prescription that is sufficient to remove any symptoms. This follows the same logic as not prescribing to asymptomatic hyperopic patients (O Leary and Evans 2003): it aids adaptation and allows the parttime wearer to cope without glasses more easily. It is also likely to help delay the dependence of the patient on glasses, which is a major concern for new wearers. The amount of partial prescription provided is obviously dependent on the patient s amplitude of accommodation (and thus age), near working distance and amount of near work performed. In the example in Table 6, the recheck examination found approximately the same correction as prescribed by the previous optometrist, but the patient s symptoms suggested that it included too much positive power and this was reduced to +1.00DS R and L. She was advised to wear these for all near work and for the TV when tired and the patient reported being very happy with the comfort and vision of the new spectacles (Werner and Press 2002). It is important to note that there is probably no absolutely correct prescription to recommend here. Werner and Press (2002) suggested making symmetrical lens changes from the habitual state, so kept the powers in the two eyes the same, but other clinicians may have prescribed R +1.50DS, L +1.00DS; to keep the equivalent sphere the same as the subjective refraction. Perhaps others would have included Table 5. Average (with 95% confidence limits) normal monocular distance visual acuity data from different age groups Age (years) Visual acuity (logmar) Visual acuity (Snellen) 20 29 0.14 ( 0.02 to 0.26) 6/4.5 +1 (6/6 +1 to 6/3 2 ) 50 59 0.10 (0.00 to 0.20) 6/5 +1 (6/6 to 6/4 +1 ) 60 69 0.06 (0.04 to 0.16) 6/5 +1 (6/6-2 to 6/4 1 ) 70+ 0.02 (0.08 to 0.12) 6/6 +1 (6/7.4 to 6/4.5) Adapted from Elliott et al. (1995). 137

D B Elliott and C Howell-Duffy Table 6. Example of a patient whose non-tol or dissatisfaction with spectacles could have been avoided with the use of the clinical guideline cut the plus Chief complaint 31-year old female. Focusing difficulties with computer and slight distance blur after a lot of near work Habitual correction No Rx worn VA 6/7.5 VA 6/6 Prescribed correction R +2.25 / 0.50 130 L +1.50DS VA 6/6 VA 6/6 Recheck complaint New glasses feel too strong and patient feels better without them. Optometrists advised that she would get used to them Recheck correction R +1.00DS L +1.00DS VA not provided Adapted from Werner and Press (2002). VA, visual acuity. the oblique cylinder, which may have been the cause of the reduced visual acuity in the right eye: R +1.75/ 0.50 130, L +1.00DS. The main point is that it was certainly not appropriate to prescribe the full hyperopic prescription for this patient. Werner and Press (2002) provide another example where they prescribed a change from +0.50DS in both eyes to +0.75DS in both eyes to a 27-year-old patient to attempt to counter fluctuating vision and eye strain symptoms that were similar to those she experienced before getting her glasses. The subjective refraction correction of R +1.25/ 0.50 125, L +1.25/ 0.50 50 was deemed too strong by the patient during a trial frame assessment, as was +1.00DS in both eyes. 8. Prescribe conservatively in older patients (0.75D or less) The evidence for this guideline is provided earlier and is particularly recommended for elderly patients and those at risk of falls (Elliott 2014b), but should be considered for patients of any age who have difficulties adapting to new spectacles (this should be recorded for future action). Large changes in spherical correction (a myopic shift) can occur in older patients with nuclear cataract (Pesudovs and Elliott 2003) and changes above 0.75DS can cause problems, including falls (Cumming et al. 2007). If at all possible, limit equivalent spherical changes to no more than 0.75DS whilst being mindful of legal standards for driving. There are obvious cost implications in partial prescribing, as the patient is likely to need a change in correction more quickly than if the full change in correction was prescribed in one go, and this should be discussed with the patient. 9. Partial prescribing for astigmatic change Once again, this guideline is particularly recommended for elderly patients and those at risk of falls (Elliott 2014b). Large changes in astigmatism can occur in older patients due to development of cortical cataract (Pesudovs and Elliott 2003) and the inevitable consequence of the refracting powers of the two principal meridians being different is that of meridional magnification. Thus prescribing for astigmatism often involves a trade-off between maximum comfort and maximum clarity (Werner and Press 2002). There is no direct research evidence to support any particular approach and hence prescribing guidelines for astigmatism are based on individual clinicians experience of their own successful techniques, particularly with cases of patient dissatisfaction. Thus we summarise the most popular guidelines here, on the assumption that if several people Table 7. Example of a patient who could easily be prescribed too powerful reading spectacles due to missing a large working distance and/or prescribing based on the reading add only Chief complaint 70-year-old male. Had cataract surgery in both eyes and reading glasses now out of focus Habitual correction R +3.00 / 0.50 90 L +3.00 / 0.50 90 VA not provided Subjective refraction Prescribed correction R 0.25 DS L 0.75 DS Add +2.00 DS @ 56cm R and L R +1.75 DS L +1.25 DS VA 6/6 VA 6/6 N5 R and L VA not provided Adapted from Werner and Press (2002). VA, visual acuity. 138

Non-tolerances and the science of prescribing spectacles independently arrived at the same approach, it is likely to be useful. Changes in cylinder power should be limited to no more than 0.75DC and preferably 0.50DC if possible. If cylinder powers are changed, consideration must be given to maintaining the spherical equivalent power. For example, if the habitual correction is +0.50/ 1.00 170 and the subjective refraction suggests +1.00/ 2.00 170, a possible partial prescription could be +0.75/ 1.50 170, keeping the equivalent sphere as plano. The sphere required could be calculated as above (Brookman 1996; Werner and Press 2002), or a best-vision sphere assessment could be performed with the modified cylindrical correction (Fletcher et al. 1998). Partial changes in cylinder axis are recommended when the axes are oblique and/or the cylinders are large and/or when the patients are elderly. This could include using the old cylinder axis and identifying the best spherical and cylindrical power using that axis (Brookman 1996) or making a partial change (typically halfway if calculated) from the habitual axis to that found during subjective refraction (Elliott 2014a; Werner and Press 2002). Small cylindrical powers of 0.25DC are typically not prescribed if oblique and/or when the accompanying spherical correction is moderate to large and/or if the cylinder was not observed during retinoscopy. 10. Be careful when making large power changes in the near prescription The reading add increases bilinearly with age (Blystone 1999; Pointer 1995; Figure 2). Between approximately the ages of 40 and 55, the add increases to compensate for the reduction in the amplitude of accommodation with age. It is typically estimated using an equation based on the working distance and amplitude. At about the age of 55 the amplitude of accommodation is zero when measured objectively (Charman 2008) and what is measured subjectively is the depth of focus. The increase in the average addition after the age of 55 years is much slower and is due to the reduction in the working distance of some patients to provide additional magnification to combat reduced near visual acuity due to age-related disease (MacMillan et al. 2001; Millodot and Millodot 1989). The importance of using the correct working distance is clear and most problems with reading spectacles are due to not fully determining the patient s required tasks and associated working distances (Hrynchak 2006). There is also a great tendency for inexperienced clinicians to confuse the reading addition with the reading prescription; for example, keeping the reading correction the same in patients who indicate they are happy with their reading spectacles, but who have a nuclear cataract-related myopic shift that changes the distance prescription. These patients require an appropriate increase in their near addition to maintain the same prescription as their current reading spectacles (Hrynchak 2006). In Table 7, the novice clinician could easily miss the long working distance of 56cm and prescribe a too high correction based on more typical working distances. The clinician might also prescribe based on the reading addition only, which would also lead to a too powerful correction (Werner and Press 2002). Figure 2. The average reading addition as a function of age, adapted from the data of Pointer (1995) and Blystone (1999). The initial steeper increase in add is due to the loss of amplitude of accommodation with age. At about age 55 years, objective measurements indicate that accommodation is zero (what can be measured subjectively is depth of focus). The more gradual slope after age 55 is due to some patients with worsening visual acuity bringing their working distance closer to gain magnification. The importance of accurate determination of the patient s working distance(s) is very clear. 11. Warn the patient of potential adaptation problems If large changes in prescription are made, particularly in astigmatism, warn the patient that the spectacles may take 1 2 weeks to get used to. This is particularly important for older patients who have greater difficulty adapting to new spectacles. Inform them that the world may swim during this period (due to adaptation of the VOR, as discussed earlier). Warn the patient of magnification changes: large myopic shifts will make things seem smaller and further away, hyperopic shifts will make things larger and closer and astigmatic changes will make straight objects look bowed, and floors and walls might slope. Although it can be useful for patients to get used to the new spectacles in their own home first, they should be advised not to swap back and forth between their new and old spectacles as they will slow the adaptation process down. If the patient has few problems adapting, this should be seen as a bonus. Patients are much happier not getting the problems they were warned may occur rather than the reverse! 139

D B Elliott and C Howell-Duffy Table 8. Summary of the partial prescribing guidelines Guideline 1. Check the prescription I: over the patient s spectacles 2. Check the prescription II: outside the exam room Brief summary Use appropriate trial case lenses over the top of the patient s own spectacles and check whether they improve vision Put the refractive error you are considering prescribing in a trial frame and take the patient outside the exam room. Can the patient walk about well in the new prescription? Can the patient see in the far distance? 3. If it ain t broke, don t fix it If a patient has no symptoms in his or her current spectacles and has good visual acuity, prescribe the patient s current spectacle power and not the subjective refraction 4. If it ain t broke, don t fix it (distance-specific) For example, if a patient has no symptoms in his or her current spectacles for distance viewing (but has symptoms at near) and has good distance visual acuity, prescribe the patient s current distance spectacle power and not the distance subjective refraction. You may just alter the reading addition in this case 5. If it ain t broke, don t fix it much If a patient has no symptoms in his or her current spectacles but vision can be improved with new lenses (as determined by guidelines 1 and 2), prescribe a slight change in prescription, perhaps halfway between the current spectacles and subjective refraction 6. Be careful when reducing the minus power in a happy myope If an older myope has no symptoms and has good visual acuity at distance and near, yet the subjective refraction suggests s/he needs less minus, prescribe a slight change in prescription, perhaps halfway between the current spectacles and subjective refraction 7. Cut the plus Younger hyperopes only need sufficient plus to remove their symptoms and a partial prescription aids adaptation, allows the parttime wearer to cope more easily without glasses and likely helps delay the dependence of the patient on spectacles 8. Prescribe conservatively in older patients (0.75D or less) 9. Partial prescribing for astigmatic change 10. Be careful when making large power changes in the near prescription 11. Warn the patient of potential adaptation problems Older patients find adaptation to new spectacles difficult and large changes can cause dizziness and falls and must be avoided. Try to keep changes to 0.75DS or less, whilst being mindful of legal standards for driving As for guideline 8, this is particularly for older patients at risk of falls. Make cylinder power and axis changes halfway between their current spectacle powers and the subjective refraction. If changing the cylinder power, remember to consider changing the sphere to retain the equivalent sphere power Also remember that patients read through their near correction (distance correction plus reading addition) and not the addition alone. Changes in reading add mean little without consideration of distance correction changes. Obtaining accurate near working distance(s) is critical Particularly important for older people who will have greater adaptation problems. This includes warning them of the perceptual changes that may occur: Distortion (astigmatic changes), things appearing smaller and further away (myopic shifts), things appearing larger and closer (hyperopic shifts) and vision swimming (adaptation of the vestibulo-ocular reflex) Summary In summary, partial prescribing (prescribing something other than the subjective refraction; typically a prescription somewhere between the subjective refraction and the patient s current spectacles) is likely to lead to a reduced number of patient spectacle dissatisfactions or non-tols. Note that the subjective refraction is not necessarily perfect, as it is determined at 6m and not infinity, and it is also variable as it is based on subjective responses from patients and many find this a very challenging task. In addition, even a perfect subjective refraction result may be too large a change for some patients, particularly older ones, and they may fail to adapt to the new correction. This can lead to serious problems such as falls and dizziness. A brief summary of the partially prescribing guidelines that can be used to avoid patient dissatisfaction with new spectacles is provided in Table 8. References Adams WJ, Banks MS, van Ee R (2001) Adaptation to threedimensional distortions in human vision. Nat Neurosci 4, 1063 4 Arndt J (1967) Role of product-related conversations in the diffusion of a new product. J Marketing Res 4, 291 5 Atchison DA, Schmid KL, Edwards KP et al. (2001) The effect of under and over refractive correction on visual performance and spectacle lens acceptance. Ophthalmic Physiol Opt 21, 255 61 Ball GV (1982) Non-tolerance to optical prescriptions. In: Symptoms in Eye Examinations. London: Butterworths, pp. 37 46 Blystone PA (1999) Relationship between age and presbyopic addition using a sample of 3645 examinations from a single private practice. J Am Optom Assoc 70, 505 8 Brookman KE (1996) Refractive Management of Ametropia. Boston, MA: Butterworth-Heinemann Brooks CW, Borish IM (1979) System for Ophthalmic Dispensing. Chicago, IL: Professional, pp. 171 7 140

Non-tolerances and the science of prescribing spectacles Bullimore MA (2000) Will the auto-refractor ever replace the optometrist? Ophthalmic Physiol Opt 20, S4 5 Buttle FA (1998) Word of mouth: understanding and managing referral marketing. J Strateg Mark 6, 241 54 Cannon SC, Leigh RJ, Zee DS et al. (1985) The effect of the rotational magnification of corrective spectacles on the quantitative evaluation of the VOR. Acta Otolaryngol 100, 81 8 Carlson NB, Kurtz D (2004) Use of a trial frame to modify a prescription. In: Carlson NB, Kurtz (eds) Clinical Procedures for Ocular Examination, 3rd edn. New York: McGraw-Hill, pp. 112 14 Charman WN (2008) The eye in focus: accommodation and presbyopia. Clin Exp Optom 91, 207 25 Cockburn DM (1987) Why patients complain about their new spectacles. Clin Exp Optom 70, 91 5 Constantine-Smith N (2002) Avoiding the non-tolerance. Optician 223, 18 21 Cumming RG, Ivers R, Clemson L et al. (2007) Improving vision to prevent falls in frail older people: a randomized trial. J Am Geriatr Soc 55, 175 81 Elliott DB (2008) The art and science of prescribing glasses. Optometry Today 48, 40 5 Elliott DB (2014a) Prescribing. In: Elliott DB (ed.) Clinical Procedures in Primary Eye Care, 4th edn. Edinburgh: Elsevier, pp. 106 9 Elliott DB (2014b) The Glenn A. Fry award lecture 2013: blurred vision, spectacle correction, and falls in older adults. Optom Vis Sci 91, 593 601 Elliott DB, Chapman GJ (2010) Adaptive gait changes due to spectacle magnification and dioptric blur in older people. Invest Ophthalmol Vis Sci 51, 718 22 Elliott DB, Yang KC, Whitaker D (1995) Visual acuity changes throughout adulthood in normal, healthy eyes: seeing beyond 6/6. Optom Vis Sci 72, 186 91 Eperjesi F, Bartlett H, Dunne M (2007) Prescribing tips and counselling. In: Eperjesi F, Bartlett H, Dunne M (eds) Ophthalmic Clinical Procedures. Edinburgh: Butterworth-Heinemann, pp. 70 3 Farbrother J (2008) Spectacle prescribing in childhood: a survey of hospital optometrists. Br J Ophthalmol 92, 392 5 Fletcher R, Still DC, Allen RJ (1998) Aspects of prescribing. In: Fletcher R, Still DC (eds) Eye Examination and Refraction, 2nd edn. Oxford: Blackwell Science, pp. 115 22 Freeman C, Evans B (2010) Investigation of the causes of non-tolerance to optometric prescriptions for spectacles. Ophthalmic Physiol Opt 30, 1 11 Fylan F, Grunfeld EA (2005) Visual illusions? Beliefs and behaviours of presbyope clients in optometric practice. Patient Educ Couns 56, 291 5 Gordon A, Amos JF (1987) The dissatisfied refractive patient. In: Amos JF (ed.) Diagnosis and Management in Vision Care. Boston, MA: Butterworths, pp. 247 61 Goss DA, Grosvenor T (1996) Reliability of refraction a literature review. J Am Optom Assoc 67, 619 30 Greenhalgh T (2006) How to Read a Paper: The Basics of Evidence-based Medicine, 3rd edn. Oxford: Blackwell Publishing, 2006. Häkkinen L (1984) Vision in the elderly and its use in the social environment. Scand J Soc Med Suppl 35, 5 60 Hamel KA, Okita N, Higginson JS et al. (2005) Foot clearance during stair descent: effects of age and illumination. Gait Posture 21, 135 40 Howell-Duffy C, Scally AJ, Elliott DB (2011) Spectacle prescribing II: practitioner experience is linked to the likelihood of suggesting a partial prescription. Ophthalmic Physiol Opt 31, 155 67 Howell-Duffy C, Hrynchak PK, Irving EL et al. (2012) Evaluation of the clinical maxim: If it ain t broke, don t fix it. Optom Vis Sci 89, 105 11 Hrynchak P (2006) Prescribing spectacles: reasons for failure of spectacle lens acceptance. Ophthalmic Physiol Opt 26, 111 15 Johnson BL, Edwards JS, Goss DA et al. (1996) A comparison of three subjective tests for astigmatism and their interexaminer reliabilities. J Am Optom Assoc 67, 590 8 Johnson L, Supuk E, Buckley JG et al. (2013) Effects of induced astigmatism on foot placement strategies when stepping onto a raised surface. PLoS One 8, e63351 Lee JR, Tahran R (2007) Vision corrections for the older adult. In: Rosenbloom AA (ed.) Rosenbloom and Morgan s Vision and Aging. St Louis, MO: Butterworth-Heinemann, pp. 201 6 Lee KE, Klein BEK, Klein R et al. (2002) Changes in refraction over 10 years in an adult population: the Beaver Dam Eye Study. Invest Ophthalmol Vis Sci 43, 2566 71 Leinonen J, Laakkonen E, Laatikainen L (2006) Repeatability (test retest variability) of refractive error measurement in clinical settings. Acta Ophthalmol Scand 84, 532 6 Leung TW, Lam AK, Deng L et al. (2012) Characteristics of astigmatism as a function of age in a Hong Kong clinical population. Optom Vis Sci 68, 984 92 MacKenzie GE (2008) Reproducibility of sphero-cylindrical prescriptions. Ophthalmic Physiol Opt 28, 143 50 MacMillan ES, Elliott DB, Patel B et al. (2001) Loss of visual acuity is the main reason why reading addition increases after the age of sixty. Optom Vis Sci 78, 381 5 Michaelides E, Schutt CA (2014) The correlation between the vestibulo-ocular reflex and multi-focal ocular correction: implications for vestibular compensation. Am J Otolaryngol 35, 572 6 Milder B (1962) The dissatisfied refraction patient. Cited by Gordon A, Amos JF (1987) The dissatisfied refractive patient. In: Amos JF (ed.) Diagnosis and Management in Vision Care. Boston, MA: Butterworths, p. 247 Milder B, Rubin ML (2004) The Fine Art of Prescribing Glasses Without Making a Spectacle of Yourself, 3rd edn. Gainesville, FL: Triad. Miller AD, Kris MJ, Griffiths AC (1997) Effect of small focal errors on vision. Optom Vis Sci 74, 521 6 141

D B Elliott and C Howell-Duffy Millodot M, Millodot S (1989) Presbyopia correction and the accommodation in reserve. Ophthalmic Physiol Opt 9, 126 32 Mwanza JC, Kabasele PM (1998) [Reasons for return of patients for consultation after prescription for corrective glasses.] Bull Soc Belge Ophtalmol 270, 79 83 Newman JM (2006) Analysis, interpretation and prescription for the ametropias and heterophorias. In: Benjamin WJ (ed.) Borish s Clinical Refraction, 2nd edn. St Louis, MO: Butterworth- Heinemann, pp. 963 1025 Obstfeld H (1988) General considerations in prescribing. In: Edwards K, Llewellyn R (eds) Optometry. London: Butterworths, pp. 465 74 O Leary CI, Evans BJW (2003) Criteria for prescribing optometric interventions: literature review and practitioner survey. Ophthal Physiol Opt 23, 429 39 Pesudovs K, Elliott DB (2003) Refractive error changes in cortical, nuclear, and posterior subcapsular cataracts. Br J Ophthalmol 87, 964 7 Pointer JS (1995) The presbyopic add I, II and III. Ophthalmic Physiol Opt 15, 235 54 Polasky M (1991) Monocular subjective refraction. In: Eskridge BJ, Amos JF, Bartlett JD (eds) Clinical Procedures in Optometry. Philadelphia, PA: Lippincott, pp. 174 88 Riffenburgh RS, Wood TR, Wu ML (1983) Why patients return after refraction. Am J Ophthalmol 96, 690 1 Saunders H (1986) A longitudinal study of the age-dependence of human ocular refraction I. Age-dependent changes in the equivalent sphere. Ophthalmic Physiol Opt 6, 39 46 Shah R, Edgar DF, Rabbetts R et al. (2009) Standardized patient methodology to assess refractive error reproducibility. Optom Vis Sci 86, 517 28 Shickle D, Griffin M, Evans R et al. (2014) Why don t younger adults in England go to have their eyes examined? Ophthalmic Physiol Opt 34, 30 7 Sims CN (1982) Micronics and overrefraction. Ophthalmology 89, 930 6 Startzell JK, Owens DA, Mulfinger LM et al. (2000) Stair negotiation in older people: a review. J Am Geriatr Soc 48, 567 80 Strang NC, Gray LS, Winn B et al. (1998) Clinical evaluation of patient tolerance to autorefractor prescriptions. Clin Exp Optom 81, 112 18 Supuk E, Alderson A, Davey CJ et al. (in press) Dizziness, but not falls rate, improves after routine cataract surgery: the role of refractive and spectacle changes. Ophthalmic Physiol Opt Walsh G (2009) Prescribing spectacles. In: Rosenfield M, Logan N (eds) Optometry: Science, Techniques and Clinical Management. Edinburgh: Butterworth-Heinemann, p. 357 Werner DL, Press LJ (2002) Clinical Pearls in Refractive Care. Boston, MA: Butterworth-Heinemann West D, Somers WW (1984) Binocular balance validity: a comparison of five common subjective techniques. Ophthalmic Physiol Opt 4, 155 9 Woods RL, Colvin CR, Vera-Diaz FA et al. (2010) A relationship between tolerance of blur and personality. Invest Ophthalmol Vis Sci 51, 6077 82 CET multiple choice questions This article has been approved for one non-interactive point under the GOC s Enhanced CET Scheme. The reference and relevant competencies are stated at the head of the article. To gain your point visit the College s website www.college-optometrists.org/oip and complete the multiple choice questions online. The deadline for completion is 31 January 2017. Please note that the answers that you will find online are not presented in the same order as in the questions below, to comply with GOC requirements. 1. What is the lowest prevalence of spectacle non-tolerance cited in this paper? 1.3% 1.6% 1.8% 2.3% 2. What is most often used as the gold standard of refraction? Wavefront aberrant refraction Retinoscopy Autorefraction Subjective refraction 3. What effect have new spectacles been found to have on falls? New spectacles can increase the likelihood of a fall New spectacles decrease the likelihood of a fall New spectacles have no effect on the incidence of falls The research was inconclusive 4. Which of the following statements is correct? Always reduce a myopic prescription by 0.25D to reduce intolerance in asymptomatic myopes Always prescribe small prescriptions of 0.75D or less in older patients to reduce likelihood of falls Reduce hypermetropic changes by 0.25D, in all hypermetropic increases Check the prescription outside the consulting room prior to prescribing 142

Non-tolerances and the science of prescribing spectacles 5. With the if it ain t broke, don t fix it prescribing strategies, which of the following is correct? A new spectacle prescription should always be prescribed to exceed patient expectations When a patient is symptomatic for near, but not for distance, incorporate the change found for the reading addition, but use the current distance spectacle correction for ease of adaptation Always try and reglaze spectacle frames where possible, to reduce dispensing intolerances Where there is a clinically significant change over 0.50D, prescribe approximately half the change 6. When prescribing conservatively in older patient, which of the following is correct? Always prescribe changes of 0.75DS or more Don t prescribe changes of 0.75DS or less Limit equivalent spherical changes to no more than 0.75DS Ensure there is not a difference of 0.75DS or more between each eye CPD Exercise After reading this article, can you identify areas in which your knowledge of non-tolerances and the science of prescribing spectacles has been enhanced? How do you feel you can use this knowledge to offer better patient advice? Are there any areas you still feel you need to study and how might you do this? Which areas outlined in this article would you benefit from reading in more depth, and why? 143

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