Presbyopic contact lenses

Presbyopic contact lenses Ahmed Sivardeen BSc (Hons), MCOptom and Professor James Wolffsohn BSc (Hons), MBA, PhD, MCOptom, FBCLA 49 Eye care practitioners need to be able to help their patients choose the most appropriate way of managing presbyopia. With the worldwide increase of ageing populations and the consequent increase of presbyopes, the demand for contact lenses to correct presbyopia will inevitably increase. This article will aid the practitioner to evaluate and compare the methods of correcting presbyopia currently available. Course code C-33399 Deadline: November 1, 2013 Learning objectives Understand the different ways of managing presbyopia and know how to choose the best option for the needs of the patient (Group 5.3.2) Know the lens design and modality options available in bifocal and multifocal contact lenses (Group 5.3.2) Know the advantages and disadvantages of spectacle lenses for presbyopia and be able to compare this to the contact lens options available (Group 4.1.5) Learning objectives Understand the different ways of managing presbyopia and know how to choose the best option for the needs of the patient Know the lens design and modality options available in bifocal and multifocal contact lenses (Group 5.5.2) About the authors Ahmed Sivardeen is a Doctor of Optometry student at Aston University and is a director of Specsavers in New Malden, Surrey. Professor James Wolffsohn is a member of the Ophthalmic Research Group and executive dean of the School of Life and Health Sciences at Aston University. For the latest CET visit www.optometry.co.uk/cet

1 CET POINT CET CONTINUING EDUCATION & TRAINING 50 Figure 1 Duane s standard curve of accommodation in dioptres in relation to age in years. (A: highest values; B: average values; C: lowest values) (from Duane,1912) Definition and historical overview of presbyopia Presbyopia is derived from presbys meaning old man or elder, and the Neo-latin suffix assumes that the zonules supporting the crystalline lens are under maximal tension when the lens is at minimum optical power. The Helmholtz theory proposes that tension is exerted by the anterior, posterior and equatorial zonules simultaneously. This theory states that the optical power of the crystalline lens is increased by relaxation of the tension on these zonules, while an increase in zonular tension causes a decrease in optical power. This theory does not explain the peripheral surface flattening and reduction in spherical aberration which have been reported to occur during accommodation. 4 Schachar Theory of Accommodation The Schachar theory of accommodation assumes that the equatorial zonules are under minimum tension when the lens is at minimum optical power. 5,6 The equatorial lens continuously increases throughout life, zonular tension simultaneously declines. This results in a reduction of baseline ciliary muscle length which is associated with both lens growth and increasing age. Since the ciliary muscle, like all muscles, has a lengthtension relationship, the maximum force the ciliary muscle can apply decreases with age as its length shortens. This explains the decline in the accommodative amplitude which results in presbyopia. 9 Various studies have failed to support Schachar s theory of accommodation and also studies of scleral expansion surgery have not reported any valuable restoration of accommodation. 10,11 It is possible that both the theories postulated by Helmholtz and Schachar are correct depending on the biometry of the system, the material properties, and the direction and strength of forces. 12 opia, meaning sightedness. No standard definition of presbyopia exists. A person may be considered presbyopic when near vision clarity is insufficient for their requirements, usually corresponding to an accommodative zonules apply increasing tension to the lens during accommodation. This increased equatorial zonular tension expands the equatorial diameter of the lens, alters the surface curvatures of the lens and, thereby, Prevalence and factors affecting the age-of-onset of presbyopia There is little information on the prevalence amplitude below three dioptres, as increases the central optical power of the of presbyopia in developing countries as accommodation declines with age (Figure lens. 7 The Schachar theory proposes that most studies on refractive error in these 1). 1,2,3 The ciliary muscle was discovered in during the accommodative process, increasing regions have been limited to distance the middle of the 19th century and in 1853, tension is exerted exclusively by the equatorial vision. 13 More information regarding its Hermann von Helmholtz, published A Theory zonules. The anterior and posterior zonules act prevalence is available in the USA, where 76.5 Of Accommodation. He observed that for like the supportive ligaments of skeletal joints million people were born during the 19 years focusing on near objects, the contraction of and are stabilising components, which are following World War Two (1946 to 1964), the ciliary muscle allows a relaxation of the tense during distance vision and relax during the baby boomer generation (US Census zonular fibres and consequently, a bulging accommodation. This causes the central Bureau; 2013). 14 This generation is now of the crystalline lens. Due to its elasticity, surfaces of the crystalline lens to steepen, the between 41-70 years of age, and includes the process is described as accommodation. central thickness of the lens to increase and many existing, or soon to be, presbyopes. Research into a fuller understanding of the the peripheral surfaces of the lens to flatten. It is reported that the average age of the process and causes of presbyopia is on-going. This results in increased central optical power population has increased from 34.1 in 1971 The principal theories proposed to explain of the lens and reduces spherical aberration. 8 to 38.2 in 2001, and is expected to rise to 43.3 presbyopia have been: As a result of the increased equatorial zonular by 2031. 15 Clearly, as the global population Helmholtz theory of accommodation tension on the lens during accommodation, the stress on the lens capsule is increased, ages, the prevalence of presbyopia will increase. Age is the major risk factor for The more widely accepted theory of and the lens remains stable and unaffected the development of presbyopia, although accommodation (von Helmholtz, 1855) by gravity. 9 As the equatorial diameter of the the condition may occur prematurely in

Age Onset in Chinese populations 36-40 years Central Americans and Africans fourth decade Hispanic and non-hispanic no difference in age of onset Hyperopia Occupation Additional accommodative demand (if uncorrected) hence presbyopia evident earlier Closer and greater near vision demands, especially in poor lighting, will result in the need for presbyopic correction earlier 51 Gender More in women Earlier onset in females (short stature, menopause) Ocular disease or trauma Systemic disease Removal or damage to lens, zonules or ciliary muscle Diabetes and the duration of diabetes; multiple sclerosis (impaired innervation), cardiovascular accidents (impaired accommodative innervation), vascular insufficiency, myasthenia gravis, anaemia, influenza, measles, HIV positive, tuberculosis, sarcoidosis, polycythaemia and leukaemia tumours Drugs Decreased accommodation is a side effect of both nonprescription and prescription drugs for example alcohol intake, chlorpromazine, hydrochlorothiazide, antianxiety agents, antidepressants, antipsychotics, antispasmodics, antihistamines, diuretics Iatrogenic factors Scatter (panretinal) laser photocoagulation, intraocular surgery Geographic factors Proximity to the equator (higher average annual temperatures, earlier onset, greater exposure to ultraviolet radiation) Other Poor nutrition, decompression sickness, lenticular changes caused by hair dye Table 1 Factors affecting the onset of presbyopia 29-44 the presence of congenital, traumatic, inflammatory, vascular, neoplastic and degenerative diseases, toxins and side effects of drugs. Common risk factors are described in Table 1. 16-28 Presbyopic correction options Spectacle options Bifocals Conventional bifocal lenses offer two zones of fixed-focus vision, separated by a visible discontinuity. This discontinuity produces an abrupt change in image size and location, known as image jump, as the line of sight passes into the region used for reading. 45 A band of blur and a potential blind area in the visual field results, as the pupil is simultaneously exposed to two different power and prismatic effects, as the line of sight passes over the discontinuity. Midrange vision through bifocal lenses is often limited, particularly as the wearer s presbyopia advances. Trifocals Trifocal lenses are made in similar styles to bifocals but with an additional segment for intermediate vision above the reading section. Trifocals are now rare as more people choose to wear progressive lenses. Progressive addition lenses Progressive addition lenses (PAL) are multifocal spectacle lenses employing surfaces which provide a continuously smooth increase in positive focal power. The area of changing power is flanked on either side by regions of blur and geometric distortion (Figure 2). Progressive lenses provide the desired addition power without any lines. This blending is achieved by incorporating various amounts of surface astigmatism or cylinder, For the latest CET visit www.optometry.co.uk/cet

1 CET POINT CET CONTINUING EDUCATION & TRAINING generally oriented at an oblique axis, in the Thermal techniques 52 lateral regions of the lens surface. 46 Surgical options Laser refractive surgery The corneal procedures available in laser surgery for correction of presbyopia include: centre-near, simultaneous-vision designs, in which the laser creates a multifocal corneal surface, and a lasik flap produces an aspheric curve to increase the depth of focus. There are also centredistance, simultaneous-vision designs, in which a decentred steep central island is created. In annular ablations, an intermediate plus, near mid-peripheral ablation pattern is used. Aspheric hyperprolate profiles increase the depth of focus and enhance monovision. Two-step ablations attempt to correct negative asphericity on the cornea to improve near vision. Flapless intrastromal ablation uses specific algorithms to create five concentric Distance Intermediate Near Progressive Corridor Blending region Figure 2 The structural features of a general purpose progressive lens include zones of stabilised distance vision, stabilised near vision, and progressively increasing intermediate vision, with blending regions of unwanted blur and distortion to either side (Modified from Sheedy, 2004a) from each other and the corneal epithelium and endothelium resulting in a steepening of the central cornea by one to two dioptres. Multifocal ablation combines remodelling of the cornea for distance, near, and intermediate visual acuities, known to be a safe, effective bilateral procedure. Non-linear aspheric ablation, which is a hyperopic monovision process and has been shown to be a well- Laser thermal keratoplasty (LTK) is a surgical refractive procedure that uses the Holmium laser, an infrared laser, to reshape the cornea. The laser heat is used gently on the stromal collagen in a ring around the outside of the pupil. Heat causes the tissue to shrink, creating an effect like tightening a belt, resulting in bulging of the centre of the cornea. As the cornea of a longsighted eye is too flat, this bulging effect, when carefully controlled corrects mild hyperopia and presbyopia. Intraocular lens implants Refractive lens replacement (RLR) surgery, removing the clear, presbyopic, crystalline lens and replacing it with a multifocal intraocular lens (IOL), is a successful alternative procedure for presbyopic patients not suitable for corneal refractive surgery, such as those with very thin corneas. This technique has become more accepted in recent years with the advancements in lens technology and stromal rings at predetermined distances tolerated and effective procedure. 47-52 improvements in surgical techniques. 53 Figure 3 Colour coded power maps for multifocal contact lenses AO multifocal (Alcon), PureVision multifocal (PV, Bausch & Lomb), Acuvue Oasys for Presbyopia (Vistakon, Johnson & Johnson) and Biofinity multifocal (BF, CooperVision). Horizontal scale indicates distance (mm) and vertical scale optical power (D). Taken from Plainis et al., 2013 with kind permission of the author

Alternatively, multifocal IOLs, or monovision can be induced when the crystalline lens has been removed as part of cataract surgery. IOLs move with the rotation of the eyes, providing simultaneous vision that is the optics split light entering the pupil between focal planes. This can be achieved through aspheric optics, concentric rings or segments of different refractive power (typically distance and near powers) or through diffractive optics, using constructive and disruptive interference patterns to create two or three principal focal planes. 54 An alternative approach is the attempt to mimic more closely the accommodative mechanism of the eye by having a more flexible IOL, which can hinge forward on its haptics or change shape with the contraction of the ciliary muscle, allowing the lens capsule to contract. 55 Corneal inlays and onlays Intracorneal inlays are implantable devices that are surgically inserted just under the superficial layers of the cornea. They alter the way that light enters the eye, thereby improving near vision. 56 Clariti 1day Proclear 1 day Focus Dailies Progressives Base curve 8.6mm 8.7mm 8.6mm Diameter 14.1mm 14.2mm 13.8mm Power range Addition Centre thickness (-3.00D) +5.00 to -6.00 Low up to +2.25D high +2.25D to +3.00D +6.00 to -6.00 (0.25D steps) -6.00 to -10.00 (0.50D steps) Designed with a single power profile. Add up to +2.50D +5.00 to -6.00 0.07mm 0.09mm 0.11mm Dk/t (at -3.00D) 86 28 23.6 Water content 56% 60% 69% Incorporating a single progressive add, effective range up to +3.00D 53 Scleral expansion surgery Schachar introduced scleral expansion bands for surgical reversal of presbyopia. 57 By increasing the working distance of the ciliary muscle, achieved by the implantation of polymethylmethacrylate (PMMA) expansion bands, the amplitude of accommodation was thought to increase. Studies have shown early implant designs to be ineffective. 58 Contact lens options Contact lenses intended specifically for presbyopia have a wide variety of optical designs. Translating (or alternating) image designs These designs contain the distance and near correction in spatially distinct portions of the lens and rely on changes in vertical eye positioning relative to the lens to ensure that the gaze is directed through the optical portion needed for a given task. 59 Such designs, which are much more common for rigid than for soft lenses, depend on a variety of factors for precise and reliable translation and tend to require greater precision when being fitted. 60-62 Modulus 0.5MPa 0.4Mpa 1MPa UV Block Manufacture process Design Material Yes UVA/UVB Injection cast moulding Aspheric back surface CN Filcon II3 Simultaneous image designs Regardless of form, all other contact lens designs are based on the principal of a simultaneous image, previously referred to as simultaneous vision. Here only a portion of the light rays received at each foveal retinal locus will have the vergence needed for the dioptric distance of the point being looked None Dry cast moulded Aspheric CN (approximate max add +0.75D) Omalfilcon A incorporating PC technology None Cast moulded with unique Lightstream Technology Aqua release CN Nelficon A Table 2 Currently marketed daily disposable multifocal soft contact lens designs at, while the remaining rays have greater or lesser vergence. 59,63 Simultaneous image lenses include concentric designs which have a centre-surround arrangement for the two lens powers necessary for the bifocal, and aspheric designs that involve a continuous change in power from the lens axis to the peripheral portion of the central optical zone,

1 CET POINT CET CONTINUING EDUCATION & TRAINING Acuvue Oasys for Presbyopia Air Optix Aqua Multifocal Biofinity Multifocal Purevision 2 for Presbyopia Clariti Multifocal 54 Power Add powers +6.00D to -9.00D LOW +0.75 to +1.25 MID +1.50 to +1.75 HIGH +2.00 to +2.50 +6.00D to -10.00D LOW up to +1.25 MED +1.50 to +2.00 HIGH +2.25 to +2.50 +6.00D to -8.00D (0.50D steps after -6.00D) +1.00, +1.50 +2.00, +2.50 D Lens N Lens +6.00D to -10.00D (0.25D steps) LOW +0.75D to +1.50D HIGH +1.75D to +2.50D +6.00D to -8.00D (0.50D after -6.00D) LOW: up to +2.25D HIGH: +2.25D to +3.00D Dk/t 147 138 142 130 86 Material Senofilcon Lotrafilcon B 33% water content plasma polymerisation Comfilcon A 48% water content Balafilcon A Filcon II3 56% water content Design Zonal aspheric design Precision transition bi-aspheric- front and back surface aspheric Centre-distance and centre near with progressive intermediate zone Centre-near aspheric optics Centre-near and peripheral distant with smooth progression of intermediate vision Base curve 8.4mm 8.7mm 8.6mm 8.6mm 8.7mm Diameter 14.3mm 14.2mm 14.0mm 14.0mm 14.2mm Centre thickness (@ -3.00D) 0.07mm 0.08mm 0.08mm 0.07mm 0.07mm Visible tint Blue Blue Sofblue Light blue None Replacement schedule Two weekly replacement Monthly replacement Monthly replacement Monthly replacement Monthly replacement Modality Daily wear or one week (six nights) extended Daily wear Daily wear or extended wear up to six nights/seven days Daily wear or up to 30 days continuous wear Daily wear UV blocking Class 1 None None None UVA and UVB Table 3 Currently marketed monthly disposable multifocal soft contact lens designs

thereby creating a multifocal effect. 64 Some manufacturers promote different designs for each eye to increase the range of clear focus combinations available to patients. Other lens types that utilise simultaneous images for the relief of presbyopia include rigid gas permeable (RGP), hybrid multifocals (RGP surrounded by a soft skirt ) and sclerals. Tables 2 and 3 show some of the currently marketed designs of daily and monthly multifocal disposable soft contact lenses. Lens centration, pupil size, optic zone diameter, and the combined spherical aberration of the eye and the contact lens are some of the many factors that affect the optical performance of simultaneous image contact lenses. 65 The single most influential feature is the lens design, as ocular aberrations and pupil size cannot be independently controlled. The power profile of a multifocal contact lens also provides insight on add power, as well as information on any variation of the profile across different regions of the optical zone and radial locations along the profile where the label power is located. This information should be scrutinised across the different sphere powers that are available, as many currently marketed multifocal designs contain inconsistencies across the power range and add-power. 66 Consistency of the power profile within each lens affects the distance vision performance and the performance of the addition power of the lens. Plainis and colleagues measured the power profile using ptychographic imaging, in which a series of diffraction patterns are recorded from neighbouring points on the lens thereby creating a lens thickness profile. 67,68 Their results illustrate the diversity of power profiles found among the currently available multifocal contact lenses (Figure 3). Research into contact lens effectiveness in correcting for presbyopia By controlling levels of spherical aberration in both bifocal and multifocal contact lenses, the image degradation and visual consequences of lens decentration can be minimised. 69 The effect of pupil size and spherical aberration on the visual performance with a centre-near aspheric multifocal shows that near visual acuity and depth of focus improve, with the effects more pronounced for small pupils and for binocular rather than monocular vision. It is not just the aberration profile of the lens that dictates visual function, but a combination of the profile and the aberrations of the individual s eyes. 70 While monovision is known to affect stereopsis, multifocal optics; with one lens biased to distance viewing and the other lens biased toward near viewing, minimally affects the stereoacuity. 71-72 Neural adaptation to multifocal correction Multifocal lenses project images from far, near and potentially intermediate distances simultaneously on the retina. Neural adaptation involves the brain learning to use these different images. As the visual cortex contains no pre-wired circuitry to digest information from multifocal lenses, the brain requires a period of adjustment known as neural adaptation which involves suppressing near vision when viewing distant objects and restricting distance vision when focusing up close. Without a neural template to single out and convey the dominant visual field into awareness, a period of neural adaptation is needed for the brain to put in place the required neural tracks, but with time the halos and the image distraction slowly decrease and disappear. 73 While a period of adaptation with multifocal contact lenses has been suggested in order to obtain optimal visual performance, its duration has not been quantified. 74 Conclusion With an increase in the ageing population worldwide and a consequent rise in the number of presbyopes, the demand for contact lenses to correct presbyopia will inevitably increase. Patients who wear contact lenses prior to the onset of presbyopia should be able to continue in this chosen modality of wear. According to Morgan and colleagues, practitioners are still under-prescribing multifocal contact lenses. 75 The perception that multifocal designs are not as successful as monovision contact lenses because they create visual problems, such as haloes and ghosting, particularly for distance vision at night, encourages the practitioner to either delay fitting multifocal contact lenses or use monovision lenses rather than multifocal lenses. However, there is no scientific evidence for these fears, particularly with modern multifocal designs. Issues to do with end-of-day discomfort increasing with age are also being addressed with modern contact lens materials and conditioning agents. The problem of positioning multiple focal elements to deliver effective near vision, without degrading distance performance or vice versa, remains a challenging one and lens designers have made great efforts to overcome these problems. In recent times vast strides have been made in multifocal contact lens design and materials, along with techniques for measuring visual performance and subjective and objective vision quality. Published research to aid selecting the optimal presbyopic contact lens for the patient in your chair is limited, although studies are currently underway. 55 MORE INFORMATION References Visit www.optometry.co.uk/clinical, click on the article title and then on references to download. Exam questions Under the new enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk/cet/exams. Please complete online by midnight on November 1, 2013. You will be unable to submit exams after this date. Answers will be published on www.optometry.co.uk/cet/exam-archive and CET points will be uploaded to the GOC every two weeks. You will then need to log into your CET portfolio by clicking on MyGOC on the GOC website (www.optical.org) to confirm your points. Reflective learning Having completed this CET exam, consider whether you feel more confident in your clinical skills how will you change the way you practice? How will you use this information to improve your work for patient benefit?