In a randomized controlled trial, cataract surgery in both eyes increased benefits compared to surgery in one eye only

Transcription

1 Journal of Clinical Epidemiology 59 (2006) In a randomized controlled trial, cataract surgery in both eyes increased benefits compared to surgery in one eye only Xavier Castells a,b, *, Merce Comas a,b, Jordi Alonso b, Mireia Espallargues c, Vicente Martınez d, Josep Garcıa-Arumı d, Miguel Castilla e a Evaluation and Clinical Epidemiology Department, Institut Municipal d Assistencia Sanitaria (IMAS), Passeig Marıtim 25-29, Barcelona, Spain b Health Services Research Unit, Institut Municipal d Investigacio Medica (IMIM-IMAS), Barcelona, Spain c Catalan Agency for Health Technology Assessment and Research (CAHTA), Barcelona, Spain d Ophthalmology Department, Hospital Vall d Hebron, Barcelona, Spain e Ophthalmology Department, Hospital de l Esperança (IMAS), Barcelona, Spain Accepted 14 June 2005 Abstract Background and Objective: Despite recommendation of surgery in both eyes in patients with bilateral cataract, there is little evidence about the benefits of second-eye surgery. The objective of this study was to compare the benefits of cataract surgery in both eyes with those of surgery in one eye only. Study Design and Setting: Two-arm randomized controlled trial involving 296 patients with bilateral cataracts of two public teaching hospitals. Patients were randomly assigned to receive surgery in one eye only (control group) or surgery in both eyes, one eye at a time (intervention group). The main outcome measures were binocular visual acuity, binocular contrast sensitivity, stereopsis, and patientreported visual disability (VF-14), measured 4 6 months postoperatively. Results: A total of 135 (91.2%) and 139 (93.9%) patients completed the trial in the control and intervention groups, respectively. Postoperatively, intervention group presented a better visual acuity (difference of 0.07; 95% CI , 0.12), stereopsis (0.62 log sec arc; 95% CI , 0.79), and VF-14 (8.2 points; 95% CI 5 4.4, 12.4). No significant differences were found for contrast sensitivity. Conclusions: Bilateral cataract patients should have surgery in both eyes. Including stereopsis and patient-reported visual disability in the assessment of cataract patients, especially after first-eye surgery, will improve the evaluation of effectiveness. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Cataract; Cataract extraction; Quality of life; Treatment outcome; Visual acuity; Binocular vision 1. Introduction An increasingly important proportion of cataract surgery rates is due to surgery of the second eye in patients with bilateral cataract [1 5], but there is still a significant unmet need for second-eye surgery [2]. Current prioritization initiatives for cataract surgery, however, intended to help reduce the negative impact of waiting lists in some countries, could compromise second-eye surgery accessibility [6,7]. Despite recommendation of surgery in both eyes in patients with bilateral cataract, there is little evidence about the benefits of second-eye surgery. Observational studies * Corresponding author. Tel.: ; fax: address: xcastells@imas.imim.es (X. Castells). have reported a benefit in terms of visual acuity and patient-reported visual disability [3,8,9], and one small study [10] reported a benefit in stereopsis (depth perception) and contrast sensitivity. The one randomized controlled trial addressing this question reported a relevant benefit in stereopsis and patient-reported visual disability, and a less relevant improvement in visual acuity and contrast sensitivity [4]. That trial, however, included only patients already scheduled for second-eye surgery, without ocular comorbidities and with a good outcome of first-eye surgery. This implies low generalizability, because not all bilateral cataract patients have second-eye surgery [2,9]. Our objective was to compare clinical and patientreported outcomes of cataract surgery in one eye only with those of surgery in both eyes (serial, not simultaneous surgery) in patients with bilateral cataract /06/$ see front matter Ó 2006 Elsevier Inc. All rights reserved. doi: /j.jclinepi

2 202 X. Castells et al. / Journal of Clinical Epidemiology 59 (2006) Methods 2.1. Patients Patients were eligible for the trial if they were scheduled for first-eye cataract surgery and presented bilateral indication for cataract surgery (visual acuity worse than 0.3 logarithm of the minimum angle of resolution [logmar] in both eyes). Exclusion criteria were as follows: presenting a severe ocular comorbidity that would contraindicate surgery in both eyes (e.g., terminal glaucoma, amblyopia, or prior strabismus surgery); undergoing surgery combined with any other ophthalmologic procedure (e.g., glaucoma or keratoplasty); and experiencing complications of firsteye surgery that would contraindicate surgery in the fellow eye. Eligible patients were recruited in the ophthalmology departments of two teaching hospitals in Barcelona, Spain, and the inclusion and exclusion criteria were reviewed by one ophthalmologist in each hospital. Trial recruitment began in July 1999 and ended in July Intervention After first-eye surgery, recruited patients were randomly allocated to either the one-eye-only surgery (control) or the both-eyes surgery (intervention) group. In the control group, patients underwent surgery in the first eye only, between 1 and 2 months after enrolling in the study. In the intervention group, patients also underwent surgery in the first eye 1 to 2 months after enrollment, and underwent surgery in the second eye 2 to 4 months after first-eye surgery. The surgery protocol (ambulatory surgery using a phacoemulsification technique with topical anesthesia, 3-mm corneal incision, and foldable lens without suture) was exactly the same in the two hospitals. Randomization and allocation was performed by means of a computerized minimization algorithm with stratification by hospital, age (!65 or >65 years), and preoperative visual acuity (O1 or <1 logmar). Patients were centrally randomized in our research unit after first-eye surgery. The random allocation was blinded to the data analyst. The study followed the tenets of the Declaration of Helsinki and was approved by the clinical research ethical committees at the two participating centers. The study was explained to eligible patients before the baseline visit, and informed consent was obtained. Patients were informed that, in case of being randomized to surgery in one eye only, they would be offered second-eye surgery at the end of the study Assessments All patients were assessed between 1 and 2 months before their first-eye surgery (baseline) and postoperatively, between 4 and 6 months after the last surgery (first eye for the control group, second eye for the intervention group). Identical vision tests and patient-reported measures were used in the two participating hospitals, administered by experienced optometrists (one in each hospital). There were four primary outcomes in this trial: three clinical vision measures (binocular visual acuity, binocular contrast sensitivity, and stereopsis) and a measure of patient-reported visual disability (the VF-14). The logmar best-corrected visual acuity was measured binocularly with an ETDRS chart calibrated for an 8-foot ( 2.5 meter) distance, by the letter-by-letter scoring method [11]. Log contrast sensitivity was also measured binocularly with a Pelli Robson chart, by the letter-by-letter scoring method [12], at 1 m. Stereopsis was assessed with the Titmus circles test; to widen the range of values, it was combined with the Fly and the TNO tests, giving a range from 3,000 to 15 seconds of arc (sec arc). The measures of stereopsis were also transformed into a log scale. Lower values of visual acuity and stereopsis and higher values of contrast sensitivity indicate good vision. The VF-14 is a patient-reported measure of functional disability related to vision based on 14 everyday activities that can be affected by cataract (e.g., reading a newspaper, watching television, or taking part in activities) [13]. VF-14 scores range from 0 (maximum disability) to 100 (no disability). The validity and internal consistency of both the original and the Spanish versions of the VF-14 have been documented [14,15]. The VF-14 was interviewer-administered by trained optometrists. Secondary outcomes were (i) the cataract symptoms score (based on a five-item symptoms questionnaire that asks patients about the degree of trouble caused by common symptoms of cataract), with scores ranging from 0 (no symptoms) to 15 (very much trouble, due to all five symptoms) [13,16]; (ii) two general questions about overall amount of trouble and satisfaction with vision [13,16]; and (iii) general health status assessed using the Short Form SF- 12 Health Survey [17], with scores ranging from 0 (worst health status) to 100 (best). Other ophthalmologic clinical information (comorbidity or surgical complications) was obtained through standardized clinical data forms, which were completed by ophthalmologists of the participating hospitals. The optometrist obtained sociodemographic characteristics at the baseline visit Statistical analysis A subgroup analysis was planned according to age groups. Sample size was calculated separately for patients younger than 65 and for patients 65 years or older to detect clinically relevant differences in two primary outcome measures: VF-14 and binocular visual acuity. With 296 patients (148 per treatment group; 36 younger and 112 older), the trial was able to detect a minimum relevant difference of 5 points (standard deviation SD 5 8 for younger and SD 5 14 for older patients) in mean postoperative VF-14 [3,18] and a minimum clinical relevant difference in postoperative visual acuity of one Snellen line [19] (SD

3 X. Castells et al. / Journal of Clinical Epidemiology 59 (2006) for younger and SD for older patients). The sample sizes took into account a significance level of 5%, a power of 80%, and an expected proportion of withdrawals of 15%. Sociodemographic factors and primary outcome variables were compared at baseline. The final outcomes analysis was performed on an intention-to-treat basis by comparing the 4 6 months postoperative visits between groups: after the second-eye surgery for the intervention group and after the first-eye surgery for the control group. Comparisons were performed on means of the final measure and on the change from baseline, as well as on three category groupings of the main outcome variables. The cutoffs were set at 0.3 and 0.1 logmar for visual acuity [20]; at 1.30 and 1.70 for log contrast sensitivity [20,21]; at 3,000 and 60 sec arc for stereopsis; and at 80 and 100 points for VF-14 scores. Nonparametric Mann Whitney U-tests for quantitative variables and chi-square tests for qualitative variables were used for comparisons. Nonparametric confidence intervals (CI) for the differences in means between groups were calculated using the bootstrap method. A secondary analysis was performed upon postoperative VF-14 and binocular visual acuity of patients in the control group (surgery in one eye only). The goal was to assess the results after surgery in one eye only and, thus, the probability of change if second-eye surgery were performed. The two variables were categorized and crossed, in order to calculate frequencies of combinations of low-level outcomes and combinations of high-level outcomes. 3. Results A total of 296 patients were recruited, 148 of whom were randomized to cataract surgery in one eye only and 148 to surgery in both eyes. The number of patients who did not complete the trial were 13 (8.8%) for the surgery in one eye only (control) group and 9 (6.1%) for the both-eyes surgery (intervention) group (Fig. 1). Baseline characteristics were similar in both groups (Table 1). The average follow-up postoperative visual acuity was 0.07 logmar units higher (95% CI , 0.12) for the intervention group than for the control group. The intervention group also presented a greater proportion of patients with a high level of visual acuity, defined as <0.1 logmar units (46.0% vs. 26.7%, P!.001), and a smaller proportion with a low-level visual acuity, defined as O0.3 log- MAR units (2.2% vs. 14.8%, P!.001). The average improvement in visual acuity was also higher (0.05 log- MAR units; 95% CI , 0.11) in the intervention group (Table 2). For contrast sensitivity, the follow-up postoperative comparisons showed no significant differences between groups: a difference of 0.04 (95% CI , 0.087) in mean contrast sensitivity and a difference of 0.02 (95% CI to 0.14) in mean change from baseline (Table 2). Postoperative stereopsis was 0.62 log units (95% CI , 0.79) better in the intervention group (Table 2). This difference was clearly reflected in the proportion presenting a high level of stereopsis, defined as <60 sec arc (69.6% vs. 19.3%, P!.001), and the proportion that presented a low-level stereopsis, defined as 296 patients Eligible and Randomized 148 assigned to surgery in one eye only 148 assigned to surgery in both eyes 8 withdrawals 5 withdrawals 2 lost to follow-up 3 lost to follow-up 3 expedited 2n eye surgery 2 died 2 switched to private sector 1 died 5 post-randomization exclusions 4 post-randomization exclusions 2 developed comorbidity 2 developed comorbidity 2 complications in 1st eye surgery 2 complications in 1st eye surgery 1 developed senile dementia 135 completed trial 139 completed trial Fig. 1. Trial flow chart.

4 204 X. Castells et al. / Journal of Clinical Epidemiology 59 (2006) Table 1 Baseline characteristics for the two study groups Characteristics Surgery in one eye only: control Surgery in both eyes: intervention Sample size n n Sociodemographic characteristics Age, years, mean (SD) (8.87) (9.07) Age!65 years, no. (%) 35 (23.6) 34 (23.0) Gender, female, no. (%) 93 (62.8) 91 (61.5) Living alone, no. (%) 24 (16.2) 26 (17.6) Education, less than primary completed, no. (%) 106 (71.6) 109 (73.6) Employed, no. (%) 9 (6.1) 10 (6.8) Clinical measures Binocular visual acuity, logmar units, mean (SD) 0.56 (0.19) 0.54 (0.17) Binocular visual acuity, decimal scale units, mean Binocular contrast sensitivity, log units, mean (SD) 1.13 (0.35) 1.14 (0.29) Stereopsis, log units, mean (SD) 2.89 (0.70) 2.86 (0.66) Ocular comorbidity, no. (%) 36 (24.3) 34 (23.0) Patient-reported measures Visual disability (VF-14), mean score (SD) (22.28) (20.59) Cataract Symptom Score, mean score (SD) 3.84 (3.43) 3.85 (3.14) Trouble with vision, mean score (SD) 3.11 (0.91) 3.11 (0.89) Satisfaction with vision, mean score (SD) 3.64 (0.60) 3.72 (0.53) General Health Status (SF-12) Physical, mean score (SD) (10.89) (9.79) Mental, mean score (SD) (10.38) (9.36) Abbreviations: logmar, logarithm of the minimum angle of resolution; SD, standard deviation. >3,000 sec arc (0.0% vs. 18.5%, P!.001). The intervention group also presented a higher improvement of 0.60 log sec arc (95% CI ) in stereopsis. In the intervention group, VF-14 score was 8.2 points higher (95% CI 5 5.3, 11.2), and 74.1% of patients in this group presented the maximum score, compared with 43.0% in the control group (P!.001). The change from baseline was 11.6 points higher (95% CI ) for the intervention group (Table 2). For the remaining patient-reported measures related to vision (trouble and satisfaction with Table 2 Primary outcomes 4 6 months postoperatively and change from baseline Outcomes Surgery in one eye only: control Surgery in both eyes: intervention Difference (95%CI) Sample size n n Clinical outcomes Binocular visual acuity, logmar, mean (SD) 0.18 (0.17) 0.11 (0.10) 0.07 (0.03, 0.12)*** Decimal scale, mean O0.3 [50.5 decimal], no. (%) 20 (14.8) 3 (2.2) *** O0.1 to <0.3, no. (%) 79 (58.5) 72 (51.8) <0.1 [50.8 decimal], no. (%) 36 (26.7) 64 (46.0) Change a, logmar, mean (SD) (0.23) (0.18) 0.05 (20.002, 0.11) Binocular contrast sensitivity, log units, mean (SD) 1.57 (0.18) 1.61 (0.1) 0.04 (20.002, 0.09)!1.30, no. (%) 10 (7.4) 2 (1.4) >1.30 to!1.70, no. (%) 69 (51.1) 77 (55.4) >1.70, no. (%) 56 (41.5) 60 (43.2) Change a, log units, mean (SD) 0.44 (0.36) 0.46 (0.32) 0.02 (20.09, 0.14) Stereopsis, log units, mean (SD) 2.37 (0.69) 1.75 (0.24) 0.62 (0.45, 0.79)*** >3.48 [53,000 sec arc], no. (%) 25 (18.5) 0 *** O1.78 to!3.48, no. (%) 84 (62.2) 42 (30.4) <1.78 [560 sec arc], no. (%) 26 (19.3) 96 (69.6) Change a, log units mean (SD) (0.79) (0.69) 0.60 (0.36, 0.85)*** Patient-reported outcomes Visual disability, VF-14, mean units (SD) 89.5 (15.9) 97.7 (7.1) 8.24 (4.35, 12.36)*** <80, no. (%) 26 (19.3) 5 (3.6) *** O80 to!100, no. (%) 51 (37.8) 31 (22.3) 100, no. (%) 58 (43.0) 103 (74.1) Change a, mean units (SD) 28.3 (20.4) 39.9 (20.7) (4.79, 18.12)*** Abbreviations: CI, confidence interval; logmar, logarithm of the minimum angle of resolution; SD, standard deviation. a Postoperative value 2 preoperative value. *** P!.001.

5 X. Castells et al. / Journal of Clinical Epidemiology 59 (2006) Table 3 Secondary outcomes 4 6 months postoperatively and change from baseline Secondary outcomes Surgery in one eye only: control Surgery in both eyes: intervention Difference (95% CI) Sample size n n Trouble with vision, mean score (SD) 1.58 (0.86) 1.17 (0.48) 0.41 (0.17, 0.64)*** No trouble with vision, no. (%) 83 (61.5) 120 (86.3) *** Change a, mean score (SD) (1.3) (1.03) 0.43 (0.06, 0.81)* Satisfaction with vision, mean score (SD) 1.53 (0.81) 1.13 (0.38) 0.40 (0.20, 0.61)*** Very satisfied, no. (%) 84 (62.2) 123 (88.5) *** Change a, mean score (SD) (1.02) (0.62) 0.51 (0.23, 0.79)*** Cataract Symptoms Score, mean (SD) 0.78 (1.9) 0.12 (0.45) 0.66 (0.21, 1.11)*** Change a, mean score (SD) (3.81) (3.13) 0.66 (20.49, 1.86) General Health Status (SF-12) Physical, mean score (SD) 46.2 (9.3) 47.5 (9.3) (24.40, 1.85) Change a, mean score (SD) 1.40 (9.2) 1.76 (10.6) (23.56, 3.04) Mental, mean score (SD) 51.2 (6.6) 53.1 (4.9) (23.79, 20.03)* Change a, mean score (SD) 2.96 (10.5) 4.27 (10.2) (24.71, 2.16) Abbreviations: CI, confidence interval; logmar, logarithm of the minimum angle of resolution; SD, standard deviation. a Postoperative value 2 preoperative value. * P!.05; *** P!.001. vision and the cataract symptoms score), the intervention group presented significantly better results after surgery and a higher improvement (Table 3). Postoperative general health status, as measured with the SF-12, was similar between groups, except that the mental component was significantly better for the intervention group (Table 3). Figure 2 shows the proportion of total improvement from baseline among the both-eyes surgery group (represented by the 100%) that could be attributed to surgery in one eye only. The change in the control group represented O70% of the change observed in the intervention group in all measures except stereopsis. That is, 88.4% of change in visual acuity after both-eyes surgery was attributable to surgery in one eye only. This percentage was 95.7% for contrast sensitivity and 70.9% for VF-14, but only 45.9% for stereopsis (Fig. 2). The combined outcome of visual acuity and VF-14 after first-eye surgery was analyzed for patients in the control group (Table 4). Thirteen (9.6%) patients showed low levels in both visual acuity and VF-14 after surgery; 33 (24.4%) 100% 80% 60% 40% 20% 0% 88.4% Visual Acuity 95.7% Contrast Sensitivity 45.9% Stereopsis 70.9% VF-14 Fig. 2. Proportion of change due to surgery in one eye only. Percents indicate, on average, the proportion over the total improvement after botheyes surgery that is achieved after one eye only surgery; thus, 100% should be interpreted as the improvement in the both-eyes group. showed low level in at least one of them; and 18 (13.3%) patients showed high levels in both measures. Within age groups (!65 and >65 years), the two trial branches presented similar characteristics at baseline. The numbers of younger patients completing the trial were 32 for surgery in one eye only and 33 for surgery in both eyes. The differences in primary outcomes observed between treatment groups after surgery were similar in younger and older patients, except that with the VF-14 older patients showed a stronger effect of the intervention (difference of 9.18 points between treatment groups, 95% CI from 5.73 to 12.63) than younger patients (difference of 5.21 points, 95% CI from 0.53 to 10.96). For secondary outcomes, older patients presented a higher benefit in satisfaction with vision in terms of the proportion of patients very satisfied with vision: 58.3% in the control group vs. 90.6% in the intervention group for older patients and 75.0% in the control group vs. 81.8% in the intervention group for younger patients. 4. Discussion Compared to surgery in one eye only, both-eyes surgery improved stereopsis twofold, patient-reported visual disability by 30%, and visual acuity moderately, but made no difference in contrast sensitivity. These data indicate that, among bilateral cataract patients, second-eye surgery is associated with a benefit both statistically significant and clinically relevant. The observed benefit in stereopsis could be explained in terms of the second surgery reducing the disparity in visual acuity and contrast sensitivity between eyes. In bilateral cataract patients, surgery in one eye usually increases differences between eyes in visual acuity, thus compromising stereopsis. It is very likely that the improvement observed in stereopsis after surgery in one eye only was due to the increase in visual acuity, because good stereopsis requires

6 206 X. Castells et al. / Journal of Clinical Epidemiology 59 (2006) Table 4 Visual acuity by patient-reported visual disability postoperatively in control group patients (first-eye surgery) Patients reporting visual disability by VF-14 score, no. (%) Visual acuity, logmar <80 O80 to!90 >90 to! Total O (9.6) 2 (1.5) 5 (3.7) 0 20 (14.8) >0.15 to! (6.7) 4 (3.0) 14 (10.4) 15 (11.1) 42 (31.1) O0.10 to! (2.2) 2 (1.5) 7 (5.2) 25 (18.5) 37 (27.4) < (0.7) 7 (5.2) 10 (7.4) 18 (13.3) 36 (26.7) Total 26 (19.3) 15 (11.1) 36 (26.7) 58 (43.0) 135 (100) Abbreviations: logmar, logarithm of the minimum angle of resolution. a minimum level of good vision [22]. As in other studies [4,10,23], our results show that the improvement in stereopsis in the both-eyes surgery group doubled that of the one-eyeonly surgery group. This difference in improvement (0.6 log sec arc) is clearly higher than the cutoff accepted as clinically relevant [24]. In addition, surgery in both eyes reduced the number of patients with a lack of binocular vision (>3,000 sec arc). The benefit in binocular visual acuity, despite being statistically significant, did not reach the clinically relevant threshold of one Snellen line [19] and was clearly smaller than the ETDRS threshold of three lines [24]. This is consistent with previous studies reporting marginal improvements in visual acuity after second-eye surgery [4,8,10,23]. The most likely explanation is the association of binocular visual acuity and contrast sensitivity with the monocular measure of the better eye, which had a great improvement after first-eye surgery and a marginal improvement after second-eye surgery [25]. Nevertheless, it is important to point out that undergoing surgery in both eyes significantly increased the probability of good binocular visual acuity (<0.1 logmar, or >0.8 decimal scale), and reduced that of bad visual acuity (>0.3 logmar, or <0.5 decimal scale). Talbot and Perkins [23] observed similar proportions of patients with failure of surgery (logmar visual acuity >0.3). For contrast sensitivity a similar effect was observed, but the differences between treatment groups did not reach statistical significance. An important improvement was observed in all the patient-reported visual disability measures (the VF-14 and the general questions about difficulty and satisfaction with vision). Note that, in particular, the improvement after both-eyes surgery in the VF-14 was clearly higher than the 5 points that have been suggested to represent a clinically significant change [3]. Consistently, there was a relevant higher proportion of patients in the both-eyes surgery group reporting not to have trouble and to be very satisfied with vision. Our results suggest a relevant influence of stereopsis in patient-reported visual disability, mainly among patients with a relatively good level of visual acuity (in the present study, after first-eye surgery). Some authors have pointed the importance of visual acuity and contrast sensitivity in patient-reported visual disability, but its association with stereopsis, as well as other clinical dimensions (including glare disability or visual fields), is less clear [10,24,26]. Available data do not fully explain the reasons for the improvement in perceived visual disability due to second-eye surgery, and further research is needed to identify the physiopathologic mechanisms that influence perceived visual disability. It is remarkable that an important proportion of patients achieved a high-level outcome after first-eye surgery: 43% were free enough of visual disability to perform basic everyday activities and 27% achieved good visual acuity. Thirteen percent of patients after first-eye surgery achieved a good outcome in both visual acuity and visual disability. These results suggest that a subgroup of patients would get little benefit from second-eye surgery. On the other hand, it is also relevant that a proportion (24%) of patients obtained a bad outcome in visual acuity or VF-14 after their first surgery; this group would be likely to get an important benefit from second-eye surgery. Even though our results show a benefit of surgery in both eyes for the whole group of bilateral cataract patients, the decision of operating the second eye should take into account the outcome of the first-eye surgery. Age has been a controversial factor in the debate for prioritization of cataract surgery [6,7], and some insurance companies have suggested limiting access to second-eye surgery [3]. Our results did not support the hypothesis that younger patients obtain more benefit from cataract surgery in the second eye, because similar results were observed within both age groups in most outcome measures, and the differences that were found suggested that older patients obtain more benefit from second-eye surgery. However, a more thorough analysis of the relationship between age and the benefits of second-eye surgery should be undertaken in future research. One limitation of our study was the impossibility of blinding treatment to patients. To avoid bias in patient expectations, patients assigned to surgery in one eye only for study purposes were scheduled to receive second-eye surgery immediately after the end of study follow-up. Another possible limitation was the ceiling effect that some outcome measures showed after surgery. We addressed this limitation with the use of a clinically meaningful categorization. The third limitation was the possible anisometropy

7 X. Castells et al. / Journal of Clinical Epidemiology 59 (2006) caused in patients operated in one eye only during the follow-up period. Because patients included in the study had only moderate refractive errors, this was tolerable. To our knowledge, this is the first study to compare outcomes of both-eyes surgery with outcomes of surgery in one eye only among bilateral cataract patients, with assessments starting prior to any surgery. Previous studies included only patients scheduled for second-eye surgery, excluding patients operated in the first eye but without an active indication for second-eye surgery. Generalizability of such studies is limited, because an important proportion ( 50%) of patients with bilateral cataracts do not undergo surgery in the second eye [2,9]. Thus, the design of these studies did not permit answering the relevant question of what is the most appropriate treatment (surgery in both eyes in two separate operations, or surgery in one eye only) for patients with bilateral cataracts when they are first indicated for surgery. The present findings suggest that, on average, bilateral cataract patients should have surgery in both eyes. The benefits of second-eye surgery are not limited to younger age groups. The decision to operate on the second eye should be supported with additional clinical measurements after the first-eye surgery: not only visual acuity, but also stereopsis and patient-reported visual disability. Acknowledgments We thank Professor Gordon Guyatt (McMaster University) for suggestions on the manuscript and Josep Tuñı (ophthalmologist at the Hospital de l Esperança) for comments about optometric tests. This work was supported by grants from the Catalan Agency for Health Technology Assessment and Research (CAHTAR) (10/31/98) and the Fondo de Investigacion Sanitaria (FIS) (99/0686). Moreover, it was carried out within the Network of Excellence IRYSS (G03/202), supported by funds from the FIS. References [1] Lundström M, Stenevi U, Thorburn W. The Swedish national cataract register: a 9-year review. Acta Ophthalmol Scand 2002;80: [2] Castells X, Alonso J, Ribo C, Nara D, Teixido A, Castilla M. Factors associated with second eye cataract surgery. Br J Ophthalmol 2000; 84:9 12. [3] Javitt JC, Steinberg EP, Sharkey P, Schein OD, Tielsch JM, Diener M, Legro M, Sommer A. Cataract surgery in one eye or both: a billion dollar per year issue. Ophthalmology 1995;102: [4] Laidlaw DAH, Harrad RA, Hopper CD, Whitaker A, Donovan JL, Brookes ST, Marsh GW, Peters TJ, Sparrow JM, Frankel SJ. Randomised trial of effectiveness of second eye cataract surgery. Lancet 1998;352: [5] Desai P, Reidy A, Minassian DC, Vafidis G, Bolger J. Gains from cataract surgery: visual function and quality of life. Br J Ophthalmol 1996;80: [6] Hadorn DC, Holmes AC. The New Zealand Priority Criteria Project. Part 1: Overview. BMJ 1997;314: [7] Bellan L, Mathen M. The Manitoba Cataract Waiting List Program. Can Med Assoc J 2001;164: [8] Castells X, Alonso J, Ribo C, Casado A, Buil JA, Badia M, Castilla M. Comparison of the results of first and second cataract eye surgery. Ophthalmology 1999;106: [9] Lundström M, Stenevi U, Thorburn W. Quality of life after first- and second-eye cataract surgery: five-year data collected by the Swedish National Cataract Register. J Cataract Refract Surg 2001;27: [10] Elliott DB, Patla A, Furniss M, Adkin A. Improvements in clinical and functional vision and quality of life after second eye cataract surgery. Optom Vis Sci 2000;77: [11] Vanden Bosch ME, Wall M. Visual acuity scored by the letterby-letter or probit methods has lower retest variability than the line assignment method. Eye 1997;11: [12] Elliott DB, Bullimore MA, Bailey IL. Improving the reliability of the Pelli Robson contrast sensitivity test. Clin Vision Sci 1991;2: [13] Steinberg EP, Tielsch JM, Schein OD, Javitt JC, Sharkey P, Cassard SD, Legro MW, Diener-West M, Bass EB, Damiano AM, et al. The VF-14: an index of functional impairment in patients with cataract. Arch Ophthalmol 1994;112: [14] Cassard SD, Patrick DL, Damiano AM, Legro MW, Tielsch JM, Diener-West M, Schein OD, Javitt JC, Bass EB, Steinberg EP. Reproducibility and responsiveness of the VF-14: an index of functional impairment in patients with cataracts. Arch Ophthalmol 1995;113: [15] Alonso J, Espallargues M, Andersen TF, Cassard SD, Dunn E, Bernth-Petersen P, Norregaard JC, Black C, Steinberg EP, Anderson GF. International applicability of the VF-14: an index of visual function in patients with cataracts. Ophthalmology 1997;104: [16] Espallargues M, Alonso J; Barcelona I-PORT investigators; International Patient Outcomes Research Team. Effectiveness of cataract surgery in Barcelona, Spain: site results of an international study. J Clin Epidemiol 1998;51: [17] Gandek B, Ware JE, Aaronson NK, Apolone G, Bjorner JB, Brazier JE, Bullinger M, Kaasa S, Leplege A, Prieto L, Sullivan M; International Quality of Life Assessment. Cross-validation of item selection and scoring for the SF-12 Health Survey in nine countries: results from the IQOLA project. J Clin Epidemiol 1998;51: [18] Castells X, Alonso J, Castilla M, Ribo C, Cots F, Anto JM. Outcomes and cost of outpatient and inpatient cataract surgery: a randomised clinical trial. J Clin Epidemiol 2001;54:23 9. [19] Steinberg EP. Variations in cataract management: patient and economic outcomes. Final report of the patient outcomes research team (PORT). Baltimore, MD: U.S. Agency for Health Care Policy and Research; [20] Rubin GS, West SK, Muñoz B, Bandeen-Roche K, Zeger S, Schein O, Fried LP. Salisbury Eye Evaluation Project. A comprehensive assessment of visual impairment in a population of older Americans: the SEE study. Invest Ophthalmol Vis Sci 1997;38: [21] Elliott DB, Sanderson K, Conkey A. The reliability of the Pelli Robson contrast sensitivity chart. Ophthalmic Physiol Opt 1990; 10:21 4. [22] Kwapiszeski BR, Gallagher CC, Holmes JM. Improved stereoacuity: an indicator for unilateral cataract surgery. J Cataract Refract Surg 1996;22: [23] Talbot EM, Perkins A. The benefit of second eye cataract surgery. Eye 1998;12: [24] Rubin GS, Bandeen-Roche K, Huang GH, Munoz B, Schein OD, Fried LP, West SK. Salisbury Eye Evaluation Project. The association of multiple visual impairments with self-reported visual disability. Invest Ophthalmol Vis Sci 2001;42: [25] Pardhan S, Elliott DB. Clinical measurements of binocular summation and inhibition in patients with cataract. Clin Vision Sci 1991;6: [26] Elliott DB, Hurst MA, Weatherill J. Comparing clinical tests of visual function in cataract with the patient s perceived visual disability. Eye 1997;4:712 7.