Estimation of the misclassification rate of self-reported visual disability.

PURPOSE: To estimate the misclassification rate of self-reported visual disabilities in a hospital-based population with known visual impairment. METHODS: Subjects (N=570) were recruited among patients aged 50 years and more and classified to three categories of visual impairment level. The questionnaire was administered to consenting patients through a telephone interview. Data collected from questionnaires and medical records were compared regarding severity of visual impairment. Sensitivity and specificity were determined for each question. Predictive ability and misclassification rates were computed for various prevalences. RESULTS: Questions related to near and far distance visual acuity with glasses have both a good sensitivity (82.6% and 81.8%) and a good specificity (85.6% and 88.9%) for the presence of severe visual impairment. CONCLUSION: The findings allow the determination of the misclassification rate and predictive ability. This could be useful to estimate the prevalence of visual impairment from health surveys.

Functional outcome and satisfaction after photorefractive keratectomy. Part 1: development and validation of a survey questionnaire.

OBJECTIVE: The aim of this study was to develop a valid, reliable, and easy-to-administer instrument to assess patient satisfaction and perceived outcome after bilateral excimer laser photorefractive keratectomy. DESIGN: Development and validation of a psychometric questionnaire. PARTICIPANTS: Consecutive patients who underwent bilateral excimer laser photorefractive keratectomy from May 1994 through May 1997 by 12 surgeons from four collaborating centers. To be eligible, a minimum of 4 months since the last surgery and a maximum of 30 months since the first surgery was required. METHODS: The new instrument was derived in part from the Prospective Evaluation of Radial Keratotomy (PERK) study 10-year psychometric questionnaire and the Visual Functional Index (VF-14), an index of functional impairment in patients with cataract. Questions were grouped in seven scales, each covering a specific aspect of quality of vision. These included global satisfaction, quality of uncorrected vision, quality of corrected vision, quality of night vision, glare, daytime driving, and night driving. MAIN OUTCOME MEASURES: Acceptability, reliability, validity, and interpretability of the instrument, as well as its ease of administration. RESULTS: The instrument scale structure was examined and scale scores were created. Item-discriminant validity ensured that questions belonged to their hypothesized scale, based on multitrait correlation analysis. The instrument was shown to be reliable by a high level of internal consistency, and all Cronbach's alpha coefficients were superior or equal to 0.83. Construct-related validity and interpretability were assessed based on correlations between scale scores and clinically recognized success criteria such as visual acuity and refraction. Respondent burden was shown to be minimal. Acceptability of the instrument was shown to be very good, with a participation rate of 74.3% (690 of 929 patients). The instrument is available in English and in French and the translation was shown to be reliable. CONCLUSIONS: The acceptability, reliability, and interpretability of the instrument, as well as its ease of administration, were shown to be adequate. This questionnaire appears clinically useful to document patient satisfaction after excimer laser photorefractive keratectomy.

Functional outcome and satisfaction after photorefractive keratectomy. Part 2: survey of 690 patients.

PURPOSE: To document patient satisfaction and self-perceived quality of vision after bilateral photorefractive keratectomy (PRK). DESIGN: Noncomparative, interventional case series. PARTICIPANTS: Consecutive patients who underwent bilateral PRK from May 1994 through May 1997 by the 12 surgeons of four collaborating centers with a minimum of 4 months since the last surgery and up to 30 months since the first surgery. METHODS: A questionnaire with known psychometric properties was self-administered by the patients. MAIN OUTCOME MEASURES: Responses to individual questions and scale scores. RESULTS: A total of 929 questionnaires were sent, of which 690 were answered and returned (74.3% response rate). The preoperative spherical equivalent ranged from -0.38 diopters [D] to -27.75 D (mean, -5.32 D; standard deviation, 2.85 D). Although 91.8% of the patients were satisfied or very satisfied with their surgery, 96.3% considered that their main goal had been reached, and 95.7% would still choose to have surgery if they had it to do over. The degree of satisfaction was proportional to the postoperative uncorrected visual acuity in the best eye expressed in LogMAR (r = -0.18, P: = 0. 0001) and was negatively correlated with the importance of the corneal haze (r = -0.23, P = 0.0001). Daytime glare was reported to be greater than before surgery by 55.1% of patients. A decrease in night vision was reported by 31.7% of patients, and 31.1% of patients reported increased difficulty driving at night because of their vision. CONCLUSIONS: Overall satisfaction after PRK for low to severe myopia appears to be very good. Glare and night vision disturbance, particularly bothersome for night driving, seem to constitute significant secondary effects that deserve further investigation and should be kept in mind for future improvements in the technique.

Contrast and glare testing in the assessment of visual performance of candidate eyes for penetrating keratoplasty.

PURPOSE: To determine whether visual acuity (VA) measurements performed at low levels of contrast and glare are a better diagnostic tool for determining whether corneal clouding warrants surgery. METHODS: Fifty-nine subjects were recruited from among the candidates for corneal graft. Monocular VA was measured with three Regan contrast VA charts: 96, 25, and 11%, with and without glare provided by the Brightness Acuity Tester (BAT). The discriminative ability of the tests was estimated using the area (AR) under receiver operating characteristic (ROC) curves. Associations between the different VA tests and the Visual Function Index (VF-14) score were studied, using Spearman coefficients. RESULTS: When comparing candidate eyes with contralateral eyes with corneal disease, lower contrasts VA tests provided greater discriminative power. VA measurements made with glare also tended to provide greater discrimination. In fact, discrimination was best with 11% contrast VA with glare, but "testability" was poor. The most practical test in a clinical setting, which retained high discriminative ability (0.798), was the 25% contrast VA with glare. The eye with the best VA correlated strongly with the VF-14, especially at 25% contrast without glare, resulting in an Rs of -0.729. CONCLUSION: Twenty-five percent contrast VA with BAT could help the practitioner to decide whether a corneal transplant is warranted when symptoms of reduced vision are more important than what high-contrast VA might indicate.

The VF-14 index of functional visual impairment in candidates for a corneal graft.

PURPOSE: To validate the Visual Function-14 (VF-14) index of functional visual impairment in candidates for a corneal graft. METHODS: One hundred thirty-four patients who were candidates for a corneal graft participated in this study between August 1996 and February 1997. Demographic, ocular history, best-corrected visual acuity, and detailed ocular examination data were collected. Functional visual impairment information was obtained by telephone interviews using the following: VF-14, SF-36 (Short Form-36, a more generic measure of general health function), and Visual Symptom Score, and four questions measuring the overall amount of trouble with vision, dissatisfaction with vision, ocular pain, and discomfort. RESULTS: The average age of corneal graft candidates was 64 +/- 18 years (range, 18 to 90 years) and 60% were women. The most frequent corneal disease was pseudophakic bullous keratopathy (41%). Ocular comorbidities included glaucoma or ocular hypertension (30%) and cataract (19%). The mean best-corrected visual acuity of the eye scheduled for surgery was 1.33 +/- 0.56 logMAR whereas the best eye best-corrected visual acuity was 0.36 +/- 0.44 logMAR. The mean VF-14 score was 73% +/- 26%, and the internal consistency was high, with a Cronbach alpha value of 0.94. The VF-14 correlated strongly with the best eye best-corrected visual acuity. It also correlated strongly with the Visual Symptom Score, the global measures of trouble and dissatisfaction with vision. Candidates for a corneal graft had low scores for all eight general health concepts evaluated with the SF-36, and the VF-14 correlated with seven of the eight SF-36 subscales. CONCLUSION: The VF-14 is a valid measure of functional visual impairment in candidates for a corneal graft. The Visual Symptom Score and the SF-36 are also useful indices in such patients.

Effects of induced transverse chromatic aberration from an afocal prismatic lens on spatio-temporal sensitivity.

The goal of this study was to evaluate the effect of ophthalmic lens-induced transverse chromatic aberrations (TCA) in natural viewing conditions on spatio-temporal thresholds. Three psychophysical experiments were performed; the first isolating the spatial component, the second isolating the temporal component and the third assessing spatio-temporal combinations. Taken together, the results show that TCA has profound effects on medium to high spatial frequencies (above 1 cpd) consistent with previous studies, and that the ratio of deficit TCA/blur can be higher than 2:1 for equivalent dioptric strengths. Furthermore, the results of Experiment 1 and 3 taken together show that the relative sensitivity loss caused by TCA can differ significantly between individuals and that a possible factor for this differential loss is the overall baseline spatio-temporal sensitivity profile of the individual.

Optical performance of aspheric concave ophthalmic lenses: the effect of vertex distance.

Variations of power errors in the periphery of concave aspheric lenses were assessed as a function of vertex distance. Comparisons were made between the performance of different types of spherical lenses and that of aspheric lenses (-6.00 and -8.00 D lenses were used). Off-axis measurements were made by means of a modified focimeter, which enabled rotation of the lens around the center of the vertex sphere. Reduction of the vertex sphere's radius from 27 to 23 mm simulated a 4-mm decrease in vertex distance. Results of the measurements are compared with a computed model. These results indicate that off-axis performance is more affected by a reduction of vertex distance in the case of aspheric lenses compared to spherical lenses. Resulting increases in oblique astigmatism (OA) and mean oblique error (MOE) are at the limit of clinical acceptance. The importance, for the practitioner, of respecting the vertex distance selected for a specific aspheric design when fitting this type of lens is emphasized.

Validation of French-language versions of the Visual Functioning Index (VF-14) and the Cataract Symptom Score.

OBJECTIVE: To produce and validate French-language versions of the Visual Functioning Index (VF-14), the Cataract Symptom Score (CSS) and two global measures of trouble and satisfaction with vision. DESIGN: Survey by means of telephone interviews conducted 2 weeks apart. SETTING: Ophthalmology clinic of a teaching hospital in Montreal. SUBJECTS: Subjects were recruited among patients with ocular media opacities, such as cataracts and corneal opacities. Of the 71 subjects recruited, 66 (41 French-speaking and 25 French- and English-speaking) completed the study. OUTCOME MEASURES: Visual acuity, scores on vision-related questionnaires and on the 36-Item Short-Form Health Survey (SF-36), a measure of perceived health status. RESULTS: The integral consistency of the French-language versions of the VF-14 and the CSS was high, with Cronbach alpha values of 0.96 and 0.82 respectively. The fidelity with regard to the English-language version, the test-retest reproducibility and the interrater agreement were high (intraclass correlation coefficients > or = 0.80). The correlation between the visual acuity of the better eye and the mean score on all four vision-related measures was statistically significant (p < or = 0.05). The VF-14 scores were also correlated with the score on five of the eight SF-36 subscales (p < or = 0.05). CONCLUSIONS: Our results show that French-language versions of the VF-14, CSS and global measures of trouble and satisfaction with vision are reliable and valid.

Luminance of projection focimeter target with oblique viewing.

In order to test the capacity of an optical projection focimeter for simultaneous use by several observers gathered around the instrument, the luminance of the projected target was measured for 3 projection focimeters (model Axil from Essilor, model LP2 from Nikon, and model LM-P5 from Topcon) when the photometer axis was perpendicular to the instrument screen and at oblique angles up to 75 degrees in 5 degrees increments. As expected, the luminance of the target decreased as obliquity of viewing increased; however, the rate of reduction is characteristic of each focimeter model. The repeatability of dioptric measurements with the Axil focimeter was assessed in the usual viewing position when the luminance of the target was reduced by optical filters (neutral density varying from 0.2 to 1 in 0.2 steps). The repeatablity remains within +/- 0.05 D for optical densities < or = 0.8. Our results show that a useful luminance is maintained over an observation angle that extends to 45 degrees. Depending on the model of focimeter, several observers may simultaneously observe and judge the focusing of the instrument.

Risk of automobile accidents among elderly drivers with impairments or chronic diseases.

A case-control study was conducted in Quebec elderly men in order to document the risk of road accidents associated with impairments or chronic medical conditions. All 1,400 drivers who had had an accident with either mild bodily injury or only property damage during their 70th year in 1988 and 1989 were selected as cases from the accident file of the "Société de l'Assurance Automobile du Québec" (SAAQ). They were compared to 2,636 controls randomly selected among drivers of the same age. Information on medical conditions was also obtained for all subjects from the SAAQ. Mileage and driving habits were documented through a mail questionnaire. Relative risk of accidents associated with medical conditions were estimated while controlling for confounders. Overall, the results suggest that elderly drivers of private vehicles with impairments or chronic medical conditions are not at increased risk of road accidents. Only those with arrhythmias had a significant increase in risk (OR = 1.63, CI: 1.00-2.65). This study does not support more severe norms for elderly drivers.

Risk of accidents among elderly car drivers with visual acuity equal to 6/12 or 6/15 and lack of binocular vision.

To document the risk of road accidents associated with minimal visual acuity (equal to 6/12 or 6/15) and lack of binocularity (stereoacuity > or = 200 sec arc), 1400 drivers who had had an accident during their 70th year were compared with 2636 controls randomly selected from the 30,000 70-year-old drivers who had had no accident during the same time. Information on visual characteristics and demerit points was obtained for all subjects from the Quebec Automobile Insurance Board. Mileage and prevailing driving conditions were documented through a mail questionnaire. The relative risks of accidents were estimated while controlling for traffic convictions, mileage, time spent and frequency of driving during rush hours. Drivers with minimal visual acuity alone had the same risk of road accidents as other drivers (OR = 0.97 CI 95%: 0.68-1.38). The risk of accidents among drivers with both minimal visual acuity and lack of binocularity was moderately higher than among other drivers (OR = 1.23, CI 95%: 0.88-1.72).

Discrepancy in the evaluation of visual impairment of elderly low-vision patients by general eye care practitioners and by low-vision practitioners.

Levels of impairment and disability determine eligibility for different welfare programs for visually handicapped persons. General eye care practitioners have to determine the level of impairment for administrative purposes, whereas the low-vision practitioner measures the level of impairment in order to plan the rehabilitation program. We compared the severity of visual impairment reported by the referring practitioners and the one reported by the low-vision specialists for the population of elderly low-vision patients receiving care from one of the largest rehabilitation centers for the visually handicapped in Quebec. Visual acuity ratings reported by general practitioners are lower than those reported by low-vision practitioners. The presence of visual handicap is generally well identified but the severity of visual impairment according to the World Health Organization (WHO)'s categories is not properly gauged by the general eye care practitioners as expressed by the sensitivity and the positive predictive value of the classification of the general practitioners in respect to the classification of the low-vision optometrists. The need to use existing standardized methods to measure visual acuity (VA) is emphasized. It may be hypothesized that this overestimation of the severity of the visual condition may have a negative impact on the process of rehabilitation of the elderly.

To use or not to use the refractive correction along with hand-held magnifiers.

Equivalent viewing power (EVP), field of view, and working distance (WD) were calculated for 4 different magnifier equivalent powers, four magnifier-to-eye distances, and for uncorrected spherical ametropias varying from +20.00 to -20.00 D in 0.25 D steps. Results show that the various viewing conditions which arise (depending on whether or not the refractive correction is worn) can differ considerably. The uncorrected unaccommodating myope has a greater EVP than the equivalent power of the magnifier if he chooses a magnifier-to-eye distance shorter than the focal length of the magnifier. In this situation, field of view is also enhanced. The uncorrected unaccommodating hyperope using a magnifier-to-eye distance longer than the focal length of the magnifier achieves a stronger EVP than the equivalent power of the magnifier. However, field of view is then reduced. For the uncorrected unaccommodating spherical ametrope, the use of a magnifier-to-eye distance corresponding to the focal length of the magnifier seems to be a good compromise between EVP, field of view, and working distance.

Subjective evaluation of a new multi-design progressive lens.

Throughout the first quarter of 1989, 14 professionals field-tested Varilux Infinity prior to its launching. The study was conducted to determine the following factors: the level of ability to adapt, length of the adaptation process, ratings of distortion and head movements, and level of satisfaction. Varilux Infinity was systematically offered to each potential user whatever the prescription requirement. Among the 720 persons who were fitted in the course of the experiment, only 8 (1.1 percent) could not adapt. After a 6-week trial period, 168 answered a survey as to their level of satisfaction with the new progressive lenses. The results show that the parameters of the prescription (ametropia, cylinder, axis, addition) are not related to either the length of the adaptation process or the other ratings of the Multi-Design progressive lens. Experienced wearers of progressive lenses adapt more quickly and are the most favorable in their evaluation of the new lens. On the other hand, first-time users of progressive lenses offer the same response as did new wearers of Varilux 2. However, wearers of Varilux Infinity do not notice as much the need for head movements. This improvement can be considered as a point in favor of the wider visual field provided by Varilux Infinity. On the whole, the most active and the least active patients respond similarly in their evaluation of the new lens. The ametropia, add power, or level of activity cannot be held as risk factors in the adaptation to Varilux Infinity.

Stereoacuity testing: an illusion of tilt when viewing two parallel vertical rods or lines.

When stereoacuity was measured, some subjects (but not all) saw the two vertical rods of the test to be tilted. The perceived tilt indicated that the top of a rod was nearer to or farther from the observer than the bottom. Sometimes one rod appeared tilted and sometimes both. It was rare for both to appear tilted in the same direction. There are 9 possible tilt combinations including both rods vertical. All were observed but only 1 of the 3 subjects observed them all. In some instances, the frequency with which a particular tilt combination was seen was influenced by which rod was nearer and by the binocular disparity presented by the rods. During a stereoacuity test, tilt can confuse the identification of the nearer rod. Uncertainty is avoided by regarding the middle of the rods. Lines drawn on paper were also seen to tilt by some subjects.

Combination of a side shield with an ocular moisture chamber.

A low vision patient suffering from dry eye symptoms was helped by use of a side shield modified so as to create a moisture chamber.