From the Departments of Ophthalmology, University of California, Irvine(Dr McDonnell), The University of Southern California, Los Angeles (Dr McDonnell), and Duke University, Durham, NC (Dr Lee); Departments of Medicine and Public Health, University of California, Los Angeles (Ms Spritzer and Dr Hays); the EMMES Corporation, Rockville, Md (Dr Lindblad), and the RAND Corporation, Santa Monica, Calif (Dr Hays). Dr McDonnell is now with the Wilmer Ophthalmological Institute, Baltimore, Md. The authors have no relevant financial interest in this article.
To evaluate the associations of presbyopia and its correction, particularly monovision optical correction, with vision-targeted health-related quality of life.
The National Eye Institute Refractive Error Quality of Life (NEI-RQL) Instrument was prospectively self-administered by subjects from 6 medical centers in the following age and correction categories: subjects with emmetropia younger than 45 years (n = 75), subjects with emmetropia aged 45 years or older (n = 38), and subjects with ametropia aged 45 years or older without monovision (n = 486) or corrected with monovision (n = 38). Differences in the 13 NEI-RQL Instrument subscale scores among subjects in the 4 groups were examined. The age of 45 years or older was used as a surrogate for presbyopia.
A comparison of older (age ≥45 years) vs younger (age <45 years) persons with emmetropia suggests that presbyopia was associated with reduced scores in 7 of 13 subscales (P<.05). In those aged 45 years or older, correction of presbyopia with monovision was associated with statistically significantly better scores on 3 subscales (expectations, dependence on correction, and appearance) compared with single-vision correction. One subscale (dependence on correction) showed worsening scores with increasing age without adjustment for need or type of correction. Older persons with monovision correction had significantly worse scores than younger subjects with emmetropia on all subscales except suboptimal correction and appearance.
Presbyopia is associated with worse vision-targeted health-related quality of life compared with younger subjects with emmetropia. Monovision correction of presbyopia is related to some improvements in health-related quality of life, but it is still worse than that for younger subjects with emmetropia in several areas.
THE FORM of optical correction chosen by a given individual reflects his or her lifestyle, including occupational and recreational needs. As such, patients active in sports and outdoor activities that require excellent distance visual acuity may desire optimal distance correction, necessitating reading eyeglasses or bifocal contact lenses for near vision if the patient is presbyopic. Presbyopia is believed to reflect a loss of accommodation due to stiffening of the lens with age, a weakening of the ciliary muscle–lens zonule apparatus, or a combination of mechanisms. Subjects in the presbyopic age range of 45 years or older who read extensively for work and pleasure may value good uncorrected near vision above all else, and choose to be undercorrected with their eyeglasses, contact lenses, or by surgery. Monovision is designed for presbyopic individuals who desire vision at both distance and near without needing to reach for reading glasses.1 As part of the surgical correction of refractive error, monovision has been recommended for those patients who seek to minimize their future need for corrective lenses in any situation.2,3
Not all patients are good candidates for monovision, however, and not all will successfully adapt to it.4,5 The contact lens literature includes several studies of the likelihood of success with monovision. In one review of published results on monovision, 1 the mean success rate was 76% (434 of 573 patients with successful monovision); exclusion of contact lens–related intolerant individuals resulted in improvement in the success rate to 81%. Thus, a noteworthy percentage of patients are not successfully corrected with monovision.
Although many patients tolerate monovision well, concerns exist regarding adverse consequences of monovision, including difficulty in performing tasks that require depth perception and good eye-hand coordination (eg, ball sports, surgical procedures, handling machinery, driving, and others). Monovision has been found to produce either no change in binocular visual acuity or a small to moderate change for both contact lens-induced1,6 or surgically created3 monovision. Contact lens–induced monovision reduces stereopsis; the magnitude of the reduction decreases with time.7 Monovision is reported to cause no measurable change in peripheral visual acuity or visual field width.8 Contrast sensitivity increases by the square root of 2 when the stimulus is viewed binocularly rather than monocularly. Thus, in the absence of monocular defocus the binocular contrast sensitivity is about 42% greater than monocular contrast sensitivity. With increasing monocular defocus, the binocular contrast sensitivity decreases steadily and then falls below that of the monocular contrast sensitivity, showing binocular inhibition. If the defocus is further increased (beyond a +2.5-diopter defocus), the binocular contrast sensitivity reverts to the monocular sensitivity level, indicating suppression of the defocused eye.9
Study findings of near task performance (such as card filing and letter editing) demonstrate a 2% to 6% reduction with contact lens-induced monovision.10 The success and safety of monovision correction in pilots remains a matter of controversy. Some authors2 claim success with monovision in pilot studies and 1 study reports the excellent performance of military pilots rendered monocular.11 The opposite conclusion is offered by The National Transportation Safety Board's investigation of the October 19, 1996, Delta Airlines Flight 554 nonfatal crash at La Guardia Airport, New York City, which concluded that "the probable cause of this accident was the inability of the captain, because of his use of monovision contact lenses, to overcome his misperception of the airplane's position relative to the runway during the visual portion of the approach."12(pvii)
The conflicting results and interpretations of specialized vision testing in patients with monovision have resulted in lingering uncertainty regarding the positive and negative aspects and the appropriate patient selection for this form of correction. This study represents the initial use of a survey to assess the effect of presbyopia on health-related quality of life and to compare monovision, single-vision forms of optical correction, and subjects with emmetropia.
Patients included in this study were individuals recruited from the practices of 6 medical centers (University of Alabama, Birmingham; University of California, San Francisco; Henry Ford Hospital, Detroit, Mich; University of Texas Southwestern, Dallas; Naval Medical Center, San Diego, Calif; and University Hospitals of Cleveland, Cleveland, Ohio). At each institution the local institutional review board approved the enrollment of subjects.
Between June 1, 1999, and January 31, 2001, 38 subjects with ametropia(those with myopia and hyperopia) aged 45 years or older with monovision correction with contact lenses or by surgery; 486 subjects with myopia and hyperopia with symmetrical correction of vision with eyeglasses, contact lenses, or by surgery in the age range of 45 years or older; 75 subjects with emmetropia younger than 45 years; and 38 subjects with emmetropia aged 45 years or older were recruited after signing an institutional review board–approved consent statement. Age was used as a surrogate for presbyopia. To be included in this study, participants were required to be able to read English fluently as a first or second language and to be able to complete a self-administered questionnaire, the National Eye Institute Refractive Error Quality of Life(NEI-RQL) Instrument.13 The participants must have had a visual acuity of 20/32 or better (≥75 letters) for near and far visual acuity in the worst eye with current correction, and they must have been using this current form and magnitude of correction for at least 3 months. If the participant had monovision, the eye corrected for near vision must have had a near visual acuity of 20/32 or better and the eye corrected for distance must have had a far visual acuity of 20/32 or better. Exclusionary criteria were as follows: chronic ocular disease or keratoconjunctivitis sicca, diabetes mellitus, a neurological disease that limits everyday activities, the inability to ascend a flight of stairs without assistance, and cognitive impairment (based on clinical judgment).
We used t tests to evaluate differences in mean scores on the 13 NEI-RQL Instrument subscales in 3 comparison groups of subjects; older (aged ≥45 years) vs younger (aged <45 years) subjects with emmetropia, older subjects with monovision vs older subjects with single-vision correction, and older subjects with monovision vs young subjects with emmetropia. In the older subjects with monovision vs young subjects with emmetropia groups, the magnitude of difference between groups was evaluated using the effect size.14 This statistic, a ratio of signal to noise, is calculated as the mean difference in scores between groups divided by the pooled standard deviation. According to guidelines provided by Cohen, 15 0.2 represents a small difference, 0.5 a medium difference, and 0.8 a large difference. Analysis of variance was used to test for association of age with the 13 subscale scores. Age groups in this analysis were defined as 50 years or younger, 51 to 60 years old, and 61 years or older. Differences were considered statistically significant at P≤.05. All scores are given as the mean (SD).
Table 1 presents the distribution of the demographic characteristics in the 4 groups of subjects. Work status was balanced in the groups restricted to the ages of 45 years or older. Several imbalances were observed. Older subjects with emetropia were more likely to have a high school diploma or less compared with the other 3 groups (32% vs≤15%; P<.01) and to earn less than $50 000 a year compared with older subjects with ammetropia (58% vs 39%; P<.01). Fewer than half of the younger subjects with emetropia were white (43%) compared with 70% or more of the other 3 groups (P<.01). Females accounted for 79% of the older monovision group compared with 56% of the older single-vision correction group (P<.05).
To assess the effect of presbyopia alone on vision-targeted quality of life, we compared the scores of younger (aged <45 years) subjects with emmetropia with those of older (aged ≥45 years) subjects with emmetropia not corrected with monovision. Table 2 presents the mean scores for each subscale by age group. The 38 subjects in the 45 years or older age group scored significantly worse (P<.05) on 7 of the 13 subscales (clarity of vision, expectations, near vision, diurnal fluctuations, symptoms, dependence on correction, and satisfaction with correction) compared with the 75 subjects in the younger age group. Comparison of mean scores among all subjects, regardless of correction, in the age groups 50 years or younger, 51 to 60 years, and 61 years or older revealed that the scores of only 1 subscale (dependence on correction) worsened consistently with increasing age (P<.001) (data not shown).
Table 3 presents the comparison of the mean scores for the 13 subscales for 38 subjects aged 45 years or older corrected with monovision with the mean scores of 486 participants aged 45 years or older with single-vision correction. Subjects with monovision correction scored statistically significantly higher then those subjects of similar age with single-vision correction on 3 of the following NEI-RQL Instrument subscales: expectations, dependence on correction, and appearance. These differences remained after adjustment for sex, race, educational level, and annual income. Subjects with monovision reported lower scores for clarity of vision (3 points), diurnal fluctuation (6 points), and glare (8 points); however, the differences were not statistically significant.
The NEI-RQL Instrument scores were significantly worse for the 38 subjects with corrected monovision aged 45 years or older than for the 75 young subjects with nonmonovision emmetropia in all subscales except suboptimal correction and appearance as shown in Table 4.Significant differences in mean scores ranged from 49 for dependence on correction and 39 for expectations to 6 or 7 for symptoms and activity limitation. Differences ranged between 9 and 23 for the remaining subscales (clarity of vision, near vision, far vision, diurnal fluctuation, glare, worry, and satisfaction). The magnitude of the difference is reflected in the effect size (Table 4). Of the 11 subscales with statistically significant differences, 7 subscales showed large differences (clarity of vision, expectations, near vision, diurnal fluctuation, glare, dependence on correction, and satisfaction), 3 subscales showed differences of medium magnitude (far vision, activity limitation, and worry), and 1 subscale showed a small difference (suboptimal correction).15 All differences remained statistically significant after adjustment for educational level, annual income, race, and sex.
The NEI-RQL Instrument subscale scores indicate that presbyopia is associated with substantial, negative effects on vision-targeted health-related quality of life. Monovision is one option for the correction of presbyopia and can be achieved with contact lenses, keratorefractive surgery, or intraocular lenses in conjunction with cataract extraction. Our data show that monovision is associated with a mix of positive and negative effects on the health-related quality of life. Subjects with monovision have better expectations for their future vision, less dependence on correction, and fewer problems with appearance. These results have face validity, as these subscales represent many of the concerns that subjects seek to address by pursuing monovision correction.
The mean scores for the near and far vision subscales were not significantly different between the monovision-corrected group and the single-vision correction group. The far vision subscale includes questions about driving and other distance activities, suggesting that those with monovision correction were not limited in their driving as a result of their correction.
Our study selected only subjects who had used their current form of vision correction for at least 3 months without change. As a consequence, we selected for subjects who had undergone the adjustment to monovision and decided to continue with this form of correction. Also, we presumably selected for subjects without monovision who had either never tried monovision or tried it and failed to adjust successfully to it, resulting in a return to single-vision lenses. This self-selection is likely to be the explanation for the observed imbalances between groups in sex and race distributions. Despite this self-selection and presumed satisfaction of subjects with their current vision correction, we were able to document some provocative differences in vision-targeted functioning and well-being. In future studies, the NEI-RQL Instrument should be administered to subjects prior to and after exposure to monovision correction to assess responsiveness of this instrument to this change in correction.
For many patients, contact lens fitting or surgery to induce monovision can result in high levels of satisfaction, while other patients fail to adapt to this form of correction for a variety of reasons.4 Compared with full correction of myopia or hyperopia to achieve maximal distance visual acuity in both eyes, which will result in dependence on corrective lenses for reading in most patients older than 45 years, monovision seems to enhance certain measures of vision-targeted health-related quality of life. Objective measurements of task performance at near or distance (including landing jets) do not demonstrate significant decline of performance as a consequence of monovision.2,11 Whether there are some individuals or occupations for which monovision is at least relatively contraindicated cannot be determined from our study. Although subjects with monovision reported lower scores for clarity of vision, diurnal fluctuations, and glare, these differences were not statistically significant. About 20% of individuals will not tolerate a trial of monovision correction successfully1; it is usually possible to detect these individuals with a trial of soft lens wear for monovision.
Our data make it clear that the highest scores are obtained with the NEI-RQL Instrument in young subjects with nonpresbyopic emmetropia. The significant differences in mean scores between these subjects and those with monovision as the means of correction, most of which are large, indicate that monovision correction does not fully restore the health-related quality of life experienced by young subjects with emmetropia who can accommodate for near vision. The ideal correction of refractive error with presbyopia would achieve scores close to those found in young subjects with emmetropia; clearly monovision correction in this study does not approximate this goal. Further efforts are, therefore, indicated to identify one or more forms of correction to allow subjects with ametropia aged 45 years or older to function at the level experienced by subjects with emmetropia with adequate accommodative reserve.
We attribute the differences in NEI-RQL Instrument scores between younger and older subjects with emmetropia as being reflective of presbyopic differences. Such differences could also be due to aging changes other than the development of presbyopia. However, presbyopia is the major change associated with aging in the otherwise normal eye. Further, all subjects in this study had normal visual acuity, and visual acuity did not vary by age group in this study. As such, it is likely that the changes in NEI-RQL Instrument scores are related to presbyopic issues rather than other aging changes with the eyes of these subjects.
The NEI-RQL Instrument may be helpful to clinicians and investigators seeking to understand the benefits and limitations of monovision correction, multifocal intraocular lenses, accommodating intraocular lenses, and other forms of correction of presbyopia with or without myopia or hyperopia, and to patients seeking to understand their options for correction of presbyopia.
Corresponding author and reprints: Peter J. McDonnell, MD, Wilmer Ophthalmological Institute, Maumenee 727, 600 N Wolfe St, Baltimore, MD 21287(e-mail: firstname.lastname@example.org).
Submitted for publication April 1, 2003; final revision received June 9, 2003; accepted June 10, 2003.
This study was supported by contracts N01-EY6-2112 (for the first 5 years of the contract) and N01-EY12113 (current contract) from the National Eye Institute, National Institutes of Health, Bethesda, Md, with additional support from the American Academy of Ophthalmology, San Francisco, Calif; Allergan Inc, Irvine; Bausch and Lomb–Contact Lens Division, Rochester, NY; Keravision Inc, Fremont, Calif; and the Visitec Company, Sarasota, Fla.
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