Vernier acuity cards: a practical method for measuring vernier acuity in infants

Vernier acuity cards: examination of development and screening validity

PURPOSE

Because vernier acuity seems to be limited by the visual cortex, it possesses excellent potential as a clinical/screening tool to detect amblyopia in infants and toddlers. Thus, we developed the vernier acuity cards specifically for this age group. We compared developmental data gathered using this new test and the Teller Acuity Cards. In addition, we compared the clinical/screening validity of the two tests by testing children old enough to complete optotype acuity testing (6.2 ± 2.5 years).

METHODS

Vernier acuity and grating acuity were assessed in 98 children and 18 adults with normal vision (age range = 2.8 months to 35.8 years). The developmental time course of the two visual functions was compared. In addition, vernier acuity and grating acuity were measured in 43 children with amblyopia and 30 nonamblyopic children with an amblyogenic condition. Each child's grating acuity and vernier acuity were classified as normal/abnormal based on age-appropriate norms. These classifications were compared with amblyopia diagnoses by crowded HOTV or Early Treatment Diabetic Retinopathy Study (ETDRS) testing.

RESULTS

Vernier acuity and grating acuity follow different developmental time courses in normal infants and children. Vernier acuity is initially poorer than grating acuity but surpasses it by the age 5 years and is adult-like by the age 8 years. Compared with the Teller Acuity Cards, the vernier acuity cards yielded higher sensitivity (81 vs. 44%) and similar specificity (73 vs. 93%) and were more sensitive to all amblyopia subtypes/levels of severity.

CONCLUSIONS

The developmental time course of vernier acuity differed from that of grating acuity, implying that it is not mediated by the retina. Also, the impressive validity of the vernier acuity cards suggests that they are an effective tool for detecting amblyopia.

Neural Correlate of Vernier Acuity Tasks Assessed by Functional MRI (fMRI)

Vernier acuity refers to the ability to discern a small offset within a line. However, while Vernier acuity has been extensively studied psychophysically, its neural correlates are uncertain. Based upon previous psychophysical and electrophysiologic data, we hypothesized that extrastriate areas of the brain would be involved in Vernier acuity tasks, so we designed event-related functional MRI (fMRI) paradigms to identify cortical regions of the brain involved in this behavior. Normal subjects identified suprathreshold and subthreshold Vernier offsets. The results suggest a cortical network including frontal, parietal, occipital, and cerebellar regions subserves the observation, processing, interpretation, and acknowledgment of briefly presented Vernier offsets.

The effect of induced monocular blur on measures of stereoacuity

PURPOSE

To determine the effect of induced monocular blur on stereoacuity measured with real depth and random dot tests.

METHODS

Monocular visual acuity deficits (range, 20/15 to 20/1600) were induced with 7 different Bangerter filters (<0.1, 0.1, 0.2, 0.3, 0.4, 0.8, and 1.0) in 15 visually normal adults. Stereoacuity was measured with Frisby and Frisby Davis Distance (FD2) real depth tests and Preschool Randot (PSR) and Distance Randot (DR) random dot tests. Stereoacuity results were grouped as either "fine" (<or=60 arcsec), "moderate" (>60 and <or=200 arcsec), or "coarse/nil" (>200 arcsec to nil) stereo.

RESULTS

Across visual acuity deficits, stereoacuity was more severely degraded with random dot (PSR, DR) than with real depth (Frisby, FD2) tests. Degradation to worse-than-fine stereoacuity consistently occurred at 0.7 logMAR (20/100) or worse for Frisby, 0.1 logMAR (20/25) or worse for PSR, and 0.1 logMAR (20/25) or worse for FD2. There was no meaningful threshold for the DR because worse-than-fine stereoacuity was associated with -0.1 logMAR (20/15). Course/nil stereoacuity was consistently associated with 1.2 logMAR (20/320) or worse for Frisby, 0.8 logMAR (20/125) or worse for PSR, 1.1 logMAR (20/250) or worse for FD2, and 0.5 logMAR (20/63) or worse for DR.

CONCLUSIONS

Stereoacuity thresholds are more easily degraded by reduced monocular visual acuity with the use of random dot tests (PSR and DR) than real depth tests (Frisby and FD2). We have defined levels of monocular visual acuity degradation associated with fine and nil stereoacuity. These findings have important implications for testing stereoacuity in clinical populations.

The effect of Bangerter filters on optotype acuity, Vernier acuity, and contrast sensitivity

PURPOSE

Bangerter filters are designed to cause progressive degradation of distance optotype acuity to predicted levels (density label indicating expected decimal acuity) and are used to treat amblyopia and diplopia. Few authors have reported data regarding induced acuity deficits. We investigated the effect of Bangerter filters on distance and near optotype acuity, vernier acuity, and contrast sensitivity.

METHODS

Fifteen subjects with best-corrected optotype acuity of at least 20/25 in each eye were blurred sequentially in one eye with 7 Bangerter filters (densities <0.1, 0.1, 0.2, 0.3, 0.4, 0.8, and 1.0). At each filter level, distance and near optotype acuity (LogMAR), vernier acuity, and contrast sensitivity were assessed. Mean log acuities were compared using generalized estimating equation methods.

RESULTS

The 1.0, 0.8, and 0.4 filters degraded distance optotype acuity to a similar degree (mean 0.22, 0.23, and 0.28 logMAR). Subsequent filters progressively degraded acuity: 0.44, 0.57, 0.93, and 1.69 logMAR. Near optotype acuity was reduced in a similar pattern. Vernier acuity was minimally degraded by 1.0, 0.8, and 0.4 filters (18, 19, and 20 arcsec), followed by progressive degradation with subsequent filters (31, 35, 113, and 387 arcsec). Contrast sensitivity was minimally reduced with filters 1.0 through 0.2 and then precipitously degraded with 0.1 and <0.1 filters.

CONCLUSIONS

The 1.0, 0.8, and 0.4 filters cause similar, minimal degradation of distance and near optotype and vernier acuity, whereas subsequent filters cause progressive degradation. Contrast sensitivity is not markedly reduced until the 0.1 filter. These results have important implications for the use of Bangerter filters therapeutically.

Amblyopia characterization, treatment, and prophylaxis

Amblyopia has a 1.6-3.6% prevalence, higher in the medically underserved. It is more complex than simply visual acuity loss and the better eye has sub-clinical deficits. Functional limitations appear more extensive and loss of vision in the better eye of amblyopes more prevalent than previously thought. Amblyopia screening and treatment are efficacious, but cost-effectiveness concerns remain. Refractive correction alone may successfully treat anisometropic amblyopia and it, minimal occlusion, and/or catecholamine treatment can provide initial vision improvement that may improve compliance with subsequent long-duration treatment. Atropine penalization appears as effective as occlusion for moderate amblyopia, with limited-day penalization as effective as full-time. Cytidin-5'-diphosphocholine may hold promise as a medical treatment. Interpretation of much of the amblyopia literature is made difficult by: inaccurate visual acuity measurement at initial visit, lack of adequate refractive correction prior to and during treatment, and lack of long-term follow-up results. Successful treatment can be achieved in at most 63-83% of patients. Treatment outcome is a function of initial visual acuity and type of amblyopia, and a reciprocal product of treatment efficacy, duration, and compliance. Age at treatment onset is not predictive of outcome in many studies but detection under versus over 2-3 years of age may be. Multiple screenings prior to that age, and prompt treatment, reduce prevalence. Would a single early cycloplegic photoscreening be as, or more, successful at detection or prediction than the multiple screenings, and more cost-effective? Penalization and occlusion have minimal incidence of reverse amblyopia and/or side-effects, no significant influence on emmetropization, and no consistent effect on sign or size of post-treatment changes in strabismic deviation. There may be a physiologic basis for better age-indifferent outcome than tapped by current treatment methodologies. Infant refractive correction substantially reduces accommodative esotropia and amblyopia incidence without interference with emmetropization. Compensatory prism, alone or post-operatively, and/or minus lens treatment, and/or wide-field fusional amplitude training, may reduce risk of early onset esotropia. Multivariate screening using continuous-scale measurements may be more effective than traditional single-test dichotomous pass/fail measures. Pigmentation may be one parameter because Caucasians are at higher risk for esotropia than non-whites.

Retest variability of human infant contrast sensitivity: how many tests are sufficient?

Retest variability of a new infant contrast sensitivity (CS) card procedure was assessed by binocular measurement of a group of 20 6-month-olds twice within a 1-week period. Coefficient of reliability analyses showed that within-subject variability between tests was only slightly less than variation across subjects, which suggests that results from a single test are a poor predictor of an infant's "true" visual functioning. To determine how many tests are needed to estimate when infant CS stabilizes to within an acceptable (0.15 log unit) criterion, a second experiment was conducted in which a small group of subjects was tested repeatedly over a 2-week period. The results showed that averaging performance on 2 to 3 tests was required before an accurate estimate of the subject's performance could be obtained. Our results suggest that caution should be taken in the interpretation of a single measurement of infant visual functioning.

Infant vision and retinal function in studies of dietary long-chain polyunsaturated fatty acids: methods, results, and implications

Animal and human studies have documented several effects of different dietary and tissue concentrations of long-chain polyunsaturated fatty acids (LCPUFAs) on retinal function and vision. The enhanced visual development associated with increased intakes of LCPUFAs, particularly docosahexaenoic acid (DHA), provides the strongest evidence for the importance of these fatty acids in infant nutrition. The 2 primary visual measures used to assess the efficacy of infant formula LCPUFA supplementation are the electroretinogram and visual acuity. This review briefly describes the methodology, neural basis, and interpretation of these measures, as well as other measures of visual development that may be used to extend the functional evaluation of infants fed formulas with different fatty acid compositions.

Preschool vision screening: rationale, methodology and outcome

Although population outcome studies support the utility of preschool screening for reducing the prevalence of amblyopia, fundamental questions remain about how best to do such screening. Infant photoscreening to detect refractive risk factors prior to onset of esotropia and amblyopia seems promising, but our current understanding of the natural history of these conditions is limited, thus limiting the prophylactic potential of early screening. Screening for strabismic, refractive and ocular disease conditions directly associated with amblyopia is more clearly proven, but the diversity of equipment, methods and subject populations studied make it difficult to draw precise summary conclusions at this point about the efficacy of photoscreening. Sensory-based testing of preschool-age children exhibits a similar combination of promise and limitations. The visual acuity tests most widely used for this purpose are prone to problems of testability and false negatives. Moreover, the utility of random-dot stereograms has been confused by misapplication, and new small-target binocularity tests, while attractive, are as yet inadequately field-proven. The evaluation standard for any screening modality is treatment outcome. However, variables in amblyopia classification and quantitative definition differences, timing of presentation, nonequivalent treatment comparisons, and compliance variability have been uncontrolled in virtually all extant studies of amblyopia treatment outcome, making it difficult or impossible to evaluate either the relative efficacy of different treatment regimens for amblyopia or the effects of age on treatment outcome within the preschool age range. The latter issue is a central one, since existence of such an age effect is the primary rationale for screening at younger rather than older preschool ages. The relatively low prevalence of amblyopia makes it difficult to achieve a high screening yield in terms of predictive value, but functionally increasing prevalence by selective screening of high risk populations causes further problems. Unless a "supertest" can be devised, with very high sensitivity and specificity, health policy decisions will be required to determine which of these two characteristics should be emphasized in screening programs. Performance of screening tests can be optimized, however, with adequate training, perhaps via instructional videotapes.

Results of a prospective evaluation of three methods of management of pediatric cataracts

BACKGROUND

Although a variety of approaches to manage cataracts in children have been studied, no consensus exists on the optimum approach. The authors, therefore, conducted a prospective, nonrandomized, consecutive study to evaluate three most commonly adopted methods of management of pediatric cataracts.

METHODS

Lensectomy anterior vitrectomy (LAV), extracapsular cataract extraction with intraocular lens implantation (ECCE + IOL) and ECCE, primary posterior capsulotomy, anterior vitrectomy with IOL (ECCE + PPC + AV + IOL) were the surgical procedures performed. Aphakia in the LAV group was corrected with spectacles or contact lenses. Intraoperative and postoperative results were analyzed. Discrete variables among the three groups were compared using chi square test.

RESULTS

One hundred ninety-two eyes were included in the study. There was no statistically significant difference in the intraoperative complications in the three groups. During a mean follow-up period of 11.3 months, postoperative obscuration of the visual axis was seen in 43.7% of eyes in the ECCE + IOL group and in 3.65% of eyes in the ECCE + PC + AV + IOL (p < 0.001). Two of the seven patients in the LAV group in whom contact lenses were prescribed developed corneal infiltrates. Severe postoperative anterior uveitis occurred in 15.9% and 13.8% of eyes in the ECCE + PPC + AV + IOL and ECCE + IOL groups, respectively. None of the eyes that underwent LAV developed this complication (P < 0.001). There was no statistically significant difference in the incidence of retinal detachment, endophthalmitis, or glaucoma in the three groups.

CONCLUSION

Of the three approaches, ECCE + PPC + AV + IOL was conducive to at least short-term maintenance of a clear visual axis, provided optimum refractive correction, and was not associated with increased risk of short-term complications. Continued follow-up of these eyes is necessary to conclude on the long term results of this technique.

Comparison of grating and Vernier acuity in infants with developmental delay

BACKGROUND

Grating acuity measured by Teller cards is mildly reduced in children with developmental delay. Vernier acuity, the ability to detect offsets, also can be measured, but has not been studied in children with developmental delay.

METHODS

In a prospective cross-sectional pilot study, 12 nonverbal children with developmental delay established by pediatric assessment of developmental milestones were tested binocularly with vernier and Teller cards. Ages ranged from 4 to 24 months. Vernier offsets ranged from 2 to 64 minutes of arc.

RESULTS

All children were testable with Teller acuity cards. Binocular grating acuity ranged from 1.7 to 7.4 cpd (median, 1.0 octaves below normal). Binocular vernier acuity ranged from unrecordable to 8 minutes of arc (median, "unrecordable"). Only four of the 12 children demonstrated a measurable vernier acuity. Normal children of this age have a vernier acuity of 2 to 16 minutes of arc measured by this technique.

CONCLUSION

The response to vernier acuity cards appears to be more severely degraded by developmental delay than the response to Teller cards.

Assessment of visual acuity in children with trisomy 18

Although 90% of children with trisomy 18 (Edwards syndrome) die in the first year of life, a small proportion survive into the second and third decade. Many do not have associated ocular abnormalities that might affect vision. Measurable visual acuity has not been reported in these profoundly developmentally delayed individuals. Five children with trisomy 18, aged six months to eight years, underwent complete eye examination including assessment of binocular grating acuity with Teller acuity cards and assessment of binocular vernier acuity with vernier cards. All children were nonverbal with profound developmental delay. Binocular grating acuity ranged from 0.9 cycles per degree (cpd) to 2.2 cpd. This represents a reduction of 1.9 to 5.1 octaves (mean 3.5 octaves, SD 1.3 octaves) compared to age matched norms. None of the children responded to any of the vernier offsets, including the largest of 64 minutes of arc. All children with trisomy 18 demonstrated a measurable grating acuity that was well below normal for age, consistent with profound developmental delay.