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PubMedDate not supplied

Early refractive development in humans.

Over recent years much interest has been directed toward understanding the process by which refractive errors develop, how this is controlled and the effect of refractive errors on subsequent visual status. There are obvious difficulties in studying such mechanisms in human subjects and for this reason many studies have employed animal models. The present paper compiles the evidence available from human subjects, examining the significance of different aspects of refractive status, normal and abnormal patterns of development and their significance in the development of normal binocular function.

Adolescent↗
PubMed2000

Outcome of sulcus fixation of dislocated posterior chamber intraocular lenses using temporary externalization of the haptics.

OBJECTIVE: This study evaluated the visual outcome and complications of repositioning and sulcus fixation of a dislocated posterior chamber intraocular lens (PC IOL) using a technique in which the haptics of the IOL are temporarily externalized for suture placement. DESIGN: Retrospective, noncomparative case series. PARTICIPANTS: Seventy-eight patients with a dislocated PC IOL. INTERVENTION: All patients underwent surgery to fixate the PC IOL using this technique. MAIN OUTCOME MEASURES: Patients were evaluated for visual acuity, refractive error, and surgical complications associated with the procedure. RESULTS: The average visual acuity before surgery was 20/205 (range, 20/20 to light perception), with a median refractive error of -1.00 diopters (D; range, -7.25-+15.00 D). After surgery, the average visual acuity improved to 20/72 (range, 20/20 to no light perception), with a median refractive error of -0.75 D (range, -5.50-+3.50 D). Patients were observed for a median of 15.5 months (range, 6-57 months). Twenty patients had postoperative cystoid macular edema (26%), 7 patients had an epiretinal membrane (ERM) (9%), and 5 patients had a retinal detachment (6%). Eight patients (10%) experienced iris capture of the sutured IOL, and in three patients (4%) the PC IOL dislocated again after surgery. CONCLUSIONS: This technique is an effective method for securing a dislocated PC IOL.

Adult↗
PubMed1994

Vision screening with the RDE stereotest in pediatric populations.

The usefulness of the Random Dot E (RDE) stereotest in screening the vision of school-aged children for vision problems has been established. As a single screening procedure, the effectivity (phi) of the RDE (phi = +0.52) is greater than the widely used Snellen acuity technique (phi = +0.36) and faster to complete. Very-low-birthweight (VLBW) children have a higher incidence of vision problems including strabismus, amblyopia, and refractive error than children born with normal-birthweights (NBW's). My purpose was to determine: (1) whether a group of young children at high risk for vision problems could perform random dot stereotesting and (2) an age appropriate pass/fail criterion for stereoacuity screening. Furthermore, categorization as pass or fail by each screening method studied [stereoacuity (RDE), visual acuity [Teller Acuity Cards (TAC) and Broken Wheel (BWA)] and refractive error] was compared for independent agreement with vision examination results. The subjects were a cohort of NBW and VLBW) (< 1500 g) children matched at birth for maternal age, ethnic origin, time of hospital birth, and parity. Results of a masked investigation of 30 children [VLBW (N = 10) and NBW (N = 20) children] tested at 3 years of age (mean age = 3.0 years, range 2.11 to 3.1 years) showed that (1) 86.7% were able to complete the 168 sec arc random dot stereoacuity task when a two-alternative forced-choice preferential-looking paradigm was used for testing, (2) the specificity and sensitivity were 88.2%, 76.9% (RDE); 81.2%, 64.3% (TAC); 52.9%, 92.3% (BWA); and 94.1%, 61.5% (refractive error), respectively, (3) the reliability the RDE stereoacuity screening was greater (k = +0.66) than any of the other procedures studied, and (4) there was 73.3% agreement on test-retest categorizations between observers.(ABSTRACT TRUNCATED AT 250 WORDS)

Child, Preschool↗
PubMed2000

Screening for amblyopia in preverbal children with photoscreening photographs: II. Sensitivity and specificity of the MTI photoscreener.

OBJECTIVE: To determine the sensitivity and specificity of vision screening using the Medical Technology and Innovations (MTI), Inc., PhotoScreener. DESIGN: Cross-sectional study. PARTICIPANTS AND TESTING: Three hundred ninety-two children less than 4 years of age received a complete ophthalmologic examination and were photographed using the MTI PhotoScreener. One hundred three children had normal examinations, and the remaining 284 children had conditions of interest for pediatric screening: ptosis, media opacity, refractive error, or strabismus. Five children were excluded. MAIN OUTCOME MEASURES: The grading of the photographs by the manufacturer's representative was compared with the results of the ophthalmologic examinations. Sensitivity and specificity of vision screening were determined. RESULTS: The analysis of all informative photographs resulted in a sensitivity of 65% and a specificity of 87%. The sensitivity of detection for children with some forms of strabismus was high, up to 95% for esotropia of 10Delta or more. Sensitivities for the detection of ptosis, media opacity, and refractive error were poor in patients where strabismus was not also present. CONCLUSIONS: The MTI PhotoScreener may play a role in preverbal vision screening; identification of two of three children with amblyopiogenic factors before age 4 would be an exciting advance in public health. However, improvement in the ability to identify children with media opacity and refractive error is necessary. Improvements may be possible with modifications of the examination failure and photograph grading criteria.

Amblyopia↗
PubMed2005

Topographical evaluation of the decentration of orthokeratology lenses.

PURPOSE: To evaluate the amount of lens decentration and various factors affecting decentration after orthokeratology lens wear and to observe the effect of decentration on the visual functions. METHODS: Two kinds of orthokeratology lenses were fitted to 270 eyes of 135 patients [initial mean refractive error: (-3.98+/-1.51)D]. Humphery Instruments ATLAS 990 was used for the computer-assisted analysis of corneal topographical maps. The examination of corneal topography was performed on patients before and after 6 months of wearing orthokeratology lenses. The amount of decentration of orthokeratology lenses was measured by finding the distance between center of optic zone and the pupil center. The factors influencing the amount of decentration were analyzed, including the initial refraction error, astigmatism, keratometry values, corneal eccentricity, and the diameter of lens. Visual symptoms including monocular diplopia, glare around lights were recorded to evaluate the effects of decentration on visual functions. RESULTS: The mean amount of decentration was (0.49+/-0.34) mm after one night's wear. The mean amount of decentration after 1 month, 3 months and 6 months was (0.57+/-0.41) mm, (0.55+/-0.48) mm and (0.59+/-0.39) mm, respectively. After one month, the amount of decentration was less than 0.50 mm in 51.1% eyes, 0.50-1.0 mm in 35.6% eyes and more than 1.00 mm in 13.3% eyes. The direction of decentration of more than 0.50 mm was mainly in the temporal quadrant (48.5%). Patients with greater initial astigmatism and smaller lenses showed greater decentration (P<0.05). There was no statistically significant difference in decentration between the two groups with different corneal eccentricities and keratometry values (P>0.05). The amount of decentration was greater in patients who complained of monocular diplopia and glare. CONCLUSIONS: The amount of decentration of orthokeratology depends on the initial refractive error, astigmatism and the design of orthokeratology lenses. Improvement in fitting technology and lens design can lead to reduced incidence of decentration and visual symptoms.

Adolescent↗
PubMed1986

Anterior chamber depth in open angle glaucoma.

Anterior chamber depth was measured in patients with primary open angle glaucoma, low tension glaucoma, pigmentary dispersion syndrome, and glaucoma suspects. Multiple linear regression analysis demonstrated that anterior chamber depth is a function of sex, age, and refractive error. Values for anterior chamber depth corrected for age and refractive error were greater in patients with pigmentary dispersion syndrome than in patients with other forms of open angle glaucoma or in glaucoma suspects.

Age Factors↗
PubMed2006

Acute effects of dietary retinoic acid on ocular components in the growing chick.

When the eyes of chicks are induced to grow toward myopia or hyperopia by having them wear spectacle lenses or diffusers, opposite changes take place in the retina and choroid in the synthesis and levels of all-trans Retinoic Acid (RA). To explore whether RA plays a causal role in the regulation of eye growth, we fed young chicks RA (doses 0.5 to 24 mg/kg) either twice a day or on alternate days or only once. Refractive error was measured with a Hartinger refractometer; ocular length, lens-thickness and choroidal thickness were measured by A-scan ultrasound. The amount of RA present in ocular tissues was determined using HPLC. Oral delivery of RA effectively increased RA in ocular tissues within 8h. During the first day after feeding RA at levels above 8 mg/kg, the rate of ocular elongation tripled, the choroid thickened and lens thickening was inhibited. The day following a dose of RA, the rate of ocular elongation was inhibited and the lens thickened more than normal. Nonetheless, the cumulative effect of repeated doses was that the eye became longer and the lens became thinner than normal, with no net change in refractive error. The rate of elongation was also increased by feeding 13-cis RA, and was reduced by citral, an inhibitor of RA synthesis. Surprisingly, birds fed RA while being kept in darkness also had normal refractive errors despite increased ocular elongation, and birds wearing either +6D or -6D spectacle lenses compensated normally for the lenses despite the enhanced ocular elongation caused by the RA. These results suggest that RA may act at the level of a coordinated non-visual regulatory system which controls the growth of the various ocular components, arguing that emmetropization does not depend entirely on vision.

Animals↗
PubMed1980

Optometric screening in achondroplasia, diastrophic dysplasia, and spondyloepiphyseal dysplasia congenita.

Visual screening tests were done on 61 individuals with various types of genetic skeletal dysplasias to determine which, if any, refractive errors are associated with each type. In individuals with achondroplasia, refractive error distribution was approximately that expected from its distribution in the general population. However, there was a significantly higher than expected frequency of strabismus in achondroplasts. A tendency to myopia was noted in diastrophic dysplasia and in those individuals with spondyloepiphyseal dysplasia.

Achondroplasia↗
PubMed1999

[Results of photorefractive keratectomy after treatment of 2053 eyes].

To evaluate the 12 months refractive results of photorefractive excimer keratectomy (PRK) in high number of eyes with different type of refractive error. Between October 1992 and December 1996. 2053 eyes of 1098 patients were treated with the Aesculap Meditec MEL 60 argon-fluoride excimer laser. Refractive results were concluded at the 12th post-PRK month. The following patient groups were used during the study: Group 1.: Eyes between -1.0 D and -6.0 D (n = 651); Group 2.: -6.0 és -9.0 D (n = 216); Group 3.: Eyes with refractive error above -9.0 D (n = 163); Group 4.: Hypermetrop eyes (n = 160); Group 5.: Eyes with myopic astigmatism (n = 746); Group 6.: Eyes with hypermetropic astigmatism; Group 7.: Pure astigmatism (n = 13). In Group 1. The preoperative average -3.94 +/- 1.3 D refractive error decreased during the 1-year follow-up period to -0.47 +/- 0.54 Dpt; in Group 2. The preoperative -7.65 +/- 1.07 D to -1.16 +/- 1.86 D; in Group 3. The preoperative average -13.58 +/- 3.51 D to -3.11 +/- 2.75 D; in Group 4. The preoperative +4.04 +/- 1.77 D to +1.02 +/- 1.16 D in Group 5. The preoperative -6.06 +/- 2.78 D spherical component decreased to -0.95 +/- 1.33 D-ra, whereas the preoperative cylindrical component from -1.5 +/- 1.08 D to -0.13 +/- 0.58 D; in Group 5. The preoperative +4.57 +/- 1.78 spherical component to +1.13 +/- 1.38 D; whereas the preoperative cylindrical component from +1.57 +/- 0.96 D to +0.38 +/- 0.77 D; in Group 7. The preoperative a -3.98 +/- 1.2 D cylinder decreased to -0.62 +/- 0.75 D cylinder. PRK decreased effectively the preoperative correction need in every treatment group. The results are the better, the smaller the preoperative correction need is.

Adolescent↗
PubMed2004

Scanning laser polarimetry in myopic and hyperopic subjects.

PURPOSE: To investigate the effect of refraction error and axial length on retinal nerve fiber layer (RNFL) measurements as obtained by scanning laser polarimetry (SLP). METHODS: Besides ophthalmological standard examination (refractive error, keratometry, visual acuity, slit-lamp examination, applanation tonometry, funduscopy), perimetry, axial length measurement by means of ultrasound, and SLP were performed. Seventy-five myopic eyes (between -0.75 D and -8.5 D), 24 hyperopic eyes (0.75 D-6.5 D) and 40 emmetropic eyes were investigated. SLP parameters were compared in the different groups. RESULTS: The statistical analysis of the absolute thickness values of SLP revealed highly significant ( P< 0.01) reductions in average thickness, ellipse average, superior average, inferior average, and superior integral in both myopic and hyperopic eyes in comparison with the emmetropic control eyes. The amount of reduction was between 12.9% (inferior average; myopia) and 30.2% (superior integral; hyperopia). There were no significant differences between myopes and hyperopes. A significant linear correlation for many of the SLP parameters with the refractive error (spherical equivalent) but not with axial length was found in both the hyperopic and the myopic group. CONCLUSIONS: Despite a wide interindividual range, SLP measurement values decrease with increasing myopia and hyperopia. In clinical practice, such reduced RNFL thickness values should be viewed with the necessary caution and additional polarimetric signs for glaucomatous damage should be taken into consideration.

Adult↗
PubMed2005

Temporal integration characteristics of the axial and choroidal responses to myopic defocus induced by prior form deprivation versus positive spectacle lens wear in chickens.

PURPOSE: In chicks, the temporal response characteristics to form deprivation and to spectacle lens wear (myopic and hyperopic defocus) show essential differences, suggesting that the emmetropization system "weights" the visual signals differently. To further explore how the eye integrates opposing visual signals, we examined the responses to myopic defocus induced by prior form deprivation vs. that induced by positive spectacle lenses, in both cases alternating with form deprivation. METHODS: Three experimental paradigms were used: 1) Form deprivation was induced by monocular occluders for 7 days. Over the subsequent 7 days, the occluders were removed daily for 12 hours (n = 13), 4 hours (n = 7), 2 hours (n = 7), or 0 hours (n = 6). 2) Birds were form-deprived on day 12. Over the subsequent 7 days, occluders were replaced with a +10 D lens for 2 hours per day (n = 13). 3) Starting at day 11, a +10 D lens was placed over one eye for 2 hours (n = 13), 3 hours (n = 5), or 6 hours (n = 10) per day and were otherwise untreated. Ocular dimensions were measured with high-frequency A-scan ultrasonography; refractive errors were measured by streak retinoscopy at various intervals. RESULTS: In recovering eyes, 2 hours per day of myopic defocus was as effective as 12 hours at inducing refractive and axial recovery (change in refractive error: +10 D vs. +13 D, respectively). By contrast, 2 hours of lens-induced defocus (alternating with form deprivation) was not sufficient to induce refractive or axial compensation (change in refractive error: -1.7 D). When myopic defocus alternated with unrestricted vision, 6 hours per day were sufficient to induce nearly full compensation (2 hours vs. 6 hours: 4.4 D vs. 8.2 D; p < 0.0005). Choroids showed rapid increases in thickness to the daily episodes of myopic defocus; these resulted in "long-term" thickness changes in recovering eyes and eyes wearing lenses for 3 or 6 hours per day. CONCLUSIONS: The response to myopic defocus induced by prior form deprivation is more robust than the response induced by positive lenses, suggesting that the underlying mechanisms differ. Presumably, this difference is related to the size of the eye at the onset. Compensatory decreases in growth rate occur without full compensatory choroidal thickening.

Adaptation, Physiological↗
PubMedDate not supplied

LASIK for myopia with the Zeiss meditec MEL 80.

PURPOSE: To prospectively evaluate a new high-speed, small spot-scanner laser for the correction of myopia and myopic astigmatism. METHODS: Seventy-six consecutive eyes with myopia and myopic astigmatism between -1.00 and -8.25 diopters (D) and up to -2.75 D astigmatism underwent LASIK treatment using the MEL 80 laser (Carl Zeiss Meditec, Jena, Germany). Parameters evaluated were uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), residual refractive error, regression of correction, and aberrometry. RESULTS: Mean preoperative BSCVA was 20/20, which improved to 20/18 postoperatively. Postoperative UCVA was 20/20 at 1 month and 20/18 at 1 year. Uncorrected visual acuity > or = 20/20 was achieved in 58 (83%) of 70 eyes at 1 month and in 60 (88%) of 68 eyes at 1 year. The average refractive error before LASIK was -4.41 +/- 1.98 D. The mean residual refractive error was 0.14 +/- 0.31 D at 1 month and 0.13 +/- 0.30 D at 1 year. At 1-month and 1-year follow-up, respectively, 66 (94%) of 70 eyes and 65 (96%) of 68 eyes were within +/- 0.50 D of intended refractive correction. No eye lost two lines. At 1 month 17% of eyes and at 1 year 13% of eyes gained two lines or more. Between 1-month and 1-year follow-up, 100% of eyes were stable. Mean root-mean-square high order aberration changed from 0.20 microm preoperatively to 0.28 microm postoperatively. CONCLUSIONS: The MEL 80 is effective and safe in the treatment of myopia and myopic astigmatism.

Adolescent↗
PubMedDate not supplied

Some variables to consider to avoid the need for LASIK surgical enhancements.

BACKGROUND: The predictability of LASIK refractive surgery is important both to the patient and the surgeon in obtaining an optimal result and in reducing the need for enhancement surgery. Some instruments, large ablation zones and possibly other variables may increase hyperopic overcorrection. METHODS: A retrospective study was undertaken of 345 myopic LASIK eyes (175 patients) treated with a Nidek EC-5000. The need for additional surgery in the form of an enhancement was determined after the patient had a stable refraction. The variables measured in the study were the patient's refractive correction, corneal curvature using an Alcon EH-290 topographer, the patient's age and Nidek excimer laser ablation optic and transition zone size. The same nomogram was used for all eyes and where possible bilateral surgery was conducted on all patients. The effect of ablation sizes, refractive errors, patient age and corneal curvature on the enhancement surgeries was evaluated using SPSS 6.0. RESULTS: The most significant variable that precipitated a LASIK enhancement was an optic zone of 6.5 mm with a transition zone of 7.5 mm (paired t-test, p < 0.0025). Multivariate analysis indicates that the older the patient and the larger the refractive error, the greater the risk of not achieving a residual refractive error of +/- 0.50 D at three months. The steeper pre-operative corneas have a greater chance of enhancement (mean of sample 44.48 +/- 1.47 D and mean of enhancements 45.30 +/- 1.65 D, p = 0.01, independent sample test). The smaller optic zone was associated with a smaller refractive over-refraction after LASIK surgery (mean for 5.5 mm optic zone, +0.71 +/- 0.29 D; mean, for 6.5 mm optic +1.27 +/- 0.50 D, paired t-test p < 0.0001). CONCLUSIONS: In this study, the 5.5 mm optic zone appears to dampen or reduce the undesirable refractive results. The optic zone size of choice with the Nidek EC-5000 laser should be 5.5 mm if the patient has small pupils and steep corneas. In this sample, the targeted emmetropic refractive state (range plano to +0.50 D sphere and plano to -0.50 D cylinder) was achieved in 93.3 per cent of cases after three months.

Journal Article↗
PubMed2006

Diurnal fluctuations and developmental changes in ocular dimensions and optical aberrations in young chicks.

PURPOSE: To investigate further the emmetropization process in young chicks by studying the diurnal fluctuations and developmental changes in the ocular dimensions and optical aberrations, including refractive errors, of normal eyes and eyes that had the ciliary nerve sectioned (CNX). METHODS: The ocular dimensions and aberrations in both eyes of eight CNX (surgery on right eyes only) and eight normal chicks were measured with high-frequency A-scan ultrasonography and aberrometry, respectively, four times a day on five different days from posthatching day 13 to 35. A fixed pupil size of 2 mm was used to analyze aberration data. Repeated-measures ANOVA was applied to examine the effects of age, time of day, and surgery. RESULTS: Refractive errors and most higher-order aberrations decreased with development in both normal and CNX eyes. However, although normal eyes showed a positive shift in spherical aberration with age, changing from negative spherical aberration initially, CNX eyes consistently exhibited positive spherical aberration. Anterior chamber depth, lens thickness, vitreous chamber depth, and thus optical axial length all increased with development. Many of these ocular parameters also underwent diurnal changes, and mostly these dynamic characteristics showed no age dependency and no effect of CNX. Anterior chamber depth, vitreous chamber depth, and optical axial length were all greater in the evening than in the morning, whereas the choroids were thinner in the evening. Paradoxically, eyes were more hyperopic in the evening, when they were longest. Although CNX eyes, having enlarged pupils, were exposed to larger higher-order aberrations, their growth pattern was similar to that of normal eyes. CONCLUSIONS: Young chicks that are still emmetropizing, show significant diurnal fluctuations in ocular dimensions and some optical aberrations, superimposed on overall increases in the former and developmental decreases in the latter, even when accommodation is prevented. The possibility that these diurnal fluctuations are used to decode the eye's refractive error status for emmetropization warrants investigation. That eyes undergoing ciliary nerve section have more higher-order aberrations but do not become myopic implies a threshold for retinal image degradation below which the emmetropization process is not affected.

Animals↗
PubMed1987

A model for emmetropization. The effect of corrective lenses.

A mechanism called emmetropization appears to control the ocular focus over the years. Emmetropization could regulate the refractive media (dimensions of cornea, lens, and axial length), detecting the focus or refractive error of the eye at rest and initiating changes to reduce the refractive error; this concept suggests that a feedback loop is operational. A feedback mechanism for ocular refraction implies that correcting ametropia with lenses initiates a change in the refractive state of the eye. The long-term effect of corrective lenses on ocular refraction is investigated with a mathematical feedback model that can predict the extent and direction of this change. The results indicate that lenses worsen existing ametropia conditions. However, the use of appropriate lenses in early life can reduce and correct developing ametropia.

Contact Lenses↗
PubMed2006

Prevalence of eye disorders in young children with eyestrain complaints.

PURPOSE: To determine whether eyestrain symptoms predict eye conditions in 6-year-old children. DESIGN: Cross-sectional population-based study. METHODS: Reports of eyestrain symptoms were sought in parental questionnaires; 1740 children (79% response) underwent eye examinations (visual acuity, cover testing, cycloplegic autorefraction, and fundus examination). RESULTS: Eyestrain information was available for 1448 children; 220 (15.2%) reported eyestrain symptoms, including 60 (3.4%) who reported near work-associated headaches. Most children (82.3%) had a normal eye examination, while refractive errors, amblyopia, and strabismus were found in 15.0%, 3.6%, and 7.3%, respectively. Corresponding rates for children without eyestrain were 9.9%, 1.4%, and 1.8%, respectively. Moreover, 78.7% of children with refractive errors, 68% with amblyopia, and 58% with strabismus reported no eyestrain. CONCLUSIONS: Most children complaining of eyestrain had a normal eye examination; whereas most children with refractive error, amblyopia, or strabismus were free of eyestrain, making this complaint a poor marker of eye conditions in young children.

Asthenopia↗
PubMed2005

Cataract progression after intravitreal triamcinolone injection.

PURPOSE: To assess cataract progression after intravitreal triamcinolone injection. DESIGN: Retrospective, interventional, case-control study. METHODS: Forty-two phakic eyes of 37 patients were injected one, two, or three times with intravitreal triamcinolone for various indications. Noninjected phakic fellow eyes served as the control. The mean follow-up time for single injection was 12 months, for multiple injections was 14 months, and for control group was 13 months. Lens status, best-corrected visual acuity, and refractive errors were recorded at baseline and at each follow-up examination. RESULTS: At the last follow-up, changes in posterior subcapsular cataract and refractive error from baseline were significantly different between single triamcinolone-injected eyes and the control group [0.7 +/- 0.2 (mean +/- SEM [arbitrary unit] vs 0.2 +/- 0.1, P = .02; and -0.5 +/- 0.1 diopter vs -0.2 +/- 0.1 diopter, P = .01, respectively). For multiple-injected eyes and control eyes, change from baseline in corticonuclear cataract (1.1 +/- 0.2 vs 0.2 +/- 0.1), posterior subcapsular cataract (1.1 +/- 0.2) and refractive error (-1.8 +/- 0.4 diopters) were significantly different (P < .001, P < .001, and P < .001, respectively). Visual acuity did not change after single injection (P = .83) and in control group (P = .19) but decreased after multiple injections (P = .006). Eleven study eyes and two control group eyes underwent cataract extraction during study period. Corticonuclear and posterior subcapsular cataract progression significantly correlated with follow-up time (P = .003 and P = .02, respectively) and number of injections (P = .01 and P = .04, respectively). CONCLUSIONS: Single intravitreal triamcinolone injection induces posterior subcapsular cataract development, whereas multiple injections result in all-layer cataract progression.

Aged↗
PubMed1980

Meridional amblyopia in monkeys.

Contrast sensitivity as a function of the orientation of a grating stimulus was determined by behavioral methods for four rhesus monkeys. Two of the monkeys had been reared with normal binocular experience, had spherical refractive errors, and showed a normal oblique effect. The other two monkeys which had been reared with one eyelid sutured (which was still sutured during these experiments), showed astigmatic refractive errors in the non-deprived eye and grating contrast sensitivity as a function of orientation that was correlated with the principal meridians of their astigmatism. Control experiments showed that the meridional amblyopia was not due to an uncorrected refractive error. Reaction time measures of contrast sensitivity for suprathreshold grating patterns showed that meridional amblyopia was not present for high contrast gratings.

Animals↗