Infant astigmatism and meridional amblyopia

doi:10.1016/0042-6989(85)90042-2

Vision Research

Volume 25, Issue 9, 1985, Pages 1269-1276

https://doi.org/10.1016/0042-6989(85)90042-2 Get rights and content

Abstract

The orientation preferences of 70 infants aged 7 to 53 weeks with significant astigmatism [1.0 or more diopters (D)] were measured using a preferential looking procedure with paired gratings. The preference data show the consequences of the blurring effects of astigmatism when these are not compensatable by accommodation. Data from infant astigmats tested with optical correction look like those of nonastigmats. We have found no evidence for the development of meridional amblyopia during the first year of life.

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Citation Excerpt :
Other studies have shown that uncorrected astigmatism can result in the formation or progression of myopia, as well.11,13,14 Most changes due to astigmatism and its effects, especially its amblyogenic and myopigenic nature, are observed in individuals under 15 years of age.9,15,16 The prevalence of astigmatism has been reported 30–75% in different age groups.17–20
To determine the prevalence of astigmatism and its determinants in schoolchildren aged 6–12 years.
The students selected by stratified cluster random sampling in Shahroud, north of Iran. Optometric examination included uncorrected visual acuity, refraction with autorefractometer, manifest refraction with retinoscopy followed by subjective and cycloplegic refraction (after two drops of cyclopentolate 1% with 5 min interval were instilled in each eye).
A cylinder power ≥0.75 diopter (D) in at least one eye was considered as astigmatism. The prevalence of astigmatism was reported based on a cylinder power higher than 0.50, 1.00, and 2.00 D in cycloplegic refraction, followed by power vector analysis.
After applying the inclusion criteria, the data of 5528 children were analyzed. The prevalence of astigmatism was 16.7% (95% CI: 15.6–17.7) in total, 16.6% (95% CI: 15.2–18.0) in boys and 16.8% (95% CI: 15.2–18.3) in girls (p = 0.920) and decreased from 21.5% in 6-year-old children to 13.7% in 10-year-olds, and then again increased to 18.3% in children aged 12 years. Moreover, 17.2% (95% CI: 16.0–18.3) of urban and 12.1% (95% CI: 10.0–14.1) of rural children had astigmatism (p < 0.001). The prevalence of with-the-rule, against-the-rule, and oblique astigmatism was 14.2%, 2.1%, and 0.33%, respectively. The mean cylinder power was −1.31, −0.46, and −0.44 D in children with spherical myopia, emmetropia, and hyperopia, respectively (p < 0.001). Urban students had a higher J₀ and boys had a higher J₄₅.
The prevalence of astigmatism in this study was lower than previous studies. Astigmatism prevalence was markedly higher in urban children.
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Citation Excerpt :
The effects of restrictive visual experience are also seen in humans who had an astigmatism as children, which distorts visual input due to a corneal aberration. If this condition remains uncorrected, these children later develop meridional amblyopia, a condition of decreased visual sensitivity for orientations blurred by their astigmatism that originates in the neural visual pathway (Gwiazda, Mohindra, Brill, & Held, 1985; Mitchell & Wilkinson, 1974; Mitchell, Freeman, Millodot, & Haegerstrom, 1973). There is also suggestion that even typically-developing humans show anisotropies in sensitivity for orientations based on the frequencies of orientations in their environment.
Careful measurements of the temporal dynamics of speech have provided important insights into phonetic properties of spoken languages, which are important for understanding auditory perception. By contrast, analytic quantification of the visual properties of signed languages is still largely uncharted. Exposure to sign language is a unique experience that could shape and modify low-level visual processing for those who use it regularly (i.e., what we refer to as the Enhanced Exposure Hypothesis). The purpose of the current study was to characterize the visual spatiotemporal properties of American Sign Language (ASL) so that future studies can test the enhanced exposure hypothesis in signers, with the prediction that altered vision should be observed within, more so than outside, the range of properties found in ASL. Using an ultrasonic motion tracking system, we recorded the hand position in 3-dimensional space over time during sign language production of signs, sentences, and narratives. From these data, we calculated several metrics: hand position and eccentricity in space and hand motion speed. For individual signs, we also measured total distance travelled by the dominant hand and total duration of each sign. These metrics were found to fall within a selective range, suggesting that exposure to signs is a specific and unique visual experience, which might alter visual perceptual abilities in signers for visual information within the experienced range, even for non-language stimuli.
Amblyopia in astigmatic preschool children
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Best-corrected acuity was measured for vertical and horizontal gratings and for recognition acuity optotypes (Lea Symbols) in a group of three- to five-year-old children with a high prevalence of astigmatism. Results showed meridional amblyopia (MA) among children with simple/compound myopic or mixed astigmatism, due to reduced acuity for horizontal gratings. Children with simple/compound hyperopic astigmatism showed no MA, but did show reduced acuity for both grating orientations. Reduced best-corrected recognition acuity was shown by both myopic/mixed and hyperopic astigmats. These results suggest that optical correction of astigmatism should be provided prior to age three to five years, to prevent development of amblyopia.
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While it is now established that astigmatism is more prevalent in infants and young children than in the adult population, little is known about the functional significance of this astigmatism, especially its role, if any, in emmetropization and the development of myopia. Manifest refractions (mean of 16 per subject) were obtained from 245 subjects starting in the first year, with 6–23 years of regular follow-up. Results showed that infantile astigmatism is associated with increased astigmatism and myopia during the school years. Two possible mechanisms underlying this association are discussed: (1) infantile astigmatism disrupts focusing mechanisms; and (2) ocular growth induces astigmatism and myopia.
Early refractive development in humans
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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.
Emmetropisation in human infancy: Rate of change is related to initial refractive error
1995, Vision Research
Animal studies show that the rate of recovery from experimentally induced refractive errors is related to the level of ametropia induced. The present study examined the rate of emmetropisation occurring in a sample of 22 human infants refracted by near retinoscopy during the first six months of life and then again between 12 and 17 months old. None of the subjects were myopic. Regression analysis revealed that emmetropisation occurred more rapidly in the presence of high refractive errors (P < 0.005 and P = 0.001 for hyperopia and astigmatism respectively). These data confirm the findings of the animal studies and suggest that non-reducing hyperopia and astigmatism in the second year of life may require correction.

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Infant astigmatism and meridional amblyopia

Abstract

Vision Res.

Vision Res.

Vision Res.

Vision Res.

Vision Res.

Effects of induced optical blur on infant visual acuity

Am. J. Optom. Physiol. Opt.

Interaction of critical periods in visual cortex of kittens

Science

Cycloplegic refraction in infants and young children

Am. J. Ophthal.

Effect of focus on the visual response to a sinusoidally modulated spatial stimulus

J. opt. Soc. Am.

Preferential looking acuity in infants from two to fifty-eight weeks of age

Am. J. Optom. Physiol. Opt.