Visual outcome in 879 children treated for strabismus: insufficient accommodation and vision deprivation, deficient emmetropisation and anisometropia

Gray matter volume alterations in patients with strabismus and amblyopia: voxel-based morphometry study

This study proposes the use of the voxel-based morphometry (VBM) technique to investigate structural alterations of the cerebral cortex in patients with strabismus and amblyopia (SA). Sixteen patients with SA and sixteen healthy controls (HCs) underwent magnetic resonance imaging. Original whole brain images were analyzed using the VBM method. Pearson correlation analysis was performed to evaluate the relationship between mean gray matter volume (GMV) and clinical manifestations. Receiver operating characteristic (ROC) curve analysis was applied to classify the mean GMV values of the SA group and HCs. Compared with the HCs, GMV values in the SA group showed a significant difference in the right superior temporal gyrus, posterior and anterior lobes of the cerebellum, bilateral parahippocampal gyrus, and left anterior cingulate cortex. The mean GMV value in the right superior temporal gyrus, posterior and anterior lobes of the cerebellum, and bilateral parahippocampal gyrus were negatively correlated with the angle of strabismus. The ROC curve analysis of each cerebral region confirmed the accuracy of the area under the curve. Patients with SA have reduced GMV values in some brain regions. These findings might help to reveal the potential pathogenesis of SA and its relationship with the atrophy of specific regions of the brain.

Repeatability and Validity of Peripheral Refraction with Two Different Autorefractors

SIGNIFICANCE

The Welch Allyn SureSight (Welch Allyn, Skaneateles Falls, NY) and Plusoptix PowerRefractor (Plusoptix, Nuremberg, Germany) are often used with infants, but little is known about the repeatability and validity of their peripheral refractive error measurements. Selecting the best instrument will support future refractive error and emmetropization studies.

PURPOSE

The purpose of this study was to determine the validity and repeatability of peripheral refractive error measurements and peripheral refraction profiles measured with the Welch Allyn SureSight and Plusoptix PowerRefractor compared with the criterion standard Grand Seiko WR-5100K (Grand Seiko Co., Hiroshima, Japan).

METHODS

Cycloplegic (tropicamide 1%) autorefraction was measured in the right eyes of 21 adult subjects (31.4 ± 10.4 years) with the three instruments in randomized order on two separate visits, at least 24 hours apart, centrally, and at 30 and 20° temporal and nasal gaze.

RESULTS

The SureSight measurements were within 0.24 D and not significantly different from the Grand Seiko WR-5100K in any gaze (P < .65), whereas the PowerRefractor measurements were more myopic by as much as -0.97 D and significantly different in four of the five gaze directions (P < .04). The 95% limits of agreement between occasions by gaze ranged from ±0.38 to ±0.61 D for the SureSight, similar to or slightly better than the WR-5100K (±0.31 to ±1.51 D) and the PowerRefractor (±0.72 to ±1.71 D). There were no significant differences between visits for any instrument in any gaze (P < .94). The repeatability of the SureSight was also better than that for the Grand Seiko when peripheral refraction was represented by quadratic fits to the data.

CONCLUSIONS

These findings suggest that the Welch Allyn SureSight is the most suitable portable autorefractor to use to monitor peripheral autorefraction based on better repeatability between occasions and better validity compared with the criterion standard Grand Seiko WR-5100K.

Fixation instability during binocular viewing in anisometropic and strabismic children

PURPOSE

Strabismus or anisometropia disrupts binocularity and results in fixation instability, which is increased with amblyopia. Fixation instability has typically been assessed for each eye individually. Recently, vergence instability was reported in exotropic adults and monkeys during binocular viewing. We evaluated fixation instability during binocular viewing in children treated for anisometropia and/or strabismus.

METHODS

160 children age 4-12 years with treated esotropia and/or anisometropia (98 amblyopic, 62 nonamblyopic) were compared to 46 age-similar controls. Fixation instability was recorded during binocular fixation of a 0.3 deg diameter dot for 20 s using a 500 Hz remote video binocular eye tracker (EyeLink 1000; SR Research). The bivariate contour ellipse area (BCEA; log deg²) for fixation instability was calculated for each eye (nonpreferred, preferred) and for vergence instability (left eye position - right eye position). Best-corrected visual acuity, Randot Preschool stereoacuity, and extent of suppression scotoma (Worth 4-Dot) were also obtained.

RESULTS

When binocularly viewing, both amblyopic and nonamblyopic children treated for anisometropia and/or strabismus had larger fixation instability and vergence instability than controls. Amblyopia primarily added to the instability of the nonpreferred eye. Anisometropic children had less nonpreferred eye instability and vergence instability than those with strabismus or combined mechanism. Nonpreferred eye instability and vergence instability were related to poorer stereoacuity and a larger suppression scotoma. Preferred eye instability was not related to any visual outcome measure. No relationships were found with visual acuity.

CONCLUSIONS

Fixation instability and vergence instability during binocular viewing suggests that discordant binocular visual experience during childhood, especially strabismus, interferes with ocular motor development. Amblyopia adds to instability of the nonpreferred eye. Vergence instability may limit potential for recovery of binocular vision in these children.

Human infants can generate vergence responses to retinal disparity by 5 to 10 weeks of age

Vergence is defined as a binocular eye movement during which the two eyes move in opposite directions to align to a target in depth. In adults, fine vergence control is driven primarily by interocular retinal image disparity. Although infants have not typically been shown to respond to disparity until 3 to 5 months postpartum, they have been shown to align their eyes from hours after birth. It remains unclear what drives these responses in young infants. In this experiment, 5- to 10-week-old human infants were presented with a dynamic random noise stimulus oscillating in disparity at 0.1 Hz over an amplitude of 2° for 30 s. Fourier transforms of the horizontal eye movements revealed significant disparity-driven responses at the frequency of the stimulus in over half of the tested infants. Because the stimulus updated dynamically, this experiment precluded the possibility of independent monocular fixations to a sustained target. These data demonstrate cortical binocular function in humans by five weeks, the youngest age tested here, which is as much as two months younger than previously believed.

The Role of Dynamic Retinoscopy in Predicting Infantile Accommodative Esotropia and Influencing Emmetropization

INTRODUCTION AND PURPOSE

To investigate the role that dynamic retinoscopy can play in reducing the occurrence of infantile accommodative esotropia and facilitating emmetropization in infants with high hyperopia.

PATIENTS AND METHODS

211 orthotropic infants under 1 year of age (3.5 to 12 months) identified as having ≥5 diopters of hyperopia in their more hyperopic eye on a routine eye exam. On enrollment, infants underwent an assessment of accommodation using dynamic retinoscopy as well as a cycloplegic refraction. Infants who showed normal accommodation were followed without spectacles. If dynamic retinoscopy showed subnormal accommodation, partial hyperopic correction that allowed for full binocular accommodative responses at near were prescribed. Main outcome measures were the occurrence of esotropia, changes in refractive error, and visual acuity.

RESULTS

Of the 211 infants enrolled, 146 showed normal accommodation and were followed without glasses (Group 1). None of these patients developed strabismus. Sixty-five patients showed subnormal accommodation and received partial hyperopic correction (Group 2). Thirty-four of the 65 (52%) in Group 2 did not develop strabismus (Group 2A) and 31 of the 65 (48%) developed strabismus (Group 2B). All 3 groups showed a reduction of hyperopia of 0.37D ± 0.25/year, 0.50D ± 0.28/year, and 0.60D ± 0.20/year in groups 1, 2A, and 2B, respectively. None of the differences between groups were statistically significant.

CONCLUSIONS

Normal accommodation on dynamic retinoscopy in orthotropic hyperopic infants is a predictor of continued good alignment and such infants can be followed without spectacles. Partial spectacle correction based on dynamic retinoscopy may have a beneficial effect on reducing the development of strabismus without impeding emmetropization. Early binocular accommodative behavior seems to be predictive of infants at risk of developing strabismus.

Observations on the relationship between anisometropia, amblyopia and strabismus

We investigated the potential causal relationships between anisometropia, amblyopia and strabismus, specifically to determine whether either amblyopia or strabismus interfered with emmetropization. We analyzed data from non-human primates that were relevant to the co-existence of anisometropia, amblyopia and strabismus in children. We relied on interocular comparisons of spatial vision and refractive development in animals reared with 1) monocular form deprivation; 2) anisometropia optically imposed by either contact lenses or spectacle lenses; 3) organic amblyopia produced by laser ablation of the fovea; and 4) strabismus that was either optically imposed with prisms or produced by either surgical or pharmacological manipulation of the extraocular muscles. Hyperopic anisometropia imposed early in life produced amblyopia in a dose-dependent manner. However, when potential methodological confounds were taken into account, there was no support for the hypothesis that the presence of amblyopia interferes with emmetropization or promotes hyperopia or that the degree of image degradation determines the direction of eye growth. To the contrary, there was strong evidence that amblyopic eyes were able to detect the presence of a refractive error and alter ocular growth to eliminate the ametropia. On the other hand, early onset strabismus, both optically and surgically imposed, disrupted the emmetropization process producing anisometropia. In surgical strabismus, the deviating eyes were typically more hyperopic than their fellow fixating eyes. The results show that early hyperopic anisometropia is a significant risk factor for amblyopia. Early esotropia can trigger the onset of both anisometropia and amblyopia. However, amblyopia, in isolation, does not pose a significant risk for the development of hyperopia or anisometropia.

Visual Function of Moderately Hyperopic 4- and 5-Year-Old Children in the Vision in Preschoolers - Hyperopia in Preschoolers Study

PURPOSE

To compare visual performance between emmetropic and uncorrected moderately hyperopic preschool-age children without strabismus or amblyopia.

DESIGN

Cross-sectional study.

METHODS

setting: Multicenter, institutional. patient or study population: Children aged 4 or 5 years. intervention or observation procedures: Visual functions were classified as normal or reduced for each child based on the 95% confidence interval for emmetropic individuals. Hyperopic (≥3.0 diopters [D] to ≤6.0 D in the most hyperopic meridian; astigmatism ≤1.50 D; anisometropia ≤1.0 D) and emmetropic status were determined by cycloplegic autorefraction.

MAIN OUTCOME MEASURES

Uncorrected monocular distance and binocular near visual acuity (VA); accommodative response; and near random dot stereoacuity.

RESULTS

Mean (± standard deviation) logMAR distance visual acuity (VA) among 248 emmetropic children was better than among 244 hyperopic children for the better (0.05 ± 0.10 vs 0.14 ± 0.11, P < .001) and worse eyes (0.10 ± 0.11 vs 0.19 ± 0.10, P < .001). Mean binocular logMAR near VA was better in emmetropic than in hyperopic children (0.13 ± 0.11 vs 0.21 ± 0.11, P < .001). Mean accommodative response for emmetropic children was lower than for hyperopic subjects for both Monocular Estimation Method (1.03 ± 0.51 D vs 2.03 ± 1.03 D, P < .001) and Grand Seiko (0.46 ± 0.45 D vs 0.99 ± 1.0 D, P < .001). Median near stereoacuity was better in emmetropic than in than hyperopic children (40 sec arc vs 120 sec arc, P < .001). The average number of reduced visual functions was lower in emmetropic than in hyperopic children (0.19 vs 1.0, P < .001).

CONCLUSIONS

VA, accommodative response, and stereoacuity were significantly reduced in moderate uncorrected hyperopic preschool children compared to emmetropic subjects. Those with higher hyperopia (≥4 D to ≤6 D) were at greatest risk, although more than half of children with lower magnitudes (≥3 D to <4 D) demonstrated 1 or more reductions in function.

Adaptation of horizontal eye alignment in the presence of prism in young children

Young children experience decreased convergence and increased accommodation demands relative to adults, as a result of their small interpupillary distance and hyperopic refraction. Those with typical amounts of hyperopic refractive error must accommodate more than an emmetrope to achieve focused retinal images, which may also drive additional convergence through the neural coupling. Adults and older children have demonstrated vergence adaptation to a variety of visual stimuli. Can vergence adaptation help younger children achieve alignment in the presence of these potentially conflicting demands? Purkinje image eye tracking and eccentric photorefraction were used to record simultaneous vergence and accommodation responses in adults and young children (3-6 years). To assess vergence adaptation, heterophoria was monitored before, during, and after adaptation induced by both base-in and base-out prisms. Adaptation was observed in both adults and young children with no significant effect of age, F(1, 34) = 0.014, p = 0.907. Changes in accommodation between before, during, and after adaptation were less than 0.5 D in binocular viewing. Typically developing children appear capable of vergence adaptation, which might play an important role in the maintenance of eye alignment under their changing visual demands.

Emmetropization, visual acuity, and strabismus outcomes among hyperopic infants followed with partial hyperopic corrections given in accordance with dynamic retinoscopy

OBJECT

To record emmetropization, visual acuity, and strabismus outcomes among hyperopic infants followed with partial hyperopic corrections given in accordance with dynamic retinoscopy (DR).

METHODS

Infants (3.5-12 months of age) with ≥5 D hyperopia were followed without glasses or partial hyperopic corrections prescribed according to their near dynamic accommodative abilities determined by DR responses at the initial visit and follow-ups. Refraction and binocular accommodative ability assessments were made at 3-month intervals up to the age of 1 and at 6-month intervals afterwards for a mean 35.4±2.1 months; main outcome measures being the development of esotropia, emmetropization rate, and visual acuity level after emmetropization period.

RESULTS

Among 211, 146 were normal accommodators initially (Group 1). These infants were followed without treatment and none presented with strabismus. Sixty-five infants were hypo-accommodators (Group 2) and received minimum DR-based corrections. Of the 65 infants 31 (48%) developed strabismus (Group 2B). The remaining 34 constituted Group 2A. Each of the three groups showed an overall reduction of hyperopia by 0.37±0.25 days per year, 0.50±0.28 days per year, and 0.60±0.20 days per year, respectively. Visual acuity assessments among Groups 1 and 2A revealed normal values (0.2-0.0 LogMAR); among Group 2B 19% were within normal range.

CONCLUSIONS

Binocular accommodative behavior at the initial visit seems to be one of the indicators for pointing out infants at risk of developing strabismus and amblyopia. Prescription of DR-based corrections to hyperopic orthotropic infants does not impede emmetropization and result in normal visual acuities after emmetropization period.

Why do only some hyperopes become strabismic?

Children with hyperopia greater than +3.5 diopters (D) are at increased risk for developing refractive esotropia. However, only approximately 20% of these hyperopes develop strabismus. This review provides a systematic theoretical analysis of the accommodation and vergence oculomotor systems with a view to understanding factors that could either protect a hyperopic individual or precipitate a strabismus. The goal is to consider factors that may predict refractive esotropia in an individual and therefore help identify the subset of hyperopes who are at the highest risk for this strabismus, warranting the most consideration in a preventive effort.

The relationship between anisometropia and amblyopia

This review aims to disentangle cause and effect in the relationship between anisometropia and amblyopia. Specifically, we examine the literature for evidence to support different possible developmental sequences that could ultimately lead to the presentation of both conditions. The prevalence of anisometropia is around 20% for an inter-ocular difference of 0.5D or greater in spherical equivalent refraction, falling to 2-3%, for an inter-ocular difference of 3D or above. Anisometropia prevalence is relatively high in the weeks following birth, in the teenage years coinciding with the onset of myopia and, most notably, in older adults starting after the onset of presbyopia. It has about one-third the prevalence of bilateral refractive errors of the same magnitude. Importantly, the prevalence of anisometropia is higher in highly ametropic groups, suggesting that emmetropization failures underlying ametropia and anisometropia may be similar. Amblyopia is present in 1-3% of humans and around one-half to two-thirds of amblyopes have anisometropia either alone or in combination with strabismus. The frequent co-existence of amblyopia and anisometropia at a child's first clinical examination promotes the belief that the anisometropia has caused the amblyopia, as has been demonstrated in animal models of the condition. In reviewing the human and monkey literature however it is clear that there are additional paths beyond this classic hypothesis to the co-occurrence of anisometropia and amblyopia. For example, after the emergence of amblyopia secondary to either deprivation or strabismus, anisometropia often follows. In cases of anisometropia with no apparent deprivation or strabismus, questions remain about the failure of the emmetropization mechanism that routinely eliminates infantile anisometropia. Also, the chronology of amblyopia development is poorly documented in cases of 'pure' anisometropic amblyopia. Although indirect, the therapeutic impact of refractive correction on anisometropic amblyopia provides strong support for the hypothesis that the anisometropia caused the amblyopia. Direct evidence for the aetiology of anisometropic amblyopia will require longitudinal tracking of at-risk infants, which poses numerous methodological and ethical challenges. However, if we are to prevent this condition, we must understand the factors that cause it to develop.

Refractive errors in students from Middle Eastern backgrounds living and undertaking schooling in Australia

BACKGROUND

  Environmental factors associated with schooling systems in various countries have been implicated in the rising prevalence of myopia, making the comparison of prevalence of refractive errors in migrant populations of interest. This study aims to determine the prevalence of refractive errors in children of Middle Eastern descent, raised and living in urban Australia but actively maintaining strong ties to their ethnic culture, and to compare them with those in the Middle East where myopia prevalence is generally low.

METHODS

  A total of 354 out of a possible 384 late primary/early secondary schoolchildren attending a private school attracting children of Middle Eastern background in Melbourne were assessed for refractive error and visual acuity. A Shin Nippon open-field NVision-K5001 autorefractor was used to carry out non-cycloplegic autorefraction while viewing a distant target. For statistical analyses students were divided into three age groups: 10-11 years (n = 93); 12-13 years (n = 158); and 14-15 years (n = 102).

RESULTS

  All children were bilingual and classified as of Middle Eastern (96.3 per cent) or Egyptian (3.7 per cent) origin. Ages ranged from 10 to 15 years, with a mean of 13.17 ± 0.8 (SEM) years. Mean spherical equivalent refraction (SER) for the right eye was +0.09 ± 0.07 D (SEM) with a range from -7.77 D to +5.85 D. The prevalence of myopia, defined as a spherical equivalent refraction 0.50 D or more of myopia, was 14.7 per cent. The prevalence of hyperopia, defined as a spherical equivalent refraction of +0.75 D or greater, was 16.4 per cent, while hyperopia of +1.50 D or greater was 5.4 per cent. A significant difference in SER was seen as a function of age; however, no significant gender difference was seen.

CONCLUSIONS

  This is the first study to report the prevalence of refractive errors for second-generation Australian schoolchildren coming from a predominantly Lebanese Middle Eastern Arabic background, who endeavour to maintain their ethnic ties. The relatively low prevalence of myopia is similar to that found for other metropolitan Australian school children but higher than that reported in the Middle East. These results suggest that lifestyle and educational practices may be a significant influence in the progression of myopic refractive errors.