Emmetropisation in normal and strabismic children and the associated changes of anisometropia

Longitudinal Changes in Refractive Development in Highly Hyperopic Children: A 2.6-11.2 Year Follow-up of Preschoolers Diagnosed with High Hyperopia

PURPOSE

This study aims to elucidate the longitudinal refractive and ocular biometric alterations in preschool children with high hyperopia who underwent early interventions.

METHODS

We conducted a retrospective analysis of preschool children diagnosed with high hyperopia at Tianjin Medical University Eye Hospital between 2011 and 2023. Inclusion criteria required an initial examination with cycloplegic refraction, bilateral spherical equivalent power (SE) ≥ +5.00D with a difference <1.00D, a minimum two-year follow-up, and at least three ocular biometric measurements. The annual axial growth rate evaluated emmetropization in highly hyperopic children. We applied Restricted Cubic Spline (RCS) models to explore potential nonlinear relationships between age and spherical equivalent, axial length, corneal curvature, and axial length-to-corneal curvature ratio. Additionally, Mixed-effects models were employed to investigate factors associated with changes in refractive error and axial length.

RESULTS

The study enrolled 60 eligible subjects, with a median initial diagnosis age of 3.5 years (IQR, 2.8-4.9 years) and a median last visit age of 9.3 years (IQR, 8.1-10.8 years). The average follow-up duration was 5.7 years. RCS analysis revealed notable nonlinear changes in spherical equivalent power, axial length, and axial length-to-corneal curvature ratio, although corneal curvature displayed no statistically significant nonlinear trend. Factors affecting SE changes included the presence of strabismus, the use of cycloplegia, baseline SE, and age. Conversely, changes in axial length solely correlated with baseline axial length and age.

CONCLUSION

Highly hyperopic preschool children undergoing early intervention display a marked emmetropization tendency, though most still remain moderately to highly hyperopic, with the progression of refractive changes showing non-uniform patterns with respect to age.

Assessing Choroidal Thickness in Pediatric Patients With Unilateral Strabismic Amblyopia by Using Spectral Domain-Enhanced Depth Imaging-Optical Coherence Tomography

Objective In this study, we aimed to evaluate the choroidal thickness in patients with unilateral strabismic amblyopia by using spectral domain-enhanced depth imaging-optical coherence tomography (SD-EDI-OCT) (Heidelberg Engineering GmbH, Heidelberg, Germany). Methods Twenty-five children with strabismic amblyopia and 20 age- and sex-matched healthy controls were included in this study. Seven sections were obtained, each comprising 25 repetitive images from each section at 200-micron intervals, and measurements were taken from nine different points at vertical and horizontal lines (1 and 3 mm from the subfoveal, superior, inferior, temporal, and nasal regions), centered on the fovea, using SD-EDI-OCT. Choroidal thickness values were obtained by measuring the distance between the basal border of the retinal pigment epithelium and the choroidoscleral border. The Mann-Whitney U test was used to compare choroidal thickness between the amblyopic and the control groups. Results The mean age of children with amblyopia and that of controls were 8.4 ±2.7 and 9.9 ±3.3 years, respectively (p=0.120). The mean subfoveal choroidal thickness was 372.8 ±78.9 μm in amblyopic eyes and 372.4 ±79.3 μm in the fellow eyes, both of which were thicker than the control eyes (310.9 ±76.3 μm; p<0.05 for each). Similarly, the mean values for the choroidal thickness of the amblyopic children at 1 mm nasal (320 ±86 μm), 1 mm superior (363 ±70 μm), and 3 mm superior (336 ±62 μm) were also significantly thicker than those of the corresponding control eyes (p<0.05 for each). There was a negative correlation between the subfoveal choroidal thickness and axial length (r=-0.332, p=0.005). There were no correlations between the choroidal thickness, age, and visual acuity. Conclusions The choroidal thicknesses of strabismic and fellow eyes were similar in patients with strabismic amblyopia. However, the choroidal thickness of both eyes in strabismic children was significantly thicker than those of the healthy controls. Emmetropization may be defective in both eyes of strabismic amblyopic patients.

Comparison of Myopia Progression among Myopic Children with Intermittent Exotropia and No Strabismus

SIGNIFICANCE

Myopia is a highly prevalent condition in the pediatric population that is commonly comorbid with intermittent exotropia. Our study found a trend toward significance in the reduction of myopia progression with strabismus correction surgery. Further investigations characterizing the interaction between myopia and strabismus may help inform future management guidelines.

PURPOSE

This study describes and compares myopic progression in the pediatric population with and without intermittent exotropia and its interaction with corrective strabismus surgery.

METHODS

This study analyzed a retrospective cohort of 1239 pediatric myopic patients who were evaluated by pediatric ophthalmologists and optometrists at a tertiary care center from 2012 to 2020. The main outcome measures were the trends in refractive error over time in those with and without intermittent exotropia as well as trends in those who did and did not undergo strabismus surgery.

RESULTS

A total of 275 patients (22%) were identified to have intermittent exotropia, and 12 (4.4%) from this group underwent surgical correction in the study period. No statistically significant difference was identified in myopic progression between those with intermittent exotropia and those without strabismus, and no difference was found in mean annual spherical equivalent change between intermittent exotropia patients who did not undergo surgery compared with those who did.

CONCLUSIONS

Pediatric myopic patients generally experience progression in the condition for several years independent of concurrent intermittent exotropia. Corrective strabismus surgery was not found to alter the natural history of myopia in children, although a reduction in myopic progression in surgically treated patients trended toward significance. Increases in the prevalence of different treatment strategies will necessitate further studies to determine best practices for this population.

Prevalence of refractive error among Chinese preschool children: The Changsha children eye study

Purpose

We aimed to investigate the refractive status and prevalence of refractive error, as well as its characteristics in Chinese preschool children aged 1-6 years old.

Methods

A population-based cross-sectional study-Changsha Children Eye Study (CCES) was conducted. The prevalence of refractive errors among children aged 1-6 years old from 18 community health service centers was surveyed. A handheld child vision screener, Suowei, was used for examination.

Results

A total of 43,105 preschool children were included. The mean spherical equivalent (SE) was 0.42 ± 1.05 D for the right eyes. The mean astigmatism (diopter of cylinder, DC) was -0.83 ± 1.02 D for the right eyes. The magnitude of refractive error was lower in older children, indicating the ongoing of the emmetropization during the 1-6-year-old children. The prevalence of myopia (SE ≤ -1.00 D), hyperopia (SE ≥ +2.00 D) and astigmatism (DC ≥1.50 D) was 2.94, 13.8 and 17.6%, respectively. The prevalence of myopia decreased with the increase of age between the six age groups (P < 0.001). The prevalence of hyperopia was lower in 5-6 years old, whereas, the prevalence of myopia was slightly higher at this period of time. With-the-rule (WTR) astigmatism (+ cylinder axis 90° ± 15°) was the most prevalent type of astigmatism than against-the-rule (ATR) astigmatism (+ cylinder axis 180° ± 15°) and oblique (OBL) astigmatism (X ² = 209.5, P < 0.001). The binary logistic regression model showed that older age and suffering astigmatism were independently associated with the development of myopia. In addition, there was no significant gender difference in the prevalence of myopia, emmetropia, and hyperopia.

Conclusions

Our population-based cross-sectional study investigated the prevalence of myopia, hyperopia, and astigmatism in preschool children aged 1-6 years old. The distribution of the refractive error was disperse in the younger group and gradually turned more centralized in older group. Similar to hyperopia, with age increased, the prevalence of myopia was lower in preschool children younger than 5 years old and then slightly increased at 5-6 years, which may indicate an early sign of myopia in school-age children. Therefore, we emphasize that more attention should be given to the children at this age.

Longitudinal Changes in Refractive Error Among Preschool Children Aged 1–6 Years: The Changsha Children Eye Study

Purpose

To investigate the longitudinal changes in refractive error of preschool children and explore the factors related to these changes and the timing of intervention.

Methods

The refractive data of preschool children aged 1–6 years were collected from 16 community Health Service Centers in Changsha during April 2016 to July 2019 for the retrospective cohort study. The refractive data of each participant was measured with a hand-held vision screener without cycloplegia. A follow-up for all the included participants was performed. The spherical equivalent change was calculated, subsequently, an analysis of risk factors related to the change was performed.

Results

Four thousand nine hundred twenty-one cases were included in the study with the follow-up for 1–2 years. The refractive status was found smoothly changed in 67.8% of children. The overall initial SE was 0.62 ± 1.13 D, and the average SE change was −0.20 ± 1.23 D per year. However, profound myopic shift was observed in 32.2% of children. The change of SE in 3-year-old group is most overt. The proportions of 1–6 years old who showed moderate and severe myopic shift (SE change ≥–1.00 D) were 21.6, 18.9, 28.2, 25.5, 13.4, and 10%, respectively. At the first visit, the younger children with greater hyperopic state exhibited more noticeable myopic shift, no significant difference was found in gender.

Conclusion

The shift from hyperopia to myopia in preschool children is smooth, with −0.20D change on average per year. We suggest that an optometry screening should start at 3-year-old to track children's refractive status. We recommend that preschool children whose SE changes more than −1.00 D per year go to the ophthalmology department for further examination. Our study also found that at the first visit, the younger the child is and the more positive initial SE is, the degree of shift of myopia is greater.

The agreement between the Irvine 4 diopter prism test and assessment of ocular fixation in microtropia with identity

Microtropia describes a primary ocular deviation of less than 10 prism diopters associated with harmonious anomalous retinal correspondence and reduced stereopsis. It is routinely accepted that children with microtropia are less likely to achieve equal vision following occlusion therapy than those with bifoveal fixation. The most commonly used methods of diagnosing a microtropia are the 4 diopter prism test (4^∆PT) and assessment of ocular fixation. This study examines the agreement between the two tests. One hundred and twelve typically developing children without a manifest strabismus who were able to undertake a linear visual acuity test and had two or more lines of anisoacuity following refractive adaption to their full cycloplegic correction underwent assessment of the 4^∆PT and ocular fixation along with their routine orthoptic examination. One hundred and twelve children (46 boys and 66 girls) attending the Orthoptic department who fitted the above criteria were included in the analysis. The mean age at examination was 6 years. 80.3% had anisometropia of at least 1.25 diopters. The 4^∆PT indicated a microtropia in 74 cases, whereas assessment of fixation indicated a microtropia in 68 cases. In 88 cases (78.6%), the results of the two tests agreed. Analysis found only moderate agreement between the two tests (k = 0.540 (CI 0.379-0.700)). Logistic regression analysis comparing those children where the two tests agreed with those where they disagreed found no difference in the level of anisoacuity (p = 0.7823), degree of anisometropia (p = 0.9385), the vision in the worst eye (p = 0.5260), the refractive error in the "worst" eye (p = 0.865), or the age at the time of testing (p = 0.4485) between the two groups. When assessing for a microtropia, it was found that not all children who elicit a central suppression response on the 4^∆PT are found to be fixing eccentrically and vice versa. This could potentially have implications for the treatment of their amblyopia. It is important not to rely on just one test at one time to make the diagnosis of microtropia. Rather, if one or other test indicates a microtropia the first time they are attempted, this should be reassessed regularly as treatment progresses and certainly before treatment is stopped and suboptimal visual acuity is accepted.

Difference in myopia progression between dominant and non-dominant eye in patients with intermittent exotropia

OBJECTIVE

To investigate the difference in the rate of myopia progression between the dominant and non-dominant eye in patients with intermittent exotropia (IXT).

METHODS

We retrospectively reviewed the medical records of 33 patients who underwent surgery and later reoperation for IXT. We included only patients whose spherical equivalent refractive errors (SER) were ≤ - 0.50 diopter (D) in at least one eye at the time of reoperation. The main outcome measurement was the rate of myopia progression, which was defined as the mean annual change in SER between the first and second surgery. We classified patients into two groups: group A, which comprised 25 patients whose non-dominant eyes showed a faster myopia progression than their dominant eyes, and group B, which comprised the remaining 8 patients showing the opposite.

RESULTS

Mean age of the patients at the time of the initial surgery was 5.64 years. Mean interval between the initial and second surgery was 4.45 years. Mean rate of myopia progression over the interval was - 0.37 D/year in the dominant eyes and - 0.50 D/year in the non-dominant eyes (P < 0.001). Group A had a significantly greater amount of distance deviation (31.0 vs. 25.6 PD, P = 0.020) and near deviation (30.8 vs 26.0 PD, P = 0.039) before the initial surgery and a significantly worse score of distance control (3.05 vs. 2.00, P = 0.023) before the second surgery than group B.

CONCLUSIONS

The non-dominant eyes experienced a faster myopia progression than the dominant eyes in patients with IXT. This faster myopia progression demonstrated in the non-dominant eyes was associated with clinically severe exotropia in terms of the amount of deviation and the degree of control.

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.

Understanding the Neural Basis of Amblyopia

Amblyopia is the condition in which reduced visual function exists despite full optical correction and an absence of observable ocular pathology. Investigation of the underlying neurology of this condition began in earnest around 40 years ago with the pioneering studies conducted by Hubel and Wiesel. Their early work on the impact of monocular deprivation and strabismus initiated what is now a rapidly developing field of cortical plasticity research. Although the monocular deprivation paradigm originated by Hubel and Wiesel remains a key experimental manipulation in studies of cortical plasticity, somewhat ironically, the neurology underlying the human conditions of strabismus and amblyopia that motivated this early work remains elusive. In this review, the authors combine contemporary research on plasticity and development with data from human and animal investigations of amblyopic populations to assess what is known and to reexamine some of the key assumptions about human amblyopia.

Clinical exhibition of increased accommodative loads for binocular fusion in patients with basic intermittent exotropia

BACKGROUND

To investigate the accommodative loads change needed to maintain binocular fusion in patients with intermittent exotropia (IXT).

METHODS

Seventeen consecutive patients with basic IXT and 15 normal controls were recruited. The WAM-5500 autorefractor (GrandSeiko, Fukuyama, Japan) was used to measure refractive error (D) under binocular and monocular viewing conditions at 6 m, 50 cm, 33 cm and 20 cm. The difference between binocular and monocular refractive error (D) at each distance defined the change in the accommodative load. The changes in accommodative load were compared between IXT patients and normal controls. We also investigated the change in accommodative loads according to the fixing preference in patients with IXT.

RESULTS

In IXT patients, the mean angles of deviation were 20.2 ± 7.19 and 21.0 ± 8.02 prism diopters at 6 m and 33 cm, respectively. Under binocular viewing, the changes in accommodative loads of each eye in IXT patients were significantly higher at 50, 33 and 20 cm than those of normal controls (p < 0.05, all). The changes in accommodative loads of fixating and deviating eyes at 6 m were not significantly different between IXT patients and normal controls (p = 0.193, 0.155, respectively). The changes in accommodative loads of the fixating eye at each distance were not significantly different from those of the deviating eye in IXT patients (p > 0.05).

CONCLUSION

The changes of accommodative loads at near fixation increased more in IXT patients than they did in normal controls while maintaining binocular fusion.

Longitudinal Development of Refractive Error in Children With Accommodative Esotropia: Onset, Amblyopia, and Anisometropia

Purpose

We investigated longitudinal changes of refractive error in children with accommodative esotropia (ET) throughout the first 12 years of life, its dependence on age at onset of ET, and whether amblyopia or anisometropia are associated with defective emmetropization.

Methods

Longitudinal refractive errors in children with accommodative ET were analyzed retrospectively. Eligibility criteria included: initial hyperopia ≥+4.00 diopters (D), initial cycloplegic refraction before 4 years, at least 3 visits, and at least one visit between 7 and 12 years. Children were classified as having infantile (N = 30; onset ≤12 months) or late-onset (N = 78; onset at 18–48 months) accommodative ET. Cycloplegic refractions culled from medical records were converted into spherical equivalent (SEQ).

Results

Although the initial visit right eye SEQ was similar for the infantile and late-onset groups (+5.86 ± 1.28 and +5.67 ± 1.26 D, respectively), there were different developmental changes in refractive error. Neither group had a significant decrease in hyperopia before age 7 years, but after 7 years, the infantile group experienced a myopic shift of −0.43 D/y. The late-onset group did not experience a myopic shift at 7 to 12 years. Among amblyopic children, a slower myopic shift was observed for the amblyopic eye. Among anisometropic children, the more hyperopic eye experienced more myopic shift than the less hyperopic eye.

Conclusions

Children with infantile accommodative ET experienced prolonged hyperopia followed by a myopic shift after 7 years of age, consistent with dissociation between infantile emmetropization and school age myopic shift. In contrast, children with late-onset accommodative ET had little myopic shift before or after 7 years.

Convergence and Accommodation Development Is Preprogrammed in Premature Infants

PURPOSE

This study investigated whether vergence and accommodation development in preterm infants is preprogrammed or is driven by experience.

METHODS

Thirty-two healthy infants, born at mean 34 weeks gestation (range, 31.2-36 weeks), were compared with 45 healthy full-term infants (mean 40.0 weeks) over a 6-month period, starting at 4 to 6 weeks postnatally. Simultaneous accommodation and convergence to a detailed target were measured using a Plusoptix PowerRefII infrared photorefractor as a target moved between 0.33 and 2 m. Stimulus/response gains and responses at 0.33 and 2 m were compared by both corrected (gestational) age and chronological (postnatal) age.

RESULTS

When compared by their corrected age, preterm and full-term infants showed few significant differences in vergence and accommodation responses after 6 to 7 weeks of age. However, when compared by chronological age, preterm infants' responses were more variable, with significantly reduced vergence gains, reduced vergence response at 0.33 m, reduced accommodation gain, and increased accommodation at 2 m compared to full-term infants between 8 and 13 weeks after birth.

CONCLUSIONS

When matched by corrected age, vergence and accommodation in preterm infants show few differences from full-term infants' responses. Maturation appears preprogrammed and is not advanced by visual experience. Longer periods of immature visual responses might leave preterm infants more at risk of development of oculomotor deficits such as strabismus.

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.

The impact of intermittent exotropia and surgery for intermittent exotropia on myopic progression among early school-aged children with myopia

AIM

To investigate the relationship between myopic progression and intermittent exotropia, and the impact of surgery for exotropia on myopic progression in early school-aged children (from 7 years to 12 years of age).

METHODS

Medical records of early school-aged patients with myopia were reviewed. Patients were divided into three groups; (A) Patients with intermittent exotropia and myopia at presentation and who underwent bilateral lateral rectus muscle recession for exotropia when 7-12 years old; (B) Patients with intermittent exotropia and myopia at presentation and who were merely observed for exotropia; and (C) Patients with myopia and straight ocular alignment. Main outcome measurements were the simple rate of myopic progression per year, the preoperative and postoperative rates of refractive growth with regards to the logarithmic age model in Group A, and the rate of high myopia development at the end of the early school period.

RESULTS

The rates of myopic progression were -0.43±0.14 dioptre (D) per year in Group A, -0.49±0.17 D/year in Group B and -0.42±0.24 D/year in Group C. There was no significant difference in the rate of myopic progression among three groups. There was no significant intergroup difference in the preoperative and postoperative rates of refractive growth in Group A. There were no significant intergroup differences in the rates of high myopia development among three groups.

CONCLUSIONS

Whether patients with intermittent exotropia underwent surgical correction for intermittent exotropia did not influence the rate of myopic progression. There was no significant difference in the rate of myopic progression between patients with accompanying intermittent exotropia and myopia and those with myopia alone.

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.

Effect of ocular alignment on emmetropization in children <10 years with amblyopia

PURPOSE

To determine whether change in refractive error is associated with ocular alignment in 105 children 3 to <7 years of age who previously participated in a randomized trial comparing atropine and patching for moderate amblyopia.

DESIGN

Prospective cohort study.

METHODS

One hundred five children 3 to <7 years of age previously participated in a randomized trial comparing atropine with patching for moderate amblyopia. Cycloplegic refraction was measured at baseline and 10 years of age. Ocular alignment at baseline was categorized as orthotropic, microtropic (1-8 Δ horizontal tropia), or heterotropic (>8 Δ horizontal tropia). Multivariate regression models evaluated whether change in spherical equivalent refractive error was associated with alignment category, after adjusting for age, baseline spherical equivalent refractive error, and type of amblyopia treatment.

RESULTS

Between enrollment and the age 10-year examination, there was a decrease in spherical equivalent refractive error from hyperopia to less hyperopia (amblyopic eye: -0.65 diopter, 95% CI -0.85, -0.46; fellow eye: -0.39 diopter, 95% CI -0.58, -0.20). A greater decrease in amblyopic eye refractive error was associated with better ocular alignment category (P = .004), with the greatest decrease occurring in orthotropic patients. There was no relationship between ocular alignment category and change in fellow-eye refractive error.

CONCLUSIONS

Among children treated for anisometropic, strabismic, or combined mechanism amblyopia, there is a decrease in amblyopic eye spherical equivalent refractive error to less hyperopia after controlling for baseline refractive error. This negative shift toward emmetropia is associated with ocular alignment, which supports the suggestion that better motor and sensory fusion promote emmetropization.

The maximal tolerable reduction in hyperopic correction in patients with refractive accommodative esotropia: a 6-month follow-up study

PURPOSE

To investigate the optimal amount of safe under-correction in patients with refractive accommodative esotropia.

DESIGN

Prospective noncomparative interventional case series.

METHODS

Patients with refractive accommodative esotropia wore trial glasses based on cycloplegic refraction, then -0.25 diopters (D) of minus sphere lenses were placed on both lenses of the trial glasses and the deviation was measured. Minus spheres of -0.25 D were continuously added until the angle of deviation increased; the minus spheres added just before the deviation increase were defined as the maximal tolerable amount of under-correction. A total of 38 patients were prescribed under-corrected spectacles up to -1.5 D and followed for 6 months.

RESULTS

Thirty-one patients underwent the maximal tolerable amount of under-correction and 7 underwent -1.5 D of under-correction. A mean -0.89 D of under-correction was performed. We observed no deterioration in visual acuity, stereoacuity, or fusional ability during the follow-up period in any of the patients. Small increase in the angle of deviation of 2 prism diopters was noted in 2 patients. The mean spherical equivalent refractive error of both eyes (P = .012) and age of onset (P = .006) showed strong positive correlations with the maximal tolerable amount of under-correction.

CONCLUSIONS

A reduction in hyperopic correction by the maximal tolerable amount of under-correction was performed without notable short-term side effects. The spherical equivalent refractive error and age of onset appear to be useful clinical indices in determining the appropriate amount of under-correction.

Longitudinal changes in refractive error of children with infantile esotropia

Aim

The aim of this study was to quantify changes in refractive status over time in children with infantile esotropia and to analyse a number of clinical factors associated with infantile esotropia to determine how they may affect emmetropisation.

Methods

Longitudinal cycloplegic refraction data were collected for 5-12 years from 143 consecutive children enrolled in a prospective study of infantile esotropia by 6 months of age. Changes in refractive error with age were summarized with descriptive statistics and the influence of amblyopia, undercorrection of hypermetropia, accommodation, and binocular factors on emmetropisation were evaluated by ANOVA and t-tests.

Results

Most had low to moderate hypermetropia on the initial visit (55% had <+3.00 D). While the initial refractive error is similar to normative data, the rapid decrease in hypermetropia that characterizes normal development during the first 9 months of life is absent in children with infantile esotropia. After 9 months of age, children with infantile esotropia follow a developmental course that is similar to the normative course; there is little change in hypermetropia during years 1-7, followed by a decline of approximately -0.5 D/yr beginning at age 8 years. None of the clinical factors examined had a statistically significant effect on the course of refractive changes with age.

Conclusions

Children with infantile esotropia exhibit a different pattern of refractive development than that seen in normative cohorts. The long term changes in refraction observed in children with infantile esotropia suggest that there is a need for long-term clinical follow-up of these children.

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

PURPOSE

To identify the effect of infant hypermetropia on residual amblyopia in children remaining after treatment.

MATERIALS AND METHODS

879 strabismic children had cycloplegic retinoscopy at the age of 6 months and later when strabismus was diagnosed. A total of 26 hypermetropes consistently wore glasses from the age of 6 months, and 305 other hypermetropes had their accommodation periodically assessed by dynamic retinoscopy before strabismus was diagnosed. The relation between the last known visual acuity after treatment and all other clinical findings was analysed using t-tests and regression analysis.

RESULTS

Vision less than 6/12 in nonfixing eyes was associated with infantile hypermetropia > +5.0D, and in rare instances in excess of -3.0D of myopia. In hypermetropes only, anisometropia was associated with worse amblyopia. Astigmatism was associated with myopia and low levels of hypermetropia but not with worse vision. The vision of fixing eyes that were hypermetropic was significantly worse than that of emmetropic or myopic eyes. Wearing spectacles from the age of 6 months was associated with better vision in the nonfixing eye. Vision in the nonfixing eye of 19 hypermetropic heterotropes who started wearing glasses between 6 and 18 months of age also was better than that of those who started wearing glasses after 18 months of age. Insufficiency of accommodation was related to the degree of infantile hypermetropia, to worse vision and to failure to emmetropise. Difference in amplitude of accommodation between the eyes was largest in hypermetropes with anisometropia > +1.50 D and was marginally associated with worse vision in microtropes who became anisometropic after infancy. Hypermetropia decreased more in fixing eyes than in nonfixing eyes, thereby causing anisohypermetropia to increase after infancy. This change was most pronounced in hypermetropic microtropes. Conversely, failure of fixing eyes to emmetropise was associated with an increase in their inability to accommodate and heterotropia.

CONCLUSIONS

On the basis of these findings, severe residual amblyopia in children remaining after treatment could be explained by additional vision deprivation. It can be reduced by starting spectacle correction of hypermetropia before the age of 18 months. Anisometropia seemed the result of deficient emmetropisation.

The development of myopia among children with intermittent exotropia

PURPOSE

To describe the long-term refractive error changes in children diagnosed with intermittent exotropia (IXT) in a defined population.

DESIGN

Retrospective, population-based observational study.

METHODS

Using the resources of the Rochester Epidemiology Project, the medical records of all children (<19 years) diagnosed with IXT as residents of Olmsted County, Minnesota, from January 1, 1975 through December 31, 1994 were retrospectively reviewed for any change in refractive error over time.

RESULTS

One hundred eighty-four children were diagnosed with IXT during the 20-year study period; 135 (73.4%) had 2 or more refractions separated by a mean of 10 years (range, 1-27 years). The Kaplan-Meier rate of developing myopia in this population was 7.4% by 5 years of age, 46.5% by 10 years, and 91.1% by 20 years. There were 106 patients with 2 or more refractions separated by at least 1 year through 21 years of age, of which 43 underwent surgery and 63 were observed. The annual overall progression was -0.26 diopters (SD +/- 0.24) without a statistically significant difference between the observed and surgical groups (P = .59).

CONCLUSION

In this population-based study of children with intermittent exotropia, myopia was calculated to occur in more than 90% of patients by 20 years of age. Observation versus surgical correction did not alter the refractive outcome.

Evaluation of refraction in a statistically significant sample: changes according to age and strabismus

PURPOSE

To assess possible refractive changes according to age and strabismus in a statistically significant cohort.

METHODS

A population-based sample of 12,534 subjects 0.5 to 20 years old, examined between 2004 and 2006, was tested. Each subject received a complete orthoptic examination, including spherocylindrical streak retinoscopy in cycloplegia. Patients were divided into those with orthophoria (7,784) and those with strabismus (4,750), and the latter group was further divided into those with esodeviation (3,026) and those with exodeviation (1,724). A statistical analysis of the spherical equivalent, astigmatism, and anisometropia was performed with an independent samples t test or one-way analysis of variance.

RESULTS

The percentage of patients with a mean spherical equivalent within +/- 1 and +/- 2 standard deviations was greater than 68% and 95%, respectively. The mean spherical equivalent of the total sample was 1.62 diopters (D) (+/- 2.88). The mean spherical equivalent was 1.10 +/- 2.94 D in the orthophoria group, 3.22 +/- 2.29 D in the esodeviation group, and 1.13 +/- 2.50 D in the exodeviation group (one-way analysis of variance; P = .000). Age-related changes in the mean spherical equivalent showed a clear and steady myopic shift, reaching mean myopic refraction at 12 to 14 years in both the total sample and the orthophoria and exodeviation groups. It assumed a more constant trend, with no myopic swing, in the esodeviation group (P = .000). Mean astigmatism was less in patients with less than 1.00 D anisometropia (0.83 +/- 0.92 D) than in those with 1.00 D or greater anisometropia (1.42 +/- 1.18 D) (t test; P = .0001).

CONCLUSION

Both the age-related trend in the spherical equivalent and the high hyperopic values of the distribution peak in patients with esodeviation confirm the importance of the hypermetropic refractive component. The statistically significantly higher incidence of astigmatism in patients with 1.00 D or greater ametropia highlights its incidence in amblyopia.

Prevalence of refractive error among preschool children in an urban population: the Baltimore Pediatric Eye Disease Study

PURPOSE

To determine the age-specific prevalence of refractive errors in white and African-American preschool children.

DESIGN

The Baltimore Pediatric Eye Disease Study is a population-based evaluation of the prevalence of ocular disorders in children aged 6 to 71 months in Baltimore, Maryland.

PARTICIPANTS

Among 4132 children identified, 3990 eligible children (97%) were enrolled and 2546 children (62%) were examined.

METHODS

Cycloplegic autorefraction was attempted in all children with the use of a Nikon Retinomax K-Plus 2 (Nikon Corporation, Tokyo, Japan). If a reliable autorefraction could not be obtained after 3 attempts, cycloplegic streak retinoscopy was performed.

MAIN OUTCOME MEASURES

Mean spherical equivalent (SE) refractive error, astigmatism, and prevalence of higher refractive errors among African-American and white children.

RESULTS

The mean SE of right eyes was +1.49 diopters (D) (standard deviation [SD] = 1.23) in white children and +0.71 D (SD = 1.35) in African-American children (mean difference of 0.78 D; 95% confidence interval [CI], 0.67-0.89). Mean SE refractive error did not decline with age in either group. The prevalence of myopia of 1.00 D or more in the eye with the lesser refractive error was 0.7% in white children and 5.5% in African-American children (relative risk [RR], 8.01; 95% CI, 3.70-17.35). The prevalence of hyperopia of +3 D or more in the eye with the lesser refractive error was 8.9% in white children and 4.4% in African-American children (RR, 0.49; 95% CI, 0.35-0.68). The prevalence of emmetropia (<-1.00 D to <+1.00 D) was 35.6% in white children and 58.0% in African-American children (RR, 1.64; 95% CI, 1.49-1.80). On the basis of published prescribing guidelines, 5.1% of the children would have benefited from spectacle correction. However, only 1.3% had been prescribed correction.

CONCLUSIONS

Significant refractive errors are uncommon in this population of urban preschool children. There was no evidence for a myopic shift over this age range in this cross-sectional study. A small proportion of preschool children would likely benefit from refractive correction, but few have had this prescribed.

Rotated prism-wear disrupts emmetropization but does not reliably induce hyperopia in the New World monkey

To determine whether a disruption of binocular vision that has been previously shown to be amblyogenic disturbs visually guided growth, and in particular to follow-up the observation by Kiorpes and Wallman [Kiorpes, L., & Wallman, J. (1995). Does experimentally-induced amblyopia cause hyperopia in monkeys? Vision Research, 35(9), 1289-1297] that monkeys in whom strabismus had been induced some years earlier were hyperopic in eyes that had become amblyopic, we induced unilateral fixation in five infant New World monkeys (marmosets) through the wearing of a Fresnel prism (of 15 or 30 prism dioptres power) in front of one eye for four weeks. The prism was rotated every three hours during the prism-wear period to encourage a preference for fixating with the contralateral eye. Refractive error and intraocular axial dimensions were measured before, and at intervals after the prism-wearing period. Fixation preference was measured behaviourally, during and after the prism-wear period. Cortical visual function was subsequently assessed through recording of pattern-reversal VEPs in each marmoset between 11 and 14 months of age to assess whether amblyopia had developed in the non-fixing eye. All marmosets used the untreated eye almost exclusively for a monocular visual task by the end of the prism-rearing period. This preference was still present up to at least 7 months after prism-wear had ceased. VEP measures showed a loss of sensitivity at low spatial frequencies (the only ones we were able to test), compatible with amblyopia having developed in the non-fixating eyes of the prism-reared marmosets. Eyes that wore prisms were not significantly different from their fellow eyes in mean refractive error or mean vitreous chamber depth (repeated measures ANOVA; P>0.05) before or at any time after prism-wear had ceased. Two marmosets developed 2-3D of anisometropia (one hyperopic and one myopic) at the end of prism-wear, that was attributable to interocular differences in vitreous chamber depth, and which decreased towards isometropia in the period following prism-wear removal. Disruption of binocular vision with rotating prisms can influence emmetropization and ocular growth, although it does not appear to do so in a consistent way.

Relationship between anisometropia, patient age, and the development of amblyopia

PURPOSE

Previous studies evaluating the effect of anisometropia on amblyopia development have been biased because subject selection occurred as a result of decreased acuity. Photoscreening identifies anisometropic children in a manner that is not biased by acuity, and allows an opportunity to evaluate how patient age influences the prevalence and depth of amblyopia.

DESIGN

Retrospective observational study of preschool children with anisometropia.

METHODS

A statewide preschool photoscreening program screened 119,311 children and identified 792 with anisometropia >1.0 diopters. We correlated age with visual acuity and amblyopia depth. Results were compared with 562 strabismic children similarly identified.

RESULTS

Only 14% (six of 44) of anisometropic children aged 1 year or younger had amblyopia. Amblyopia was detected in 40% (32 of 80) of 2-year-olds, 65% (119 of 182) of 3-year-olds, and 76% of 5-year-olds. Amblyopia depth also increased with age. Moderate amblyopia prevalence was 2% (ages 0 to 1), 17% (age 2), and rose steadily to 45% (ages 6 to 7). Severe amblyopia was rare for children aged 0 to 3, 9% at age 4, and 14% at age 5. Children with strabismus had a relatively stable prevalence (30% ages 0 to 2; 42% ages 3 to 4; and 44% ages 5 to 7) and depth of amblyopia.

CONCLUSIONS

Younger children with anisometropia have a lower prevalence and depth of amblyopia than older children. By age 3, when most children undergo traditional screening, amblyopia has usually already developed. New vision screening technologies that allow early detection of anisometropia provide ophthalmologists an opportunity to intervene early, perhaps retarding or even preventing the development of amblyopia.

The accommodative element in accommodative esotropia

PURPOSE

To evaluate the effect of reducing the hyperopic correction on the state of binocular accommodative response in fully accommodative esotropia and to determine the "comfortable" amount of reduction in hyperopic correction.

DESIGN

A cohort study.

METHODS

Hyperopic corrections of children with a baseline refractive error of +1.50 to +5.0 diopters were gradually reduced in 0.50-diopter increments. Binocular accommodative ability was assessed by dynamic retinoscopy (monocular estimate method). Similar binocular accommodative responses were ascertained among patients with a baseline hyperopic correction of < or =3.0 of hyperopia and >3.0 of hyperopia, and patients were divided into two groups, group 1 (13 patients) and group 2 (18 patients), accordingly.

RESULTS

After a reduction of 2.0 diopters in group 1 and 1.0 diopter in group 2, there was a decrease in accommodative response initially in the nondominant eye, accompanied by the dominant eye with a further reduction of 0.50 diopter. To overcome the bilateral accommodative lag, a reinstatement of a 0.50-diopter stronger hyperopic correction was required. Patients in group 1 tolerated a mean undercorrection of 2.37 diopters, and 77% were weaned from their spectacles. All of the children in group 2 were dependent upon spectacles at the completion of the study period. The final spectacle worn was a median of -1.67 diopters less than their full cycloplegic refraction.

CONCLUSIONS

A complete binocular accommodative ability seems to be a prerequisite for the establishment of "comfortable" hyperopic undercorrections. It does not seem to be a reasonable approach to consider further reductions in hyperopic correction in the presence of a bilateral decreased accommodative performance.

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.