Eye Size and Shape in Relation to Refractive Error in Children: A Magnetic Resonance Imaging Study.

Purpose: The purpose of this study was to determine the association between eye shape and volume measured with magnetic resonance imaging (MRI) and optical biometry and with spherical equivalent (SE) in children. Methods: For this study, there were 3637 10-year-old children from a population-based birth-cohort study that underwent optical biometry (IOL-master 500) and T2-weighted MRI scanning (height, width, and volume). Cycloplegic refractive error was determined by automated refraction. The MRI images of the eyes were segmented using an automated algorithm combining atlas registration with voxel classification. Associations among optical biometry, anthropometry, MRI measurements, and RE were tested using Pearson correlation. Differences between refractive error groups were tested using ANOVA. Results: The mean volume of the posterior segment was 6350 (±680) mm3. Myopic eyes (SE ≤ -0.5 diopters [D]) had 470 mm3 (P < 0.001) and 970 mm3 (P < 0.001) larger posterior segment volume than emmetropic and hyperopic eyes (SE ≥ +2.0D), respectively. The majority of eyes (77.1%) had an oblate shape, but 47.4% of myopic eyes had a prolate shape versus 3.9% of hyperopic eyes. The correlation between SE and MRI-derived posterior segment length (r -0.51, P < 0.001) was stronger than the correlation with height (r -0.30, P < 0.001) or width of the eye (r -0.10, P < 0.001). Conclusions: In this study, eye shape at 10 years of age was predominantly oblate, even in eyes with myopia. Of all MRI measurements, posterior segment length was most prominently associated with SE. Whether eye shape predicts future myopia development or progression should be investigated in longitudinal studies.

Genome-wide association meta-analysis of corneal curvature identifies novel loci and shared genetic influences across axial length and refractive error.

Corneal curvature, a highly heritable trait, is a key clinical endophenotype for myopia - a major cause of visual impairment and blindness in the world. Here we present a trans-ethnic meta-analysis of corneal curvature GWAS in 44,042 individuals of Caucasian and Asian with replication in 88,218 UK Biobank data. We identified 47 loci (of which 26 are novel), with population-specific signals as well as shared signals across ethnicities. Some identified variants showed precise scaling in corneal curvature and eye elongation (i.e. axial length) to maintain eyes in emmetropia (i.e. HDAC11/FBLN2 rs2630445, RBP3 rs11204213); others exhibited association with myopia with little pleiotropic effects on eye elongation. Implicated genes are involved in extracellular matrix organization, developmental process for body and eye, connective tissue cartilage and glycosylation protein activities. Our study provides insights into population-specific novel genes for corneal curvature, and their pleiotropic effect in regulating eye size or conferring susceptibility to myopia.

Prevalence of amblyopia and refractive errors in an unscreened population of children.

PURPOSE: To describe the frequency of refractive errors and amblyopia in unscreened children aged 2 months to 12 years from a rural town in Poland. METHODS: Five hundred ninety-one children were identified by medical records and examined in a standardized manner.Visual acuity was measured using LogMAR charts; refractive error was determined using retinoscopy or autorefraction after cycloplegia. Myopia was defined as spherical equivalent (SE) ≤ -0.50 D, emmetropia as SE between -0.5 D and+0.5 D, mild hyperopia as SE between +0.5 D and +2.0 D, and high hyperopia as SE Q+2.0 D. Amblyopia was classified as best-corrected visual acuity ≥0.3 (≤ 20/40) LogMAR, in combination with a 2 LogMAR line difference between the two eyes and the presence of an amblyogenic factor. RESULTS: Refractive errors ranged from 84.2% in children aged up to 2 years to 75.5% in those aged 10 to 12 years.Refractive error showed a myopic shift with age; myopia prevalence increased from 2.2% in those aged 6 to 7 years to 6.3% in those aged 10 to 12 years. Of the examined children, 77 (16.3%) had refractive errors, with visual loss; of these,60 (78%) did not use corrections. The prevalence of amblyopia was 3.1%, and refractive error attributed to the amblyopiain 9 of 13 (69%) children. CONCLUSION: Refractive errors are common in Caucasian children and often remain undiagnosed. The prevalence of amblyopia was three times higher in this unscreened population compared with screened populations. Greater awarenessof these common treatable visual conditions in children is warranted.

Vertical position of the orbits in nonsyndromic plagiocephaly in childhood and its relation to vertical strabismus.

PURPOSE: To determine the existence of a correlation between the vertical angle of strabismus and the vertical angle between the orbital axes in nonsyndromic plagiocephaly in childhood. METHODS: Patients were included when diagnosed with plagiocephaly. Orthoptic measurements showed a vertical strabismus and three-dimensional computed tomographic (CT) imaging of the skull was available. Patients were excluded if plagiocephaly was part of a syndrome or if any surgical intervention had taken place before our measurements. Three-dimensional CT imaging was used to calculate the vertical angle between the orbital axes in 3 reference planes (VAO) perpendicular to a line of reference through the lower borders of the maxilla (VAOmax), both auditory canals (VAOaud), and the lower points of the external occipital protuberances (VAOocc). RESULTS: Fourteen patients were included (mean age, 14 mo). Three-dimensional CT measurements showed a mean (SD) VAOmax of 1.70 (2.31) degrees, VAOaud of -1.54 (1.46) degrees, and VAOocc of -2.06 (4.29) degrees (a negative value indicates that the eye on the affected side was situated lower in the head). The mean vertical angle of strabismus was -2.39 (4.69) degrees in gaze toward the affected side, 3.66 (3.77) degrees in gaze ahead, and 8.14 (5.63) degrees in gaze toward the nonaffected side. The Pearson test showed no significant correlations. CONCLUSIONS: The clinical observation that vertical strabismus in adult plagiocephaly is correlated with the vertical angle of the orbital axes could not be confirmed in young children.

Objective survey of the prescription of occlusion therapy for amblyopia.

PURPOSE: To identify the variation within and consistency amongst orthoptists when prescribing occlusion therapy for amblyopia in an objective survey. METHODS: A questionnaire was designed with five case examples of amblyopic children and distributed at annual meetings of orthoptists in The Netherlands and Germany. It was filled in simultaneously within 15 min in complete silence to avoid any exchange of opinions between orthoptists that would reduce variability. For each case the orthoptists were asked to give their prescription of hours or days of occlusion. RESULTS: The questionnaire was filled in by 177 Dutch orthoptists and 227 German orthoptists. Their prescriptions of occlusion therapy were classified into five main regimens: part-time; part-time not every day; full-time; also occluding the amblyopic eye; alternating; and no occlusion therapy. The variation was large: the standard deviation was half the average prescribed hours of occlusion for each regimen in each of the five cases. All orthoptists were assigned a rank number for each of the five cases depending on whether their prescription was above or below average. These five rank numbers were not consistently above or consistently below average value per case. CONCLUSIONS: The number of prescribed hours of occlusion varied widely per regimen per case. Orthoptists were not consistently strict or lenient in their prescription of occlusion therapy.

Electronically measured compliance with occlusion therapy for amblyopia is related to visual acuity increase.

PURPOSE: We set out to determine whether the children who have low compliance (measured electronically) with occlusion therapy for amblyopia are those with insufficient increase of visual acuity. METHODS: In 14 newly identified amblyopic children (mean age 4.3+/-1.9 years), compliance was measured electronically over a period of 1 week, 6 months after the start of occlusion therapy. Compliance was measured with an Occlusion Dose Monitor (ODM). The measurements took place during planned domiciliary visits. The children were diagnosed with anisometropia (n=5), strabismus (n=4) and anisometropia and strabismus (n=5). Compliance was expressed in percentages of the electronically registered time compared with the prescribed occlusion time. Satisfactory acuity increase following 6 months of occlusion therapy was defined on reaching any of the following criteria: acuity increase expressed as a ratio between acuity of the amblyopic eye and acuity of the good eye of more than 0.75, acuity of the amblyopic eye exceeding 0.5 as measured on the E-Chart or Landolt-C, or three LogMAR lines of increase in acuity. RESULTS: Measured compliance averaged 80% in the eight children who had a satisfactory acuity increase and 34% in the six children who had an unsatisfactory visual acuity increase. Children with low acuity increase had statistically significantly lower compliance (P=0.038). CONCLUSION: The general assumption among orthoptists, that compliance with occlusion therapy for amblyopia is low in children with insufficient acuity increase, has been validated by electronic, objective means.