The prevalence of anisometropia in population base study

Anisomyopia and orthokeratology for myopia control - Axial elongation and relative peripheral refraction

PURPOSE

To investigate axial elongation (AE) and changes in relative peripheral refraction (RPR) in anisomyopic children undergoing orthokeratology (ortho-k).

METHODS

Bilateral anisomyopic children, 7-12 years of age, were treated with ortho-k. Axial length (AL) and RPR, from 30° nasal (N30°) to 30° temporal (T30°), were measured at baseline and every 6 months over the study period. AE, changes in RPR and changes in the interocular AL difference were determined over time.

RESULTS

Twenty-six of the 33 subjects completed the 2-year study. The AE of the higher myopic (HM) eyes (at least 1.50 D more myopia than the other eye) (0.26 ± 0.29 mm) was significantly smaller than for the less myopic (LM) eyes (0.50 ± 0.27 mm; p = 0.003), leading to a reduction in the interocular difference in AL (p = 0.001). Baseline RPR measurements in the HM eyes were relatively more hyperopic at T30°, N20° and N30° (p ≤ 0.02) and greater myopic shifts were observed at T20° (p < 0.001), T30° (p < 0.001), N20° (p = 0.02) and N30° (p = 0.01) after lens wear. After 2 years of ortho-k lens wear, temporal-nasal asymmetry increased significantly, being more myopic at the temporal locations in both eyes (p < 0.001), while AE was associated with the change in RPR at N20° (β = 0.134, p = 0.01). The interocular difference in AE was also positively associated with the interocular difference in RPR change at N30° (β = 0.111, p = 0.02).

CONCLUSIONS

Ortho-k slowed AE in bilateral anisomyopia, with slower growth in the HM eyes leading to a reduction in interocular AL differences. After ortho-k, RPR changed from hyperopia to myopia, with greater changes induced in the HM eyes, and slower AE was associated with a more myopic shift in RPR, especially in the nasal field of both eyes.

Prevalence of anisometropia and its associated factors in school-age children

PURPOSE

To determine the prevalence of anisometropia and the associated demographic and biometric risk factors in children.

METHODS

This cross-sectional study was conducted on the elementary school children of Shahroud, east of Iran, in 2015. All rural students were recruited, while multistage cluster sampling was used to select the students in urban areas. All children underwent optometric examinations including the measurement of uncorrected and corrected visual acuity, autorefraction, and subjective refraction with cycloplegia. Biometric components were measured using the Allegro Biograph. Myopia and hyperopia were defined as a spherical equivalent ≤-0.5 and ≥ +2.00 diopter, respectively. Students with a history of ocular trauma or lack of cycloplegic refraction at least in one eye were excluded from the study.

RESULTS

Of 6624 selected children, 5620 participated in the study. After applying the exclusion criteria, the data of 5357 students (boys: 52.8%, n = 2834) were analyzed. The mean age of the subjects was 9.2 ± 1.7 years (range: 6-12 years). The prevalence of anisometropia ≥ 1 D was 1.1% (95% CI: 0.8 to 1.4) in all children, 1.0% (95% CI: 0.7-1.3) in boys, 1.3% (95% CI: 0.8-1.7) in girls, 1.1% (95% CI: 0.8-1.4) in urban children, and 1.4% (95% CI: 0.5-2.3) in rural children. The prevalence of anisometropia was 8.8% (95% CI: 5.3-12.2) in myopic and 5.7% (95% CI: 2.8-8.5) in hyperopic children. Axial length asymmetry (OR = 40.9; 95%CI: 10.2-164.1), myopia (OR = 17.9; 95% CI: 9.4-33.9), and hyperopia (OR = 10.1; 95% CI: (5.1-19.7) were associated with anisometropia in multiple logistic regression model. More anisometropia was associated with more severe amblyopia. The odds of amblyopia (OR = 82.3: 38.2-177-3) and strabismus (OR = 17.6: 5.5-56.4) were significantly higher in anisometropic children. The prevalence of amblyopia was 21.7% in children with myopic anisometropia ≥ 3D, 66.7% in children with hyperopic anisometropia ≥ 3D, and 100% in cases with antimetropia ≥ 3D.

CONCLUSION

The prevalence of anisometropia was low in Iranian school children. However, a high percentage of anisometropic students had amblyopia and strabismus. Axial length was the most important biometric component associated with anisometropia.

Prevalence of myopia among senior students in Fenghua, Eastern China, before and during the COVID-19 pandemic

Background

Myopia is a common cause of vision impairment worldwide. In China, the prevalence, the affected population, and the onset age of myopia are prominent issues. Prevention and intervention of myopia are great public health concerns.

Methods

This school-based retrospective study retrieved visual acuity and refractive data of senior students (grade 12th) from six high schools in Fenghua City, Zhejiang Province, eastern China, from 2016 and 2022. Noncycloplegic autorefraction was performed for refractive status. Students were divided into three subgroups by their school types. The overall myopia prevalence, as well as the prevalence of low myopia, moderate myopia, and high myopia, were calculated separately for each year. Statistical analyzes were performed using SPSS 25.0 and Graphpad Prism software.

Results

The mean myopia prevalence in Fenghua was 84.5% (95% CI: 84.0-85.0%), and a slightly downward trend was found in myopia prevalence after 2019, but the change was not statistically significant (p = 0.078). The overall prevalence of myopia was 79.6, 85.2, and 86.1% in vocational high schools, general high schools, and key high schools, respectively, with statistically significant differences (p < 0.001). The prevalence of myopia among senior students in the vocational high school was significantly lower than that in the other two high schools. There's no significant change in the overall prevalence of myopia (84.7% vs. 84.3%, p = 0.265) before and during the COVID-19 pandemic, and it remained statistically insignificant after stratifying by gender (male p = 0.207, female p = 0.918) or school types (vocational high school p = 0.112; general high school p = 0.299; key high school p = 0.393).

Conclusion

The prevalence of myopia among senior students in Fenghua is relatively high, and the COVID-19 pandemic has no significant impact on it. The prevalence of myopia among vocational high school students is lower than that of general high school and key high school. Attention should be paid to the effects of educational pressure on the prevalence of myopia among students.

Interocular Symmetry Analysis of Corneal Elevation Using the Fellow Eye as the Reference Surface and Machine Learning

Unilateral corneal indices and topography maps are routinely used in practice, however, although there is consensus that fellow-eye asymmetry can be clinically significant, symmetry studies are limited to local curvature and single-point thickness or elevation measures. To improve our current practices, there is a need to devise algorithms for generating symmetry colormaps, study and categorize their patterns, and develop reference ranges for new global discriminative indices for identifying abnormal corneas. In this work, we test the feasibility of using the fellow eye as the reference surface for studying elevation symmetry throughout the entire corneal surface using 9230 raw Pentacam files from a population-based cohort of 4613 middle-aged adults. The 140 × 140 matrix of anterior elevation data in these files were handled with Python to subtract matrices, create color-coded maps, and engineer features for machine learning. The most common pattern was a monochrome circle (“flat”) denoting excellent mirror symmetry. Other discernible patterns were named “tilt”, “cone”, and “four-leaf”. Clustering was done with different combinations of features and various algorithms using Waikato Environment for Knowledge Analysis (WEKA). Our proposed approach can identify cases that may appear normal in each eye individually but need further testing. This work will be enhanced by including data of posterior elevation, thickness, and common diagnostic indices.

Effects of stereopsis on vection, presence and cybersickness in head-mounted display (HMD) virtual reality

Stereopsis provides critical information for the spatial visual perception of object form and motion. We used virtual reality as a tool to understand the role of global stereopsis in the visual perception of self-motion and spatial presence using virtual environments experienced through head-mounted displays (HMDs). Participants viewed radially expanding optic flow simulating different speeds of self-motion in depth, which generated the illusion of self-motion in depth (i.e., linear vection). Displays were viewed with the head either stationary (passive radial flow) or laterally swaying to the beat of a metronome (active conditions). Multisensory conflict was imposed in active conditions by presenting displays that either: (i) compensated for head movement (active compensation condition), or (ii) presented pure radial flow with no compensation during head movement (active no compensation condition). In Experiment 1, impairing stereopsis by anisometropic suppression in healthy participants generated declines in reported vection strength, spatial presence and severity of cybersickness. In Experiment 2, vection and presence ratings were compared between participants with and without clinically-defined global stereopsis. Participants without global stereopsis generated impaired vection and presence similarly to those found in Experiment 1 by subjects with induced stereopsis impairment. We find that reducing global stereopsis can have benefits of reducing cybersickness, but has adverse effects on aspects of self-motion perception in HMD VR.

Effect of orthokeratology on anisometropia control: A meta-analysis

BACKGROUND

The effectiveness of orthokeratology in retarding anisometropic progression has been investigated in several small-sample studies. This quantitative analysis aimed to elucidate the efficacy of orthokeratology for anisometropia control.

METHODS

We searched PubMed, Embase, and Cochrane databases for relevant studies through September 2020. Axial length (AL) data at baseline and final follow-up were extracted, and AL elongation and difference were calculated. Methodological quality was evaluated using the risk of bias in non-randomized studies of interventions (ROBINS-I) tool. Meta-analyses were performed using a fixed-effect model based on the heterogeneity.

RESULTS

A total of 10 cohort studies (nine retrospective studies; one prospective study) were included. The pooled results for the unilateral myopia group showed that the mean AL elongation difference between myopic and emmetropic eyes was -0.27 mm (95% CI, -0.31 to -0.22; p < 0.01) at the one-year follow-up (four studies) and -0.17 mm (95% CI, -0.33 to -0.02; p = 0.03) at the two-year follow-up (two studies). In the bilateral anisomyopic group, mean AL elongation difference between high and low myopic eyes was -0.06 mm (95% CI, -0.09 to -0.04; p < 0.01) at the one-year follow-up (seven studies) and -0.13 mm (95% CI, -0.21 to -0.06; p < 0.01) at the two-year followup (three studies).

CONCLUSION

This study demonstrated that orthokeratology can effectively retard myopic progression and reduce anisomyopic values. However, additional wellstructured randomized controlled trials or prospective studies with longer follow-up periods are warranted to address this topic in more detail.

The effect of amblyopia on clinical outcomes of children with astigmatism

BACKGROUND

Amblyopia is more common in children with high astigmatism, but factors contributing to development of amblyopia and visual outcomes are not fully understood.

OBJECTIVE

To evaluate the effect of amblyopia on the clinical outcomes in children with ⩾1.75 diopter (D) astigmatism.

METHODS

We reviewed the medical records of children with ⩾1.75 D astigmatism with and without amblyopia (amblyopes group and non-amblyopes group). The mean age, gender, amount and type of ocular deviation, presence of convergence insufficiency (CI), stereopsis, time of initial spectacle use and follow-up time, differences in best-corrected visual acuity (VoD) and spherical equivalent (SE) between eyes were assessed and compared between the groups. Best-corrected visual acuity (BCVA), mean SE, astigmatism measurements were assessed and compared between amblyopic, fellow, and non-amblyopic eyes.

RESULTS

The records included 68 eyes of 34 children with amblyopia and 56 eyes of 28 children without amblyopia. The mean age, gender, amount and type of ocular deviation, presence of CI, stereopsis, time of initial spectacle use, follow-up time, and the difference in SE did not differ between groups. In amblyopes, exodeviation was more common and statistically greater in near (33 cm) than at distance (6 m) (p = 0.005). The mean BCVA and astigmatism values were statistically different between amblyopic, fellow, and non-amblyopic eyes.

CONCLUSION

A greater near than distance exodeviation and higher mean astigmatism value were found in amblyopic children with astigmatism.

Heredity of interocular similarities in components of refraction: a population-based twin study among 66- to 79-year-old female twins

PURPOSE

To examine genetic influences on interocular similarities in ocular refraction and components of refraction among elderly female twins.

METHODS

Refraction was assessed in 94 monozygotic (MZ) and 74 dizygotic (DZ) female twins aged 66-78 years. Absolute values of interocular differences (Aniso variables) in spherical refraction (SR), refractive astigmatism (AST), spherical equivalent (SE), corneal refractive power (CR), corneal astigmatism (CAST), anterior chamber depth (ACD) and axial length (AL) were calculated. The differences between sisters in each of the Aniso variables were calculated and graded into two categories, best differentiating the groups, here isometropic and anisometropic values. The cut-offs for grading as isometropic were AnisoSR < 0.75 D, AnisoAST < 0.5 D, AnisoSE < 1.0 D, AnisoCR < 0.5 D, AnisoCAST < 0.50 D, AnisoACD < 0.1 mm and AniosAL < 0.1 mm. Genetic influences on these traits were investigated by comparing the prevalence of isometropic and anisometropic differences between the MZ and DZ pairs in the Aniso variables and the interrelationships between the Aniso variables.

RESULTS

When the Aniso variables were treated as continuous, no significant differences were found between the MZ and DZ subjects. When the proportions of isometropic intratwinpair interocular differences in the Aniso variables in the MZ and DZ cotwins were compared, the prevalences (MZ/DZ) were AnisoSR: 68%/60%; AnisoAST: 66%/57%; AnisoSE: 87%/68%; AnisoCR: 83%/78%; AnisoCAST: 69%/35%; AnisoACD: 77%/63%; and AnisoAL: 76%/60%. The differences were statistically significant for Aniso SE (p = 0.035, Fisher's exact test) and CAST (p = 0.007). The greater homogeneity in the interocular differences between the MZ sisters supports the assumption that isometropia of different elements of refraction is genetically influenced and tending to continue up to older ages. In cases where AnisoSE was <1.0 D, higher CR in one eye was associated with shorter AL (r = -0.398, p < 0.001), thereby contributing to emmetropization, irrespective of zygosity. In the cases of AnisoSE ≥1 D, no similar influence on emmetropization was observed. The difference between sisters in AnisoSE was associated with the intratwinpair difference in Aniso AL, but not with the intratwinpair differences in AnisoCR, irrespective of zygosity.

CONCLUSION

The higher prevalence of similarities in isometropia of the spherical equivalent and corneal astigmatism between the MZ pairs compared to DZ pairs is consistent with the view that genetic influences on the refractive elements of the eye, tending to isometropia, continue into older age. The interrelation between CR and AL tends to maintain isometropia of SE irrespective of zygosity.

Assessment of Binocular Imbalance with an Augmented Virtual Reality Platform in a Normal Population

We examined and analyzed binocular imbalance in a group of randomly selected normal subjects with corrected visual acuity of 0.8 or more in both eyes without ocular diseases, by using augmented virtual reality system. This study will quantify the correlation between binocular imbalance in these normal subjects and various spatial frequencies and temporal frequencies in the integrated binocular stimulation mode. A retrospective study was carried out and data from 97 patients (51 males and 46 females) who were diagnosed with no eye diseases, and with corrected binocular visual acuity of 0.8 or more, were collected. Their binocular visual function, Hirschberg test refraction status, and binocular imbalance were assessed using the quantified visual perception stimulation mode in an augmented virtual reality platform. When normal subjects (with corrected binocular vision of 0.8 or more without ocular diseases) were assessed using the integrated binocular stimulation mode with different temporal and spatial frequencies, a gradual reduction of binocular imbalance could be observed when spatial frequencies were increased. When contrast balance was adjusted, binocular imbalance was more prevalent in the horizontal state compared with the vertical state. This was seen when patients were stimulated by different temporal frequencies in the virtual reality testing mode. 17.53% and 29.90% of participants reached complete binocular fusion under low temporal frequency stimulation and high temporal frequency stimulation, respectively, while binocular imbalance was found in 65.9% and 62.89% of participants who were stimulated, respectively, by low temporal frequency and high temporal frequency. In addition, 16.5% and 7.21% experienced severe binocular imbalance under low temporal and high temporal frequency stimulation, respectively. The integrated binocular stimulation mode under low temporal frequency was more sensitive in detecting binocular imbalance. The status of binocular balance in normal subjects was not the same when stimulated by the augmented virtual reality platform, as many showed varying degrees of binocular imbalance. The results from our clinical study demonstrate that integrated binocular stimulation with different spatial and temporal frequencies enables a more sensitive detection of binocular imbalance, making it a powerful new tool for the diagnosis and analysis of clinical binocular abnormalities. In addition, since more than half of the normal subjects (without eye diseases who has corrected vision of 0.8 or more) exhibited binocular imbalance in our study, we believe that this brief binocular imbalance is likely a transient physiological phenomenon, which is not pathological to visual acuity and function, and should only be seen as pathological when binocular imbalance is prolonged, causing functional deficits such as reading impairment.

Comparison of perceptual eye positions among patients with different degrees of anisometropia

The aim of this study is to compare the perceptual eye positions (PEPs) among patients with different degrees of anisometropia.A total of 157 patients were recruited into this retrospective study. A detailed ophthalmic examination was conducted on each patient. The degree of refractive errors in the presence of astigmatism was converted into the degree of spherical equivalent (SE). Patients were divided into 3 groups according to the interocular SE difference: severe anisometropia group with interocular SE difference ≥2.50D, mild anisometropia group with interocular SE difference ≥1.00D and <2.50D, and non-anisometropia group with interocular SE difference <1.00D. The vertical and horizontal PEP were measured by a computer-controlled perceptual examination evaluation system. The results obtained from the 3 groups were compared and analyzed.A total of 157 patients were enrolled including 32 patients in the severe anisometropia group, 37 patients in the mild anisometropia group, and 88 patients in the non-anisometropia group. The quartiles of vertical PEP pixels were as follows: 7.50 (5.00, 16.75) in the severe anisometropia group, 5.00 (2.00, 7.50) in the mild anisometropia group, and 5.00 (3.00, 9.00) in the non-anisometropia group, respectively. The vertical PEP pixel was much higher in the severe anisometropia group than that in the other two groups (P < .05). The quartiles of horizontal PEP pixels were as follows: 27.50 (10.75, 67.50) in the severe anisometropia group, 17.00 (7.00, 54.50) in the mild anisometropia group, and 21.50 (11.00, 60.75) in the non-anisometropia group. There were no statistically significant differences among the 3 groups (P > .05).There was an obvious deviation of vertical PEP in patients with anisometropia ≥2.50D, indicating that the instability of vertical PEP might be associated with the development of severe anisometropia.

Anisometropia of spherical equivalent and astigmatism among myopes: a 23-year follow-up study of prevalence and changes from childhood to adulthood

PURPOSE

To study anisometropia of spherical equivalent and astigmatism from the onset of myopia at school age to adulthood.

METHODS

A total of 240 myopic schoolchildren (mean age 10.9 years), with no previous spectacles, were recruited during 1983-1984 to a randomized 3-year clinical trial of bifocal treatment of myopia. Examinations with subjective cyclopedic refraction were repeated 3 years later (follow-up 1) for 238 subjects and thereafter at the mean ages of 23.2 (follow-up 2) and 33.9 years (follow-up 3) for 178 and 134 subjects. After exclusions, the 102 subjects who attended all three follow-ups were included in the analyses. Corneal refractive power and astigmatism and anterior chamber depth was measured with Pentacam topography and axial length with IOL master at study end. Prevalence and changes in anisometropia of spherical equivalent (AnisoSE) and astigmatism (AnisoAST) and their relationships with refractive and axial measures were studied.

RESULTS

Mean (±SD) of spherical equivalent (SE), AnisoSE and AnisoAST increased from baseline to follow-up end from -1.44 ± 0.57 D to -5.11 ± 2.23 D, from 0.28 ± 0.30 D to 0.68 ± 0.69 D and from 0.14 ± 0.18 D to 0.37 ± 0.36 D, respectively. Prevalence of AnioSE, ≥1 D, increased from 5% to 22.6% throughout follow-up. Higher AnisoSE was associated with SE in the less myopic eye at baseline and at follow-up 1, and with SE in the more myopic eye in follow-ups 2 and 3 in adulthood. At study end, AnisoSE was associated with the interocular difference in axial length (AL) (r = 0.612, p < 0.001) but not with the interocular difference in corneal refraction (CR) (r = -0.122, p = 0.266). In cases of low AnisoSE(≤1.00 D), the negative correlation between the real interocular differences (value of right eye minus value of left eye) in CR and AL (r = -0.427, p < 0.001) decreased the influence of the interocular difference in AL on AnisoSE, causing emmetropization in AnisoSE. The interocular difference in corneal astigmatism was the main factor associated with AnisoAST (r = 0.231, p = 0.020). No significant relationship was found between AnisoAST and level of SE.

CONCLUSION

Anisometropia of the spherical equivalent (AnisoSE) increased along with the myopic progression and at study end was mainly associated with the interocular difference in AL. AnisoAST was mainly explained by the interocular difference in corneal astigmatism. In cases with low AnisoSE (≤1.0 D), the interrelationship between CR and AL decreased AnisoSE causing emmetropization in AnisoSE.

Exome sequencing identifies a novel UNC5D mutation in a severe myopic anisometropia family: A case report

INTRODUCTION

Severe myopic anisometropia has been identified to have heritability, but the pathogenesis of anisometropia still remains obscure.

CASE DESCRIPTION

Here, we presented a Chinese severe myopic anisometropia family with 5 members affected. Though using the exome sequencing, we identified a novel mutation in the UNC5D gene (c.1297C>T, p.R433C), which was predicted to have a damage effect on the protein function and kept highly conserved throughout evolution across species. As previously described, the UNC5D gene belongs to the UNC5 protein family and may have functions to regulate neuronal migration, axon guidance, and cell survival. The expression of UNC5D was also co-located at the visual areas of the mouse cortical regions at early postnatal ages.

CONCLUSION

Our data provide the first evidence for involvement of UNC5D gene in the severe myopic anisometropia.

Anisometropia of ocular refractive and biometric measures among 66- to 79-year-old female twins

PURPOSE

To examine the prevalence of anisometropia of spherical refraction (AnisoSR), astigmatism (AnisoAST) and spherical equivalent (AnisoSE) and their associations with spherical refraction (SR), refractive astigmatism (AST), spherical equivalent (SE) and interocular differences of ocular biometric parameters among elderly female twins.

METHODS

Refraction of 117 monozygotic (MZ) and 116 dizygotic (DZ) female twin subjects aged 66-79 years was assessed with an auto-refractor (Topcon AT) and controlled by subjective refraction. Corneal refraction, anterior chamber depth and axial length were measured with a Zeiss IOL Master. Participants with eyes operated for cataract or glaucoma were excluded, but the grade of nuclear opacity was not recorded. The associations between the absolute values of AnisoSR, AnisoAST and AnisoSE with SR, AST, SE, corneal refractive power (CR), corneal astigmatism (CAST), anterior chamber depth (ACD) and axial length (AL) and with their interocular differences were calculated. When calculating the interdependencies of the differences, the real and absolute differences between the right and left eye were used.

RESULTS

Means ± standard deviations for AnisoSR, AnisoAST and AnisoSE were 0.67 ± 0.92 D, 0.42 ± 0.41 D and 0.65 ± 0.71 D, respectively. AnisoSR, AnisoAST and AnisoSE >1.0 D were present in 14.7%, 4.2% and 17.7% of cases, respectively. Anisometropia of spherical refraction (AnisoSR), AnisoAST and AnisoSE were higher the more negative the values of SR or SE. Hyperopic ametropia did not increase these anisometropia values. The correlations of AnisoSR and AnisoSE with the absolute values of interocular differences in CR and AL were non-significant. Using the real values of the interocular differences, the respective correlations were significant. The correlation between the real interocular differences in CR and AL was negative (r = -0.258, p < 0.001). Thus, the combined effect of the real interocular differences in CR and AL was a decrease in AnisoSR and AnisoSE (emmetropization).

CONCLUSION

Higher AnisoSR and AnisoSE were associated with more myopic refraction and longer AL. Higher AnisoAST was associated with more negative SR and higher AST and CAST. The negative correlation between real interocular differences in CR and AL indicated their influence of emmetropization in AnisoSR and AnisoSE.

Ganglion Cell-Inner Plexiform Layer, Peripapillary Retinal Nerve Fiber Layer, and Macular Thickness in Eyes with Myopic β-Zone Parapapillary Atrophy

Purpose. To assess the correlations of myopic β-zone parapapillary atrophy (β-PPA) with the optic nerve head (ONH) and retina. Methods. We selected 27 myopic patients who showed prominent β-PPA in one eye and no β-PPA in the other eye. We studied their macula, macular ganglion cell-inner plexiform layer (mGCIPL), peripapillary retinal nerve fiber layer (pRNFL) thickness, and ONH parameters using optical coherence tomography. Results. The average of five out of six sectors and minimum values of mGCIPL thicknesses in eyes with prominent β-PPA discs were significantly less than those of the control eyes. The results of clock-hour sector analyses showed significant differences for pRNFL thickness in one sector. In the ONH analyses, no significant difference was observed between myopic β-PPA and control eyes. The macular thickness of the β-PPA eyes was thinner than control eyes in all sectors. There was a significant difference between the two groups in three sectors (the inner superior macula, inner temporal macula, and inner inferior macula) but there was no significant difference in the other sectors, including the fovea. Conclusions. The myopic β-PPA eyes showed thinner mGCIPL, parafovea, and partial pRNFL layers compared with myopic eyes without β-PPA.

Refractive Changes in Amblyopic Children with High Anisometropia

PURPOSE

To demonstrate the refractive changes of amblyopic children attributed to high anisometropia in the myopia endemic in Taiwan.

METHODS

Amblyopic children younger than 10 years with myopic or hyperopic anisometropia 3 diopters (D) or more who had follow-up for more than 2 years and had final visual acuity of 20/30 or better in the amblyopic eye were included.

RESULTS

The average age on the first visit was similar for the 13 myopic children (5.5 years) and 17 hyperopic children (5.3 years). Initially, the mean anisometropia was significantly different (myopic, 7.25 D vs. hyperopic, 3.89 D), but the visual acuity of the amblyopic eye (logarithm of the minimum angle of resolution) was similar between both groups at baseline (0.50 vs. 0.57). Myopization of the sound eye surpassed that of the amblyopic eye in the myopic group, which resulted in a yearly reduction of anisometropia of 0.51 D. However, hyperopia decreased synchronously in both eyes of the hyperopic children. The final degree of anisometropia was not significantly different between the two groups (4.07 D vs. 3.62 D).

CONCLUSIONS

Growing up in a country with a high prevalence of myopia, children with myopic and hyperopic anisometropia in this study inevitably had myopization in both eyes. Myopic anisometropia decreases significantly over time, but hyperopic anisometropia remains constant.

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.