Zone of Clear Single Binocular Vision in Myopic Orthokeratology.

PURPOSE: To examine the zone of clear single binocular vision (ZCSBV) in myopic children and young adults after 12 months of orthokeratology (OK) wear, in comparison with single-vision soft contact lens (SCL) wear. METHODS: Twelve children (8-16 years) and 8 adults (18-29 years) were assessed with a series of near-point binocular vision tests when myopia was corrected using single-vision SCLs and again after 1 and 12 months of OK wear, and axial length was measured. The ZCSBV was constructed for baseline SCL wear and after 12 months of OK wear. RESULTS: After 1 month of OK wear, increased accommodative responses were noted in children (C) and adults (A) as increased binocular amplitude (C:P=0.03, A:P=0.04) and reduced accommodative lag (C:P=0.01, A:P=0.01). Divergence reserves improved after 1 month in both groups (P<0.04), and a near exophoric shift was evident at 12 months (C:P=0.01, A:P=0.04). All changes at 1 month maintained stability at 12 months. An increase in accommodation and vergence responses without reduction in range resulted in an expansion of the ZCSBV in both age groups. Axial length did not significantly change in either children (P=0.25) or adults (P=0.72). CONCLUSION: In both pediatric and young adult myopes, the ZCSBV expands toward a more divergent, increased accommodation response in OK compared with SCL wear. This occurs without a corresponding loss of convergence or accommodation deactivation, indicating improved depth of focus. These findings are relevant to visual acceptance and possible mechanisms of OK's efficacy for myopia control.

Stability of peripheral refraction changes in orthokeratology for myopia.

PURPOSE: Orthokeratology (OK) is known to alter relative peripheral refraction (RPR) with this presumed to be its key myopia control mechanism. A prospective, longitudinal study was performed to examine stability of OK-induced RPR changes in myopic children and young adults. METHODS: RPR of twelve children (C)(8-16 years) and eight adults (A)(18-29 years) with spherical equivalent refraction of -0.75 to -5.00D were measured unaided and while wearing single vision soft contact lenses (SCL). Measurements were repeated after 1, 6 and 12 months of OK wear. RPR was measured using an open-field Shin Nippon SRW-5000 autorefractor at 10, 20 and 30 degrees nasally (N) and temporally (T), converted into power vectors M, J0 and J45. On-axis refractions and axial lengths (IOL Master) were also measured. RESULTS: Compared to the unaided state, 1-month of OK wear shifted the RPR in the myopic direction at 30 T (C: p = 0.023; A:, p = 0.002) and 30 N (C&A, p = 0.003) and was stable thereafter, with similar changes compared to SCL wear. J0 showed a myopic shift in comparison to both unaided and SCL correction in children but not adults, and J45 did not change in either group. The on-axis OK correction was predictive of the RPR shift in both children and adults at 30 T (C: r=-0.58, p = 0.029; A: r=-0.92, p < 0.001) and 30 N (C: r=-0.60, p = 0.024; A: r=-0.74, p = 0.013) with symmetry of RPR shifts (C: r = 0.67, p = 0.008; A: r = 0.85, p = 0.004). No relationships between changes in RPR and axial length were found after twelve months of OK wear; level of myopia was stable in both groups. CONCLUSION: Relative to both unaided and single vision SCL correction, OK shifted the RPR in the myopic direction; the RPR was stable from 1 to 12 months. The RPR shift in OK wear varied with the degree of myopia but was not correlated with myopia progression.

Near binocular visual function in young adult orthokeratology versus soft contact lens wearers.

PURPOSE: To compare near point binocular vision function of young adult myopes wearing orthokeratology (OK) lenses to matched single vision soft disposable contact lens (SCL) wearers. METHODS: A retrospective clinical record analysis of all OK wearers (18-30 years) presenting over an 18 month period was undertaken. Data was extracted for 17 OK wearers, with 17 SCL wearers matched for age, refractive error and duration of contact lens wear. Binocular vision data included horizontal phoria (phoria), horizontal base-in (BIFR) and base-out fusional reserves (BOFR) and accommodation accuracy (AA). RESULTS: The OK group was 25.8±3.2years, with a duration of wear of 45.7±25months and refractive error of R -2.09±1.23D, L -2.00±1.35D. Compared to matched SCL wearers the OK group were significantly more exophoric (OK -2.05±2.38Δ; SCL 0.00±1.46Δ, p=0.005) and had better accommodation accuracy (OK 0.97±0.33D; SCL 1.28±0.32D, p=0.009). BIFR and BOFR were not different in the two groups. Frequency histograms showed that more SCL wearers had high lags of accommodation (AA≥1.50D: 8 SCL,2 OK) and esophoria (≥1Δ: 5 SCL,1 OK) than OK wearers. A positive correlation was found between refraction and phoria in the SCL group (r=0.521, p=0.032). CONCLUSION: Young adult myopes wearing OK lenses display more exophoria and lower accommodative lags at near compared to matched single vision SCL wearers. Young adult myopes with specific binocular vision disorders may benefit from OK wear in comparison to single vision SCL wear. This has relevance to both the visual acceptance of OK lenses and in managing risk factors for myopia progression.

Vision Problems and Reduced Reading Outcomes in Queensland Schoolchildren.

PURPOSE: To assess the relationship between vision and reading outcomes in Indigenous and non-Indigenous schoolchildren to determine whether vision problems are associated with lower reading outcomes in these populations. METHODS: Vision testing and reading assessments were performed on 508 Indigenous and non-Indigenous schoolchildren in Queensland, Australia divided into two age groups: Grades 1 and 2 (6-7 years of age) and Grades 6 and 7 (12-13 years of age). Vision parameters measured included cycloplegic refraction, near point of convergence, heterophoria, fusional vergence range, rapid automatized naming, and visual motor integration. The following vision conditions were then classified based on the vision findings: uncorrected hyperopia, convergence insufficiency, reduced rapid automatized naming, and delayed visual motor integration. Reading accuracy and reading comprehension were measured with the Neale reading test. The effect of uncorrected hyperopia, convergence insufficiency, reduced rapid automatized naming, and delayed visual motor integration on reading accuracy and reading comprehension were investigated with ANCOVAs. RESULTS: The ANCOVAs explained a significant proportion of variance in both reading accuracy and reading comprehension scores in both age groups, with 40% of the variation in reading accuracy and 33% of the variation in reading comprehension explained in the younger age group, and 27% and 10% of the variation in reading accuracy and reading comprehension, respectively, in the older age group. The vision parameters of visual motor integration and rapid automatized naming were significant predictors in all ANCOVAs (P < .01). The direction of the relationship was such that reduced reading results were explained by reduced visual motor integration and rapid automatized naming results. CONCLUSIONS: Both reduced rapid automatized naming and visual motor integration were associated with poorer reading outcomes in Indigenous and non-Indigenous children. This is an important finding given the recent emphasis placed on Indigenous children's reading skills and the fact that reduced rapid automatized naming and visual motor integration skills are more common in this group.

A Visual Profile of Queensland Indigenous Children.

PURPOSE: Little is known about the prevalence of refractive error, binocular vision, and other visual conditions in Australian Indigenous children. This is important given the association of these visual conditions with reduced reading performance in the wider population, which may also contribute to the suboptimal reading performance reported in this population. The aim of this study was to develop a visual profile of Queensland Indigenous children. METHODS: Vision testing was performed on 595 primary schoolchildren in Queensland, Australia. Vision parameters measured included visual acuity, refractive error, color vision, nearpoint of convergence, horizontal heterophoria, fusional vergence range, accommodative facility, AC/A ratio, visual motor integration, and rapid automatized naming. Near heterophoria, nearpoint of convergence, and near fusional vergence range were used to classify convergence insufficiency (CI). RESULTS: Although refractive error (Indigenous, 10%; non-Indigenous, 16%; p = 0.04) and strabismus (Indigenous, 0%; non-Indigenous, 3%; p = 0.03) were significantly less common in Indigenous children, CI was twice as prevalent (Indigenous, 10%; non-Indigenous, 5%; p = 0.04). Reduced visual information processing skills were more common in Indigenous children (reduced visual motor integration [Indigenous, 28%; non-Indigenous, 16%; p < 0.01] and slower rapid automatized naming [Indigenous, 67%; non-Indigenous, 59%; p = 0.04]). The prevalence of visual impairment (reduced visual acuity) and color vision deficiency was similar between groups. CONCLUSIONS: Indigenous children have less refractive error and strabismus than their non-Indigenous peers. However, CI and reduced visual information processing skills were more common in this group. Given that vision screenings primarily target visual acuity assessment and strabismus detection, this is an important finding as many Indigenous children with CI and reduced visual information processing may be missed. Emphasis should be placed on identifying children with CI and reduced visual information processing given the potential effect of these conditions on school performance.

Repeatability and validity of lens densitometry measured with Scheimpflug imaging.

PURPOSE: To assess the repeatability and validity of lens densitometry derived from the Pentacam Scheimpflug imaging system. SETTING: Eye Clinic, Queensland University of Technology, Brisbane, Australia. METHODS: This prospective cross-sectional study evaluated 1 eye of subjects with or without cataract. Scheimpflug measurements and slitlamp and retroillumination photographs were taken through a dilated pupil. Lenses were graded with the Lens Opacities Classification System III. Intraobserver and interobserver reliability of 3 observers performing 3 repeated Scheimpflug lens densitometry measurements each was assessed. Three lens densitometry metrics were evaluated: linear, for which a line was drawn through the visual axis and a mean lens densitometry value given; peak, which is the point at which lens densitometry is greatest on the densitogram; 3-dimensional (3D), in which a fixed, circular 3.0 mm area of the lens is selected and a mean lens densitometry value given. Bland and Altman analysis of repeatability for multiple measures was applied; results were reported as the repeatability coefficient and relative repeatability (RR). RESULTS: Twenty eyes were evaluated. Repeatability was high. Overall, interobserver repeatability was marginally lower than intraobserver repeatability. The peak was the least reliable metric (RR 37.31%) and 3D, the most reliable (RR 5.88%). Intraobserver and interobserver lens densitometry values in the cataract group were slightly less repeatable than in the noncataract group. CONCLUSION: The intraobserver and interobserver repeatability of Scheimpflug lens densitometry was high in eyes with cataract and eyes without cataract, which supports the use of automated lens density scoring using the Scheimpflug system evaluated in the study.

Granular dystrophy of the cornea.

BACKGROUND: Granular corneal dystrophy is the commonest of the dystrophies and usually results in visual disability in the fourth or fifth decades. CASE HISTORY: A patient with granular corneal dystrophy is reported and the clinical characteristics described. DISCUSSION: The classical clinical features and the pathology and management of granular dystrophy are reviewed. Two unusual variations of the corneal dystrophy, namely, juvenile granular dystrophy and Avellino dystrophy, which is a concurrence of the features of granular and lattice dystrophies, are also described.

Visual performance requirements for post-PRK police recruits.

BACKGROUND: New Zealand Police regulations (1996) allow the unaided visual acuity requirement of 6/12 to be achieved following refractive surgery (except radial keratotomy or keratoplasty) provided applicants also achieve normal (95 per cent confidence limit data from the literature): glare disability, contrast sensitivity, and low luminance visual acuity, one year or more after treatment. METHODS: To confirm the limits adopted, 80 young normal adults were subjected to the tests in the regulations. To examine the operation of the current standards, the results of 34 post-photorefractive keratectomy (post-PRK) police applicants are reported. Glare disability was the loss of high contrast visual acuity (VA) with the Mentor Brightness Acuity Tester at medium intensity. Contrast sensitivity (CS) was examined using both Melbourne Edge Test thresholds and the VA difference between high and low contrast Bailey-Lovie charts. Low luminance VA was measured using high contrast Bailey-Lovie charts viewed through a one per cent transmittance filter. RESULTS: The 95 per cent confidence limits found for normal performance were as follows. Glare disability: no more than 10 letters worse than VA without glare. Contrast sensitivity: no more than 12 letters difference between high contrast and low contrast letter acuity together with an edge contrast threshold of not less than 20 dB (CS = 100). These results were close to the values adopted for the current standard. The 95 per cent confidence limit for low luminance VA was a loss of 24 letters (almost five lines) and not the three lines of loss estimated from the literature. Two of the 34 post-PRK applicants failed. One was unable to achieve 6/6 acuity with best refraction. The second could not meet the low luminance VA limit (loss no more than three lines). No failures have been due to glare disability or poor contrast sensitivity even though one applicant had obvious corneal haze.