Chameen Samarawickrama

Macular and nerve fiber layer thickness in amblyopia: the Sydney Childhood Eye Study.

PURPOSE To examine macular and peripapillary retinal nerve fiber layer (RNFL) thickness in amblyopia. DESIGN Population-based cross-sectional study. PARTICIPANTS Of 4118 children examined in the Sydney Childhood Eye Study (incorporating the Sydney Myopia Study) from 34 randomly selected primary schools and 21 secondary schools from 2003 to 2005, 3529 (85.7%) were included in this analysis. The median age of the 2 samples was 6 years (n = 1395) and 12 years (n = 2134), respectively. METHODS A detailed eye examination was conducted on all children, including determination of best-corrected visual acuity (logarithm of the minimum angle of resolution [logMAR]), autorefraction (RK-F1 autorefractor, Canon, Tokyo, Japan) after cyclopentolate (1%), cover testing to identify strabismus, and optical coherence tomography (StratusOCT, Carl Zeiss Meditec, Dublin, CA) through dilated pupils to obtain macula and peripapillary RNFL thickness. Amblyopia was defined as best visual acuity <0.3 logMAR units not explained by any obvious underlying eye or visual pathway abnormalities. Anisometropia was defined as an interocular difference of at least 1.0 diopter of the spherical equivalent refraction. MAIN OUTCOME MEASURES Macular and peripapillary RNFL thickness. RESULTS Amblyopic eyes had slightly greater foveal minimum thickness than the normal fellow eye (by 5.0 microm; 95% confidence interval 0.1-9.9) and right eyes of non-amblyopic children (by approximately 10 microm), both P<0.05. This was more pronounced in 6-year-old children (6.9 microm) than 12-year-old children (4.2 microm). Amblyopic eyes also had slightly thicker central macula (1 mm diameter region) in both comparisons, although these differences were not statistically significant. The inner macular ring (outer radius 1.5 mm) was thinner in amblyopic than normal fellow eyes. Peripapillary RNFL thickness was not significantly different between amblyopic and normal fellow eyes or normal eyes of non-amblyopic children. CONCLUSIONS In children aged predominantly 6 and 12 years, central macular thickness may be increased in eyes with amblyopia, although it is uncertain if this precedes or follows the development of amblyopia. No differences in peripapillary RNFL thickness were found when compared with normal eyes. FINANCIAL DISCLOSURE(S) The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Ethnic differences in optic nerve head and retinal nerve fibre layer thickness parameters in children.

Aim To examine ethnic differences in optic nerve head and retinal nerve fibre layer (RNFL) parameters between European Caucasian and East Asian children aged 6–12 years. Methods Of 4118 children examined in the Sydney Childhood Eye Study (incorporating the Sydney Myopia Study) from 34 randomly selected primary and 21 secondary schools during 2003–5, 3382 (82.1%) had optical coherence tomography (OCT; Zeiss Stratus) data suitable for analysis. ‘Fast’ optic disc and RNFL scans were used. Ethnicity was defined only when both parents were of the same ethnicity. Results East Asian children tended to have a lower birth weight, were shorter with a smaller body mass index and were less hyperopic than European Caucasian children of the same age. After adjusting for age, gender, axial length, birth weight and optic-disc area, East Asian children had similar mean vertical disc diameters to European Caucasians (p=0.38, p=0.64 for 6–12 years, respectively) but 30–43% larger mean vertical cup diameters (p<0.0001 for both), resulting in larger mean cup/disc ratios (p<0.0001 for both). Compared with European Caucasians (101.95 μm and 104.57 μm, respectively), East Asian children had thicker mean average RNFL (105.45 μm and 107.92 μm, respectively; p=0.0006 and 0.0001) and thicker non-nasal RNFL quadrants in both ages. Conclusions Compared with European Caucasian children, East Asian children generally had thicker RNFL and larger mean cup/disc ratios. Given the relatively lower prevalence of open angle glaucoma in Asians, these anatomical variations could contribute to better understanding of apparent racial differences in glaucoma susceptibility.

Influence of OCT Signal Strength on Macular, Optic Nerve Head, and Retinal Nerve Fiber Layer Parameters

PURPOSE To examine the influence of different signal strengths on measurements made with optical coherence tomography (OCT) of macular, optic nerve head, and retinal nerve fiber layer (RNFL) parameters. METHODS From 2003 to 2005, 2092 children, mostly aged 12 years, were examined, and macular, optic nerve head, and RNFL parameters were measured by OCT. Multiple fast scans were acquired, and only right eyes were included in the analyses. Signal strength category was determined after averaging individual signal strengths from each scan and classifying scans as providing moderate (average signal strength, 5-7.49), good (average signal strength, 7.5-9.49), and excellent (average signal strength, >or=9.5) image quality. General linear models were used after adjustment for covariates. RESULTS Significant differences were observed between measurements obtained at excellent signal strengths compared with those obtained at moderate and good signal strengths for both macular and optic nerve parameters. However, although statistically significant, the magnitude of the differences in macular parameters was very small (approximately 5 microm, or a 2% difference). Differences in optic nerve head parameters were much greater (up to a 32% difference), with larger measurements recorded for most parameters with increasing signal strength category. Significant differences in RNFL parameters with increasing signal strength were not demonstrated. CONCLUSIONS Significantly larger macular and optic nerve head OCT measurements were obtained with increasing signal strength measurements, although absolute differences in macular measurements were small and are of questionable clinical importance. The results support the robustness of OCT in providing precise macular imaging.

P2Y2 receptor agonists for the treatment of dry eye disease: a review

Recent advances in the understanding of dry eye disease (DED) have revealed previously unexplored targets for drug therapy. One of these drugs is diquafosol, a uridine nucleotide analog that is an agonist of the P2Y2 receptor. Several randomized controlled trials have demonstrated that the application of topical diquafosol significantly improves objective markers of DED such as corneal and conjunctival fluorescein staining and, in some studies, tear film break-up time and Schirmer test scores. However, this has been accompanied by only partial improvement in patient symptoms. Although evidence from the literature is still relatively limited, early studies have suggested that diquafosol has a role in the management of DED. Additional studies would be helpful to delineate how different subgroups of DED respond to diquafosol. The therapeutic combination of diquafosol with other topical agents also warrants further investigation.

Visual Impairment and the Incidence of Falls and Fractures Among Older People: Longitudinal Findings From the Blue Mountains Eye Study

PURPOSE We assessed the impact of visual impairment on the incidence of falls and fractures in older persons. METHODS Of 3654 baseline participants, 2334, 1952, and 1149 were re-examined after 5, 10, and 15 years. Presenting visual acuity (VA) was measured at each examination. Bilateral and unilateral visual impairment was defined as VA worse than 20/40 in the better and worse eye, respectively. Incident visual impairment was defined in eyes with VA 20/40 or better at baseline, which subsequently developed visual impairment. Incidence of falls was assessed over the 12 months before each visit, whereas incidence of fractures was assessed over the 5 years between two visits. Discrete logistic-regression models with time-dependent variables were used to assess associations between visual impairment and subsequent falls and fractures after adjusting for potential confounding variables. RESULTS The proportions of participants reporting ≥2 falls ranged between 10% and 14%, and proportions reporting fractures ranged between 12% and 21%, across the three follow-up visits. Participants with incident visual impairment were more likely to report ≥2 falls in 5 years, OR (odds ratio) 1.46, 95% confidence interval (CI) 1.04 to 2.04 (bilateral), and OR 1.22, 95% CI 0.98 to 1.51 (unilateral). Compared to participants with normal vision, those with incident unilateral visual impairment had a higher incidence of fractures over 5 years (OR, 1.27; 95% CI, 0.98-1.51). No increased incidence of falls or fractures was evident after 5+ years among participants with visual impairment. CONCLUSIONS In this older cohort, recent development of visual impairment was associated with increased likelihood of subsequent falls and fractures in the next 5 years, independent of other confounding variables.

Prevalence and risk factors for visual impairment in preschool children the sydney paediatric eye disease study.

PURPOSE To assess the prevalence and associations of visual impairment (VI) in preschool children. DESIGN Cross-sectional, population-based study. PARTICIPANTS A total of 2461 children (73.8% participation rate), aged 6 to 72 months, were examined in the Sydney Paediatric Eye Disease Study during 2007-2009; of whom 1188, aged 30 to 72 months, with complete visual acuity (VA) data in both eyes, were included in this report. METHODS Measurement of VA was attempted on all children using the Electronic Visual Acuity (EVA) system or a logarithm of the minimum angle of resolution (logMAR) chart. Visual impairment was defined as presenting VA <20/40 in children aged ≥48 months and <20/50 in those aged <48 months. Post-cycloplegic refraction was measured, and myopia was defined as spherical equivalent (SE) ≤-0.50 diopters (D), hyperopia was defined as SE ≥2.00 D, astigmatism was defined as cylinder ≥1.00 D, and anisometropia was defined as SE difference ≥1.00 D between 2 eyes. Ethnicity, birth parameters, and sociodemographic information were collected in questionnaires completed by parents. MAIN OUTCOME MEASURES Visual impairment prevalence and its associations with child demographic factors and birth parameters. RESULTS Visual impairment was found in 6.4% of the worse eye and 2.7% of the better eye in our sample. Refractive errors (69.7%) and amblyopia (26.3%) were the principal causes of VI in the worse eye. Astigmatism (51.3%) and hyperopia (28.9%) were the main refractive errors causing VI. In regression analysis controlling for other factors, VI was independently associated with low birthweight of <2500 g (odds ratio 2.4, 95% confidence interval, 1.1-5.3), but not with age, gender, ethnicity, or measures of socioeconomic status (P > 0.05). CONCLUSIONS Visual impairment in at least 1 eye was found in 6.4% of Australian preschool children, with bilateral VI found in 2.7%. Uncorrected refractive errors and amblyopia were the principal ocular conditions associated with VI. Low birthweight was a significant risk factor independent of age, gender, and ethnicity. FINANCIAL DISCLOSURE(S) The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Retinoic acid and the ocular surface.

Retinoic acid is known to improve cutaneous wound healing and, in recent years, its application in ophthalmology has been investigated. This review looks at the role of retinoic acid on the ocular surface. Retinoic acid can be produced synthetically, and its mechanism of action includes both nuclear and non-nuclear receptor mediated pathways. It has been shown to improve full and partial thickness corneal lacerations as well as corneal epithelial defects. Retinoic acid plays a critical role in cell differentiation at the cornea, conjunctiva, and limbus, and may have an anti-tumor role. Its positive effect is only achieved at the correct concentration, however; excess concentrations of retinoic acid have a deleterious effect. The main limiting factor of retinoic acid use is its detrimental effect on meibomian glands, resulting in cell death, atrophy of acini, hyposecretion of oils, and altered gene expression, eventually resulting in dry eye symptoms. This effect is reversible on discontinuation of the drug.

Impact of Ethnicity on the Correlation of Retinal Parameters with Axial Length

PURPOSE To examine whether the relationship of axial length (AL) to retinal nerve fiber layer (RNFL) and macular parameters measured by optical coherence tomography (OCT) differs according to ethnicity. METHODS As part of the Sydney Myopia Study, 2353 children from grade 7 (age range, 11.1-14.4 years) completed detailed ocular examinations in the 2004-2005 school year. AL was measured with noncontact interferometry and Stratus OCT was performed (Carl Zeiss Meditec, Jena, Germany). RESULTS East Asian children displayed larger AL correlations with average RNFL, inferior RNFL, nasal RNFL, outer macula, and macular volume (r = -0.25, -0.36, -0.31, -0.35, and -0.31 respectively; P < 0.001) than did Caucasian children (r = -0.14, -0.20, -0.12, -0.17, and -0.13 respectively; P < 0.001). Positive correlations between the temporal RNFL and AL were found only among East Asian and South Asian children (r = 0.28, P < 0.001; and r = 0.27, P = 0.03, respectively). In Caucasian children, the foveal minimum and central macula correlated significantly with AL (r = 0.11 and r = 0.13, respectively, P ≤ 0.001). CONCLUSIONS Retinal parameters measured by OCT correlated with AL, and the extent of this correlation varied by ethnicity. It may therefore be that ethnicity should be considered when interpreting OCT scans on individuals with AL outside the usual range.

Measurement of Optic Nerve Head Parameters: Comparison of Optical Coherence Tomography With Digital Planimetry

PurposeTo compare the measurements of optic nerve head parameters from digital photographic images and optical coherence tomography (OCT) in normal children. MethodsThe Sydney Childhood Eye Study assessed 1765 children aged 6 years from 34 randomly selected primary schools during 2003 to 2005. Optic nerve head parameters were measured from digital photographs captured using a Canon fundus camera (CF-60Uvi)/EOS 10D and OCT3 (Zeiss Stratus) using the “fast” optic disc protocol. Retinal images of 333 sequential child participants were graded using both methods and are included in analyses. Optic disc and cup area, vertical and horizontal disc and cup diameters, vertical and horizontal cup/disc diameter ratios, and cup/disc area ratios were calculated using both modalities. Magnification of the planimetric images was corrected using the Bengtsson formula. ResultsMean vertical and horizontal disc and cup diameter and mean disc and cup area, as measured using OCT (1.76, 1.50, 0.71, and 0.68 mm and 2.15 and 0.47 mm2, respectively) were significantly (P<0.0001; cup area P=0.0014) smaller than when measured using digital photography (1.85, 1.66, 0.76, and 0.74 mm and 2.40 and 0.51 mm2, respectively). All 3 cup/disc ratio measures did not vary significantly (P>0.05) between the 2 methods (0.41, 0.45, and 0.22 vs. 0.41, 0.44, and 0.21, respectively). ConclusionsLinear and area measures by Stratus-OCT, compared with digital planimetry measurements, are around 10% smaller; however, all 3 cup/disc ratios were preserved. Where OCT produces unexpectedly small cup/disc ratios, manual viewing is advisable. However, OCT can be considered moderately reliable in measuring and monitoring cup/disc ratio in clinical settings.

Relationship between Retinal Structures and Retinal Vessel Caliber in Normal Adolescents

PURPOSE To describe the normal physiological relationship between retinal arteriolar and venular caliber and retinal nerve fiber layer (RNFL), macular, and optic nerve head parameters. METHODS The Sydney Childhood Eye Study assessed 2038 adolescents aged 12 years. Retinal vessel calibers were measured from digital fundus photographs using standardized protocols. Optical coherence tomography measurements of RNFL, macular, and optic nerve head parameters were obtained with the Fast-scan protocol of the Stratus OCT (Carl Zeiss Meditec, Inc., Dublin, CA). Mixed model analyses were performed. RESULTS After adjustment for covariates, each micrometer increase in RNFL thickness was associated with a 0.22-microm (0.15%, P < 0.0001) and 0.49-microm (0.23%, P < 0.0001) increase in mean arteriolar and venular caliber, respectively. This positive association existed across all RNFL quadrants (0.07%-0.24%, P <or= 0.002). Each micrometer increase in macular thickness (inner/outer) and cubic millimeter increase in macular volume was associated with a 0.12/0.15-microm (0.08%-0.10%, P < 0.0001) and 5.31-microm (3.53%, P < 0.0001) increase in mean arteriolar caliber and a 0.22/0.31-microm (0.10%-0.15%, P < 0.0001) and 10.95-microm (5.08%, P < 0.0001) increase in mean venular caliber, respectively. Finally, each millimeter increase in vertical optic disc diameter and each square millimeter increase in optic disc area was associated with a 2.83-microm (1.88%, P = 0.02) and 2.02-microm (1.35%, P = 0.01) increase in mean retinal arteriolar caliber and a 5.73-microm (2.66%, P = 0.001) and 5.02-microm (2.33%, P < 0.0001) increase in mean retinal venular diameter, respectively. CONCLUSIONS In normal adolescent retinas, thicker RNFL and macula parameters and larger optic discs correlate with larger retinal vascular caliber. Understanding these normal anatomic relationships is essential for determining their significance in studying the vascular etiology of ocular and systemic diseases.