An investigation of the relationship between the structure and function of the myopic eye. Correlating the optical, functional and structural aspects of ametropia in young adult humans.

The increasing prevalence of myopia over the past few decades and its association with potential ocular complications make myopia an important research topic. The present work is concerned with the structural and functional characteristics of a group of myopic and emmetropic individuals. The technical experiments in this work investigated firstly the effect of instrument alignment on peripheral refraction measurements and revealed that the corneal vertex was an acceptable alignment position of the Shin-Nippon NVision-K 5001 autorefractor, allowing consistent alignment with other instruments used in this research. Secondly, spectacles could be used to provide comparable vision to contact lenses in the visual performance studies. In the main experimental parts of this work, visual performance and multiple aspects of ocular structure were assessed across a wide range of eccentricities along the horizontal and vertical meridians within the same eyes. The structural properties of the myopic eye were measured through central and peripheral autorefraction, and through cornea to retina dimensions using non-contact biometry. In addition, the central and peripheral resolution acuities of myopic and emmetropic eyes for high and low contrast levels were investigated. Our structural and functional measurements revealed relatively prolate myopic eyes with reduced high contrast resolution acuity, compared to emmetropic eyes. Moreover, multiple regression analyses were performed at the fovea and outermost retinal eccentricities common to all core experiments but revealed no strong relationship between the structure and function of the myopic eye. Finally, regarding asymmetry, the nasal and superior retinae were found to be longer and to perform better in comparison to the temporal and superior retinae respectively

The Effect of Contact Lens–spectacle Reversed Galilean Telescope on the Visual Field of Patients with Open-angle Glaucoma

Purpose: Glaucoma causes irreversible visual field defects. This study aims to evaluate the effect of a reversed Galilean telescope on the visual field of patients with open-angle glaucoma. Methods: Fifty-two glaucoma patients with a restricted visual field were recruited for this study. Central 30° visual field measurements were performed using a Humphrey visual field analyzer before and after applying the reversed Galilean telescope. To be more cosmetically acceptable, a combination of contact lens–spectacle was used as the reversed Galilean telescope. Results: Our data analysis showed that the reversed Galilean telescope had a significant effect on all measured perimetric indices. Visual field index (VFI) improved from a basic value of 44.38 ± 26.96 percent to 49.30 ± 29.83 percent by using the reversed telescope (P < 0.001). Moreover, the mean deviation (MD) was significantly improved from the initial value of –19.91 ± 7.19 dB to a value of –18.69 ± 7.73 dB (P < 0.001). However, our results showed a significant reduction in the pattern standard deviation (PSD) comparing before (9.83 ± 2.82) and after (8.51 ± 3.30) values using the reversed Galilean telescope (P < 0.001). Conclusion: The contact lens–spectacle combination reversed Galilean telescope significantly improved the central 30° visual field of glaucoma patients with the restricted visual field

Part-time versus full-time occlusion therapy for treatment of amblyopia: A meta-analysis

YesPurpose: To compare full-time occlusion (FTO) and part-time occlusion (PTO) therapy in the treatment of amblyopia, with the secondary aim of evaluating the minimum number of hours of part-time patching required for maximal effect from occlusion. Methods: A literature search was performed in PubMed, Scopus, Science Direct, Ovid, Web of Science and Cochrane library. Methodological quality of the literature was evaluated according to the Oxford Center for Evidence Based Medicine and modified Newcastle-Ottawa scale. Statistical analyses were performed using Comprehensive Meta-Analysis (version 2, Biostat Inc., USA). Results: The present meta-analysis included six studies (three randomized controlled trials [RCTs] and three non-RCTs). Pooled standardized difference in the mean changes in the visual acuity was 0.337 [lower and upper limits: 0.009, 0.683] higher in the FTO as compared to the PTO group; however, this difference was not statistically significant (P ¼ 0.056, Cochrane Q value ¼ 20.4 (P ¼ 0.001), I2 ¼ 75.49%). Egger's regression intercept was 5.46 (P ¼ 0.04). The pooled standardized difference in means of visual acuity changes was 1.097 [lower and upper limits: 0.68, 1.513] higher in the FTO arm (P < 0.001), and 0.7 [lower and upper limits: 0.315, 1.085] higher in the PTO arm (P < 0.001) compared to PTO less than two hours. Conclusions: This meta-analysis shows no statistically significant difference between PTO and FTO in treatment of amblyopia. However, our results suggest that the minimum effective PTO duration, to observe maximal improvement in visual acuity is six hours per day

Effect of Computer Tasks in Straight Gaze on Corneal Topographic Indices

Abstract Purpose: To investigate the effect of the near visual task of movie-watching in the straight gaze position on corneal topographic parameters. Methods: Thirty myopic young adults with an average age of 25.10 ± 4.13 years were recruited for the study. The designed near visual task consisted of watching a movie in the straight gaze position at a distance of 40 cm for 30 minutes. Corneal topography was performed using Oculus Keratograph 4 (OCULUS, Wetzlar, Germany) before and immediately after watching the movie, as well as at 10, 20, and 30 minutes intervals after completing this near visual task. Zernike coefficients, asphericity indices, refractive parameters, and diagnostic indices of keratoconus were recorded for statistical analysis. Results: Movie-watching at a close distance solely using the straight gaze position had no effect on Zernike coefficients (P > 0.130). Also, watching the movie had no effect on other corneal topography parameters including irregularities (P = 0.208), spherical eccentricity (P = 0.270), maximum decentration (P = 0.553), axis of maximum decentration (P = 0.186), peripheral astigmatism (P = 0.179), and average asphericity of the quadrants at 10 to 30º (P > 0.163). Conclusion: The results of the present study showed that watching movies in the straight gaze position had no effect on corneal topographic parameters and did not cause errors in corneal topographic measurements

White-to-white corneal diameter:normal values in healthy Iranian population obtained with the Orbscan II

AIM:To determine the normative values of white-to-white corneal diameter with Orbscan II Topography System and to compare right and left eyes data in the normal young population.Methods:A total of 1001 healthy participants aged 18-45y participated in this observational cross-sectional study. The study population consisted of 616 female and 385 male subjects. The corneal diameter was measured with the Orbscan II. The differences between genders, between right and left eyes and age-related changes were evaluated. Statistical analyses were performed using Student’s t-test.RESULTS:The average white-to-white distance in our study population was recorded as 11.65±0.36 mm (median:11.60 mm, mode:11.70 mm, minimum:10.50 mm and maximum:13.60 mm). The white-to-white distance was 11.60±0.35 mm in males and 11.71±0.36 mm in females which was statistically different between genders (P&lt;0.01). However, white-to-white distance was not statistically different between right and left eyes. In addition, this parameter decreased with increasing age. Considering 95% confidence interval, corneal diameter less than 10.93 mm and greater than 12.34 mm would be considered as microcornea and megalocornea, respectively based on this study population, using the Orbscan II topography.CONCLUSION:Detailed description and analysis of corneal diameter with Orbscan demonstrate that the obtained average value of horizontal white-to-white is higher in male than female and decreases slightly with increasing age. Our data also suggests the cut off values for definition of microcornea and megalocornea, which can be employed with this population

Visual performance fall-off with eccentricity in myopes versus emmetropes

Purpose: To compare the central and peripheral visual performance of myopic and emmetropic eyes. Methods: Thirty emmetropic (−0.50 to +0.50 D) and 60 myopic (−2.00 to −9.62 D) subjects were recruited. Resolution acuity was assessed at central and 12 peripheral retinal locations (±10°, ±20°, ±30° along the horizontal meridian, and ±10°, ±20°, ±25° along the vertical meridian) using a modified version of the Contrast Acuity Assessment test at low (δl/l = 14%) and high (δl/l = 100%) contrast levels. The central and peripheral data were analysed using univariate and repeated-measures analysis of variance respectively. In addition, asymmetries in visual function, along both the horizontal (temporal versus nasal) and vertical (superior versus inferior) meridians, were investigated. Results: When analysed in terms of acuity fall-off with eccentricity, repeated measures ANOVA exhibited a statistically significant difference in peripheral visual performance between refractive groups for high contrast stimuli (p = 0.025), with a more rapid fall-off in myopes compared to emmetropes. Nasal and superior retinal regions performed better than temporal (high contrast: p < 0.001, low contrast: p < 0.001) and inferior (high contrast: p < 0.001, low contrast: p = 0.003) regions for both refractive groups, consistent with differences between quadrants in neural cell density reported by histological studies. Conclusion: The myopic patients evaluated in this study exhibited reduced peripheral visual performance compared to their emmetropic counterparts when assessed using the Contrast Acuity Assessment test at high contrast level

Comparison of cyclopentolate versus tropicamide cycloplegia: A systematic review and meta-analysis

Purpose: The aim of the present meta-analysis is to compare the efficacy of cyclopentolate and tropicamide in controlling accommodation during refraction. Methods: A comprehensive literature search was performed in PubMed, Scopus, Science direct and Ovid databases by the key words: “tropicamide”; “cyclopentolate”; “cycloplegia” and “cycloplegic” from inception to April 2016. Methodological quality of the literature was evaluated according to the Oxford Center for Evidence Based Medicine and modified Newcastle-Ottawa scale. Statistical analyses were performed using Comprehensive Meta-Analysis (version 2; Biostat Inc., USA). Results: The present meta-analysis included six studies (three randomized controlled trials and three case–control studies). Pooled standardized difference in the mean changes in the refractive error was 0.175 D [lower and upper limits: −0.089; 0.438] more plus in the cyclopentolate group compared to the tropicamide group; however, this difference was not statistically significant (p = 0.194; Cochrane Q value = 171.72 (p < 0.05); I2 = 95.34%). Egger's regression intercept was −5.33 (p = 0.170). Considering type of refractive errors; refractive assessment procedure and age group; although cycloplegic effect of cyclopentolate was stronger than tropicamide; however, this effect was only statistically significant in children; hyperopic patients and with retinoscopy. Conclusion: We suggest that tropicamide may be considered as a viable substitute for cyclopentolate due to its rapid onset of action. Although these results should be used cautiously in infants and in patients with high hyperopia or strabismus when using tropicamide as the sole cycloplegic agent especially in situations that the findings are variable or there is no consistency between the examination results and clinical manifestations of the visual problems. Resumen: Objetivo: El objetivo del presente meta-análisis es comparar la eficacia de ciclopentolato y tropicamida a la hora de controlar la acomodación durante la refracción. Métodos: Se realizó una búsqueda amplia en la literatura en las bases de datos de PubMed, Scopus, Science direct y Ovid, utilizando las palabras clave: “tropicamida”, “ciclopentolato”, “cicloplejia” y “ciclopléjico” desde sus inicios a Abril de 2016. La calidad metodológica de la literatura se evaluó con arreglo a Oxford Center for Evidence Based Medicine y la escala Newcastle-Ottawa modificada. Los análisis estadísticos se realizaron utilizando el software Comprehensive Meta-Analysis (versión 2, Biostat Inc., EEUU). Resultados: El presente meta-análisis incluyó seis estudios (tres ensayos controlados aleatorizados y tres estudios de casos-control). La diferencia estandarizada combinada de los cambios medios del error refractivo fue de 0,175 D [límites inferior y superior: −0,089, 0,438], más acusada en el grupo ciclopentolato con respecto al grupo tropicamida aunque, sin embargo, esta diferencia no fue estadísticamente significativa (p = 0,194, Valor Q de Cochrane = 171,72 (p < 0,05), I2 = 95,34%). El valor del intercepto de regresión de Egger fue de −5,33 (p = 0,17). Considerando el tipo de errores refractivos, el procedimiento de valoración refractiva y el grupo de edad, aunque el efecto ciclopléjico de ciclopentolato fue más fuerte que el de tropicamida, dicho efecto fue únicamente significativo en niños, pacientes hipermétropes, y con retinoscopia. Conclusión: Sugerimos la consideración de tropicamida como sustituto viable de ciclopentolato, debido a su rápido inicio de acción. Aunque estos resultados deberían utilizarse con precaución en niños y en pacientes con elevada hipermetropía o estrabismo al utilizar tropicamida como único agente ciclopléjico, especialmente en situaciones en las que los hallazgos sean variables, o no exista consistencia entre los resultados del examen y las manifestaciones clínicas de los problemas visuales. Keywords: Tropicamide, Cyclopentolate, Cycloplegia, Cycloplegic, Palabras clave: Tropicamida, Ciclopentolato, Cicloplejia, Ciclopléjic

Distribution of different sized ocular surface vessels in diabetics and normal individuals

Purpose: To compare the distribution of different sized vessels using digital photographs of the ocular surface of diabetic and normal individuals. Methods: In this cross-sectional study, red-free conjunctival photographs of diabetic and normal individuals, aged 30-60 years, were taken under defined conditions and analyzed using a Radon transform-based algorithm for vascular segmentation. The image areas occupied by vessels (AOV) of different diameters were calculated. The main outcome measure was the distribution curve of mean AOV of different sized vessels. Secondary outcome measures included total AOV and standard deviation (SD) of AOV of different sized vessels. Results: Two hundred and sixty-eight diabetic patients and 297 normal (control) individuals were included, differing in age (45.50 ± 5.19 vs. 40.38 ± 6.19 years, P < 0.001), systolic (126.37 ± 20.25 vs. 119.21 ± 15.81 mmHg, P < 0.001) and diastolic (78.14 ± 14.21 vs. 67.54 ± 11.46 mmHg, P < 0.001) blood pressures. The distribution curves of mean AOV differed between patients and controls (smaller AOV for larger vessels in patients; P < 0.001) as well as between patients without retinopathy and those with non-proliferative diabetic retinopathy (NPDR); with larger AOV for smaller vessels in NPDR (P < 0.001). Controlling for the effect of confounders, patients had a smaller total AOV, larger total SD of AOV, and a more skewed distribution curve of vessels compared to controls. Conclusion: Presence of diabetes mellitus is associated with contraction of larger vessels in the conjunctiva. Smaller vessels dilate with diabetic retinopathy. These findings may be useful in the photographic screening of diabetes mellitus and retinopathy