Transient change in the binocular visual function after femtosecond laser-assisted in situ keratomileusis for myopia patients.

Purpose: The goal of this study was to compare the difference in binocular visual function for high and low-moderate myopes before and after femtosecond laser-assisted in situ keratomileusis (FS-LASIK). Methods: Thirty-three subjects (17 males and 16 females) were divided into two groups according to their preoperative refractive errors in spherical equivalent (SE): low-moderate myopia group (SE ≥-6.00 D) and high myopia group (SE <-6.00 D). The binocular visual function including accommodative amplitude (AA), accommodative facility (AF), positive and negative relative accommodation (PRA and NRA, respectively), horizontal phoria measurement, positive and negative fusion vergence, accommodative-convergence over accommodation (AC/A) ratio, and stereopsis were assessed with the best-corrected vision before patients received FS-LASIK and 7 and 30 days after the surgery. Repeated measures analysis of variance (ANOVA) was applied to study the change in binocular visual function. Results: The AF values in both groups were significantly reduced after 7 days of FS-LASIK (baseline vs. day 7 (mean): high myopia group: 7.85 vs. 5.62 cpm, repeated ANOVA, P = 0.01; low-moderate myopia group: 5.95 vs. 4.40 cpm, repeated ANOVA, P = 0.04). This change returned to the baseline level 30 days after the operation. In addition, the horizontal phoria values in both groups were significantly reduced for both distant (P = 0.019 and P = 0.001, respectively) and near (P = 0.003 and P = 0.049, respectively) 7 days after the operation, but they rebound to preoperative state after 30 days. Conclusion: A transient change in binocular visual function was noticed after 7 days of FS-LASIK operation, which could cause symptoms of asthenopia. Our data showed all the binocular visual functions returned to baseline level after 30 days of operation.

Childhood exposure to constricted living space: a possible environmental threat for myopia development.

PURPOSE: People in Hong Kong generally live in a densely populated area and their homes are smaller compared with most other cities worldwide. Interestingly, East Asian cities with high population densities seem to have higher myopia prevalence, but the association between them has not been established. This study investigated whether the crowded habitat in Hong Kong is associated with refractive error among children. METHODS: In total, 1075 subjects [Mean age (S.D.): 9.95 years (0.97), 586 boys] were recruited. Information such as demographics, living environment, parental education and ocular status were collected using parental questionnaires. The ocular axial length and refractive status of all subjects were measured by qualified personnel. RESULTS: Ocular axial length was found to be significantly longer among those living in districts with a higher population density (F2,1072  = 6.15, p = 0.002) and those living in a smaller home (F2,1072  = 3.16, p = 0.04). Axial lengths were the same among different types of housing (F3,1071  = 1.24, p = 0.29). Non-cycloplegic autorefraction suggested a more negative refractive error in those living in districts with a higher population density (F2,1072  = 7.88, p < 0.001) and those living in a smaller home (F2,1072  = 4.25, p = 0.02). After adjustment for other confounding covariates, the population density and home size also significantly predicted axial length and non-cycloplegic refractive error in the multiple linear regression model, while axial length and refractive error had no relationship with types of housing. CONCLUSIONS: Axial length in children and childhood refractive error were associated with high population density and small home size. A constricted living space may be an environmental threat for myopia development in children.

Human electroretinal responses to grating patterns and defocus changes by global flash multifocal electroretinogram.

The electrical response of the retina was examined as a function of retinal region, using stimuli of various spatial frequencies in the first experiment. In the second experiment, the regional response of the retina to defocus at high and low spatial frequencies was investigated. Twenty three subjects were recruited for global flash multifocal electroretinogram (mfERG) in experiment 1. Black and white gratings (printed on plastic transparent sheets) of four spatial frequencies (SF), 0.24, 1.2, 2.4 and 4.8 cycle per degree were presented in front of the mfERG stimulation. The amplitudes and implicit times of the direct (DC) and induced (IC) components of mfERG responses were pooled into six concentric rings for analysis. There was low amplitude DC at low SF, which increased with increasing SF, and which decreased with increasing eccentricity. The IC was high in amplitude at all SF and reduced in amplitude with increasing eccentricity. Our findings suggested that outer and inner retina had different characteristics in processing spatial details. In experiment 2, Twenty-three young adults were recruited for mfERG measurement. The retinal electrical responses for low (0.24cpd) and high (4.8cpd) SF under fully corrected conditions of short-term negative defocus (-2D) and short term positive defocus (+2D) conditions were measured. There was a sign-dependent response to defocus in the DC response, mainly in peripheral regions. The sign dependent response at low SF was more obvious than that at high SF, and was located more peripherally. The IC response showed no clear trends for either defocus condition. The human retina seems to have a decoding system for optical defocus, which was tuned for low spatial frequency, and was located in the retinal near periphery.

Prevalence of visual impairment and refractive errors among different ethnic groups in schoolchildren in Turpan, China.

BACKGROUND: There is currently limited information about ethnic differences in myopia prevalence within mainland China, especially in rural or semi-rural areas. We examined the prevalence of refractive errors, visual impairment and spectacle coverage in school children of varying ethnicity in Turpan, Xinjiang province. METHODS: A community eye care service was provided for five schools. Presenting monocular distance and near visual acuity (VA), and ocular alignment were assessed. Retinoscopy and cycloplegic subjective refraction were performed for participants with presenting visual impairment (distance VA worse than 0.3 logMAR; Snellen 6/12 or 20/40) or abnormal binocular vision. Questionnaires administered prior to the eye examinations were used to collect information regarding personal lifestyle and parental myopia. RESULTS: A total of 646 out of 690 (94%) subjects aged four to 19 years (11.9 ± 2.6; mean ± S.D.) completed the eye examination. Three hundred and eighty-two (59%) of participants were of Uyghur ethnicity, followed by Han, 176 (27%) and Hui, 74 (12%). The mean age of Uyghur, Han and Hui students was 12.3 ± 2.7, 11.4 ± 2.6 and 11.4 ± 2.3 years respectively, in which the Uyghur students were significantly older than the Han and Hui students (F(3,631) = 5.58 p < 0.001). In total, 170 (27%) and 85 (13%) subjects failed the screening examination for one eye or both eyes, respectively. The prevalence of presenting visual impairment was not significantly different among the ethnic groups (p = 0.26). After cycloplegic refraction, most subjects' VA (98%) improved to better than 0.3 logMAR (Snellen 6/12 or 20/40). The prevalence of "clinically-significant myopia" (≤-0.50 dioptres) was 27%, 18% and 13% in Han, Hui and Uyghur children, respectively (p < 0.001). In contrast, Uyghur students had the highest prevalence of astigmatism (Uyghur 12%, Han 5%, Hui 4%). The overall spectacle coverage was 36%, while spectacle coverage among ethnic groups were similar (Han, 41%; Uyghur, 32%; Hui, 41%; χ(2) = 2.23, df = 2, p = 0.33). CONCLUSION: The prevalence of clinically significant myopia varied markedly with ethnicity in school children sampled from a semi-rural region of mainland China (Han > Hui > Uyghur). As reported previously, uncorrected/under-corrected refractive error was the main cause of presenting visual impairment.

Effect of lycium barbarum (wolfberry) polysaccharides on preserving retinal function after partial optic nerve transection.

Lycium Barbarum Polysaccharides (LBP) are the active components of Wolfberry (a traditional Chinese medicine) which has long been used for improving visual function. This study aims to investigate localized changes of retinal function in a partial optic nerve transection (PONT) model, and effects of LBP on visual function. The multifocal electroretinograms (mfERG) were obtained from 30 eyes of 30 Sprague-Dawley rats. The rats were divided into 6 groups (five treatment groups and one control group). Starting from the first day of the experiment, the rats in the (PONT+LBP) group and the (LBP) group were dosed with LBP; rats in the (PONT+PBS (phosphate buffered saline)) group and the (PBS) group were dosed with PBS via nasogastric tube every day until euthanized. The dorsal part of the optic nerve was transected in the (PONT), (PONT+LBP) and (PONT+PBS) groups at the end of week 1 (day 7 after LBP or PBS feeding began). The mfERG was measured at three time points: week 2, week 3 and week 5. Significant reduction of P1 and PhNR amplitudes of the mfERG were observed in all retinal regions a week after PONT. Feeding with LBP prior to PONT preserved retinal function. All mfERG responses returned to the normal range in the superior retina, which corresponds to the transected dorsal region of the optic nerve, while most of the inferior retinal responses were significantly increased at week 4 after PONT. The ventral part of the retina had secondary degeneration which was not only limited to the ganglion cell layer, but is a widespread effect affecting the outer retina. LBP altered the functional reduction caused by PONT by regulating the signal from the outer retina.