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The effect of part-time wear of 2-zone concentric bifocal spectacle lenses on refractive error development & eye growth in young chicks
摘要： The purpose of this study is to characterize in young chicks the myopia control effects of part-time wear of two-zone concentric bifocal lenses. Nine-day-old chicks (n = 115) were first made myopic with monocular ?10 Diopter (D) single vision (SV) lenses worn for 3 days. Over the 6 days following myopia induction, either 1) two-zone bifocal lenses (?10 D center/?5 D periphery, BFDC) were worn for 12 (full-time), 10, 8, or 6 h, with ?10 D SV lenses worn for the remainder of the day, or 2) BFDC or BFNC (?5 D center/?10 D periphery) lenses were worn every other day (EOD). Control birds wore ?10 D SV lenses every day. Refractive error (RE) and axial ocular dimensions were monitored every three days with retinoscopy and high frequency A-scan ultrasonography respectively. Mean interocular RE and axial length differences after 3 days of myopia induction ( ± SEM) were ?9.6 ± 0.19 D and 0.26 ± 0.01 mm across the groups. At the end of the following 6-day treatment period, equivalent values were: ?10.66 ± 0.28 D, 0.42 ± 0.02 mm (SV-control); 1) ?4.61 ± 0.29 D, 0.26 ± 0.02 mm (BFDC, 12 h); ?4.82 ± 0.23 D, 0.28 ± 0.02 mm (BFDC, 10 h); ?5.21 ± 0.27 D, 0.24 ± 0.02 mm (BFDC, 8 h); ?6.34 ± 0.34 D, 0.25 ± 0.03 mm (BFDC, 6 h); 2) ?8.29 ± 0.29 D, 0.32 ± 0.03 mm (BFDC, EOD), and ?8.83 ± 0.36 D, 0.33 ± 0.03 mm (BFNC, EOD). Overall, full-time BFDC and part-time BFDC and BFNC lens groups exhibited similar changes and were less myopic than the SV group. The results suggest that bifocal lenses may have myopia control effects even when worn part-time, interleaved with standard (SV) myopic corrections, especially if worn for at least 6 h per day.
关键词： Myopia,Axial length,Chicks,Bifocal lenses,Refractive error
更新于2025-09-23 15:23:52
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Repeatability assessment of biometric measurements with different refractive states and age using a swept-source biometer
摘要： Background: We aim to assess if refractive error or age may influence the repeatability of measurements using a swept-source biometer. Methods: A total of 61 subjects were evaluated with IOLMaster 700 acquiring measurements of axial length (AL), central corneal thickness (CCT), white-to-white distance (WTW), anterior aqueous depth (AQD), lens thickness (LT), and keratometry (K) readings. Repeatability was evaluated classifying the sample according to the refractive state and age by the calculation of the within-subject standard deviation (Sw), coefficient of repeatability, and intraclass correlation coefficient. Results: Very similar Sw was acquired among groups for AL, CCT, and WTW. Differences found for AQD, LT, keratometry and astigmatism among refractive and age groups were not clinically significant. Refractive groups obtained a Sw for AQD between 0.016 and 0.026, while for LT was between 0.023 and 0.029 mm. Besides, Sw showed values from 0.014 to 0.029 mm for keratometry. Age groups obtained a Sw of 0.025 and 0.016 mm for AQD, and 0.029 and 0.018 mm for LT, respectively. Sw was 0.019 vs 0.018 mm for K1, 0.014 vs 0.031 mm for K2. Conclusions: IOLMaster 700 showed good repeatability for biometric and keratometric parameters in eyes classified according to their refractive error or age.
关键词： anterior segment,Repeatability,biometry,swept-source biometer,refractive error,age
更新于2025-09-23 15:23:52
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Portable Autorefractors for Detecting Axial Length Changes in Space
摘要： We evaluated the reproducibility of two portable, self-administered autorefractors (Netra and SVOne Pro) to assess the time course of visual changes on the ISS. METHODS: We measured cycloplegic refractive error at 5 visits at least a week apart in 13 subjects (6 women, 7 men, 30 6 9 yr) using both devices seated and also prone with lower body positive pressure (LBPP) applied. Axial length was measured with an optical biometer. Subjects completed a questionnaire on device preferences. RESULTS: The SVOne seated intrasession reproducibility coefficient (RPC) was 0.37 diopters (D), while the Netra's was 0.41 D. Intersession seated results were: RPC 5 0.67 D for the SVOne and RPC 5 0.54 D for the Netra. The average seated to prone LBPP differences were significantly different from zero for both the SVOne and Netra. The SVOne was preferred in four out of five categories on the questionnaire and took half the time to complete a measurement set compared to the Netra. DISCUSSION: Users preferred the SVOne and it took less time. An SVOne refraction change of 0.67 D from baseline would happen by chance less than 5% of the time. If multiple separate measurements were taken, the detection limit could be reduced (e.g., three repeated measurements could reduce it to 0.38 D). Since astronauts with visual changes show spherical equivalent changes of 0.5 to 1.0 D, in-flight autorefractors could help determine the time course of refractive changes in space from which changes in axial length could be inferred.
关键词： spaceflight-associated neuro-ocular syndrome,portable autorefractor,axial length,refractive error
更新于2025-09-23 15:23:52
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Lack of cone mediated retinal function increases susceptibility to form-deprivation myopia in mice
摘要： Retinal photoreceptors are important in visual signaling for normal eye growth in animals. We used Gnat2 cplf3/cplf3 (Gnat2-/-) mice, a genetic mouse model of cone dysfunction to investigate the influence of cone signaling in ocular refractive development and myopia susceptibility in mice. Refractive development under normal visual conditions was measured for Gnat2-/- and age-matched Gnat2+/+ mice, every 2 weeks from 4 to 14 weeks of age. Weekly measurements were performed on a separate cohort of mice that underwent monocular form-deprivation (FD) in the right eye from 4 weeks of age using head-mounted diffusers. Refraction, corneal curvature, and ocular biometrics were obtained using photorefraction, keratometry and optical coherence tomography, respectively. Retinas from FD mice were harvested, and analyzed for dopamine (DA) and 3,4-dihydroxyphenylacetate (DOPAC) using high-performance liquid chromatography. Under normal visual conditions, Gnat2+/+ and Gnat2-/- mice showed similar refractive error, axial length, and corneal radii across development (p>0.05), indicating no significant effects of the Gnat2 mutation on normal ocular refractive development in mice. Three weeks of FD produced a significantly greater myopic shift in Gnat2-/- mice compared to Gnat2+/+ controls (-5.40 ± 1.33 D vs -2.28 ± 0.28 D, p=0.042). Neither the Gnat2 mutation nor FD altered retinal levels of DA or DOPAC. Our results indicate that cone pathways needed for high acuity vision in primates are not as critical for normal refractive development in mice, and that both rods and cones contribute to visual signalling pathways needed to respond to FD in mammalian eyes.
关键词： mouse,form-deprivation,dopamine,Gnat2,Refractive error,cone photoreceptors
更新于2025-09-23 15:23:52
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Paediatric Refractive Errors in an Eye Clinic in Osogbo, Nigeria
摘要： BACKGROUND: Paediatric ophthalmology is an emerging subspecialty in Nigeria and as such there is paucity of data on refractive errors in the country. This study set out to determine the pattern of refractive errors in children attending an eye clinic in South West Nigeria. METHODS: A descriptive study of 180 consecutive subjects seen over a 2-year period. Presenting complaints, presenting visual acuity (PVA), age and sex were recorded. Clinical examination of the anterior and posterior segments of the eyes, extraocular muscle assessment and refraction were done. The types of refractive errors and their grades were determined. Corrected VA was obtained. Data was analysed using descriptive statistics in proportions, chi square with p value <0.05. RESULTS: The age range of subjects was between 3 and 16 years with mean age = 11.7 and SD = 0.51; with males making up 33.9%.The commonest presenting complaint was blurring of distant vision (40%), presenting visual acuity 6/9 (33.9%), normal vision constituted >75.0%, visual impairment20% and low vision 23.3%. Low grade spherical and cylindrical errors occurred most frequently (35.6% and 59.9% respectively). Regular astigmatism was significantly more common, P <0.001. The commonest diagnosis was simple myopic astigmatism (41.1%). Four cases of strabismus were seen. CONCLUSION: Simple spherical and cylindrical errors were the commonest types of refractive errors seen. Visual impairment and low vision occurred and could be a cause of absenteeism from school. Low-cost spectacle production or dispensing unit and health education are advocated for the prevention of visual impairment in a hospital set-up.
关键词： Low-cost spectacle dispensing unit,Eye clinic,Child,Refractive error
更新于2025-09-23 15:22:29
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Effect of Refractive Status and Axial Length on Peripapillary Retinal Nerve Fibre Layer Thickness: An Analysis Using 3D OCT
摘要： Background: Accurate measurement of retinal nerve fiber layer (RNFL) is now possible with the high resolution optical coherence tomography (OCT). Effect of refractive status of the eye on RNFL thickness may be relevant in the diagnosis of glaucoma and other optic nerve diseases. Aim: To assess the RNFL thickness and compare its correlation with refractive status and axial length of the eye. Material and Methods: Three hundred eyes of 150 patients were included in this study, who underwent RNFL analysis using TOPCON 3D OCT 2000. Analysis of variance has been used to find the significance of study parameters between the study groups. Results: The study showed that refractive status/axial length affected the peripapillary RNFL thickness significantly. Conclusion: The study suggests that the diagnostic accuracy of OCT may be improved by considering refractive status and axial length of the eye when RNFL is measured.
关键词： Optical coherence tomography,Refractive error
更新于2025-09-23 15:22:29
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Femtosecond Laser Implantation of a 355-Degree Intrastromal Corneal Ring Segment in Keratoconus: A Three-Year Follow-Up
摘要： Purpose. To evaluate the outcomes of femtosecond laser-assisted implantation of a 355-degree intracorneal ring (ICR) (Keraring) in patients with keratoconus in the three-year follow-up. Setting. Future Femtolaser Center, Sohag, Egypt. Design. Prospective interventional case series. Patients and Methods. A prospective case series of 38 eyes of 26 patients with keratoconus had implantation of the 355-degree ICR keraring after tunnel creation with a femtosecond laser. The uncorrected visual acuities (UCVA) and best-corrected visual acuities (BCVA), sphere, cylinder, and manifest refraction spherical equivalent (SE), and mean keratometry (K), K max, and K min were evaluated preoperatively and 3, 6, 12, 24, and 36 months postoperatively, and all complications were reported. Results. 38 eyes of 26 patients with mean age 25.92 ± 5.44 years were enrolled in the study, 11 were males (42.3%). The mean UCVA improved from 0.93 ± 0.21 to 0.63 ± 0.21 logMAR (P ≤ 0.001) and the mean BCVA from 0.67 ± 0.22 to 0.43 ± 0.26 logMAR (P < 0.001). The mean sphere, cylinder, and spherical equivalent have been changed dramatically from preoperative to 3 month postoperative, which is statistically signi?cant (P ≤ 0.001), and the changes between 1 and 2 years and 2 and 3 years are also considerable and statistically signi?cant; the K max and K min and K mean improved and the changes were statistically signi?cant (P ≤ 0.001), and the changes between one, two, and three years were also statistically signi?cant. The safety and e?cacy indices were changed through the three-year follow-up. The complications were corneal neovascularization (36.84%), corneal melting (26.3%), and ring extrusion (31.5%) at the end of the study. Conclusions. Implantation of a 355-degree intracorneal keraring using femtosecond laser improved the visual, refractive, and topographic parameters in keratoconus patients, with a high rate of ICR extrusion and instability. The study has been registered for the Pan African Clinical Trial Registry (http://www.pactr.org) database within No: PACTR201810796878908 on 29 October 2018.
关键词： keratoconus,Keraring,refractive error,femtosecond laser,visual acuity,corneal topography,intracorneal ring
更新于2025-09-12 10:27:22
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Relationships between retinal break locations and the shapes of the detachments
摘要： Purpose: Detecting primary breaks and confirming detachment preoperatively are important. Lincoff stated that retinal detachments progress according to gravity; his law has become popular. We evaluated Lincoff’s law with a slight modification to determine whether it remains suitable for present cases independent of refractive error and previous cataract surgery. Patients and methods: Group 1 included superior region detachments not exceeding the 12 o’clock midline; the original break was within 1 1/2 clock hours of the highest detachment border. Group 2 included shallow inferior detachment; the original break corresponded to the more spread side of the 6 o’clock midline. Group 3 detachments were beyond 12 o’clock; the original break was within a triangle with a 12 o’clock apex (A) or within 1 1/2 hours of 12 o’clock (B); (A) and (B) were stated in the original report. Another five classifications were applied for small numbers of detachments. Consecutive initial rhegmatogenous retinal detachment surgery patients were included; medical records and detachment charts were examined. Eyes were classified into categories and rates were calculated. Eyes that had never undergone previous cataract surgery besides those in which the macula remained attached were divided into groups at a –6 D cutoff (Groups 1, 2, and 3[B]); we compared groups in each category. We compared phakic eyes, pseudophakic eyes, and eyes ruptured at the posterior capsule (Groups 1, 2, and 3[B]). Results: Finally, 747 eyes were categorized. In Groups 1, 2, 3(A), and 3(B), corresponding rates were 92, 86, 70, and 89%, respectively. Between the above and below -6 D groups, there was no significant difference in rate in any category. There were no significant differences between phakic, pseudophakic, and ruptured eyes. Conclusion: Lincoff’s law was suitable for the present cases and independent of refractive error and previous cataract surgery.
关键词： rhegmatogenous retinal detachment,shapes of detachments,retinal break locations,refractive error,previous cataract surgery
更新于2025-09-10 09:29:36
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Self-adjustable glasses in the developing world
摘要： Uncorrected refractive errors are the single largest cause of visual impairment globally. Refractive errors are an avoidable cause of visual impairment that are easily correctable. Provision of spectacles is a cost-effective measure. Unfortunately, this simple solution becomes a public health challenge in low- and middle-income countries because of the paucity of human resources for refraction and optical services, lack of access to refraction services in rural areas, and the cost of spectacles. Low-cost approaches to provide affordable glasses in developing countries are critical. A number of approaches has been tried to surmount the challenge, including ready-made spectacles, the use of focometers and self-adjustable glasses, among other modalities. Recently, self-adjustable spectacles have been validated in studies in both children and adults in developed and developing countries. A high degree of agreement between self-adjustable spectacles and cycloplegic subjective refraction has been reported. Self-refraction has also been found to be less prone to accommodative inaccuracy compared with non-cycloplegic autorefraction. The benefits of self-adjusted spectacles include: the potential for correction of both distance and near vision, applicability for all ages, the empowerment of lay workers, the increased participation of clients, augmented awareness of the mechanism of refraction, reduced costs of optical and refraction units in low-resource settings, and a relative reduction in costs for refraction services. Concerns requiring attention include a need for the improved cosmetic appearance of the currently available self-adjustable spectacles, an increased range of correction (currently -6 to +6 diopters), compliance with international standards, quality and affordability, and the likely impact on health systems. Self-adjustable spectacles show poor agreement with conventional refraction methods for high myopia and are unable to correct astigmatism. A limitation of the fluid-filled adjustable spectacles (AdSpecs, Adaptive Eyecare Ltd, Oxford, UK) is that once the spectacles are self-adjusted and the power fixed, they become unalterable, just like conventional spectacles. Therefore, they will need to be changed as refractive power changes over time. Current costs of adjustable spectacles are high in developing countries and therefore not affordable to a large segment of the population. Self-adjustable spectacles have potential for “upscaling” if some of the concerns raised are addressed satisfactorily.
关键词： spectacles,refractive error,eye disease,developing countries
更新于2025-09-10 09:29:36
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Analysis of Factors that Influence on Accuracy of Intraocular Lens Power Calculation
摘要： To investigate which factors primarily influence refractory errors between various formulas used to calculate intraocular lens (IOL) power. Methods: Records of 266 eyes of 191 patients who underwent uneventful cataract surgery were reviewed retrospectively. IOL power was determined using SRK/T, HofferQ (H/Q), Master SRK/T (M/T), Master HofferQ (M/Q), Master Holladay (M/Hol), and Master Haigis (M/Hai). The mean absolute error (MAE) of each formula was compared; MAE was defined as the difference between the postoperative spherical equivalence (SE) determined 1 month after surgery and the predicted SE. Factors that could have influenced interformula refractive errors were analyzed. Patients were divided into 3 groups based on average keratometric value (Kavg) and the inter-group differences of the AE of each formula were analyzed. Effects of corneal curvature on changes in AE of each formula were evaluated by linear regression. Results: The MAE was minimized in the M/T formula, followed by the M/Hol, M/Hai, SRK/T, H/Q, and M/Q formulas. Interformula MAE differences were not statistically significant. Kavg and AXL were significantly influenced by the different predictive values between formulas in univariate analysis, but only AXL was significant in multivariate analysis. The AE in each formula among the 3 groups according to keratometry was significantly different in SRK, M/Hol, and M/Hai. Linear regression analysis showed a significant negative correlation between Kavg, AE of SRK/T and the MHai formula. In particular, this effect was more pronounced in those with short AXL (<22.5 mm). Conclusions: There were no significant MAE differences between formulas. AXL was a significant factor that influenced the differences between formulas. SRK/T and M/Hai may be affected by outside the normal range of corneal curvatures.
关键词： Corneal curvature,Refractive error,Intraocular lens power calculation,Axial length
更新于2025-09-09 09:28:46