Contrast Sensitivity of ON and OFF Human Retinal Pathways in Myopia.

The human visual cortex processes light and dark stimuli with ON and OFF pathways that are differently modulated by luminance contrast. We have previously demonstrated that ON cortical pathways have higher contrast sensitivity than OFF cortical pathways and the difference increases with luminance range (defined as the maximum minus minimum luminance in the scene). Here, we demonstrate that these ON-OFF cortical differences are already present in the human retina and that retinal responses measured with electroretinography are more affected by reductions in luminance range than cortical responses measured with electroencephalography. Moreover, we show that ON-OFF pathway differences measured with electroretinography become more pronounced in myopia, a visual disorder that elongates the eye and blurs vision at far distance. We find that, as the eye axial length increases across subjects, ON retinal pathways become less responsive, slower in response latency, less sensitive, and less effective and slower at driving pupil constriction. Based on these results, we conclude that myopia is associated with a deficit in ON pathway function that decreases the ability of the retina to process low contrast and regulate retinal illuminance in bright environments.

Edentulousness among Patients Visiting a Dental Unit of a Tertiary Care Centre: A Descriptive Cross-sectional Study.

Introduction: Edentulousness (partial or complete) is a sequel of tooth loss and is an indicator of the oral health status of a population. Edentulousness has a series of deleterious consequences for oral and general health. The aim of this study was to find out the prevalence of edentulousness among patients visiting the dental unit of a tertiary care centre. Methods: A descriptive cross-sectional study was carried out based on hospital records of patients visiting the Department of Oral Medicine and Prosthodontics of a tertiary care centre from 1 January 2019 to 30 December 2019 to see the prevalence of edentulousness. Ethical approval was obtained from the Institutional Review Committee (Reference number: 077/ 078 /40). A convenience sampling method was used. Point estimate and 95% Confidence Interval were calculated. Results: Among 4697 patients, edentulousness was found in 403 (8.58%) (7.78-9.38, 95% Confidence Interval). Partial edentulous were 263 (65.30%) and complete edentulous were 140 (34.70%). Of the total partial edentulous patient, Kennedy's class III found in 200 (76.05%) was the most common pattern followed by Kennedy's class I in 32 (12.17%), class II in 21 (7.98%) and class IV in 10 (3.80%) patients respectively. Conclusions: The prevalence of edentulousness was similar to other studies done in similar settings. Since edentulousness is a preventable problem, it should be addressed with high priority. Keywords: dental health service; edentulous mouth; Nepal; prevalence.

Differences in visual stimulation between reading and walking and implications for myopia development.

Visual input plays an important role in the development of myopia (nearsightedness), a visual disorder that blurs vision at far distances. The risk of myopia progression increases with the time spent reading and decreases with outdoor activity for reasons that remain poorly understood. To investigate the stimulus parameters driving this disorder, we compared the visual input to the retina of humans performing two tasks associated with different risks of myopia progression, reading and walking. Human subjects performed the two tasks while wearing glasses with cameras and sensors that recorded visual scenes and visuomotor activity. When compared with walking, reading black text in white background reduced spatiotemporal contrast in central vision and increased it in peripheral vision, leading to a pronounced reduction in the ratio of central/peripheral strength of visual stimulation. It also made the luminance distribution heavily skewed toward negative dark contrast in central vision and positive light contrast in peripheral vision, decreasing the central/peripheral stimulation ratio of ON visual pathways. It also decreased fixation distance, blink rate, pupil size, and head-eye coordination reflexes dominated by ON pathways. Taken together with previous work, these results support the hypothesis that reading drives myopia progression by understimulating ON visual pathways.