Age-related decline in function of ON and OFF visual pathways.

PURPOSE: A simple psychophysical paradigm is available as a digital application in iOS devices such as iPad to measure the function of ON and OFF visual pathways. However, an age-matched normative database is not readily available. The purpose of the study is to evaluate the response of ON and OFF visual pathways as a function of age. METHODS: 158 normal healthy adults (84 males and 74 females) whose age ranged 18-80 years participated in the study. None of them had any ocular disease (except cataract of grade II or less) and visual acuity of ≤ 20/25. Monocular testing (only one eye) was performed on the 'EyeSpeed' application on an iPad at 40cm distance. The targets ranged between 1 to 3 light or dark squares presented randomly in a noise background and participants responded by indicating the number of squares by touching the screen as fast as possible. The main outcome variables are reaction time, accuracy and performance index (1 / speed * accuracy). RESULTS: The median reaction time was shorter (Median (IQR): 1.53s (0.49) [dark] Vs 1.76s (0.58) [light], p < 0.001) and accuracy was higher (97.21% (3.30) [dark] Vs 95.15% (5.10) [light], p < 0.001) for dark targets than the light targets. Performance index and reaction time for both target types significantly correlated with age (ρ = -0.41 to -0.43; p < 0.001). CONCLUSIONS: This normative database will be useful to quantify disease-specific defects. More importantly, the ON pathway function can potentially serve as a surrogate for rod photoreceptor function.

Blue Light-Induced Retinal Neuronal Injury and Amelioration by Commercially Available Blue Light-Blocking Lenses.

Blue light exposure-induced retinal damage has been extensively studied. Although many in vitro studies have shown the benefits of blue light-blocking lenses (BBL) there have been few comprehensive in vivo studies to assess the effects of BBL. We investigated the influence of blue light exposure using light-emitting diodes on retinal histology and visual cortex neurons in rodents. We also considered whether retinal and cortical changes induced by blue light could be ameliorated with blue light-blocking lenses. A total of n = 24 (n = 6 in each group; control, light exposure without lenses, two different BBLs)) male Wistar rats were subjected to blue light exposure (LEDs, 450-500 lux) without or with BBLs (400-490 nm) for 28 days on a 12:12 h light-dark cycle. Histological analysis of retinae revealed apoptosis and necrosis of the retinal pigment epithelium (RPE), photoreceptors, and inner retina in the light exposure (LE) group, along with increase caspase-3 immunostaining in the ganglion cell layer (p < 0.001). BBL groups showed less caspase-3 immunostaining compared with the LE group (p < 0.001). V1-L5PNs (primary visual cortex layer 5 pyramidal neurons) demonstrated reduced branching and intersections points for apical (p < 0.001) and basal (p < 0.05) dendrites following blue light exposure. Blue light-blocking lenses significantly improved the number of basal branching points compared with the LE group. Our study shows that prolonged exposure to high levels of blue light pose a significant hazard to the visual system resulting in damage to the retina with the associated remodeling of visual cortex neurons. BBL may offer moderate protection against exposure to high levels of blue light.

A perimetric test procedure that uses structural information.

PURPOSE: To develop a perimetric test strategy, Structure Estimation of Minimum Uncertainty (SEMU), that uses structural information to drive stimulus choices. METHODS: Structure Estimation of Minimum Uncertainty uses retinal nerve fiber layer (RNFL) thickness data as measured by optical coherence tomography to predict perimetric sensitivity. This prediction is used to set suprathreshold levels that then alter a prior probability distribution of the final test output. Using computer simulation, we studied SEMU's performance under three different patient error response conditions: No Error, Typical False Positive errors, and Extremely Unreliable patients. In experiment 1, SEMU was compared with an existing suprathreshold cum thresholding combination test procedure, Estimation of Minimum Uncertainty (EMU), on single visual field locations. We used these results to finalize SEMU parameters. In experiment 2, SEMU was compared with full threshold (FT) on 163 glaucomatous visual fields. RESULTS: On individual locations, SEMU has similar accuracy to EMU, but is, on average, one presentation faster than EMU. For the typical false-positive error condition, SEMU has significantly lower error compared with FT (SEMU average 0.33 dB lower; p < 0.001) and the 90% measured sensitivity range for SEMU is also smaller than that for FT. For unreliable patients, however, FT has lower mean and SD of error. Structure Estimation of Minimum Uncertainty makes significantly fewer presentations than FT (1.08 presentation on average fewer in a typical false-positive condition; p < 0.001). Assuming that a location in the field is marked abnormal if it falls below the 5th percentile of normal, SEMU has a false-positive rate of less than 10% for all error conditions compared with FT's rate of 20% or more. CONCLUSIONS: On average, simulations show that using RNFL information to guide stimulus placement in a perimetric test procedure maintains accuracy, improves precision, and decreases test duration for patients with less than 15% false-positive rates.

Change in iris parameters with physiological mydriasis.

PURPOSE: A pilot study to analyze the association of change in iris parameters with physiological mydriasis in angle closure eyes compared with normal control eyes among south Indian participants. METHODS: Sixteen eyes diagnosed with primary angle closure and 14 age, gender-matched open-angle control eyes were selected. All participants underwent anterior segment imaging using anterior segment optical coherence tomography in dim and bright illumination. The iris area (IA), iris volume (IV), and pupillary diameter were calculated using customized image processing software. RESULTS: The IA and IV were found to be lesser in angle closure compared with normal controls. Average IA (dim and bright) was found to be 3.4 and 3.7 mm(2) in normals and 3.03 and 3.35 mm(2) in angle closure, and average IV (dim and bright) was found to be 24.28 and 26.09 mm(2) in normals and 21.38 and 22.6 mm(2) in angle closure. The IA and IV decreased significantly with pupillary dilation in normals and in angle closures. However, decrease in the IA (slope = 0.52 and 0.42; p = 0.012) and IV (slope = 1.97 and 1.41; p = 0.014) with pupillary dilation was significantly higher in normals compared with angle closures, respectively. CONCLUSIONS: IA and IV were found to decrease as pupil dilates in normal and angle closure eyes among South Indians. Loss in the IV was found to be lower in angle closure eyes.

Plateau Iris Configuration and Dark-Light Changes in Anterior Segment Optical Coherence Tomography.

The angle opening distance (AOD) was analyzed using anterior segment optical coherence tomography (ASOCT) in dark-light conditions in 14 convex iris configuration (CIC) and 12 plateau iris configuration (PIC) patients. AOD500 measured in dark and bright conditions in nasal quadrants were 0.156 +/- 0.072 mum; 0.186 +/- 0.084 mum for CIC (P = .025) and 0.177 +/- 0.121 mum; 0.186 +/- 0.116 mum for PIC (P = .38). AOD750 in dark and bright conditions in nasal quadrants were 0.235 +/- 0.082 mum; 0.280 +/- 0.097 mum for CIC (P = .000) and 0.294 +/- 0.181 mum; 0.306 +/- 0.172 mum for PIC. PIC showed no significant difference in the dynamic changes, whereas the nasal quadrant in CIC showed significant changes. The AOD parameters from ASOCT can be used to analyze the dark-light changes of the anterior chamber angle to differentiate between CIC and PICs.