Resolution acuity and spatial summation of chromatic mechanisms in the peripheral retina.

Green stimuli are more difficult to detect than red stimuli in the retinal periphery, as reported previously. We examined the spatial characteristics of chromatic mechanisms using stimuli, modulated from an achromatic background to each pole of the "red-green" cardinal axis in DKL space at 20 deg eccentricity. The "blue-yellow" cardinal axis was also studied for comparison. By measuring both grating discrimination at the resolution limit (resolution acuity) and spatial summation, assessed by the Michaelis-Menten function, we demonstrated a marked "red-green" asymmetry. The resolution acuity was worse and spatial summation more extended for "green" compared to "red" stimuli, while showing significant individual variations. Ricco's area was also measured, but not determined for "green" spots because of the poor small stimuli detection. These results cannot be explained by differences in L- and M-cone numerosity and/or spatial arrangement, but rather have postreceptoral origin, probably at the cortical level.

The Effect of Age on the Temporal Summation of Achromatic Perimetric Stimuli.

PURPOSE: To examine the temporal summation of a Goldmann III-sized stimulus under the conditions of standard automated perimetry in healthy participants of varying age. METHODS: Twenty-seven healthy individuals of varying age (24-80 years) were tested. Achromatic contrast thresholds were measured for seven 0.48° diameter (near Goldmann III) spot stimuli of varying presentation duration (1-24 frames, 1.8-191.9 ms) at 8.8° eccentricity in the visual field along the 45°, 135°, 225°, and 315° meridians. All stimuli were displayed on a CRT display with a background set to 10 cd/m2. Iterative two-phase regression analysis was used to estimate the critical duration from each localized temporal summation function. RESULTS: A significant decrease in contrast sensitivity for all stimulus durations examined in this study was observed with increasing age in both the superior and inferior hemifield (P < 0.001). Despite this, no significant change in the critical duration was observed as a function of age in either the superior (r² = 9.1 × 10⁻9, P = 0.99) or inferior hemifield (r² = 2.4 × 10⁻5, P = 0.98). CONCLUSIONS: Age-related changes in the visual system, although leading to a reduction in contrast sensitivity, are not accompanied by a change in temporal summation for a detection task with an achromatic 0.48° diameter spot stimulus. This is important to know when proceeding to examine temporal summation changes in diseases like glaucoma.

Spatiotemporal Summation of Perimetric Stimuli in Early Glaucoma.

PURPOSE: To investigate achromatic temporal summation under the conditions of standard automated perimetry (SAP), using a Goldmann III (GIII) stimulus and a stimulus scaled to the local area of complete spatial summation (Ricco's area) in open-angle glaucoma (OAG) patients and healthy age-similar control participants. METHODS: Twenty patients with OAG (mean age, 63 years; mean MD, -3.3 dB) and 15 healthy controls (mean age, 64 years) were recruited. Contrast thresholds were measured for seven stimulus durations (1-24 frames, 1.8-191.9 ms) using a near-GIII stimulus (0.48° diameter) and stimuli scaled to the local Ricco's area, in four oblique meridians at 8.8° eccentricity in the visual field. The upper limit of complete temporal summation (critical duration) was estimated using iterative two-phase regression analysis. RESULTS: Median critical duration values were significantly longer (P < 0.05) in the OAG group for the near-GIII (107.2 ms; interquartile range [IQR], 38.0-190.5) and Ricco's area-scaled (83.2 ms, 41.7-151.4) stimuli, compared to those in healthy subjects (near-GIII, 34.7 ms; 18.2-47.9; Ricco's area-scaled, 49.0 ms; 25.1-64.6). The greatest difference in contrast thresholds between healthy and OAG subjects (i.e., disease signal) was found when stimuli were scaled to Ricco's area and shorter than or equal to the critical duration in healthy observers. CONCLUSIONS: Temporal summation is altered in glaucoma. The stimulus duration and area of conventional SAP may be suboptimal for identifying early functional damage. Simultaneously modulating stimulus duration, area, and luminance during the examination may improve the diagnostic capability of SAP and expand the dynamic range of current instruments.

Effect of varying CRT refresh rate on the measurement of temporal summation.

PURPOSE: To quantify the effect of cathode-tube-ray (CRT) monitor refresh rate on the measurement of the upper limit of complete temporal summation (critical duration) in the peripheral visual field of healthy observers. METHODS: Contrast thresholds were measured for seven achromatic spot stimuli (diameter 0.48°) of varying duration (nominal values: 10-200 ms) at an eccentricity of 8.8° along the 45°, 135°, 225° and 315° meridians of the visual field in three healthy, psychophysically experienced observers. Stimuli were presented on a CRT display with a refresh rate of 60 and 160 Hz. Contrast thresholds were expressed as contrast energy with stimulus durations being estimated using (1) the sum-of-frames (SOF) method and (2) Bridgeman's method incorporating measurements of phosphor persistence. Estimates of the critical duration were produced using iterative two-phase regression analysis. RESULTS: With stimulus duration expressed as SOF equivalent the critical duration was, on average, 10.6 ms longer with a refresh rate of 60 Hz (mean 45.7 ms, S.D. 10.1 ms) relative to 160 Hz (35.1 ms, S.D. 7.6 ms). When the Bridgeman method was used, minimal differences (1.8 ms) in critical duration values between the two refresh rates (60 Hz: 33.0 ms, S.D. 9.4 ms; 160 Hz: 31.2 ms, S.D. 7.0 ms) were observed. Identical trends were observed in all three subjects. CONCLUSIONS: Psychophysical measurements of temporal summation are independent of variations in CRT refresh rate when the Bridgeman method, incorporating measured values of phosphor persistence, is used to estimate stimulus duration. This has significant implications for the specification of stimulus duration in psychophysical studies of vision employing conventional display monitors.

The Effect of Cataract on Early Stage Glaucoma Detection Using Spatial and Temporal Contrast Sensitivity Tests.

BACKGROUND: To investigate the effect of cataract on the ability of spatial and temporal contrast sensitivity tests used to detect early glaucoma. METHODS: Twenty-seven glaucoma subjects with early cataract (mean age 60 ± 10.2 years) which constituted the test group were recruited together with twenty-seven controls (cataract only) matched for age and cataract type from a primary eye care setting. Contrast sensitivity to flickering gratings at 20 Hz and stationary gratings with and without glare, were measured for 0.5, 1.5 and 3 cycles per degree (cpd) in central vision. Perimetry and structural measurements with the Heidelberg Retinal Tomograph (HRT) were also performed. RESULTS: After considering the effect of cataract, contrast sensitivity to stationary gratings was reduced in the test group compared with controls with a statistically significant mean difference of 0.2 log units independent of spatial frequency. The flicker test showed a significant difference between test and control group at 1.5 and 3 cpd (p = 0.019 and p = 0.011 respectively). The percentage of glaucoma patients who could not see the temporal modulation was much higher compared with their cataract only counterparts. A significant correlation was found between the reduction of contrast sensitivity caused by glare and the Glaucoma Probability Score (GPS) as measured with the HRT (p<0.005). CONCLUSIONS: These findings indicate that both spatial and temporal contrast sensitivity tests are suitable for distinguishing between vision loss as a consequence of glaucoma and vision loss caused by cataract only. The correlation between glare factor and GPS suggests that there may be an increase in intraocular stray light in glaucoma.

Estimating the critical duration for temporal summation of standard achromatic perimetric stimuli.

PURPOSE: To estimate the critical duration of temporal summation for achromatic Goldmann III stimuli under the conditions of standard automated perimetry (SAP) and quantify response variability for short-duration stimuli. METHODS: Contrast thresholds were gathered using the method of constant stimuli for seven circular (0.48° diameter) incremental stimuli of varying duration (sum-of-frames equivalent: 8.3-198.3 ms), at an eccentricity of 8.8° along the four principal meridians of the visual field in two healthy, psychophysically experienced observers. Stimuli were presented on a high-resolution cathode ray tube display with a background luminance of 10 cd/m(2). Psychometric functions were fitted using a probit model and nonparametric local-linear analysis. The critical duration was estimated using iterative two-phase regression analysis, the results also being compared with values produced using previously published methods of analysis. RESULTS: The median critical duration estimated using iterative two-phase regression analysis was 27.7 ms (IQR 22.5-29.8). A slight steepening of the psychometric function slope (lower variability) was observed for longer stimulus durations, using both probit and local-linear analysis techniques, but this was not statistically significant. CONCLUSIONS: Critical duration estimates in this study are substantially shorter than those previously reported for a Goldmann III stimulus, under the conditions of SAP. Further work is required to firmly establish the relationship between measurement variability and the degree of local temporal and spatial summation.

Changes in Ricco's area with background luminance in the S-cone pathway.

PURPOSE: The area of complete spatial summation (Ricco's area) for achromatic stimuli has previously been shown to decrease with increased background luminance. A popular hypothesis is that such a phenomenon reflects increased center-surround antagonism within the receptive field of the retinal ganglion cell. We wished to investigate if similar changes in Ricco's area occur with blue background luminance for the S-cone pathway, guided by the knowledge that the retinal ganglion cells with S-cone input do not display S-cone-mediated center-surround antagonism (S+/S-). METHODS: Spatial summation functions were measured for four young healthy observers under S-cone pathway isolation by presenting blue test stimuli on a background consisting of intense fixed yellow (600 cd/m) component in combination with a variable blue component (background range, 1.78 to 2.82 log S-Td). Ricco's area was estimated by two-phase regression analysis. RESULTS: All subjects demonstrated a notable decrease in Ricco's area with increasing blue background luminance. On average, Ricco's area decreased in size by 0.39 log units per log unit increase in blue background luminance. CONCLUSIONS: The change in Ricco's area with the blue background component is not what one would initially expect given the known organization of S-cone-driven cells at the retinal level. Spatial reorganization by the suppressive surround of the receptive fields at a cortical level and a reduction in the contribution from S-cones with the lowest weights in the retinal receptive field periphery are among the possible mechanisms of the summation changes observed. These findings have implications for the design of clinical tests of the S-cone pathway.

Sensitivity loss in early glaucoma can be mapped to an enlargement of the area of complete spatial summation.

PURPOSE: The area of complete spatial summation (Ricco's area) is the largest stimulus size for which area × intensity is constant at threshold. The authors sought to investigate whether Ricco's area changes in early glaucoma to account for the decreased visual signal/noise ratio that may accompany retinal ganglion cell loss. METHODS: Spatial summation functions were measured, and Ricco's area was determined at four 10° retinal locations in 24 patients with early glaucoma (total deviation at test locations, mean, -1.3 dB; range, +2 dB to -8 dB) and 26 age-similar healthy subjects under achromatic and S-cone isolation conditions. Achromatic grating resolution acuity was measured at the same locations to estimate functional ganglion cell density. RESULTS: Ricco's area was enlarged in patients compared with controls for both achromatic (enlarged by: superior field, 0.57 log units, P < 0.01; inferior field, 0.72 log units, P < 0.01) and chromatic (enlarged by: superior field, 0.26 log units, P < 0.01; inferior field, 0.25 log units, P = 0.065) stimuli, with negligible vertical summation curve shifts along the intensity axis. Resolution acuity was significantly reduced in glaucoma patients in both hemifields (P < 0.001). There was a weak, but significant, relationship between Ricco's area and resolution acuity. CONCLUSIONS: Enlargement of Ricco's area completely compensates for reduced perimetric sensitivity in early glaucoma to maintain constant threshold at Ricco's area, suggesting an increase in signal pooling in response to ganglion cell loss. The rightward displacement of the spatial summation curve indicates that perimetric stimuli should be capable of modulating in size as well as/instead of contrast, which may boost the glaucoma signal within measurement noise.

The effect of age on the area of complete spatial summation for chromatic and achromatic stimuli.

PURPOSE: Previously, an association between the area of complete spatial summation (Ricco's area) and age under scotopic conditions had been found. The authors sought to determine whether Ricco's area is similarly associated with age under photopic achromatic and selective S-cone conditions in peripheral vision and whether any association relates to a loss of ganglion cell density as determined by measurements of peripheral grating resolution acuity. METHODS: Achromatic spatial summation functions were plotted for 68 healthy subjects (aged 20-77 years) in four oblique meridians on a gray background field of 10 cd/m(2). Similar functions were generated for the S-cone pathway (isolated using Stiles' two-color threshold method) for the same locations. Ricco's area was determined using two-phase regression analysis. Achromatic peripheral grating resolution acuity was measured at the same locations using high-contrast Gabor stimuli, as an estimate of localized functional ganglion cell density. RESULTS: There was a notable decrease in overall contrast sensitivity with age for all stimulus sizes. However, there was no evidence of age-related change in Ricco's area for either achromatic (superior field, r(2) = 0.05; inferior field, r(2) = 0.0007; all P > 0.05) or chromatic (superior field, r(2) = 0.01; inferior field, r(2) = 0.006; all P > 0.05) stimuli, despite a significant decrease in peripheral grating resolution acuity with age (superior field, r(2) = 0.15; inferior field, r(2) = 0.17; both P < 0.05). CONCLUSIONS: An age-related decline in functional ganglion cell density is not accompanied by a significant change in Ricco's area for achromatic or chromatic stimuli.

The robustness of various forms of perimetry to different levels of induced intraocular stray light.

PURPOSE: To compare directly the robustness of standard automated perimetry (SAP), short-wavelength automated perimetry (SWAP), frequency-doubling perimetry (FDP), and grating-resolution perimetry (GRP) stimuli to different degrees of intraocular stray light induced by commercially available opacity-containing filters. METHODS: Five white opacity filters of increasing density were used to simulate the typical forward light scatter and stray light values associated with age-related lens opacification and significant cataract. The individually induced intraocular stray light value for each filter was quantified with a stray light meter and plotted against individual perimetric thresholds for the right eyes of three normally sighted trained observers for SAP, SWAP, FDP, and GRP. RESULTS: All tests were significantly but differently affected by increasing stray light. Overall average declines over a 1 log unit change in the stray light values were as follows: SAP, 4.85 dB; SWAP, 9.03 dB; FDP, 4.29 dB; and GRP, 1.36 dB. Standardized (z) scores were calculated after normalization to the spread of the normative data values for each instrument. These indicated that the standardized changes from baseline over the range of the five filters per log stray light unit were as follows: SAP, 2.177; SWAP, 1.96; FDP, 1.277; and GRP, 1.04. CONCLUSIONS: The increased stray light values induced by cataract-simulating filters has a significant effect on all tests. However, GRP, which is known to be limited by retinal sampling rather than contrast, remains the most robust of the tests to the effects of intraocular stray light. The degree to which the normative "sensitivity" range for different types of perimetry might incorporate a component caused by individual differences in intraocular stray light is discussed and requires further research.

On the search for an appropriate metric for reaction time to suprathreshold increments and decrements.

Weber contrast, DeltaL/L, is a widely used contrast metric for aperiodic stimuli. Zele, Cao & Pokorny [Zele, A. J., Cao, D., & Pokorny, J. (2007). Threshold units: A correct metric for reaction time? Vision Research, 47, 608-611] found that neither Weber contrast nor its transform to detection-threshold units equates human reaction times in response to luminance increments and decrements under selective rod stimulation. Here we show that their rod reaction times are equated when plotted against the spatial luminance ratio between the stimulus and its background (L(max)/L(min), the larger and smaller of background and stimulus luminances). Similarly, reaction times to parafoveal S-cone selective increments and decrements from our previous studies [Murzac, A. (2004). A comparative study of the temporal characteristics of processing of S-cone incremental and decremental signals. PhD thesis, New Bulgarian University, Sofia, Murzac, A., & Vassilev, A. (2004). Reaction time to S-cone increments and decrements. In: 7th European conference on visual perception, Budapest, August 22-26. Perception, 33, 180 (Abstract).], are better described by the spatial luminance ratio than by Weber contrast. We assume that the type of stimulus detection by temporal (successive) luminance discrimination, by spatial (simultaneous) luminance discrimination or by both [Sperling, G., & Sondhi, M. M. (1968). Model for visual luminance discrimination and flicker detection. Journal of the Optical Society of America, 58, 1133-1145.] determines the appropriateness of one or other contrast metric for reaction time.

The effect of age-related lens yellowing on Farnsworth-Munsell 100 hue error score.

PURPOSE: To investigate the effects of real and simulated age-related changes in crystalline lens yellowing on Farnsworth-Munsell (FM) 100 hue performance. METHODS: FM 100 hue total and partial error scores (PES) were measured in a group of younger (n=10, mean age=22.2+/-2.65 years) and a group of older (n=10, mean age=54.5+/-2.64 years) normal observers along with psychophysical estimates of crystalline lens optical density and pupil size. Three younger observers underwent repeated FM 100 hue testing under a variety of simulated age-related lens yellowing conditions, using filters with well-defined transmittance properties which attempted to mimic the real age-related lens yellowing changes of the older group. RESULTS: FM 100 hue total and PES were significantly higher in the older age group compared with the younger group (p<0.01). Lens density measures were significantly higher in the older age group compared with the young group (p<0.01), but showed less scatter than individual FM 100 hue error scores. Simulated lens yellowing in the three younger observers, equivalent to the level of that of the older observers, did not affect any of their FM 100 hue total or PES. CONCLUSIONS: Simulation of age-related lens yellowing in younger observers has little effect on FM 100 hue error score. A variety of other factors such as pupil size, background illumination level, iris colour and macular pigment density may contribute to the age-related increase in FM 100 hue scores.

How does the short-wavelength-sensitive contrast sensitivity function for detection and resolution change with age in the periphery?

To determine the age-related change in the peripheral short-wavelength-sensitive (SWS) grating contrast sensitivity function (CSF), cut-off spatial frequency (acuity) and contrast sensitivity for both a detection and resolution task were measured at 8 degrees eccentricity under conditions of SWS-cone isolation for 51 subjects (19-72 years). The acuity for both the detection and resolution task declined with age, the detection acuity being significantly higher than the resolution acuity at all ages (p<.01). The CSF for both detection and resolution shifted towards lower spatial frequencies with increasing age. The contrast sensitivity for detection remained higher than that for resolution for all ages at the highest spatial frequencies. The age-related loss in the SWS resolution CSF at high spatial frequency probably reflects a loss occurring at the ganglion cells level.

Resolution acuity for equiluminant gratings of S-cone positive or negative contrast in human vision.

We measured resolution acuity separately for gratings with positive (+S) and negative (-S) S-cone contrast at different eccentricities in the temporal retina to determine if the resolution performance is limited by a single bipolar opponent mechanism. Gratings were modulated from an achromatic background in either the 90 or 270 deg direction in DKL space. Two additional directions were tested to examine the effects of increased lens yellowing and macular pigment absence in the periphery. The gratings used slow temporally rising hue (co-sinusoidal step) to aid selective S-cone ON or OFF stimulation. Resolution acuity was measured using different luminance ratios of the grating bars with the background around the equiluminant point. The data displayed a plateau where the acuity was minimal and mediated by the sparse S-cone pathway, with observer performance rising on either side. The acuity at the minimum was consistently higher for +S gratings than -S gratings beyond 10 deg eccentricity. Above the resolution limit, an aliased pattern was detected for both types of gratings, indicating that the resolution acuity was limited by the density of postreceptoral neurons. The results suggest that the resolution of gratings with opposite S-cone contrast polarity is limited by separate and rectified mechanisms of different distribution.

Severity staging by early features of age-related maculopathy exhibits weak relationships with functional deficits on SWS grating acuity.

PURPOSE: To examine the relationship between short-wavelength-sensitive (SWS) resolution acuity and epidemiologically defined stages of early age-related maculopathy (ARM). METHODS: Subjects consisted of 88 adults aged 51 to 87 years. Psychophysical testing was undertaken in only one eye of each subject (the study eye). All study eyes had a LogMAR acuity of 0.30 (20/40 Snellen) or better. SWS and achromatic grating resolution acuity were measured at 6 degrees eccentricity from the fovea. Stereoscopic color fundus photographs centered on the macula were taken on both eyes of each subject and were graded using the Wisconsin Age-Related Maculopathy Grading System (WARMGS). After grading, features of ARM were combined to assign a severity stage from 0 to 5 using the methods described by the Rotterdam Eye Study. Relationships between visual function, study eye ARM stage, and fellow eye status were examined with the use of standard statistical analysis. RESULTS: Although SWS resolution acuity was significantly reduced in eyes classified as having any ARM compared with eyes classified as having no ARM (P = 0.002), there was no relationship between the severity of functional deficits and the morphologic severity from stage 1 to stage 4. On reassigning subject eyes to a revised severity staging (stage 0, stages 1 to 4 combined, and stage 5), SWS acuity was significantly different among these three groups (P < 0.001). No significant relationship was found between achromatic resolution acuity and ARM staging. The status of the fellow eye (advanced macular degeneration present or absent) was not significantly related to visual function in the study eye. CONCLUSIONS: Significant functional deficits in SWS resolution acuity were found in eyes with ARM features, but the severity of functional loss did not correlate well with the currently accepted method of assigning a morphologic severity stage. Longitudinal studies may reveal further information on the relationships between functional deficits, ARM status, disease progression, and outcome.

The effect of simulated lens yellowing and opacification on blue-on-yellow acuity and contrast sensitivity.

Short-wavelength-sensitive (SWS) resolution acuity has been reported to be limited by the density of the responding ganglion cells for people without appreciable age-related lenticular change. This study measured the robustness of SWS-cone acuity and contrast sensitivity (CS) to simulated lens yellowing and opacification. Resolution acuity at 8 deg eccentricity proved robust to significant amounts of yellowing and remained lower than detection acuity, indicating that the resolution continued to be limited by ganglion cell density. Both the detection and resolution CS functions were affected by simulated lens yellowing, except for resolution close to the CS cut-off. For simulated opacification, only dense opacity significantly affected performance. SWS resolution acuity and CS close to the resolution limit are resistant to moderate simulated age-related lens changes and continue to be mediated by the density of the responding ganglion cells, indicating important clinical potential to measure SWS neural losses of vision in older subjects.

Changes in human short-wavelength-sensitive and achromatic resolution acuity with retinal eccentricity and meridian.

Psychophysical measurements using achromatic grating resolution acuity in peripheral vision show a prominent retinal asymmetry in acuity which is consistent with predicted values based on available estimates of midget ganglion cell density. Recent studies have shown that peripheral grating resolution acuity values for short-wavelength-sensitive (SWS) isolating gratings in normal observers are closely related to predicted values based on the underlying small bistratified ganglion cell density. By measuring SWS resolution acuity at different locations across the visual field, we wished to see if any significant acuity asymmetry exists for the short-wavelength system. In addition to this, we wanted to compare SWS and achromatic resolution acuity at different retinal locations of equal eccentricity. SWS and achromatic grating resolution acuity was measured in two observers at a number of different retinal meridians of 10- and 25-deg eccentricity from the fovea, and out to 35-deg eccentricity along the horizontal meridian. Achromatic resolution acuity was higher than SWS resolution acuity at all locations. At 10-deg eccentricity there was slight radial asymmetry in SWS and achromatic acuity, both displaying highest acuity along the horizontal meridian. At 25-deg eccentricity, SWS and achromatic acuity showed significant asymmetry with acuity being higher in the nasal retina compared to the temporal retina and with higher acuity in the superior retina compared to the inferior retina. At 35-deg eccentricity, the acuity asymmetry along the horizontal meridian was maintained with acuity for both significantly higher in the nasal retina. The SWS acuity changes with eccentricity and meridian were qualitatively similar to that found for achromatic acuity at the majority of retinal locations. Like achromatic acuity, SWS acuity shows significant asymmetry at different retinal locations of equal eccentricity. This suggests that both the midget and small bistratified ganglion cell population density changes significantly with retinal location and eccentricity. SWS acuity appears to change in parallel with achromatic acuity for the majority of retinal locations measured, although the amount of nasotemporal asymmetry appears to be slightly less for the SWS system at 25- and 35-deg eccentricity.

Human S-cone vision: relationship between perceptive field and ganglion cell dendritic field.

We measured the S-cone contrast threshold for stimuli of different size modulated along the white -90 deg direction in the isoluminant plane of DKL color space. The stimuli were presented at eccentricities of 5-30 deg in the horizontal temporal retinal meridian. Ricco's area of complete spatial summation was estimated using a bilinear fit of the log threshold/log area function. Ricco's area increased towards the retinal periphery to include an increasing number of S-cones while remaining 1.6-1.8 times larger than the dendritic field area of the small bistratified and parasol retinal ganglion cells. Assuming constant coverage factor by the dendritic field, Ricco's area incorporated a constant number (three to four) of small bistratified cells. It was also found that the threshold contrast for stimuli that matched Ricco's area was constant across the studied eccentricity range, similar to previous findings for achromatic vision. Our data support the point of view that this invariance is the result of a constant number of cells involved in stimulus detection.

Peripheral resolution for achromatic and SWS gratings in early to moderate glaucoma and the implications for selective ganglion cell density loss.

PURPOSE: To investigate whether there is significant selective reduction in short-wavelength-sensitive (SWS) ganglion cell density in early to moderate glaucoma. METHODS: Peripheral achromatic resolution acuity (an indirect measure of the underlying midget ganglion cell density) and peripheral chromatic resolution acuity under conditions of blue cone isolation (an indirect measure of the underlying small bistratified ganglion cell density) were measured at 13 degrees eccentricity in four oblique meridians in 15 eyes (mean age, 64.6 +/- 9.6 years) with early to moderate glaucoma. The results from the subjects with glaucoma were compared with those in a group of 17 age-matched normal eyes (mean age, 62.5 +/- 6.6 years). RESULTS: Mean achromatic resolution acuity across the four locations was significantly lower in the subjects with glaucoma than in the normal subjects (2.92 vs. 4.01 cyc/deg). Mean chromatic resolution acuity across the four locations was also significantly lower in the subjects with glaucoma than the normal subjects (0.78 vs. 0.99 cyc/deg). There was no selective loss of mean SWS acuity in the subjects with glaucoma. Individual location analysis revealed that the chromatic-achromatic resolution ratio was not significantly different in the subjects with glaucoma who had early glaucomatous damage when compared with the normal subjects. The chromatic-achromatic resolution ratio was lower than normal at certain locations in certain individuals with early glaucoma. CONCLUSIONS: The results indicate that there is no evidence of significant selective reduction in global SWS ganglion cell density in early to moderate glaucoma. However, there may be selective loss of SWS ganglion cell density at individual locations in individual eyes.

Short-wavelength acuity: optical factors affecting detection and resolution of blue-yellow sinusoidal gratings in foveal and peripheral vision.

Previous studies have indicated that peripheral achromatic grating resolution is limited by the sampling density of the neural array (sampling limited), and largely unaffected by large amounts of optical defocus and significant changes in luminance. Under certain conditions, peripheral short-wavelength sensitive (SWS) grating acuity is also sampling limited. We wished to determine how the sampling-limited nature of SWS-driven grating resolution was affected by changing optical defocus and stimulus luminance. Using SWS-cone isolation techniques, detection and resolution acuity were measured for sinusoidal gratings under varying levels of stimulus mean luminance and optical defocus in the fovea and at 20 degrees eccentricity. From 1.4 down to 0.3 cd/m(2) peripheral detection acuity was superior to resolution acuity, accompanied by observations of aliasing: there was little change in resolution performance throughout this range. For defocus up to 3-4 dioptres, peripheral detection acuity was superior to resolution but fell steadily: resolution performance remained flat throughout the same range. Unlike achromatic acuity, foveal resolution performance displayed some robustness to defocus but to a lesser degree than the periphery. Peripheral SWS-driven resolution remains sampling limited for large changes in stimulus luminance and optical defocus, and should thus be useful as a clinical test of SWS-driven ganglion cell density.