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

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

Elimination of the color discrimination impairment along the blue–yellow axis in patients with hypothyroidism after treatment with levothyroxine as assessed by the Farnsworth–Munsell 100 hue test.

Our previous study has shown that individuals with untreated hypothyroidism display significantly higher partial error scores (√PES) along the blue–yellow axis compared to the red–green axis than normal individuals using the Farnsworth–Munsell 100 hue test [J. Opt. Soc. Am. A 37, A18 (2020)]. We wished to determine how color discrimination may change when hypothyroidism has been treated to the point of euthyroidism. Color discrimination was reassessed for 17 female individuals who had undergone treatment for hypothyroidism, and the results were compared with 22 female individuals without thyroid dysfunction. No statistically significant difference was found in the total error score (√TES) for the first and second measurements for both groups (&gt;0.45). The √PES for the hypothyroid group improved significantly in the previously impaired color regions after the treatment. Color discrimination defects found in untreated hypothyroidism can be negated with treatment of the condition over an appropriate time period

Case Report: Changes in Spatial Summation for Chromatic Stimuli in a Patient with Hypothyroidism Due to Autoimmune Thyroiditis Before and After Treatment with Levothyroxine.

Introduction: Acquired hypothyroidism is associated with a wide range of deficits including visual effects. Investigating colour vision mediated by S-cones has shown potential to detect diseases such as glaucoma or diabetes, however, studies of colour vision in hypothyroidism are scarce. Case presentation: In the present study we report spatial summation data of a patient with hypothyroidism due to autoimmune thyroiditis tested with S-cone specific stimuli. The area of complete spatial summation (Ricco’s area) is believed to reflect neural convergence and has been widely used to study structural changes to compensate for cell loss. We measured Ricco’s area before and after treatment with levothyroxine. Colour contrast thresholds were measured as a function of stimulus area in the retinal periphery, under S-cone isolating conditions. Ricco’s area was determined from the Threshold vs Area curve for either blue (S-cone increments) or yellow (S-cone decrements) stimuli. The patient’s data before treatment showed enlarged Ricco’s area (3 to 10 times larger) only for yellow stimuli compared to participants without hypothyroidism. After a treatment with levothyroxine and having reached euthyroidism, Ricco’s area decreased significantly (p < 0.05) for yellow stimuli, but remained unchanged for blue stimuli (p = 0.177). A second subject without hypothyroidism, who participated in both experiments did not show any significant differences for either blue (p = 0.081) or yellow stimuli (p = 0.78). Conclusion: The observed increase in Ricco’s area in hypothyroidism may be related to increased convergence to compensate for ganglion cell dysfunction. The results suggest that this process can be reversible after treatment. Examination of the S-cone system provides the potential to monitor this condition

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 msec), 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 CRT display with a background luminance of 10 cd/m2. Psychometric functions were fitted using a probit model and non-parametric 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 msec (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

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/m2. 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, r2 = 0.05; inferior field, r2 = 0.0007; all P > 0.05) or chromatic (superior field, r2 = 0.01; inferior field, r2 = 0.006; all P > 0.05) stimuli, despite a significant decrease in peripheral grating resolution acuity with age (superior field, r2 = 0.15; inferior field, r2 = 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

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

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/m2) 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

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