• Development & Evaluation of a Contrast Sensitivity Perimetry Test for Patients with Glaucoma

      Hot, Aliya (2007-05-29)
      PURPOSE: To design a contrast sensitivity perimetry test with the potential to improve clinical management of glaucoma by decreasing test-retest variability in defective areas while maintaining good sensitivity to glaucomatous loss. METHODS: Twenty patients with glaucoma, ten age-similar control subjects and ten young control subjects were recruited. One eye was tested per subject. All subjects were tested with contrast sensitivity perimetry (CSP), and conventional automated perimetry (CAP). Stimuli for CSP were Gabor patches with a peak spatial frequency of 0.375 cpd and a two-dimensional spatial Gaussian envelope with the most of the energy concentrated within a central circular region 4 degrees in diameter. For CSP, stimuli were presented at 26 locations over the central visual field, excluding the central 5 degrees and with the emphasis on the nasal hemifield. Neuroretinal rim area of the patients was measured using retinal tomography (HRT II). Young subjects were tested on CSP using 4-reversal and 8-reversal staircases to estimate variability and test duration. Bland-Altman analysis of agreement was used to assess test-retest variability, to compare depth of defect for the two perimetric tests, and to investigate the relation between contrast sensitivity and neuroretinal rim area. RESULTS: With 4-reversal staircases, for both Size III stimuli and Gabor stimuli, variability increased as sensitivity decreased (r2 > 5%, p<0.001), but at a shallower rate for the Gabor stimuli (Z > 2.9, p<0.005). With 6- and 8- reversal staircases, the correlation between sensitivity and variability was not significant (r2 = 0.05%, p>0.5) and the slope of the regression line was shallower than for the 4-reversal staircases (Z>2.4, p< 0.01). Depth of defect was on average similar for the two devices, but for some patients the size III stimuli tended to yield deeper defects than Gabors in regions of lower sensitivity. The relation between rim area and perimetric sensitivity was more consistent for contrast sensitivity perimetry than for conventional perimetry (Z=9.3, p < 0.0005). For control subjects there was a significantly shallower decline in sensitivity with eccentricity using Gabor stimuli than with conventional size III stimuli (Z=3.78, p<0.0005), and overall test-retest variability was similar for staircases with 4 to 8 reversals. CONCLUSION: Contrast sensitivity perimetry demonstrated reasonably low test-retest variability and good ability to detect defect. It also showed a structure-function relation that was independent of the degree of glaucomatous loss. Further research on contrast sensitivity perimetry is needed to evaluate its utility in monitoring progression of glaucoma and effects of treatment.
    • Evaluating Equiluminant Chromatic Stimuli as Stimuli for Assessing Glaucomatous Damage

      Ly-Schroeder, Emily (2008-01-10)
      Purpose: To examine the potential clinical utility of equiluminant chromatic stimuli for assessing glaucomatous damage. Pan et al. (2006) found that equiluminant red-green chromatic stimuli could have good ability to detect defects as well as low test-retest variability, but clinical utility was limited due to the small dynamic ranges for their stimuli. The current study increased the dynamic range by using larger stimuli and including tritan stimuli. Methods: Luminance, red-green (R-G), and tritan stimuli were created by modulating a large square (3 degrees per side) from an equal energy white (20 cd/m2) along three cardinal directions in color space. Contrast sensitivity was measured at four locations with an eccentricity of 12 deg. along the 45, 135, 225, and 315 degree meridia. Twenty-five patients with glaucoma and twenty-six control subjects free of eye disease were tested monocularly at two separate sessions within a two-week time period. Sensitivities were reported in decibel (dB) units, where 1 dB=-1 (log contrast threshold) x 10. Results: The dynamic ranges were 11 and 13 dB for the tritan and red-green stimuli. Test-retest variability was dependent on depth of defect for the two chromatic stimuli (r>0.2, p<0.25) but not for the achromatic stimuli (r=0.01, p=0.46). Matched t-tests found that, on average, defect depths were similar for the red-green and luminance stimuli (t=0.5, p=0.30), and were slightly deeper for the luminance stimulus than for the tritan stimulus (t=4.2, p<0.0001). The relationship between defect depths for the luminance and tritan stimuli was dependent on mean defect (r=-0.42, p<0.0001). Discussion: The effort to increase the dynamic range for the chromatic stimuli by increasing the size of the stimulus and using tritan modulation were successful. However, this came at the cost of increased test-retest variability and decreased ability to detect glaucomatous defects. Conclusion: Equiluminant chromatic stimuli in CRT-based tests may not be clinically useful as perimetric stimuli, since increased dynamic range comes at the expense of increased test-retest variability and decreased ability to detect visual loss. Those findings further support the works of Hart (1988) and Sample et al. (2006).
    • Objective Assessment of Retinal Ganglion Cell Function in Glaucoma

      Joshi, Nabin (2017-09-25)
      Glaucoma refers to a group of diseases causing progressive degeneration of the retinal ganglion cells. It is a clinical diagnosis based on the evidence of structural damage of the optic nerve head with corresponding visual field loss. Structural damage is assessed by visualization of the optic nerve head (ONH) through various imaging and observational techniques, while the behavioral loss of sensitivity is assessed with an automated perimeter. However, given the subjective nature of visual field assessment in patients, visual function examination suffers from high variability as well as patient and operator- related biases. To overcome these drawbacks, past research has focused on the use of objective methods of quantifying retinal function in patients with glaucoma such as electroretinograms, visually evoked potentials, pupillometry etc. Electroretinograms are objective, non-invasive method of assessing retinal function, and careful manipulation of the visual input or stimulus can result in extraction of signals particular to select classes of the retinal cells, and photopic negative response (PhNR) is a component of ERG that reflects primarily the retinal ganglion cell function. On the other hand, pupillary response to light, measured objectively with a pupillometer, also indicates the functional state of the retina and the pupillary pathway. Hence, the study of both ERGs and pupillary response to light provide an objective avenue of research towards understanding the mechanisms of neurodegeneration in glaucoma, possibly affecting the clinical care of the patients in the long run.