Effect of localized defocus on detection thresholds for different sized targets in the fovea and periphery

Abstract

ABSTRACT.Purpose: Previous studies of optical blur in perimetry have measured the effect of foveal refractive error on peripheral perimetric detection thresholds. Since peripheral refractive error can be significantly different from that of the fovea we wished to remove the ambiguity of previous results by correcting the actual peripheral refractive error first before adding blur. Methods: We measured detection thresholds in the fovea and at 30 degrees in the horizontal temporal field in two trained observers. Peripheral refractive error was determined at each location and thresholds measured at the same locations for stimuli ranging in size from 0.2 to 6.4 degrees and refractive errors between ∫4.00 diopters. Results: Foveal thresholds increased immediately with increasing refractive error, particularly for smaller stimulus sizes. At 30 degrees, thresholds for smaller stimuli were less affected by defocus initially and then increased more sharply. Larger stimuli were relatively unaffected by defocus such that when stimulus size reached 1.6 degrees there was little or no increase in threshold for refractive error between ∫4.00 diopters. Conclusions: Peripheral refractive error, largely forgotten by perimetrists, has a significant effect on performance, particularly for smaller stimuli. Differences in foveal vs peripheral viewing can be explained by differences in ganglion cell receptive field sizes.

Choice of Stimulus Range and Size Can Reduce Test-Retest Variability in Glaucomatous Visual Field Defects

“…Furthermore, modeling of neural processes indicates that edges may be important for detection of Goldmann stimuli, 46 and modeling of geometrical optics indicates that peripheral defocus can reduce perimetric sensitivity when stimuli have sharp edges. 31 Similarly, the size V stimulus is large enough to be resistant to effects of blur, 47 so with a suitable floor it may give results similar to the fixed blob. Further research is needed to determine whether smooth edges reduce variability for larger hard-edged stimuli such as the size V stimulus.…”

Factors That Influence Standard Automated Perimetry Test Results in Glaucoma: Test Reliability, Technician Experience, Time of Day, and Season

“…Proper instructions, 4 correct refraction, 3,5 and ensuring optimal conditions contribute to reliable test results, whereas supervision plays only a minor role. [24][25][26] As far as we know, no publications exist that examined the association between the degree of experience of technicians and the test result.…”

“…1,2 Other factors are patient motivation and technician performance, the latter via appropriateness of refraction and patient instruction, reassurance before the test, and patient monitoring during the test. [3][4][5] Circadian rhythms and seasonal influences may also contribute to the variability. These periodicities may influence SAP test results in at least two different ways.…”

Sign-Dependent Sensitivity to Peripheral Defocus for Myopes due to Aberrations

“…[8][9][10][11] Whether there are neural or optical factors that limit peripheral vision is dependent on the type of psychophysical task; detection and low-contrast resolution are optically limited, whereas highcontrast resolution is neurally limited. [12][13][14] The image quality on the peripheral retina has been proposed to influence the development of myopia. [15][16][17] One difference between myopes and emmetropes lies in the relative peripheral refraction (RPR), defined as the difference between peripheral and foveal refraction; emmetropes generally have a myopic RPR, whereas myopes tend to have a hyperopic RPR.…”