Abstract
Abstract: :
Purpose:To characterize microperimetry as a clinical visual function assessment tool. Microperimetry (µιΚρoν–περι–µετρoν) by definition aims to measure on a high resolution scale the functional characteristics of visual space using the retina as a fiducial reference. This form of perimetry is the latest and most advanced of several "fundus perimetry" techniques that have been developed since the projecting ophthalmoscope of Trantas in the late 1950s, followed by indirect projection methods of a visual field onto the fundus image, and the use of modified fundus cameras. Methods:To project visual stimuli onto the retina, microperimetry employs either a liquid crystal spatial light modulator, CCD spatially resolved imaging and incoherent light sources or an acousto–optic modulation of a scanning Gaussian visible laser beam with an avalanche photodiode for temporally resolved imaging. The common and defining feature of both approaches though is a robust two–dimensional normalized gray–scaling correlation algorithm, in real–time at video–rates, to correct for eye movements. A near infra–red wavelength is used for imaging. Typical measurements include light sensitivity, acuity and retinal locus of fixation mapping. Highly efficient AFC and PEST–like algorithms are used for this purpose. Results:Microperimetry is useful for measuring the visual functioning of visible lesions on the retina as well as obtaining a high resolution representation of the loss pattern in visual space unrelated to fundus appearance, e.g. in the case of neuro–ophthalmological and glaucomatous field disturbances. Significant findings so far have had a bearing on low vision rehabilitation and different laser treatment strategies for macular diseases. Conclusions:At present however, a better understanding of the proper choice of background intensity for each clinical situation is needed. Also, normal range values are still not available for the dark–adapted zero background absolute threshold measurements for different wavelengths.
Keywords: perimetry • visual fields • visual acuity