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Perceptual Impairments
Published in Julie A. Jacko, The Human–Computer Interaction Handbook, 2012
Julie A. Jacko, V. Kathlene Leonard, Molly A. McClellan, Ingrid U. Scott
Visual field is classically defined as a three-dimensional graphic representation of differential light sensitivity at different positions in space. Perimetry refers to the clinical assessment of the visual field. Typically, visual field is assessed with kinetic or static perimetry. During kinetic perimetry, a test object of fixed intensity is moved along several meridians toward fixation and points where the object is first perceived are plotted in a circle. During static perimetry, a stationary test object is increased in intensity from below threshold until perceived by the patient, and threshold values yield a graphic profile section. While peripheral visual field loss often produces difficulty for patients in orientation and mobility functions, macular field loss (either centrally or paracentrally) often causes difficulties with reading. For instance, the presence of central or paracentral visual field loss is a more powerful predictor of reading speed than is visual acuity (Fletcher et al. 1994).
Introduction
Published in Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza, Computer-Aided Glaucoma Diagnosis System, 2020
Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza
Visual field testing (perimetry) is a test that measures the patient’s vision. The patient will look straight ahead at a small light and will then be asked to tell the examiner when he sees a light flash to the side of his peripheral vision.
Glaucoma Detection Using Optical Coherence Tomography Images: A Systematic Review of Clinical and Automated Studies
Published in IETE Journal of Research, 2022
Hina Raja, Muhammad Usman Akram, Taimur Hassan, Aneeqa Ramzan, Amtual Aziz, Hira Raja
Time domain OCT technology has some limitations such as slow scanning speed and low resolution. Spectral domain OCT has high scan acquisition speed and resolution, thus achieving improved accuracy and reproduction. Spectral domain OCT provides a topographical evaluation of the optic nerve head: it also includes the cup, neuroretinal rim, optic disc area, and volume. There are various studies that scrutinized the accuracy of spectral domain OCT and diagnostic power for the detection of glaucoma. Gracitelli et al. [28] presented a review of the state of the art literature and determined the accuracy of glaucoma detection by SD-OCT. This work highlighted the clinical usage and limitation of SD-OCT. The image quality is of essential importance it can be degraded by artifacts such as media opacities, eye movements, and failure of the segmentation algorithm. The degradation of image quality may have led to spurious layers’ thicknesses. It has been reported that topographic optic disc parameters acquired by SD-OCT may be less effective in classifying glaucoma in subjects with high myopia. Thickness map of RNFL, macular and ONH obtained by SD-OCT has been proven discriminating parameters for diagnosing glaucoma and also for enumerating risk in glaucoma suspects. It was concluded that perimetry along with the SD-OCT measurements may be advantageous to detect retinal loss and deterioration glaucoma. Figure 4 demonstrates the RNFL thickness map that helps in glaucoma diagnosis; it was also revealed that SD-OCT exposes the defects better than the fundus image.
Conceptual design considerations for a wireless intraocular pressure sensor system for effective glaucoma management
Published in Journal of Medical Engineering & Technology, 2019
Wolfgang Fink, Shaun Brown, Andres Nuncio Zuniga, Eui-Hyeok Yang, Thomas George
Using visual field loss as an indicator for glaucoma is largely inadequate in testing for and diagnosing glaucoma, since an impairment or decrease in one’s visual field is an indicator that irreversible glaucomatous damage to the eye has already occurred without the possibility for recovery. Preceding visual field loss, retinal ganglion cell atrophy and optic nerve fibre reduction are clinically detected in individuals who exhibit normal visual fields as assessed by perimetry [11], i.e., irreversible damage to the eye occurs before perimetry can psychophysically confirm the presence of visual field loss. Potential earlier detection of the onset of visual field loss in ocular hypertensives has been reported using a threshold Amsler Grid testing technology [12]. Moreover, it has been concluded that 40% to 50% of nerve fibres subject to glaucomatous atrophy can be lost in the absence of visual field defects [13,14]. Nevertheless, measuring IOP before observing the deleterious effects of its elevation reduces the potential for ocular damage in individuals with glaucoma, and allows for earlier treatment with improved clinical outcomes.