Use of high spatial resolution perimetry to identify scotomata not apparent with conventional perimetry in the nasal field of glaucomatous subjects.
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AIM: To examine whether high spatial resolution perimetry (HSRP) could identify fine scale scotomata which may not be apparent with conventional perimetry. The HSRP was performed in the nasal field, as this location is a recognised site for the early occurrence of glaucomatous defects. METHOD: 16 early glaucoma eyes, 17 glaucoma suspect eyes, and 20 age matched healthy control eyes underwent conventional automated perimetry using the 24-2 program of the Humphrey field analyser (HFA) and HSRP. The HSRP was performed in the nasal field by testing 9 x 9 degrees of 100 tested points separated by 1 degree and the results compared with the HFA 24-2 program. RESULTS: Mean HSRP thresholds were significantly abnormal in the suspect and glaucoma eyes, with elevated levels of asymmetry between the superior and inferior nasal field. Overall, 7/17 (41%) suspect eyes (95% confidence interval 5/17 (29%) to 7/17 (41%)) had nasal scotomata on HSRP, although their HFA 24-2 fields failed to identify any defects. In glaucomatous eyes, 15/16 (94%) eyes had HSRP scotomata (95% CI 14/16 (88%) to 15/16 (94%)). In 12 these coexisted with HFA 24-2 defects at the same location, while in three eyes only HSRP identified scotomata in the nasal field. CONCLUSION: HSRP can identify scotoma in glaucomatous eyes in the nasal field which may be missed with the lower spatial resolution of conventional perimetry. (+info)
Homonymous visual field defects and stroke in an older population.
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PURPOSE: The objective of the present study was to describe the prevalence of homonymous visual field defects in a defined older urban population and associations with self-reported stroke. METHODS: Homonymous visual field defects were assessed from screening automated visual field tests of both eyes in 3654 persons aged > or =49 years who were participating in the Blue Mountains Eye Study. This represented 82.4% of eligible residents from a defined area west of Sydney, Australia. A detailed eye examination was performed, and the medical history was taken. Masked grading of visual fields was used to classify the presence of homonymous visual field defects. RESULTS: Homonymous visual field defects were found in 25 persons (prevalence 0.8%, 95% CI 0.5% to 1.1%). Stroke history was reported by 194 participants (5.3%, 95% CI 4.6% to 6.1%). A strong relationship was found between homonymous visual field defects and history of stroke, age-, and sex-adjusted odds ratio (OR) 23.4 (95% CI 9.9 to 55.7). Homonymous field defects were present in 8.3% of all persons who reported experiencing a stroke. Among those with homonymous field defects, 52% reported a history of stroke. Only 2 of 10 persons (20%) with homonymous field defects without a history of stroke reported having stopped driving, whereas 6 of 9 (67%) reporting stroke had stopped driving (P=0.07). Increasing age (OR 1.4 per decade, 95% CI 1.2 to 1.8) was significantly associated with homonymous visual field defects, with adjustment for sex, whereas a history of hypertension (OR 2.7, 95% CI 1.2 to 6.1), diabetes (OR 2.1, 95% CI 1.4 to 3.2), and renal impairment (OR 2.8, 95% CI 1.0 to 8.1) also was associated, with adjustment for age and sex. CONCLUSIONS: This study provides accurate prevalence data for homonymous visual field defects in an older population. About half the participants did not report stroke. (+info)
Reading with multiple preferred retinal loci: implications for training a more efficient reading strategy.
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The reading strategies in individuals with central scotomas and more than one preferred retinal locus (PRL) were investigated using a scanning laser ophthalmoscope in order to understand the visual requirements that lead to the need to use more than one PRL during reading. It was found that: (1) PRL function can be deduced from variation in PRL usage for different size and length of isolated words; (2) each subject used two or more PRL to accomplish the functions of global viewing and discrimination, suggesting that these are two of the minimum requirements for reading; (3) reading strategies can change depending on the position of words in visual space; (4) line-changing strategies can revert to horizontal and vertical component movements. These findings have implications for improving reading performance through training in patients with central scotomas. (+info)
Junctional scotoma in giant cerebral aneurysm.
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A brain lesion located at the lateral side of the sella turcica can produce a junctional scotoma by compressing the ipsilateral optic nerve and the contralateral inferonasal nerve fiber. This study reports a female patient with a junctional scotoma caused by a cerebral aneurysm. At the initial visit, she complained of visual disturbance in both eyes and the right optic disc was atrophied. The visual field showed right blindness and left superotemporal quadrantopsia. A brain CT indicated an approximately 3 cm sized brain mass located superolateral to the sella turcica. The brain MRI showed the lesion to be more like an aneurysm than a pituitary adenoma. Therefore, 4 vessels angiography was done, and this lesion was confirmed to be a sellar variant of an aneurysm located at the right carotid siphon. Like a tumor of the optic chiasm, a cerebral aneurysm can cause visual disturbance and visual field defects. Therefore, an early differential diagnosis is important because the prognosis and treatment of an aneurysm differ. (+info)
Filling-in of retinal scotomas.
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In this study we examined the perception of one- and two-dimensional patterns across central retinal scotomas, caused by age-related macular degeneration. In contrast with previous studies of disrupted visual input that used the blind spot and artificial scotomas, the current study used large central scotomas caused by physical retinal damage. Such damage is associated with atrophy and long-term cortical reorganization, and it was therefore unclear whether perceptual completion in the damaged system will be similar to that reported for artificial scotomas and the blind spot. In addition, the scotomas under study were much larger and more central than artificial scotomas for which perceptual completion has been reported. For 1-D line and grating patterns, we found perceptual completion across large central scotomas (up to radius of 7 degrees ), which is significantly beyond the range of perceptual completion in artificial scotomas. Gratings completion was better than that of a single line, and increased with bars density. The use of central scotomas allowed us to test the completion of 2-D patterns that are difficult to study in peripheral vision. We found completion of two-dimensional dot arrays over large regions that improved with pattern density and regularity. The results show that in the physically damaged system the range of perceptual completion is increased compared with artificial scotomas, they strongly support the view of an active filling-in process rather than simply ignoring the damaged location, and they show that perceptual completion of physical scotomas is likely to involve cortical processing at multiple levels. We finally discuss implications of the results to the possible use of image enhancement techniques to facilitate the perception of low-vision individuals. (+info)
The fine structure of multifocal ERG topographies.
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The multifocal electroretinogram (mfERG) allows for functional field mapping by concurrently deriving responses from a large number of retinal locations. The stimulus resolution most commonly used consists of 103 hexagonal elements. Here, we stimulated with an array of 509 elements. To determine the extent to which the multifocal ERG shows anatomical and physiological details, such as shadows cast by the retinal vasculature, we obtained mfERGs from two subjects using two different stimulus luminance levels and three light spectra. Good correspondence of some depressions with major blood vessels suggests relative angioscotomata. However, some reproducible local depressions cannot be attributed to blood vessel shadows cast on the retina, but more likely reflect local inhomogeneities in the physiological response characteristics. (+info)
A precise retinotopic map of primate striate cortex generated from the representation of angioscotomas.
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Shadows cast by retinal blood vessels are represented in striate cortex of the squirrel monkey. Their pattern was exploited to generate a true retinotopic map of V1. For calibration, retinal landmarks were projected onto a tangent screen to measure their visual field location. Next, the retina was warped onto striate cortex, distorting it as necessary to match each retinal vessel to its cortical representation. Maps from four hemispheres of two normal adult squirrel monkeys were created and used to derive expressions for cortical magnification factor (M). A mean map was produced by averaging the individual maps. To address the controversial issue of whether the ratio of retinal ganglion cell (RGC) density to M is constant at all eccentricities, we stained a retinal whole mount from one of the two monkeys for Nissl substance. A ganglion cell density map was compiled by sampling the concentration of cells at 171 retinal points. Allowance was made for displaced amacrine cells and for the centripetal displacement of RGCs from central photoreceptors. After these corrections the V1 surface area and RGC density were compared at each eccentricity. The cortical representation of the macula was found to be amplified, even beyond the magnification expected from its high density of RGCs. For example, the central 4 degrees of visual field were allotted 27% of the surface area of V1 but were supplied by only 12% of RGCs. We conclude that, in monkey striate cortex, more tissue is allocated per ganglion cell for the analysis of information emanating from the macula as compared with the peripheral retina. (+info)
Patients with AMD and a large absolute central scotoma can be trained successfully to use eccentric viewing, as demonstrated in a scanning laser ophthalmoscope.
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Twenty patients with age-related macular degeneration, an absolute central scotoma and a mean visual acuity of 0.04 (20/475) were studied. A scanning laser ophthalmoscope (SLO) was used for microperimetry and determination of preferred retinal locus, often located to the left of the retinal lesion (corresponding to a location to the left of the visual field scotoma), which is considered unfavorable for reading. All 20 patients were trained to use a new and more favorable retinal locus for reading, above (or occasionally below) the retinal lesion (corresponding to a location below or above the visual field scotoma), first by reading scrolled text under simultaneous fixation monitoring and instruction in the SLO and then by reading printed text, using high magnification (mean 14.3x). For the 18 patients who learned to use eccentric viewing, reading speed with adequate magnification prior to training was 9.0+/-5.8 words/min. With training (mean 5.2 hours), it increased significantly (p<0.001) to 68.3+/-19.4 words per min. Training of eccentric reading has thus proved to be very successful. (+info)