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PubMed2005

Migrainous scintillating scotoma and headache is ocular in origin: A new hypothesis.

Brain neuronal dysfunction has been implicated in pathogenesis of migraine but direct evidence is lacking. Scintillating scotoma of migraine is generally believed to originate at the visual cortex. While cortical spreading depression is a relatively late physiological alteration in migraine, its protective role in neuronal ischaemia is increasingly being recognized. Atenolol, nadolol, or verapamil prevent migraine but do not readily cross the blood-brain barrier or critically influence any brain or peripheral neuronal function. Typical migraine headache, aura, or scintillating scotoma has not been reported following enucleation or evisceration of the eye. In humans, pain and temperature fibres from only the ophthalmic division of the trigeminal nerve reach the upper cervical spinal segments. Pain in migraine attacks including occipital and nuchal discomfort reflects selective involvement of the ophthalmic nerve. Photophobia is largely a retinal reflex involving the ophthalmic division of the trigeminal nerve. Key clinical features of the migrainous scintillating scotoma are consistent with retinal origin. Spreading depression in the retina is well-established. A subtle regional ocular sympathetic deficit prevails in migraine patients and possibly impairs regulation of intraocular choroidal blood volume and intraocular pressure. Several first-line migraine prophylactic agents lower the intraocular pressure. The neuro-ophthalmological basis for a monocular origin of migrainous scintillating scotomata due to mechanical deformation of the posterior segment of the corneo-scleral envelope consequent to choroidal venous congestion and rise in intraocular pressure is presented. Study of distribution and displaceability of the migrainous scintillating scotoma can settle its site of origin. Headache of migraine possibly arises from a similar mechanical deformation of the anterior eye segment followed by antidromic discharge in the trigeminovascular system. Lateralizing negative deficits such as homonymous hemianopia probably reflect vasospastic complications of migraine. A rational explanation for the most characteristic clinical features of migraine and a new template to elucidate the pharmacological basis of anti-migraine drugs is offered.

Eye↗
PubMed2004

Retinotopic mapping of the visual cortex using functional magnetic resonance imaging in a patient with central scotomas from atrophic macular degeneration.

PURPOSE: To describe retinotopic mapping of the visual cortex when a central scotoma is present. DESIGN: Single observational case report. METHODS: Scanning laser ophthalmoscope perimetry was used to define the site and stability of fixation and the area of dense scotoma. Functional magnetic resonance imaging of the visual cortex was performed while the patient viewed an expanding annular stimulus. RESULTS: Retinotopic mapping of the visual cortex for a patient with a horseshoe scotoma from geographic atrophy involving the macular region showed a loss of stimulation to the cortical areas representing the site of the atrophic lesion. CONCLUSIONS: Cortical retinotopic mapping can be performed successfully in patients with central scotomas from macular disease. This study can serve as a basis for the future investigation of cortical plasticity in visual cortex.

Brain Mapping↗
PubMed2005

Preferred retinal loci and macular scotoma characteristics in patients with age-related macular degeneration.

Many patients with macular scotomas due to age-related macular degeneration do not perceive black spots in the visual field where the scotomas are located. Rather, they describe objects as "vanishing," "jumping out of nowhere" or "having blurry parts," or a combination of features. In addition, when the macular scotoma affects the fovea, the visual system uses 1 or more preferred retinal loci (PRLs) as a "pseudofovea" to perform visual tasks. Visual function testing with the scanning laser ophthalmoscope has provided a wealth of information regarding how patients perceive the visual world and how the oculomotor system directs eye movements. This article describes 2 specific functions of the oculomotor system, fixation stability and refixation precision, with data collected from normally sighted people and patients with visual field loss. The implications of the characteristics of PRLs and macular scotomas for clinical testing are discussed.

Eye Movements↗
PubMed1999

Phosphenes and transient scotomas induced by magnetic stimulation of the occipital lobe: their topographic relationship.

Transcranial magnetic stimulation (TMS) of the visual cortex is known to induce phosphenes and is able to suppress visual perception. To address the topographic relationship of phosphenes and transient scotomas, the visual field of 10 normal subjects was investigated using a perimetric approach. The central visual field (diameter: 20 degrees) was tested at 32 sites. Perceptual thresholds were determined by presenting 1 ms test spots flashed with varying intensity in random order. TMS was applied with a focal figure-of-eight coil placed over the inion. All subjects perceived phosphenes, mostly restricted to one of the lower quadrants within the visual field. In 13 out of 15 investigations, a magnetic stimulus triggered 100 ms after the visual target resulted in a relative scotoma with threshold changes of 8 dB or more. In 9 of 13 investigations, scotomas coincided spatially with sketches of phosphenes made by subjects in a separate test. Scotomas covered only a small percentage of the total visual field, which may explain the failure of previous studies to find perceptual suppression with the focal coil. The present result demonstrates that phosphenes evoked during TMS can serve as a guide for optimal visual stimulus alignment in neuropsychological experiments.

Adult↗
PubMed2003

Scotoma size and reading speed in patients with subfoveal occult choroidal neovascularization in age-related macular degeneration.

PURPOSE: To investigate the correlation between reading speed and scotoma size in patients with subfoveal occult with no classic choroidal neovascularization (CNV) in age-related macular degeneration (AMD) participating at 2 of 28 centers in the Verteporfin in Photodynamic Therapy trial. DESIGN: Prospective, observational case series. PARTICIPANTS: Twenty-two eyes of 22 patients with occult with no classic CNV in AMD. METHODS: Patients' reading speed was examined using a German-language reading test (Radner Lesetest). Scotoma size was measured using the microperimetry program 2.01 of the Rodenstock Scanning Laser Ophthalmoscope. MAIN OUTCOME MEASURES: Reading acuity, reading speed, size of absolute (AS) and relative scotoma (RS). RESULTS: There was a significant correlation between the size of AS and reading speed (r = -0.48, P = 0.023), as well as AS and reading acuity (r = 0.52, P = 0.013). No correlation was seen between RS and reading speed or reading capacity. CONCLUSION: The size of absolute scotoma correlated significantly with reading capacity and reading speed and may influence these measures.

Aged↗
PubMed1999

Effects of cataract and scotoma on visual acuity: a simulation study.

Central field loss (CFL) and cataract both decrease visual acuity. For patients with CFL, visual acuity is further reduced when the acuity target is more visually complex. We tested visual acuity for targets of varying complexity (letters alone, letters flanked by one or two x's on each side, and words) in subjects with normal vision and in the presence of a simulated cataract, simulated scotoma, and their combination (scotoma + cataract). Visual acuity was best with normal vision and worst with scotoma + cataract for all of the acuity targets. There was little difference in visual acuity between the letters alone and flanked letters, and visual acuity was best for words under all vision conditions. The cataract had a greater impact on visual acuity when the subject's central visual field was clear (normal vision) than when it was occluded by the simulated scotoma.

Adult↗
PubMed1995

Adaptation to macular scotomas in persons with low vision.

Persons with scotomas in their central 20 degrees of vision often do not notice these blind spots within their visual field and have visual performance difficulties far exceeding what would be expected from standard vision tests. Before persons with macular scotomas can be assisted to optimally use their remaining vision for a better quality of life, more must be known about how the visual system adapts to a macular scotoma. Important issues include spatial and temporal characteristics of perceptual completion and metamorphopsia, development of preferred retinal loci for fixation and visual search, and dynamics of the preferred retinal locus development in terms of the changes in the eye movement system. With a full understanding of the visual system's adaptation to macular scotomas, new low vision devices and training techniques can be proposed to promote independence in activities of daily living for the person with low vision.

Activities of Daily Living↗
PubMedDate not supplied

A novel high-resolution kinetic method for visual field mapping of scotoma in age-related macular degeneration.

BACKGROUND AND OBJECTIVE: To examine a new high-resolution kinetic mapping method for scotoma in age-related macular degeneration. PATIENTS AND METHODS: A computer-based program for kinetic visual field mapping was tested in 10 healthy subjects and 14 patients with age-related macular degeneration and fixed preferred retinal locus. The stimulus was presented using a back projector on a screen located 40 cm from the subject. The findings were then compared with static results. RESULTS: Control group mapping revealed good congruency with the anatomic blind spot. Mapping of the 14 patients with age-related macular degeneration was rapid and revealed good accuracy. The average deviation of the mapping border from the anatomic scotoma border was no more than 3.1% of the scotoma radius. Static mapping of 7 of the patients with age-related macular degeneration was longer and revealed lower accuracy. CONCLUSIONS: The proposed method is more rapid, accurate, and consistent than static mapping. It allows accurate mapping of central scotoma with suprathreshold stimulus, and may be used in the future for detecting the early stages of age-related macular degeneration using subthreshold stimulus.

Adult↗
PubMed1988

Eccentric fixation with macular scotoma.

People with macular scotoma tend to read and visually scan more slowly than others with equivalently reduced visual acuity but intact central fields. We measured fixation eye movements and considered the contribution of fixation variability and centripetal eye drift to poor visual performance. These factors might confound efforts to consistently use an optimum retinal locus outside of the macula. We measured monocular horizontal and vertical eye movements using a search coil eyetracker while subjects with naturally occurring central scotomata or control subjects with simulated scotomata eccentrically fixated a single character that was sized to their visual acuity. Motivated subjects with long-standing stable maculopathies were chosen to estimate attainable performance limits. During attempts to eccentrically fixate, an ubiquitous foveal pursuit or centripetal drift tendency was not found; rather a pattern of drift was idiosyncratic from subject to subject. This finding was confirmed by an analysis of eye drift of 32 eyes with long-standing bilateral macular scotomata. Moreover, the eye drift speeds (15-200 minarc/sec) were too low to be of functional significance. Drift speeds during eccentric fixation with a visible target were not significantly different than those after the target was extinguished; however, drift speeds were greater than during foveal fixation. This suggests that the fovea has a specialized control of slow eye movements. Fixation variability increased with scotoma size for both simulated and real scotomata, with an abrupt rise when scotomata diameters exceeded 20 degrees C. A significant minority of subjects (39%) adopted two or more distinct preferred retinal loci (PRL) during fixation. Multiple PRL were also more likely if scotoma size exceeded 20 degrees C. Reasonably steady fixation is thus attainable when central scotoma sizes are smaller than approximately 20 degrees C.

Adult↗
PubMed1987

Reading with a macular scotoma. II. Retinal locus for scanning text.

To elucidate how patients with macular scotomas use residual functional retina for inspecting visual detail and reading, we tested three patients with dense macular scotomas using a scanning laser ophthalmoscope that allows an examiner to view and record stimuli on the retina while the patient views them. Using standard psychophysical techniques, we determined the retinal position of scotomas, the retinal areas used for fixating and inspecting acuity targets, and the retinal area used for reading simple, three-letter, nonsense syllables. We found that each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma, for fixating, inspecting acuity targets, and scanning simple, nonsense-syllable text. This preferred retinal locus (PRL) was at different retinal eccentricities (relative to the foveola) for each patient and was not always as close as possible to the foveola. There appears to be no simple rule by which patients "select" a particular PRL. Plots of text placement on the retina revealed considerable differences in patients' abilities to execute an orderly text scan. Two patients read text more rapidly with a novel retinal area than with their PRL, suggesting that the PRL may not be optimal for text reading.

Eye Movements↗
PubMed1995

Scotoma perception in white-noise-field campimetry and postchiasmal visual pathway lesions.

The authors examined 59 patients (32 women and 27 men) suffering from homonymous hemianopia by white-noise-field campimetry (Tübingen Electronic Campimeter) and by conventional perimetry (Tübingen Automatic Perimeter or Tübingen Manual Perimeter) and by computerized tomography (CT) or magnetic resonance imaging (MR). In all, 56 patients showed neuroradiologically detectable cerebral lesions, which were superimposed in a reconstructed "reference brain". Of these 56 patients, 18 were not capable of perceiving any white-noise-field scotoma, although their conventional perimetric findings showed defects. Lesions of these patients were concentrated along the optic radiation and spared the primary visual cortex. The lesions of the remaining 38 patients with scotoma detectable in both methods were accumulated in area V1, the primary visual cortex. The lesions of 6 patients, who had had persistent scotoma perception for more than 2 years, were situated at the occipital pole. The lesions of 8 patients with vanishing scotoma were concentrated in more rostral areas.

Adolescent↗
PubMed1986

[The blind spot: a critical review of the value of scanning perimetry in scotoma of known size].

Using programs 33 and 34 of the Octopus 2000 automated perimeter the field within 30 degrees was examined in 20 normal eyes: The blind spot was rarely missed (2 X), quite often interpreted as a relative scotoma (21 X), less frequently as a small absolute scotoma (7 X) or as an absolute plus relative scotoma (10 X). These findings are also valid for all scotomas of equal or of smaller size located elsewhere within the examined field.

Humans↗
PubMed1989

[Central physiologic relative scotoma after dark adaptation].

The paper describes data on conditions for appearance of a physiologic central retinal scotoma of dark adaptation. Examinations of 80 eyes with normal visual functions have shown that central scotoma of dark adaptation is revealed in conditions of scotopic illumination 20-25 minutes after dark adaptation. The optimal duration of dark adaptation is 40-45 minutes. More frequently scotoma is displaced upwards from the point of fixation, its sizes varying from 4 degrees to 10 degrees by the horizontal meridian and from 3 degrees to 8 degrees by the vertical meridian. The presence of this scotoma should be considered when examining the state of the visual analyser in conditions of scotopic illumination. This can play a certain role in differential diagnostics of clinical ophthalmopathology.

Adolescent↗
PubMed1987

Homonymous paracentral scotomas.

Of 230 patients with homonymous visual field defects of central origin, 3 had paracentral scotomas. All complained of severe photophobia and difficulty in reading. Two patients suspected that the scotoma had developed as a result of glare; the visual disorder resolved in these cases, but persisted in the third patient. With the exception of the visual field defect defined by perimetry, no neurological or neuropsychological deficit were found. The scotomas was attributed to generalized cerebral hypoxia in two cases but remained undefined in the third patient. A lesion in the striate region was suspected, but imaging procedures did not show any abnormalities.

Adult↗
PubMed1986

The rate of progression of scotomas in glaucoma.

We conducted a retrospective study of 45 eyes of 45 patients with chronic open-angle glaucoma to evaluate the rate of progression of scotomas. "Scotoma mass" was calculated and regressed on time to obtain the rate of visual field change. Twenty-two eyes (49%) showed a linear type of progression, nine (20%) showed a curvilinear progression, three (7%) showed episodic progression, and 11 (24%) showed no significant progression. The mean scotoma mass was significantly lower in the curvilinear group than in the linear group.

Adult↗
PubMed1993

Resolution of an absolute scotoma and improvement of relative scotomata after successful macular hole surgery.

Visual loss in eyes with full-thickness macular holes is thought to be caused by the absence of retinal function in the area of the neurosensory defect as well as reduction in retinal function in the surrounding area of neurosensory retinal detachment. To improve characterization of the visual function of eyes after successful macular hole surgery, we studied six eyes preoperatively and postoperatively with macular microperimetry using the scanning laser ophthalmoscope. Best-corrected visual acuity was improved postoperatively in all eyes. Microperimetry performed preoperatively demonstrated an absolute scotoma that corresponded to the neurosensory defect in all eyes, with surrounding concentric isopters of relative scotomata. No detectable absolute scotoma was found in any eye postoperatively. All eyes showed partial or complete resolution of the surrounding relative scotomata. Improvements in visual acuity after successful macular hole surgery may be related to disappearance of a detectable absolute scotoma as well as improvement in the surrounding retinal function.

Aged↗
PubMed1999

Compression of the prechiasmatic optic nerve produces a junctional scotoma.

PURPOSE: To demonstrate the clinical-radiologic correlation between a junctional scotoma and a focal lesion compressing the prechiasmatic segment of the distal optic nerve. METHODS: Case report involving a man with a pituitary adenoma. Clinical correlation was determined by reviewing visual field evaluations and magnetic resonance images. RESULTS: The tumor compressed the prechiasmatic segment of the distal optic nerve but not the optic chiasm, producing a junctional scotoma documented by Goldmann and automated perimetry. The visual field defect resolved after neurosurgical decompression of the anterior visual pathway. CONCLUSIONS: A junctional scotoma can be caused by focal as well as large and diffuse lesions injuring the anterior visual pathway, specifically at the junction of the optic nerve and chiasm. This finding supports the existence of Wilbrand fibers.

Adenoma↗
PubMed2003

Patients with AMD and a large absolute central scotoma can be trained successfully to use eccentric viewing, as demonstrated in a scanning laser ophthalmoscope.

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.

Aged↗