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At least 19 recordsLinked to original sources
PubMed1986

Reading with a macular scotoma. I. Retinal location of scotoma and fixation area.

To investigate how patients with macular scotomas use residual functional retinal areas to inspect visual detail, a scanning laser ophthalmoscope (SLO) was used to map the retinal locations of scotomas and areas used to fixate. Three patients with dense macular scotomas of at least 20 months duration and with no explicit low vision training were tested. SLO stimuli were produced by computer modulation of the scanned laser beam, and could be placed on known retinal loci by direct observation of the retina on a television monitor. Videotaped SLO images were analyzed to produce retinal maps that are corrected for shifts of stimulus position due to fixational eye movement, thus showing the true retinal locations of scotomas and fixation loci. Major findings were as follows: 1) each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma to fixate, and did not attempt to use the nonfunctional foveola, 2) fixation stability with the eccentric fixation locus was as good as, or better than, that of ocularly normal subjects trying to fixate at comparable eccentricities, 3) fixation stability was not systematically related to clinical visual acuity, and 4) there is good agreement as to the shape and overall size of SLO and standard clinical tangent screen scotoma maps for these three patients.

Adult↗
PubMed2001

Scotoma and fixation patterns using scanning laser ophthalmoscope microperimetry in patients with macular dystrophy.

PURPOSE: We used scanning laser ophthalmoscope microperimetry to evaluate the retinal scotoma and the fixation points in the patients with macular dystrophy. METHODS: We studied 10 eyes of five patients with macular dystrophy (three patients with cone dystrophy and two patients with Stargardt disease). The mean patient age was 37 years (range, 13 to 64 years). An estimation of scotoma and fixation points on the retina was performed using scanning laser ophthalmoscope microperimetry. RESULTS: All 10 eyes (100%) had one of two types of dense scotoma: type one was a dense ring scotoma (five eyes, 50%), and type two was a dense central scotoma (five eyes, 50%) that included the center of the fovea. In all eyes with a dense ring scotoma, the fixation points were stable and did not shift. In all eyes with a dense central scotoma, the fixation shifted. The logarithm of minimal angle of resolution of the visual acuity in the eyes with the dense central scotoma was significantly worse than that of eyes with the dense ring scotoma type (P =.005). CONCLUSIONS: Scanning laser ophthalmoscope microperimetry findings demonstrate two types of dense scotoma (dense ring scotoma and dense central scotoma) in the patients with macular dystrophy. The two types of dense scotoma affect the shifting of the fixation points and the stability of fixation and may result in the difference in visual acuity in the patients with macular dystrophy.

Adolescent↗
PubMed1994

Effect of experimental scotoma size and shape on the binocular and monocular pattern visual evoked potential.

A small experimental, central scotoma significantly attenuates the human pattern visual evoked potential. The steady-state pattern visual evoked potential was recorded from seven visually normal adults who viewed a reversing checkerboard with 24' checks and a central scotoma that varied in size and shape. We found that square scotomas had to be at least 3 x 3 degrees to significantly (p < 0.05) attenuate the pattern visual evoked potential. Receptor density has been shown to be greater along the horizontal meridian than the vertical meridian. We hypothesized that this results in greater cortical representation of the horizontal meridian than the vertical meridian and, therefore, the pattern visual evoked potential might be significantly attenuated by a smaller rectangular scotoma oriented along the horizontal meridian than along the vertical meridian. One dimension of the rectangular scotoma was fixed at either 1 degree or 3 degrees, while the other dimension was varied from 1 degree to 8 degrees. The threshold scotoma size that significantly (p < 0.05) attenuated the pattern visual evoked potential was a horizontal scotoma subtending 1 x 4 degrees and a vertical scotoma subtending 5 x 1 degree (vertical x horizontal). Meridional differences in cortical representation were not apparent to the larger scotoma series in which the fixed dimension subtended 3 degrees (3 x 2 degrees and 2 x 3 degrees). Further analysis of the data revealed that the apparent meridional difference for the 1 degree scotoma series was a function of data variability. The determinant of the PVEP amplitude was scotoma area, not orientation. Monocular and binocular threshold scotoma sizes were the same, which could be due to the level of binocular summation demonstrated by our subjects.

Adult↗
PubMed2003

Filling-in of retinal scotomas.

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.

Aged↗
PubMed1997

Preferred retinal loci relationship to macular scotomas in a low-vision population.

PURPOSE: The authors identified patterns in preferred retinal locus (PRL) ability and location relative to macular scotomas in a low-vision patient population. METHODS: Scanning laser ophthalmoscope macular perimetry and PRL testing were performed on 825 patients with low vision. The PRL location was determined, and a PRL scoring system was devised and used to measure the pursuit ability, fixation stability, and saccadic ability of the PRL. The characteristics of dense scotomas within 2.5 degrees of the PRL were noted. RESULTS: Eighty-four percent (1130 of 1339 eyes) of the eyes had an established PRL. Preferred retinal loci varied across the full range of ability scores and varied in size for fixation stability from 1.0 degrees to 9.0 degrees in diameter. There was a central dense scotoma in 82.5% of the eyes, whereas 8.4% had a paracentral dense scotoma. In 14.8% of the eyes, the PRL had no dense scotomas on any of its borders; one, two, three, or four (a ring) borders had a dense scotoma in 39.7%, 19.0%, 9.0%, and 17.4% of eyes, respectively. When the PRL had only one scotomatous border, the resulting field defect was located superior in 39.0%, right in 33.7%, left in 19.9%, and inferior in 7.5% of eyes. CONCLUSIONS: The majority of patients with low vision, as many as four of five patients, have dense scotomas encumbering the PRL for visual tasks. Approximately one of six patients with low vision have the PRL completely surrounded by dense scotomas. The visual system shows a strong tendency not to place a PRL anatomically above a scotoma (field defect below fixation) and a weaker tendency not to place the PRL anatomically to the right of a scotoma (field defect to the left of fixation). Macular perimetry and PRL evaluations can provide considerable information on the functional status of the macula, which may be useful to rehabilitation professionals.

Humans↗
PubMed1999

Relative locations of macular scotomas near the PRL: effect on low vision reading.

Patients referred for low vision rehabilitation had Minnesota Reading Acuity (MNRead), visual acuity (VA), and scanning laser ophthalmoscope (SLO) macular function testing performed in their initial evaluation to determine whether dense macular scotomas near the preferred retinal locus (PRL) have a significant effect on the characteristics of reading based on rate. The 99 subjects had macular scotoma characteristics relative to the fovea/PRL of: 22% only to the right; 15% only to the left; 26% both the right and left; 19% above or below; 17% had no dense scotomas. Reading performance (maximum reading speed, critical print size, and reading acuity) was significantly different between the non-scotoma group and all of the scotoma groups. There was no statistically significant difference in the characteristics of reading based on rate between the four scotoma groups: within each there was a wide variation in the characteristics of reading based on rate not fully explained by either VA or scotoma location. The position of the scotoma relative to the PRL was not a statistically significant factor in determining reading rate as found in studies on normally sighted people with artificial scotomas. Other factors (e.g., maybe PRL ability in fixation and saccadic eye movements and/or cognitive ability) are significantly involved in determining reading rate characteristics in people with macular scotomas.

Humans↗
PubMed1996

Fixation patterns and reading rates in eyes with central scotomas from advanced atrophic age-related macular degeneration and Stargardt disease.

PURPOSE: To study fixation patterns and reading rates in eyes with central scotomas from geographic atrophy (GA) of age-related macular degeneration and to compare fixation patterns with those of patients with Stargardt disease. METHODS: Scanning laser ophthalmoscope analysis of fixation patterns in eyes with 20/80 to 20/200 visual acuity. Included were 41 eyes of 35 patients with GA and 10 eyes of 5 patients with Stargardt disease. The patients with GA also were tested for maximum reading rate, and the size of the areas of atrophy were measured by fundus photograph analysis. RESULTS: Sixty-three percent of GA eyes fixating outside the atrophy placed the scotoma to the right of fixation in visual field space, 22% placed the scotoma above fixation, and 15% placed it to the left, regardless of the laterality of the GA eye. Fixation was stable in subsequent years of testing for scotoma placement to the right of or above fixation. All GA eyes fixated immediately adjacent to the atrophy. In contrast, seven of ten eyes with Stargardt disease fixated at a considerable distance from the scotoma border, with the dense scotoma far above the fixation site in visual field space. For the patients with GA, the maximum reading rate was highly correlated with size of the atrophic area, but not with age or visual acuity within the limited visual acuity range tested. There was a trend to more rapid reading with the scotoma above fixation and slower reading with the scotoma to the left. CONCLUSION: There is a preference for fixation with the scotoma to the right in eyes with GA. Patients with Stargardt disease use different strategies for fixation, perhaps due to subclinical pathology adjacent to the atrophic regions. The size of the atrophic area in GA plays the predominant role in reading rate for eyes that have already lost foveal vision.

Adolescent↗
PubMed2002

Optokinetic nystagmus elicited by filling-in in adults with central scotoma.

PURPOSE: Filling-in is the perceptual completion of physiological, pathologic, or artificial scotomas. Three patients are described, in whom optokinetic nystagmus (OKN) was present during filling-in. METHODS: Three patients with age-related macular degeneration with large central scotomas were included in the study. OKN was elicited with black and white stripes moving nasally to temporally or temporally to nasally at four velocities. OKN gain was measured using infrared oculography. RESULTS: While looking at the OKN stimuli, the patients either did not see the stimulus (without perceiving a positive scotoma) or filled in the scotoma and perceived the stripes. Simultaneously with filling in the scotoma, OKN eye movements were elicited in all three patients. The filling-in phenomenon was present for all stimulus directions and velocities, appeared within seconds, and was followed immediately by eye movements corresponding to OKN. OKN gains during filling-in were similar to those of age-matched control subjects without scotomas. No asymmetry was noted between temporal to nasal or nasal to temporal stimulation. CONCLUSIONS: Motion-sensitive areas of the visual cortex may be activated and trigger the generation of OKN, supporting an active process. Alternatively, OKN is suppressed when subjects are not filling-in, while the subjects are fixating the central scotoma or edges of the scotoma. That the subjects did not perceive positive scotomas suggests that an active process is more likely.

Aged↗
PubMed2006

Prediction of future scotoma on conventional automated static perimetry using frequency doubling technology perimetry.

AIM: To see if scotoma detected with frequency doubling technology (FDT) is confirmed by Humphrey field analyser (HFA) 3 years later. METHODS: Subjects were first examined with the screening C-20-1 program of FDT. The visual field was examined annually for 4 years using HFA program C30-2. The central 58 test points in HFA were assigned to one of the 17 clusters corresponding to FDT test points. Each cluster was represented as the lowest probability symbol of total deviation (TD) of the HFA test points included in the cluster. Clusters were graded normal, suspected scotoma, and scotoma depending on probability of TD-5% or more, 5%-1%, less than 1%, respectively. Relative risk (RR) of abnormality on FDT for future scotoma on HFA was estimated. RESULTS: 80 eyes of 42 patients were followed up for 4 years. While 4.0% of normal clusters of HFA with normal FDT results developed into scotoma cluster, 20.8% of normal clusters with abnormal FDT results developed into scotoma cluster with HFA at the third year. RR for future scotoma was 5.24 (95% CI, 2.75 to 10.0, p<0.05). CONCLUSION: An abnormal result in FDT shows a high risk of future scotoma on HFA after 3 years even if the original HFA perimetry showed normal results.

Adult↗
PubMed2004

Development of a viewing strategy during adaptation to an artificial central scotoma.

Although many individuals with a central scotoma develop eccentric fixation most often beneath or left of the scotoma, little is known about how they come to develop a particular viewing strategy. We investigated this by asking eight subjects with normal vision to read isolated letters, words and text passages while an artificial scotoma covered a central portion of the visual field. We quantified viewing strategy and analysed changes in their viewing behaviour over 8-10 sessions within a two-week period. Subjects read while either a horizontal (n=4) or vertical bar scotoma (n=4), 10 degrees wide, covered the entire horizontal or vertical meridian of the stimulus field. For the horizontal scotoma group: (1) there was an increasing preference to use the inferior visual field for isolated letters/words and text passages, which was essentially complete within the test period; (2) the superior visual field was preferred when reading letters/words initially presented in upper visual space and the inferior visual field when reading letters/words initially presented in lower visual space; (3) in general, variation in viewing strategy according to stimulus position diminished over the sessions for all stimuli. For the vertical scotoma group: (1) two subjects used the left and right visual fields in approximately equal proportion to view isolated letters/words, one subject showed a weak preference to use the left visual field and one subject developed a strong preference for using the right visual field; (2) the text passages could be read with combined use of left and right visual fields in a specific manner; (3) the left visual field was preferred to view stimuli initially presented in left visual space while the right visual field was preferred for words initially presented in right visual space. This effect diminished across sessions. Overall, these findings indicate that (1) a specific viewing strategy can be developed through as little as 5 hours of reading experience without guided training; (2) two distinctly separate retinal areas can be used in an integrated manner during reading; (4) stimulus position in visual space can influence viewing strategy; (5) in general, reading encourages a preference for the inferior over the superior visual field, but not the left over right visual field. Letter/word/text recognition and reading speeds increased progressively across sessions, even after scotoma lateralisation appeared stabilised suggesting that multiple mechanism are involved in adaptive changes.

Adaptation, Physiological↗
PubMed2006

Eye-movement responses to disparity vergence stimuli with artificial monocular scotomas.

The effects of artificial monocular scotomas on eye-movement responses to horizontal disparity vergence stimuli were studied in six subjects with normal binocular vision. Subjects viewed stereoscopic 1.5 degrees horizontal step disparity vergence stimuli through liquid crystal shutter glasses. The central portion of the stimulus presented to the right eye was removed to simulate monocular artificial scotomas of variable diameters (2 degrees to 10 degrees ). Eye movements were recorded with a binocular head-mounted eye tracker. Responses included pure vergence, vergence followed by saccades, and pure saccadic eye movements. The rate of responses with saccadic eye movements increased with the diameter of the artificial scotoma (p < 0.0001); there was an increase in the rate of responses starting with saccades (p < 0.0001), as well as an increase in the rate of saccades after initial vergence responses (p < 0.01). The probability of saccades after initial vergence responses was affected by the open-loop gain of the vergence response (p < 0.001). The open-loop gain decreased with increased diameters of the artificial scotomas (p < 0.0001). As the diameter of the artificial scotomas increased, the amplitude of the initial vergence eye-movement responses decreased, and the prevalence of saccadic eye movements and asymmetric vergence increased. The effects of the diameter of artificial monocular scotomas on eye-movement responses in subjects with normal binocular vision are consistent with the effects of diameter of suppression scotomas on eye-movement responses to disparity vergence stimuli in patients with infantile esotropia.

Adolescent↗
PubMed1999

The "thin man" phenomenon: a sign of cortical plasticity following inferior homonymous paracentral scotomas.

AIM: To investigate an image distortion, experienced by patients with homonymous paracentral scotomas. METHODS: Two consecutive patients with right inferior homonymous paracentral scotomas resulting from ischaemic brain insults were examined. Neuro-ophthalmological examination included tangent screen and Amsler grid evaluation. In addition, the patients were asked to describe a figure showing two vertical lines, identical in length and symmetrically located on either side of a fixation point. This figure was presented in such a way that when the subject looked at the fixation point the right line crossed the scotoma. Finally, the patients were asked whether, when looking at the face of an interlocutor, both sides of the body looked the same. RESULTS: In both patients field defects were markedly smaller when delineated with Amsler grids than using a tangent screen. With the parallel line test, the right line appeared uninterrupted in patient 1, whereas in patient 2 it looked slightly blurred in a two degree long segment corresponding to the middle of the scotoma. To both subjects the right line appeared shorter than the left line. Finally both subjects indicated that, after steadily fixating their interlocutor's face or neck for 5-10 seconds, the left shoulder appeared narrower than the right one, which made him look surprisingly thin. This perceptual alteration was called the "thin man" phenomenon. CONCLUSIONS: Paracentral homonymous scotomas can be associated with perceptual completion and shape distortion, owing to apparent displacement of images adjacent to the scotoma towards the field defect. Occurrence of such a perceptual change should alert one to the possibility of paracentral homonymous scotomas, which often go undetected when using routine visual field testing procedures.

Brain Ischemia↗
PubMed1988

The effect of simulated scotomas on visual search in normal subjects.

A simulated scotoma was stabilized on the fovea of 23 normal human subjects while they searched for acuity targets in arrays of non-targets. Search time doubled with a 20 min arc scotoma, and eye fixation duration increased by about 15% when compared to no-scotoma control conditions. Search difficulty was graded by adjusting acuity target size, search element density and contrast. Search time and eye fixation duration generally increased with display difficulty in no-scotoma conditions. Results are discussed in terms of sensory loss and motor disruption due to the simulated scotoma. The simulated scotoma method may be useful in studying adaptation to visual field loss in patient populations where the size, position and severity of the scotoma can be controlled.

Adolescent↗
PubMed1985

Horizontal fusional responses to stimuli containing artificial scotomas.

Horizontal fusional responses were studied with stimuli containing binocular or monocular, artificial, stabilized, scotomas. Binocular scotomas of 5-deg, 10-deg, and 15-deg diameters were utilized. The fusional responses to scotomatic stimuli were compared with full-field stimulus responses. All responses contained significant motor and nonmotor (sensory) components. Overall motor compensation to stimuli with 10-deg and 15-deg scotomas was reduced, while the overall motor compensation to stimuli with 5-deg scotomas was not. With full-field stimuli and with stimuli containing binocular scotomas, the changes in the two eyes' lines of sight were often asymmetric in response to symmetric disparity changes. This response asymmetry was exacerbated by the presence of monocular scotomas. Fixation was less steady with stimuli containing 10-deg or 15-deg binocular scotomas than it was in response to full-field stimulation. The fusional responses to annular stimuli were similar to those elicited by scotomatic stimuli.

Convergence, Ocular↗
PubMed2005

Central scotoma associated with intraocular silicone oil tamponade develops before oil removal.

BACKGROUND: Unexplained sudden visual loss after removal of silicone oil from the eye has recently been described. We report the occurrence and features of unexplained central scotoma developing with silicone oil in situ in the vitreous cavity. METHODS: A retrospective case series of five patients (from two centres) who reported a central scotoma commencing during silicone oil tamponade was studied. All patients had vitrectomy for macula-on retinal detachment, with ultra-purified silicone oil tamponade (four out of five had giant retinal tear). Investigations included visual acuity, intraocular pressure, optical coherence tomography, fluorescein angiography, visual fields and electrophysiology. RESULTS: All patients reported a central scotoma that appeared during oil tamponade. Visual acuity fell by a mean of 0.93 LogMAR units after onset of the scotoma. After cataract extraction and oil removal, vision remained reduced by a mean of 0.8 units. The mean duration of oil in the eye was 2.7 months when the scotoma was noted by the patient. Investigations were performed after removal of oil. Fluorescein angiography (FFA) was performed in two cases and optical coherence tomography (OCT) in five patients. No abnormality was demonstrated. Electrophysiology was performed in five patients with pattern electroretinography suggestive of macular dysfunction in four patients. CONCLUSION: This is the first case series describing central scotoma associated with silicone oil in situ. Electrophysiology indicated macular dysfunction in most cases. We suggest that early removal of oil in cases with good visual potential should be considered to avoid this sight-threatening complication.

Adult↗
PubMed1999

The effects of simulated cataract on reading with normal vision and simulated central scotoma.

Reading rates are slower for persons with low vision than for normally-sighted persons. This study investigated the change in reading performance and reading eye movements when we simulated the two most common causes of low vision--central field loss and cataract--and their combination (scotoma + cataract). Three subjects read sentences with each of these simulated impairments at five different letter sizes. They required larger letters to read with the cataract or scotoma than they did with normal vision, and larger still to read with scotoma + cataract; the change in eye movements relative to normal vision was similar across conditions. When reading large letters (1.61 degrees), the cataract had almost no effect, while the scotoma and scotoma + cataract reduced reading rate for two of the subjects. The cataract had a greater impact on performance relative to normal vision for these same two subjects, while for the third subject the cataract had a greater impact with the scotoma in place. Cataract extraction tends to be postponed in patients with central field loss because it is not perceived to be beneficial. The findings from this study, as well as others, suggest that patients with central field loss would benefit from cataract extraction.

Adult↗
PubMed2002

Association of preoperative photoreceptor displacement and improved central scotoma after idiopathic macular hole surgery.

OBJECTIVE: To investigate the relationship between preoperative photoreceptor displacement and postoperative scotoma after unilateral idiopathic macular hole surgery. DESIGN: Prospective nonrandomized comparative self-controlled trial. PARTICIPANTS: Twenty patients who underwent successful surgery for unilateral idiopathic macular hole participated in the study. METHODS: Kinetic perimetry using red and green filter glasses, black binocular fixation targets, and red and green selective monocular stimuli was performed preoperatively. Scanning laser ophthalmoscope (SLO) microperimetry was performed preoperatively and postoperatively. RESULTS: Sixteen patients had photoreceptor displacement preoperatively. In preoperative SLO microperimetry, all eyes with a macular hole had a scotoma; postoperatively, 12 of 16 had no scotoma. All four eyes with no preoperative photoreceptor displacement were noted to have a postoperative scotoma. The prevalence of postoperative scotoma in patients with preoperative photoreceptor displacement (4 of 16; 25%) was significantly lower than that in patients without preoperative photoreceptor displacement (4 of 4; 100%) (P = 0.03). CONCLUSIONS: The presence or absence of photoreceptor displacement preoperatively should affect postsurgical visual function. Photoreceptor damage may occur in eyes without photoreceptor displacement preoperatively, resulting in scotoma postoperatively.

Aged↗