Scotoma Size Research Articles

Evaluation of functional defects in branch retinal vein occlusion before and after laser treatment with scanning laser perimetry

Objective This study was aimed at localizing and quantifying retinal defects in patients with branch retinal vein occlusion by means of scanning laser perimetry and analyzing the mechanism involved in the functional recovery after laser therapy. Design Prospective nonrandomized clinical trial with concurrent comparison group. Participants Fifty-eight patients with isolated branch retinal vein occlusion. Thirty-nine eyes received laser treatment; 19 eyes were observed without treatment. Intervention Argon laser photocoagulation was performed according to the Branch Vein Occlusion Study recommendations. Main outcome measures Retinal functional deficits were evaluated with scanning laser perimetry and fluorescein angiography first at baseline, at 3-month follow-up visits and 3 months after laser treatment. Results After laser treatment, the scotoma encroached on foveal fixation in 31% of eyes, remained stable in 36%, and regressed from the foveal avascular zone in 33%. Improvement in vision was correlated with increasing scotoma distance from fixation. Total scotoma size increased in 50% of eyes after treatment. Depth of scotoma and degree of angiographic leakage showed no direct correlation. Conclusions Stabilization and increase in visual acuity after laser treatment did not correlate with an overall decrease in scotoma size. Improved central visual function seen in 25% of treated eyes appeared to be due to withdrawal of scotoma from the fovea.

Micro-perimetric documentation of retinal function in photodynamic therapy of choroid neovascularizations

Photodynamic therapy provides occlusion of choroidal neovascularization by intravascular endothelial damage. The photodynamic approach offers the potential to occlude choroidal neovascularization selectively without altering adjacent sensory retina and therefore to preserve visual acuity. To determine the selectivity of photodynamic therapy photoreceptor function was measured by microperimetry allowing topic mapping of retinal function. A Rodenstock scanning laser ophthalmoscope was used to document preservation of central visual fields before and after photodynamic therapy. Single photodynamic therapy without known efficient parameters was performed in 13 patients and repeated photodynamic therapy using optimised light doses was performed in 10 patients with subfoveal choroidal neovascularization using benzoporphyrin derivate (verteporfin). Intensity and dimension of central scotomas were measured, using a grading system of stimuli ranging from 0-32 dB. Areas of absolute and relative defect were defined and fixation localisation was monitored. Perimetric testing was done pre photodynamic therapy, one week, one month and three months post photodynamic therapy. Postoperative scotomas after single photodynamic therapy were smaller in 8%, identical in 61% and larger in 31% compared with preoperative findings. After repeated photodynamic therapy postoperative scotomas were smaller in 70%, identical in 30% and larger in no case. The observed increase was less than 25% of the original size. Postoperative defects were always significantly smaller than the entire size of the irradiated area. No new scotomas were found after photodynamic therapy. Angiographically visible occlusion post photodynamic therapy was in general larger than scotoma size. Documentation of the retinal function by microperimetry after photodynamic therapy of subfoveal choroidal neovascularization shows no new scotoma in the treated area. This can also be documented in the hypofluorescent area around the lesion one week after the treatment. After repeated treatment a reduced scotoma size due to choroidal neovascularization could be seen in 2/3 of the patients after 3 months. No initial vision loss as seen in conventional photocoagulation could be documented after photodynamic therapy.

Quantitative visual fields under binocular viewing conditions in primary and consecutive divergent strabismus.

Although there have been a number of studies on the size of the suppression scotoma in divergent strabismus, there have been no reports on the full extent (i.e. size as well as depth) of this scotoma. Binocular static perimetry was used to measure suppression scotomas in five patients with primary divergent strabismus and ten patients with consecutive divergent strabismus. Four control subjects were also included in the study. With two modified Friedmann visual field analysers, we measured the visual field of both eyes under monocular and binocular viewing conditions. The objective angle of squint ranged from 3 degrees to 25 degrees. Best corrected visual acuity was at least 0.4, but mostly 1.0 in both eyes. All subjects had normal visual fields for each eye under monocular viewing conditions. In 12 of the 15 subjects, we found a large area of suppression encompassing the projection of the fixation point as well as that of the fovea in the non-fixating eye under binocular viewing conditions. In 2 of these 12 patients, one with primary and one with consecutive divergent strabismus, the area of suppression was located nasally to the position of the fovea in the field of the non-fixating eye (nasal hemisuppression). In another two patients with divergent squint combined with vertical deviation, a small fixation-point suppression scotoma was found. The depth of suppression ranged from 3 dB to 16 dB. In one subject only, no suppression was found. Our findings indicate that the shape of the suppression scotoma is not related to the origin of divergent strabismus or to the angle of squint. Our results also indicate that the critical age for the development of suppression in divergent squint might be up to 14 years.

Indocyanine Green Angiography and Retinal Sensitivity After Photodynamic Therapy of Subfoveal Choroidal Neovascularization

Photodynamic therapy (PDT) is currently being evaluated in clinical trials for the treatment of choroidal neovascularization (CNV). Preliminary results indicate that PDT achieves immediate absence of leakage from CNV while maintaining visual acuity. Indocyanine green angiography reveals a reduction in CNV size and a persistent decrease in leakage activity after PDT. PDT appears to be characteristically accompanied by choroidal perfusion changes that regularly resolve within 3 months. Microperimetry shows an improvement of the central visual field with a decrease in scotoma size and intensity. Repeated PDT applications do not cause additional damage to the treated area, but might further enhance the recovery of macular function. A placebo-controlled, multi-center trial (TAP trial) evaluating the benefit of repeated PDT treatments in 3-month intervals is currently underway.

Vision rehabilitation for age-related macular degeneration.

Though the numbers of patients with ARMD are high, associated referrals for vision rehabilitation are not. Practitioners need to refer patients with age-related maculopathy when medical and surgical treatment are no longer possible, and patients need to be educated to that fact. The impact of improving activities of daily living may be monumental and benefits society as a whole. People who are visually impaired are often ill-prepared to deal with the substantial adjustment involved, further stressing their entire support system. It may not be safe for visual and systemic reasons for older adults to cook, clean, and maintain their home. Poor vision contributes to the already increased risk of falls and subsequent fractures in these patients. Individuals who may have already been told they can no longer drive now face the possibility of being unable to live in their houses. Their independence may be threatened dramatically and abruptly. All these circumstances contribute to anxiety and depression. Patients with ARMD need to be educated about their disease process (teaching that can never be assumed to have been initiated). They need to be educated that they will not go completely blind and that, with assistance, they can accomplish a great deal. With today's technology, it is not difficult to help visually impaired individuals with ARMD, unless they are not referred or lack motivation. The primary complaint of an individual with ARMD is recognition of central detail. This affects all activities of daily living, and patient performance is subject to the duration and severity of the disease (including the size, density, and location of the central scotoma) and to their understanding of the disease. Rubin and coworkers, found that slow reading performance of patients with a dense central scotoma might reflect inherent limitations of peripheral retina for complex visual tasks. ARMD in most cases lends itself to magnification that enlarges the object beyond the blind spot for visual recognition. Visual devices for distance, intermediate, and near tasks are usually helpful after patient education regarding their predicament and education for adaptation. Eccentric fixation techniques should be one of the first exercises mastered prior to further visual rehabilitation. Activities of daily living should be addressed with every individual, and appropriate assessment of existing problems and modifications to those problems should be implemented. Orientation and mobility should be offered to any individual who is legally blind or has difficulty with safe travel. A great deal of empathy is required on the part of the vision rehabilitation team. However, when patients lack of motivation, feel despair, or exhibit psychosocial overtones of reliance on others, they needs to be confronted, and appropriate action must be taken. Social work consultation and access to a support group can go a long way in mental strengthening and socialization. The author conducted a support group that, over a 10-year period, had a negligible dropout rate owing to the positive socialization obtained from attending the meetings. Older adults who are still working should be referred to an agency for vocational and financial resources if so desired. There is the issue of driving. In the United States, maintaining a driver's license is an important part of the quality of life. Older adults are the most rapidly growing segment of the driving population in the United States. The percentage of drivers older than 65 is expected to increase 17% by the year 2020. The rate of traffic fatalities among older adults has increased substantially, although the overall rate of fatalities is declining. The elderly drive fewer miles but have the highest rate of crashes per miles driven. Many important issues regard the older adult driver. (ABSTRACT TRUNCATED)

Reading with central scotomas: What can we learn from simulation studies?

Age-related macular degeneration (ARMD) is the leading cause of visual impairment in adults 65 years of age and older. ARMD often results in scotomas affecting the fovea, leading to central field loss. We used simulated scotomas in normally sighted young adults to test the impact of scotoma size and location on reading. We measured reading rate and eye movement patterns and found that the number of letters masked by the scotoma is more important than the size of the scotoma in degrees of visual angle and that forcing subjects to attend below a simulated scotoma results in better reading than when they are forced to attend to either the left or the right.

Difficulty in performing everyday activities in patients with juvenile macular dystrophies: comparison with patients with retinitis pigmentosa

AIMSTo ascertain the level of perceived difficulty experienced by patients with central vision loss due to juvenile macular dystrophies in the performance of everyday activities. A second objective was to...

Effects of experimental scotomata on sequential pattern-onset, pattern-reversal and pattern-offset visual evoked potentials.

The effect of experimental scotomata on visual evoked potentials to half-field stimulation using sequential checkerboard onset, reversal and offset was investigated in 10 normal subjects to assess the relative sensitivity of the three stimulus modes, and the contributions of pathways subserving macular and paramacular parts of the visual field. Four scotoma sizes (0-1.5 degrees , 0 degrees - 2 degrees, 0 degrees -3 degrees and 0 degrees -4.5 degrees ) were used to mask the central part of the stimulus field (0 degrees -12 degrees ). Five check sizes (6', 12', 20', 50' and 80') were presented for each scotoma size. Peak-to-peak amplitudes and peak latencies of components on the ipsilateral and contralateral sides of the scalp to the stimulated half-field were measured. Scotoma size was highly significant in influencing component amplitude (p < 0.0001) and latency (p < 0.03) of all ipsilateral and contralateral onset components and all ipsilateral reversal and offset components. Components that were attenuated to the greatest extent with the smallest 0 degrees -1.5 degrees scotoma were the contralateral onset P105 and ipsilateral reversal P100 and N145. Onset CIII, reversal N80, and offset N85 and P110 only showed a significant attenuation after the use of scotomata of 0 degrees -3 degrees and larger. Our results show that scotoma size is a significant factor in influencing all the major visual evoked potential components, with the exception of reversal and offset contralateral potentials (N105 and N115), probably reflecting their paramacular origins. Reversal, ipsilateral P100 and N145, and onset, contralateral P105, appear to be predominantly of macular origin and the most sensitive potentials for detecting effects of small central scotomata.

Apparent glaucomatous visual field defects caused by dermatochalasis.

We have studied the effects of dermatochalasis on Humphrey automated perimetry of the central 24 degrees visual field. Fifteen visual fields of 9 ocular hypertensive patients (18 eyes) were found to be incongruous with their apparently healthy optic discs. Examination revealed dermatochalasis, which was felt to be responsible for the field defects. This was confirmed by reversal of the defects on repeating the field test (programme 24-2) with the redundant upper lid skin taped up, or in 2 cases following blepharoplasty. The defects always involved the superior visual field. The deepest and largest defects were sited in the supero-temporal quadrant in 13 of the 15 affected fields and the supero-nasal quadrant in 2 fields. The most common pattern was a temporally skewed defect which reflected the tendency of the loose upper lid skin to be greater in extent temporally than nasally. In 7 fields the supero-temporal defect extended to fuse with the blind spot, mimicking a superior arcuate scotoma. Temporal extension of the field defects below the horizontal meridian occurred in 5 fields. In cases where visual field testing was repeated without taping up the lid inter-test fluctuation in scotoma size and depth was observed, although the position of scotomas when present within the visual field remained constant. We conclude that dermatochalasis has the potential to confound diagnostic automated visual field testing for glaucoma.

Does the fundus perimetry determined edge of the blind spot depend on the superficial form of the papilla?

We wanted to find out whether the borders of the blind spot depend on the surface topography of the optic disc and its surrounding area. We therefore examined ten eyes with parapapillary atrophy adjacent to the temporal side of the disc. Fundus perimetry was performed under direct fundus control using a Rodenstock scanning laser ophthalmoscope. We examined the horizontal meridian of the optic discs in 0.5 degree steps using Goldmann IV-stimuli with 10 different degrees of brightness and the Goldmann stimulus 1, 0 dB (greatest luminance). Six eyes with symmetric, "normal" excavation served as controls. Optic disc topography was measured with the Heidelberg Retina Tomograph (HRT). Stimuli with a large luminance power (Goldmann IV, 4 dB) were seen up to 0.8 degree centrally (i.e., towards the optic disc center) from the temporal edge of the parapapillary atrophy, but up to 1.9 degrees centrally from the nasal optic disc border (P < 0.01). Horizontal HRT section profiles of the optic disc consistently showed prominent nasal disc borders contrasting with a shallow excavation within the temporal parapapillary atrophy. In all six subjects with a normally shaped disc there was no such "nasotemporal asymmetry." The size of scotomas depends on the surface topography of the tested area. The prominent nasal part of the optic disc appears less "blind" than the shallow temporal part, probably due to more intensive light scattering by the prominent nasal part of the disc.

Blind spot size depends on the optic disc topography: a study using SLO controlled scotometry and the Heidelberg retina tomograph

AIMSTo find out whether the size of the blind spot area, determined by static perimetry, depends on the surface topography of the optic disc and its surrounding area.METHODSTen eyes were...

Reading rates with artificial central scotomata with and without spatial remapping of print.

People with central field defects resulting from age-related macular degeneration (ARMD) read very slowly. In this study, oral reading rates were determined for unrelated sequences of words in samples of normal young and old subjects with simulated central scotomata of 2 degrees, 4 degrees, and 8 degrees. Scotomata were stabilized at the fovea of the right eye by electronic feedback of eye position, monitored using a SRI dual-Purkinje Eyetracker. Reading rates were determined by jumping print after each stationary presentation through an increasing number of character spaces on different trials. This procedure mimicked the sequence of retinal images produced during the saccades and fixations of normal reading, but without requiring subjects to make accurate eye movements. In Experiment 1, the letter size that yielded the optimal reading rate was found to increase systematically with scotoma size. However, the optimal reading rate decreased more or less linearly as the scotoma size increased. Experiment 2 showed that the optimal reading rate was obtained for essentially the same duration of text presentation, regardless of scotoma size. Experiment 3 investigated the effect of spatial remapping, in which print obscured by the scotoma was stretched electronically to reappear at the scotoma margin. Compared to a nonremapped control condition, spatial remapping produced small but significant increases in reading rate for both 4 degrees and 8 degrees scotomata. Across experiments, average reading rates were faster for the young than the old subjects. Overall, the results define how reading rate is expected to decrease for central scotomata of different sizes and suggest that spatial remapping of print may improve reading rates in patients with ARMD.

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.

Pattern electroretinogram and visual evoked potential amplitudes are influenced by different stimulus field sizes and scotomata.

The pattern electroretinogram and the visual evoked potential were recorded simultaneously with various stimulus fields and artificial scotomata of increasing sizes. In contrast to an earlier study, a smaller check size (20') and two stimulus field sizes (20 degrees x 20 degrees and 10 degrees x 10 degrees) for the scotomata were used. With a concentric decreasing stimulus field, a reduction of both the pattern electroretinogram and visual evoked potential was found. Both showed a simultaneous reduction of amplitudes, but, compared with the amplitude in the full field, the reduction was more extensive for the pattern electroretinogram at each test field size. This implies a greater contribution to the pattern electroretinogram from more eccentric retinal parts. An artificial central scotoma of increasing size in the 20 degrees x 20 degrees field had less influence on the pattern electroretinogram than on the visual evoked potential. The percentage amplitude loss of the visual evoked potential was more pronounced. The visual evoked potential was eventually abolished by a scotoma size from 10 degrees x 10 degrees upward, while the pattern electroretinogram was still registrable. When scotomata of similar size were introduced in a smaller (10 degrees x 10 degrees) field, percentage pattern electroretinogram and visual evoked potential amplitude losses were less separated than in a larger (20 degrees x 20 degrees) test field.

Validity and Interpretation of Amsler Grid Reports

To compare the reports of scotomas and metamorphosia in standard and threshold Amsler grid testing with the location and extent of scotomas in the macular region as determined by standard and threshold fundus perimetry. Fundus perimetry determined the existence, size, and retinal location of macular scotomas. Amsler grid testing was performed with the scanning laser ophthalmoscope and the TA-300 system (Stereo Optical, Chicago, Ill). All testing was done at both standard and threshold light conditions. Fifty-five patients with vision loss in the macular region and 10 normally sighted subjects. Nearly half of the standard and threshold scotomas were not detected by Amsler grid testing. For scotomas of 6 degrees or less in diameter, 77% of standard and 87% of threshold scotomas were not detected by Amsler grid testing. Of the eyes with central scotomas involving the fovea, 66% used an eccentric preferred retinal locus for fixating the center of the grid. Finally, more than half of the distortion reported in Amsler grids was at the retinal area that corresponded to the scotoma area, not a nonscotoma retinal area. Amsler grid reports have poor validity and cannot be accurately interpreted for use in the clinical diagnosis of retinal defects.

Evolutive patterns of the visual field in optic neuritis

Sixty eyes with optic neuritis in 50 patients were treated with high doses of methyl-prednisolone. A follow-up of the visual field (VF) with automated static perimetry performed with Vision Monitor (Metrovision) was realized to determine the evolutive pattern. In spite of treatment four patients showed neither improvement nor deterioration. The 56 other eyes improved dramatically. A normalization of the VF with no definite pattern was observed in 15 eyes. The evolutive pattern of the three cases with a peripheral constriction was impossible to assess because of the limits of the programme. A progressive centripetal amelioration was observed in the majority of the eyes (n = 38). The evolution was concentric with a progressive reduction of the size of the central scotoma. A fragmentation could appear and the scotoma adopted an intermediate aspect of a trifoliated pattern (three-leaf clover).

Visual Requirements for Reading

We have applied research on the visual psychophysics of reading to low vision assessment. Research on different aspects of the reading process found that reading rate rather than reading comprehension is more sensitive to variations in a subject's visual functioning or the stimulus properties of print. The research identified four different visual factors that significantly affect reading rate: (1) acuity reserve [print size relative to acuity threshold], (2) contrast reserve [print contrast relative to contrast threshold], (3) field of view [number of letters visible], and (4) in cases of maculopathy, central scotoma size. Our research indicates that fluent reading rates can be attained with a restricted field of view, as little as four characters. However, attainment of fluent reading levels requires that print size and contrast should be several times threshold and the diameter of a central scotoma should be less than 22 degrees. Although important clinical studies are lacking, we derived specific visual requirements for different reading rates from published experimental research to provide a starting point and to illustrate how visual requirements could be derived, even with poor correlations. Research has made significant progress toward the development of a comprehensive low vision assessment that will allow the practitioner to identify visual impediments to reading, other than reduced visual acuity. Having more fully characterized a visual impairment, the practitioner may tailor devices or interventions to the individual's needs and capabilities.

Laser Treatment of Subfoveolar Choroidal Neovascular Membranes

We prospectively studied the safety and efficacy of subfoveolar laser treatment of choroidal neovascular membranes (CNVM) in 29 eyes. With one to four treatments, all CNVMs were successfully eradicated. Central visual acuity improved in 31% and stabilized in 69%. Vision did not deteriorate in any of the eyes. In appropriately selected eyes, subfoveolar treatment appears safe and effective in halting the exudative response and minimizing scotoma size, thus facilitating the use of low-vision aids.

The suppression effect of simulated anisometropia

Although there is evidence that differential interocular image clarity degrades binocular performance (for example, reducing stereo sensitivity) little is known about how this sensitivity reduction occurs. As there is evidence that suppression scotomas are induced in the more defocused eye, the presence and approximate size of suppression scotomas induced with uni-ocular defocus was investigated in five binocularly normal subjects. The targets comprised a fusional lock and a suppression check for each eye and the task of each subject was to report the presence of the suppression check with varying amount of defocus. There was a range of simulated anisometropia over which suppression did not occur (approximately +/- 0.50 DS). Thereafter the probability of suppressing a small foveal target increased approximately linearly until the target was always suppressed. Greater amounts of simulated anisometropia produced larger suppression scotomas. However, less anisometropia was required to produce an equivalent sized suppression scotoma if greater amounts of fusional detail were provided. These results suggest that the decrement in binocular performance which accompanies simulated anisometropia may occur because of localized inhibition in the more defocused eye and is not solely due to loss of resolution in that eye.

The suppression effect of simulated anisometropia

Although there is evidence that differential interocular image clarity degrades binocular performance (for example, reducing stereo sensitivity) little is known about how this sensitivity reduction occurs, As there is evidence that suppression scotomas are induced in the more defocused eye. the presence and approximate size of suppression scotomas induced with uni-ocular defocus was investigated in live binocularly normal subjects. The targets comprised a fusional lock and a suppression check For each eye and the task of each subject was to report the presence of the suppression check with varying amount of defocus. There was a range of simulated anisometropia over which suppression did not occur (approximately ± 0.50 DS). Thereafter the probability of suppressing a small foveal target increased approximately linearly until (the target was always suppressed. Greater amounts of simulated anisometropia produced larger suppression scotomas. However, less anisomeiropia was required to produce an equivalent sized suppression scotoma if greater amounts of fusional detail were provided. These results suggest that the decrement in binocular performance which accompanies simulated anisomeiropia may occur because of localized inhibition in the more defocused eye and is not solely due to loss of resolution in that eye.