Patient Awareness Of Binocular Central Scotomas In AMD and Implications For Low Vision Referral

DONALD C. FLETCHER, MD • RONALD A. SCHUCHARD, PhD • LAURA L. WALKER, PhD

Retinal physicians must devote a large portion of their time in practice to treating patients with AMD. While much vision can be saved through these interventions, most patients must deal with some degree of decrease in visual function, and some must deal with a lot.

Visual acuity and OCT images of the macula are monitored frequently and carefully, but little attention is given to the central visual field. While the central field does not directly play into intervention decisions, research has demonstrated that reading performance is greatly impacted by central and paracentral scotomas.¹

LACK OF PATIENT AWARENESS

Another important consideration is that most patients with binocular scotomas are not aware of their existence.² Many AMD patients may benefit from referral for low-vision rehabilitation to address these field defects, even when acuity may be relatively good and they are unaware of central field disruption.

Patients with central scotomas have visual performance difficulties far exceeding those expected from reduced VA alone. Ninety percent of people entering vision rehabilitation services have been found to have dense scotomas in the central 10°, and as many as 80% of them have central scotomas that partially or totally affect foveal function.³

Because people with scotomas normally perform visual activities with both eyes open, we as clinicians must address the characteristics of binocular scotomas. Rehabilitation efforts are generally directed toward developing skills in compensatory eye movements to move the scotomas out of the visual field of interest during visual tasks.

When foveal function is lost, this often includes eccentric viewing training to utilize a nonfoveal or eccentric preferred retinal locus (PRL), sometimes referred to as a “pseudofovea.”

In this rehabilitation education process, clinicians have frequently noted that patients are not aware of the presence of their central scotomas.^4,5 The common hypothesis has been that the process of perceptual completion occurs for central scotomas just as it occurs with the physiological blind spot under monocular viewing.^4,6-8

The proportion of patients aware of their scotomas is not known, but it seemed quite useful to rehabilitation service delivery. We assessed whether AMD patients were aware of binocular central visual field defects as they presented for low vision rehabilitation.

We measured what proportion could see their scotomas, what proportion could not see them but that had some awareness of the defects, and what proportion were completely unaware of the presence of binocular scotomas.

OUR STUDY

Over a four-month period, 153 consecutive AMD patients undergoing their initial low vision rehabilitation evaluations were immediately asked at the beginning of their visits:

● Were you able to see any blind spots or defects in your field of vision? and

● Do you have any evidence or experiences that led you to believe that you had defects in your field of vision.

The questions were asked before any testing was performed or instructions were given that might have raised the patients’ awareness of their scotomas. The patients’ functional histories were completed, and then the usual battery of visual function testing was performed in the low vision rehabilitation clinic.

As noted, patient’s typical visual perception in everyday life activities is with both eyes open. Any perception or awareness of their scotomas would be expected to be noticed, or not noticed, in their binocular visual field. Thus, binocular central visual field testing was felt to be more closely related to scotoma awareness than monocular testing.

The California Central Visual Field Test (CCVFT; a tabletop tangent field test) was administered with both of the patient’s eyes open, to identify dense and relative scotomas.⁹ The test stimuli were presented as short flashes to the field (binocular viewing) with red laser pointers that emitted a spot of light approximately 1 mm in diameter.

The brightest/densest stimuli were provided by an unfiltered laser while the weaker/more relative stimuli had neutral density filters introduced, which decreased the intensity to 10% of the bright/dense stimulus. The stimuli were presented on a piece of white paper in normal room lighting at a 57-cm testing distance. At this distance, 1 cm is approximately equal to one degree of the field. Dense or relative scotomas within 2.5º of fixation were noted, and their mean diameter was measured.

Visual acuity was assessed with an ETDRS chart at 1 m, and the letter-by-letter scoring system was used.¹⁰ Binocular reading performance was evaluated with the SK Read charts.⁹ The SK Read charts use noncontinuous text/unrelated words and letters with text sizes from 8 M units to 0.4 M units (the 1 M unit is newsprint).

The SK Read chart is valuable in predicting scotoma interference with reading, especially without contextual clues, such as telephone numbers and bank statements. Accuracy on the SK Read chart is recorded as the average number of errors out of 16 items on each block that is read.

Figure 1. Relationship between dense and relative scotoma sizes, as measured with the CCVFT. Relative scotomas tend to be larger than dense scotomas.

THIS IMAGE APPEARS COURTESY OF WOLTERS KLUWER AND WAS ORIGINALLY PUBLISHED IN FLETCHER DC, SCHUCHARD RA, RENNINGER LW. PATIENT AWARENESS OF BINOCULAR CENTRAL SCOTOMA IN AGE-RELATED MACULAR DEGENERATION. OPTOM VIS SCI. 2012;89:1395-1398.

OUR RESULTS

The patients’ median age was 84 years, with a range of 61 to 98 years. All the patients had AMD, 48% with the dry form and 52% with the wet form. Of the wet AMD patients, 76% had received anti-VEGF injection treatments. The mean duration of AMD symptoms was seven years, with a range of 0.5 to 23 years. Median visual acuity was 20/253 with a range of 20/40 to hand movements.

All of the patients were able to understand and complete the binocular central visual field testing. Only 12% did not demonstrate a binocular scotoma within 2.5º of fixation. Sixty-six percent had binocular dense scotomas with possible relative scotomas, and 22% had only a relative scotoma.

The mean relative scotoma diameter was 12.1º with a range of 0º to 30º. The mean dense scotoma diameter was 8.6º with a range of 0º to 30º. In all the patients, relative scotomas (if they existed) tended to be larger than dense scotomas (Figure 1).

Fifty-six percent (75/134) of patients with binocular scotomas were totally unaware of their presence, even with dense scotomas measuring up to 30º in diameter. They were aware of “bad vision” but could see no “hole in their vision” and were not able to recall situations in which things would disappear.

Two of 134 patients (1.5%) could fleetingly see defects in their visual fields. Each of these two patients noted the defect upon awakening. One described being able to see a dark spot on the ceiling when first opening the eyes in the morning. As soon as an upright posture and movement were initiated, the dark spot would disappear.

The other patient described seeing a dark area in the center of her vision when awakening at night and trying to navigate to the bathroom before turning on the light. As soon as the light was turned on, the missing area of vision was no longer noticed.

Forty-four percent (59/134) were not able to see missing areas of their vision but nevertheless related experiences of things “disappearing” on them. The most common report was of words and letters disappearing while attempting to read. Letters or numbers would disappear and reappear, often causing great aggravation.

One very observant patient reported that while attempting to step on a cockroach, the insect ran into an area of her vision, where it momentarily disappeared. She could not resume trying to step on the roach until it reappeared out of its “hiding spot”!

The size of the scotoma was not useful in predicting scotoma awareness, as there were no significant differences in the sizes of scotomas for patients who were completely unaware versus those who had some awareness of their scotomas.

The presence of scotomas decreased reading accuracy, but some awareness of the scotomas seemed to improve accuracy. The SK Read mean error rate for the unaware group was 5.4 errors per block, and the aware group’s rate was 3.3 errors per block.

The SK Read mean error rate for the no scotoma group was 1.0 error per block. Awareness of scotoma was associated with fewer errors on the SK Read test (P < .01). No significant relationship was apparent between awareness of the scotoma and age, acuity, scotoma size, density, or duration of disease onset.

CONCLUSIONS

On initial evaluation, 88% of AMD patients referred for low vision rehabilitation demonstrated binocular scotomas near fixation, and more than half were totally unaware of their presence. Increasing size of scotoma did not increase awareness, as might be expected. It was noted that scotomas as large as 30° in diameter could go undetected by the patient.

Neither retinal specialists nor low vision clinicians can depend on patients to report the presence of significant scotomas; thus, appropriate screening and testing are indicated. Unfortunately, common testing techniques, such as the Amsler grid, are not effective.¹¹ It appears that macular testing with the CCVFT and SK Read is appropriate for scotoma screening.

The presence of scotoma decreased reading accuracy independent of acuity score. Interestingly, some awareness of scotoma had a tendency to improve reading accuracy. Referring patients with central field defects to low vision rehabilitation programs aimed at increasing patient awareness of their scotomas appears appropriate.

When we accept the responsibility to care for patients with AMD, when does our obligation end? Is it complete when the macula is dry, or is it complete when patients no longer respond to available treatments?

No: A caring physician will consider more than the macula — specifically how the two maculas are operating together in the life of the patient. RP

REFERENCES

1. Fletcher DC, Schuchard RA, Watson G. Relative locations of macular scotomas near the PRL: effect on low vision reading. J Rehabil Res Dev. 1999;36:356-364.

2. Fletcher DC, Schuchard RA, Renninger LW. Patient awareness of binocular central scotoma in age-related macular degeneration. Optom Vis Sci. 2012;89:1395-1398.

3. Fletcher DC, Schuchard RA. Preferred retinal loci relationship to macular scotomas in a low-vision population. Ophthalmology. 1997;104:632-638.

4. Schuchard RA. Adaptation to macular scotomas in persons with low vision. Am J Occup Ther. 1995;49:870-876.

5. Crossland M, Rubin G. The Amsler chart: absence of evidence is not evidence of absence. Br J Ophthalmol. 2007;91:391-393.

6. Wittich W, Overbury O, Kapusta MA, Watanabe DH, Faubert J. Macular hole: perceptual filling-in across central scotomas. Vision Res. 2006;46:4064-4070.

7. Safran AB, Landis T. From cortical plasticity to unawareness of visual field defects. J Neuroophthalmol. 1999;19:84-88.

8. Safran AB, Landis T. Plasticity in the adult visual cortex: implications for the diagnosis of visual field defects and visual rehabilitation. Curr Opin Ophthalmol. 1996;7:53-64.

9. Fletcher DC. Central field defects and reading errors in low vision patients analyzed with binocular low tech tests. Poster presented at: Annual meeting of the Association for Research in Vision and Ophthalmology; Fort Lauderdale, FL; May 2-6, 2010.

10. Bailey IL, Bullimore MA, Raasch TW, Taylor HR. Clinical grading and the effects of scaling. Invest Ophthalmol Vis Sci. 1991;32:422-432.

11. Schuchard RA. Validity and interpretation of Amsler grid reports. Arch Ophthalmol. 1993;111:776-780.

12. Fletcher DC, Schuchard RA, Renninger LW. Patient awareness of binocular central visual field defects in age-related macular degeneration (AMD). Invest Ophthalmol Vis Sci. 2011;52:4236.

THIS WORK WAS FIRST PRESENTED AS A 2010 ARVO CONFERENCE ABSTRACT IN FORT LAUDERDALE, FL¹² AND WAS PUBLISHED AS A RESEARCH ARTICLE². DCF DEVELOPED THE CCVFT AND SK READ TESTS AND RECEIVES MODEST COMMISSION FROM ITS MANUFACTURER, MATTINGLY LOW VISION (MATTINGLYLOWVISION.COM). THIS RESEARCH WAS FUNDED BY THE PACIFIC VISION FOUNDATION AND THE SMITH-KETTLEWELL EYE RESEARCH INSTITUTE.