CASE STUDY

Acuity Alone Does Not Indicate the Extent of Macular Disease

Central visual field disruption can impair reading independent of visual acuity

DONALD C. FLETCHER, MD · LAURA RENNINGER, PhD

An 80-year-old woman was referred for a low vision rehabilitation consultation with the complaint of difficulty with several near detail-oriented tasks. She complained of increasing difficulty with all types of reading activities and noted problems with her hobby of drawing and painting (Figure 1). She was an articulate, well-educated, retired bookkeeper in good health. She found the changes in her vision to be extremely aggravating, to the point where it had significantly decreased her quality of life.

Figure 1. Sample of patient's artwork. Drawing courtesy of Thomas Reynolds Gallery, San Francisco.

She had been diagnosed with exudative AMD in both eyes. There was an old, well-established macular scar in her right eye and she indicated that her vision in that eye had been very poor for about 15 years (Figure 2). In spite of those problems, she had been managing well her activities of daily living with her good left eye until it also began to cause her problems 1 year earlier. She had received a number of injections in her left eye with an anti-VEGF drug (Figure 3). She was told that she was having a good response to treatment.

Figure 2a. SLO image of the right eye utilizing infrared laser. Large central scar did not allow appreciation of bright fixation target.

Figure 2b. The fixation target could be appreciated in the far temporal periphery.

Figure 3. Fixation is at cross. Note some RPE atrophy immediately nasal to fixation.

Visual acuity testing using the ETDRS chart at 1 m showed acuities of OD 20/600 and OS 20/80. Using a letter-by-letter scoring system, the acuities were OD 20/919 and OS 20/110. With her right eye, finding any letters was a very difficult, slow process with much searching and effort. Of particular note: In her better eye, on 5 separate lines she omitted the first (left side) letter (Figure 4).

Central visual field analysis was performed using 2 testing methods, a modified central tangent field test (the California Central Field Test) and macular perimetry with the scanning laser ophthalmoscope (Rodenstock SLO 101 model). Both tests showed steady fixation with a significant scotoma immediately to the left of fixation in her better (left) eye. The right eye had a large central dense scotoma with a poorly established pattern of eccentric fixation (Figures 5-7).

Figure 5. California Central Field Test performed binocularly. Tangent field of the central 15°, using a laser pointer on a test sheet at a distance of 57 cm. Note the scotoma immediately to the left of fixation, indicated by the red circle. In this area the patient did not appreciate the stimulus.

Figures 6a (left) and b (right) show SLO macular perimetry of OS. In Figure 6a, fixation is at the cross. Red dots indicate stimuli not appreciated by patient (50000 trolands). Green dots are stimuli appreciated by patient. Figure 6b shows a graphical representation of the functional field loss, used in our research setting. The location of the fovea (F) is estimated using the optic disk and a blurring function that increases with eccentricity diminishes the effect of more peripheral field losses. In this image, blue is scotoma and red is seeing retina.

Figure 7. SLO macular perimetry of the right eye. PRL was at the area of the green circle. The areas indicated as dense scotoma in red were not able to appreciate a 50000 troland stimulus. The cross was not appreciated in the position where this image was taken.

Reading performance was measured using the MN Read and SK Read tests (Figures 8 and 9). The MN Read test utilizes sentences with meaning while the SK Read uses random words that do not have meaning.¹ Both tests have the same format with varying text sizes from 8M to smaller than 1M unit size fonts (1M is equivalent to newsprint-size text and 8M is 8x larger than newsprint). On the MN Read test, the patient was able to read print accurately (0 errors) but with reduced fluency to 2M size text. On the SK Read test, she was able to read the same range of text sizes but made frequent left-sided mistakes, totalling 15 errors in all (Figure 10).

Figure 8. The MN Read test utilizes continuous text in simple sentences.

Figure 9. The SK Read test utilizes random words without meaning.

Magnifiers and intense illumination were useful but did not solve the patient's reading problems alone. She greatly benefitted from an occupational therapy training program that increased her awareness of the scotoma to the left of fixation and taught her compensatory eye movement strategies. With just a few hours of training, she was able to read the random word test accurately. This had carry-over to real-world activities of daily living as well.

SUMMARY

This patient's moderately good acuity of 20/80 did not alone tell the whole story of her reading difficulty. The scotoma immediately to the left of her fixation slowed her reading and in particular caused mistakes where contextual clues could not help her. Activities like balancing her checking account were painfully difficult in spite of the fact that her career had been as a bookkeeper. Comprehensive low vision rehabilitation with occupational therapy training improved her compensatory skills resulting in increased reading speed and accuracy. Even though her scotoma did not change, with increased awareness and new scanning strategies, she stopped making the left-sided mistakes. She anticipates a significant improvement in her quality of life with increased ability to do important tasks like reading and her artwork.

Scanning laser ophthalmoscope macular perimetry studies of low vision patients have demonstrated that the vast majority of those referred to low vision rehabilitation have scotomas in their central fields that cause difficulty with reading and other activities of daily living.^2,3 By identifying and addressing these scotomas in comprehensive rehabilitation, lives can be positively impacted. RP

REFERENCES

1. Ahn SJ, Legge GE, Luebker A. Printed cards for measuring low-vision reading speed. Vis Res. 1995;35:1939-1944.
2. Fletcher DC, Schuchard RA. Preferred retinal loci relationship to macular scotomas in a low vision population. Ophthalmology. 1997;104:632-638.
3. Fletcher DC, Schuchard RA, Watson G. Relative Locations of macular scotomas near the PRL: effect on low Vision reading. J Rehab Res Develop. 1999;36:356-364.