Strategies to help reading for the AMD patient with central scotomas
| Written by Joan Stelmack, O.D., MPH, a member of the AOA’s Vision Rehabilitation Committee
Patients with low vision caused by macular diseases frequently have distortion, blur or scotomas in their central visual field that interfere with reading activities and result in slow or inaccurate reading performance. Scotomas can cause parts of letters or words to be missing or blurry such that patients lose their place or have difficulty finding the beginning or end of a line of text.
To compensate, patients with a central scotoma may use small areas of viable retina with lower resolution, referred to as a preferred retinal locus (PRL), that are located outside of the affected foveal/macular area. Relocating the image into a new retinal viewing area is referred to as eccentric viewing, and the process of training patients' oculomotor skills to more effectively use their PRLs is called eccentric viewing training. PRLs usually develop above, below, to the left or right of the scotoma border within six months of vision loss in the second eye. The mechanism used by the visual system to choose a particular PRL is not known.
Evaluating scotomas that interfere with reading
The Smith-Kettlewell Reading Test (SK Read) is used to identify scotomas that interfere with reading and to educate patients through discussion and demonstration that straight ahead or central vision now has a blind spot that causes a pattern of reading errors. The test also can be used to document improvement in patient performance.
As described in the testing manual, SK Read Charts use blocks of text ranging from 8 M down to 0.4 M. Each block consists of 47 letters or 60 characters including spaces. Included are six single letters, one two-letter word, two three-letter words, three four-letter words, three five-letter words and one six-letter word. Single letters are used to facilitate misidentification of two-letter words as a single letter. Words that contain smaller words are included to identify errors that occur when the first or last letters of a word are missed. The text is meaningless to avoid contextual cues. Testing is performed with optimal lighting and testing distance, and the patient's standard reading correction or a low-vision device. Patients are encouraged to read out loud as quickly as they can and to read as far down the chart as is possible. A stop watch is used to time reading of each block; a score sheet with blank space to record misidentifications, omissions and the time spent reading each text block is included.
Interpretation of test results is summarized in the SK Read manual:
- Rapid accurate reading for all font sizes usually implies that scotomas are not interfering with reading.
- The more frequent the reading errors, the more likely that scotomas are present.
- Mistakes such as dropping or misidentifying the first letters of words are classified as "left-sided" mistakes; with a pattern of "left-sided" mistakes, scotomas are likely to be located on the left side of fixation.
- Mistakes that drop or misidentify the last letters of words are classified as "right-sided' mistakes; with a pattern of "right-sided" mistakes, scotomas are likely to be located on the right side of fixation.
- Mistakes may be found on both the left and right side of fixation if scotomas are present on both sides of fixation.
- Errors with no clear pattern are thought to be associated with a poor-quality retinal fixation area.
- A pattern of slow reading of large font sizes with many mistakes, faster reading with fewer errors with moderate-size text and slower reading speed for small fonts is often found when ring scotomas are present.
- If all sizes of print are read slowly with frequent mistakes, patients may benefit from instruction to improve reading performance.
Instruction to improve reading performance of patients with central scotomas
Instruction starts with an explanation of "blind spots" (scotomas) and how they interfere with one's ability to see straight ahead. Clinicians should emphasize the importance of using your side vision and looking away from a word to see it better. This technique can be demonstrated with letters or small words on a computer monitor.
Tell the patient to imagine looking at a clock. Ask the patient to look directly at the letter or word with the scotoma blocking it, then slowly move their eye to different clock hours until the word appears most clear. The clock hour is the direction of eccentric viewing (not the location of the retinal image). Patients should practice looking toward the eccentric viewing clock hour to identify single letters, two-letter words, three-letter words, and scanning longer words, seeing the first two or three letters in one glance and then quickly and efficiently saccading to the end of the word. When patients can accurately locate their EV spot, hold their gaze still and scan longer words, reading exercises with sentences and short paragraphs are introduced.
Patients can practice eccentric viewing at home with activities such as finding and circling specific letters within word lists or sentences and performing exercises with a standard deck of playing cards. The deck of cards should be held far enough away to make the exercises challenging. Three exercises are recommended:
- Learning to efficiently and accurately eccentrically view: viewing individual cards and using eccentric viewing to read the number or symbol at the upper left corner of the playing card.
- Fixating with eccentric viewing: stabilizing the eccentric viewing position on the top, left-hand corner of a deck of cards and quickly removing one card at a time while trying to maintain eccentric viewing.
- Scanning with eccentric viewing: fanning approximately seven playing cards and practicing reading the numbers and symbols on the card quickly and accurately.
In summary, development of eccentric viewing skills to improve eye control and manage scotomas helps optimize the patient's reading performance with low-vision devices. However, practice is required to develop competence so that the technique will not be burdensome to use.
Learn more about vision rehabilitation and how to manage individuals with low vision and/or brain injury.
Disclaimer: The information contained in this article represents the opinion of the author and not the AOA. These are not clinical practice guidelines, nor has the evidence been peer reviewed.
There are additional aspects to this topic that may not be presented, or considered, based on the specifics of the case.
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