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Low Vision Blog

PRL Case Study

(05/23/2011)

PRL Case Study:

Personal Data:

Mr. S.F. is an 84 year old white male living alone in a single story home. He is able to perform activities of daily living and home management tasks while using his home appliances with tactile reinforcements and compensatory skills. His home appliances have been appropriately adapted using locator dots and full spectrum lighting throughout his home.

Description of the case as it applies to the identified competency/indicator:

When central vision is damaged by retinal disease, such as with macular degeneration or diabetic retinopathy, a new area of maximal (albeit reduced) retinal sensitivity can develop. With training and practice, Mr. S.F. learned to develop and use this new preferred retinal loci of highest sensory, called the PRL, to enhance visual functioning. In the initial stage of low vision management the development of a PRL was sometimes prevented due to lack of understanding on the fixation away from the target. But most of the problems encounter at the beginning of his PRL training involved the results from a recent retinal transplantation. However, during his 3rd week of training Mr. S.F. had the ability to read on the close circuit TV (CCTV) at magnification of about 45X. With practice and much effort from his part Mr. S.F. reduced the magnification to 25-30X by the 5th week of training. It should be noted that on initial consultation, Mr. S.F. was unable to read words on same CCTV at 72X, it's highest magnification.

The biological task of eccentric viewing is complex. It requires the eyes and the brain to learn a new method of seeing, which means developing new habits and skills. This can usually be accomplished over a period of about six visits with a trained low vision therapist. In addition, home practice is important for supplementing the training and speeding the progress. It is important to remember that training in eccentric viewing will not improve the condition of the retina. The patient may feel that vision has improved as a result, but that is simply because existing vision has been maximized, as was the case with Mr. S.F. who by week 6 had increased his reading comprehension despite reading at slow but more accurate levels with 15X magnification.

The first step in the training is identifying the blind areas (scotomas). After that, techniques are introduced which help the patient learn to work around those areas. These techniques include tracing, identifying cards, and other methods used to improve reading and writing skills. Most of the training done with Mr. S.F. was on a Merlin CCTV since he had access to the device both in clinic and in his home. Detail vision will not be fully regained by eccentric viewing training, but vision can be greatly improved when coupled with enlargement, enhanced contrast, and appropriate magnification devices. The level of reading ability that can be attained is determined in large part by each individual's visual condition and determination. Mr. S.F. made significant improvements, from no reading at all despite maximizing the magnification in his CCTV to 60X, to presently reading on the same CCTV using both eccentric viewing and 12X to 15X magnification.

In the case of our patient, Mr. S.F., the use of TV also greatly improved his capability due to the enjoyment of seeing something other than words. Hence, movies and shows filmed in daylight or with brighter scenes were preferred over films with events taking place in dark and difficult to see backgrounds. Mr. S.F. not only improved his ability to read with his CCTV but also reported increased color and sharpness on the TV shows and movies he continues to enjoy. It is fair to add that by the time of Mr. S.F. discharge from vision rehab ten weeks later, he had increased his ability to read, write and enjoy occasional leisure tasks, like watching TV and enjoying shows and movies at the theater. Additionally, his orientation and mobility skills also improved with the use of a white support cane and eccentric viewing to allow him increased management on uneven terrain. Today, Mr. S.F. is seen at our clinic once every six months to ensure the use of his devices and techniques remain successful. Eccentric viewing or using PRL techniques is a skill that patients must continue to perform on their own for the rest of their lives as this is their only vision remaining that allows them to safely perform activities of daily living.