Eccentric Viewing Assessment and Training

Stanley Woo, O.D., M.S., F.A.A.O., Clinical Associate Professor, University of Houston, College of Optometry, Center for Sight Enhancement

In the presence of central visual field loss, the ability to use the remaining functional vision may be an integral part of the low vision rehabilitation program.  A patient who has looked straight ahead to see straight ahead all their life suddenly must find another way to see.  On the surface, it may seem pretty intuitive, but the actual implementation of eccentric viewing may be much more complicated for both the practitioner and the patient.

Studies of the retina in real-time with scanning laser ophthalmoscopy have been able to identify a preferred retinal locus (PRL), and even multiple ones in the same eye, which may function as a pseudofovea for oculomotor control in the presence of central field loss.  Some argue that these PRLs are adopted spontaneously while others challenge that they may be trained.  The truth probably lies somewhere in between as patients with PRLs do not always exhibit optimal control, and may indeed benefit from eccentric viewing (EV) training.

From an anatomical perspective, it is important to recognize that the larger the central field loss the greater the loss in visual acuity.  Though not a linear relation, Weymouth reported that at 1 degree of eccentricity the expected visual acuity is 20/30 while at 10 degrees of eccentricity the visual acuity is expected to be 20/160.  A review of the macula by non-contact funduscopy or by photograph should provide a rough estimation of where the optimal area of functional retina should be located.  In particular, the closer the edge of functional vision to the fovea the better the anticipated visual acuity.  Thus, the size and orientation of the lesion may lead the optometrist to encourage a particular EV position if the patient has not already adopted one on their own. 
                                     
There are a number of clinical signs and symptoms that may be indicative of the need for EV training that do not require access to an SLO.  For instance, patients may report that they lose their place while reading headlines in the newspaper or that the words run together.  Upon directing patients to move their eyes around to find the best “window of vision,” it may be observed that rather than moving their eyes they simply move their heads while maintaining the same relative fixation.  While measuring entering visual acuity the patient may adopt unusual head posture or eye direction in order to “see” better.  By turning their head either left or right in extreme gaze, they may be pinning the eye to one side.  Consequently, the head movement may be easier to control to shift the point of fixation slightly away from the area of the central scotoma.  A disparity between single letter and continuous text reading acuity and variable response to magnification may also be a sign.  The variability in eye position at distance and near along with the consistency in response may be telltale signs that the patient may benefit from EV training.

Another tool for identifying the direction and stability of EV is the Amsler grid.  Rather than directing the patient to center the scotoma where the diagonal lines intersect, the patient is instructed to move their eye in whatever direction enables them to best see the center fixation dot.  It stands to reason that in order to see the dot, the scotoma will be moved to a different location.  This direction correlates with the eccentric viewing position.  For instance, if the scotoma is now above the fixation target, the patient is using superior eccentric viewing in order to see straight ahead.  (i.e. superior retina is used to see straight ahead since the scotoma is located above the target of regard).  The size and depth of the scotoma is not of primary interest, rather it is the location and consistency in EV position.  This may be assessed monocularly for each eye followed by a simultaneous viewing with both eyes to determine if binocular rivalry may also be a contributory issue.

The goal of EV training is to establish a stable and consistent response to magnification in the better- seeing eye.  Independent of whether a PRL is present or not, a stable area of functional retina should be used under ideal conditions.  If EV is not consistent, the response to fixed optical magnification may vary resulting in variable responses and increased probability of frustration for examiner and patient alike.  EV training has been around for many decades and included tasks such as a clock face, slide projector, prism relocation, among others.  Much research has been conducted by leaders in the field such as Backman, Inde, Goodrich, Quillman, Maplesden, Jose, Freeman, and many others.  The reader is referred to textbooks and papers by these authors for a more exhaustive review beyond the scope of this article.

One aspect of our EV training program consists of a relatively simple series of tasks that the patient can conduct at home.  The advantages of a home-based EV training program are that it limits chair time, is less expensive, and is more convenient for the patient.  The training kit consists of a stand magnifier (6x or 8x), a series of sheets with printed letters varying from 0.8M to 2.0M or higher, and a clip board.  The isolated single letters are randomly listed in lines with equal spacing.  Other pages of increasing complexity include short words, short phrases, and simple sentences of varying sizes.  The patient utilizes the stand magnifier on the clipboard to read each letter as accurately as possible.  If they are able to read the letter, it reinforces the position of the eye needed to place the target of regard onto an EV position.  When they lose their place, it may be a result of re-fixating to the habitual fovea which coincides with the central scotoma.  Thus, the patient must continue to redirect their gaze until the letter comes in view.  Each letter read successfully is like an “eye muscle push-up” to reinforce the proper control of eye position.  The patient is instructed to do the training 15 minutes q.i.d. for 2-3 weeks.  Within the time period allotted they may proceed from the larger (and easier) letters towards the smaller (and more difficult) print sizes.  The purpose of using smaller letter sets is to encourage more accurate control of the EV position.

The theory behind this home-based training program is that the magnifier provides a fixed width aperture.  It confines the extent to which the patient may eccentrically view in a reasonable area and encourages eye movement rather than head movement in order to see.  The magnification provides an initial visual feedback to start off on a positive and encouraging note.  However, as the print size diminishes, it challenges the patient to further refine their oculomotor control.  The smaller the letter the closer to the PRL they need to be.  By using their hand to hold the stand magnifier, it is postulated that kinesthetic feedback is also provided to assist in better localization.  In the same way that a patient knows where their hand is in space with their eyes closed, the additional sensory information may help to provide another form of feedback for EV.  Secondarily, patients quickly learn that bringing the material closer may increase the field of view and ease with which they may view the print.  As they decrease the working distance while they practice, initial resistance to the notion of holding things close are broken down.  This facilitates acceptance of subsequent prescriptive, adaptive aids whether they be spectacles, microscopes, or illuminated stand magnifiers.

The results of the EV training vary.  Some patients report an improvement in performance and control, which may be reflected by an improvement in VA.  Though the VA may be better, it is important to recognize that the underlying lesion has not changed for the better.  Thus, the improvement may simply be a result of better and more consistent oculomotor control.  Similarly, some patients report a subjective improvement without corresponding change in VA.  Regardless, if a more stable EV position is established, the next step in magnification evaluation may proceed with greater confidence and consistency.  If a stable position is not established, additional training may be indicated or the range of prescriptive adaptive aids may be narrowed to those affording a larger range of magnification to compensate for the poor EV control.  Ultimately, the patient must continue to exhibit measurable improvement in visual performance in order to justify the time, effort, and cost associated with continued training.

In summary, eccentric viewing training is an integral component to low vision rehabilitation.  There are many approaches and strategies that are available, and one simple home-based technique has been described here.  However, the reader is encouraged to attend additional courses and review textbooks and the literature to develop their own approach.  Other disciplines also have expertise to share including certified low vision therapists, occupational therapists, and teachers for the visually impaired, among others.  Optometrists can play a key role in developing a comprehensive low vision rehabilitation program for their patients in order to maximize their quality of life, and eccentric viewing training is one of the early stepping stones.

 

Selected references

  • Fletcher, D.C. & Schuchard, R.A. (1997). Preferred retinal loci relationships to macular scotomas in a low vision population. Ophthalmology. 104, 6732-38.
  • Freeman, P. and Jose, R. (1997). The Art and Practice of Low Vision-2nd edition. Butterworth and Heinemann, Newton, MA.
  • Goodrich GL & Mehr, E.B. (1986) Eccentric viewing training and low vision aids:  current practice and implications of peripheral retinal research.  Am J Optom Physiol Opt. 63(2):119-26.
  • Goodrich, GL & Quillman RD. (1977) Training eccentric viewing.  J of Visual Impairment & Blindness.  71(9):377-81.
  • Inde, K. (1978). Low Vision Training in Sweden. Journal of  Visual Impairment and Blindness. 72, 307-10.
  • Jose, R.T. (1995). Clinical Wisdoms: home training for eccentric viewing. Journal of Vision Rehabilitation. 9(2), 4-6.
  • Peli E.  (1986) Control of eye movements with peripheral vision:  implications for training of eccentric viewing.  Am J Optom Physiol Opt. 63(2):113-8.
  • Schuchard, R.A. & Fletcher, D.C. (1994). Preferred Retinal Locus: a review with applications in low vision rehabilitation. Ophthalmology Clinics of  North America. 7(2), 243-256.
  • Sunness, J.S., Applegate, C.A., Haselwood, D. and Rubin, G.S. (1996). Fixation Patterns and Reading rates in eyes with central scotoma from advanced atrophic ARMD and Stargardt’s Disease. Ophthalmology. 103:1458-66.
  • Timberlake, G.T., Mainster, M.A., Peli, E., Augliere, R.A., Essock, E.A. & Arend, L.E. (1986). Reading with a Macular Scotoma. 1. Retinal location of scotoma and fixation area. Invest. Ophthalmology Vision Science. 27, 1137-47.
  • Verezen CA.  (1996)  Eccentric viewing spectacles in everyday life, for the optimum use of residual functional retinal areas, in patients with age related macular degeneration.  Optom Vis Sci.  73(6):  413-7.
  • Zeevi YY, Peli E. Stark L.  (1979)  Study of eccentric fixation with secondary visual feedback.  J Opt soc Am.  69(5):669-75.