Low Vision Rehabilitation Network (LVRN)

Low Vision Rehabilitation Network (LVRN)

We invite you to join LVRN and depending on eligibility

Participate in the online Low Vision Rehabilitation Consensus Project
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Participate in live online low vision case conferences
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Help plan the Low Vision Rehabilitation Outcomes Project

Membership in LVRN is free and open to low vision rehabilitation practitioners, researchers, students, educators, administrators, policy-makers, business people, and anyone else who is interested in advances in the field of low vision rehabilitation.

If you are interested in joining the LVRN, complete the registration page and enter the requested information. Upon registering, you will be a member of LVRN. After we have reviewed your enrollment information, your login name and password will be sent to you by email and you will be notified of your eligibility for certain components of LVRN that are limited to practicing clinicians and/or researchers.

VA ECCENTRIC VIEWING STUDY

[Supported by VA Rehabilitation Research and Development Service]

Patients with low vision from macular or other retinal diseases frequently have disturbances in their central vision resulting in blur, distortion or blind spots. These blind spots called scotomas cause visual performance difficulties such as objects" jumping in or out of nowhere" or "parts of letters or words appearing to be missing or blurry". The presence of dense central scotomas¹ and possibly dense paracentral or juxtafixational scotomas decreases performance of many activities of daily living (reading, face recognition, visual search and space perception) and visual functions (contrast sensitivity, contrast discrimination, stereoscopic depth perception and fixation stability/precision). To compensate, patients with a central scotoma rely on a small area(s) of viable retina spared from damage or an area of retina outside of the damaged foveal/macular area.

In principle, low vision rehabilitation forces the use of alternate areas of retina with lower resolution that are often located outside of the affected foveal/macular area. As the image of interest is relocated from the fovea toward the peripheral retina, the ability to resolve fine detail decreases. The lower resulting visual acuity is compensated through use of optical magnification. The process of aligning the image into a new retinal viewing area is referred to as eccentric viewing (EV). In some cases patients may spontaneously develop EV consistently using an area to substitute for the fovea, a preferred retinal area (PRL) to perform visual tasks previously performed by the non-functioning fovea^2-6. It is uncertain, however, if the PRL is the best area for optimal visual function. Patients might see better if they use another area for their "pseudofovea" that is chosen on the basis of retinal integrity, or the size, shape and placement of scotomas. Even if the PRL is the optimal area of retina for vision, skillful use of this area might still be improved which could translate to improvement in daily functioning. These are the rationales for EV training.

EV evaluation and training techniques were introduced early in the development of VA blind rehabilitation training programs^7-9 and are documented in low vision training manuals^10-11. These manuals describe identification of the optimal areas for "pseudofovea" location, training its' use, and determining efficacy of viewing skills with the prescribed retinal area. Based upon our experience at the Hines Blind Rehabilitation Center and reports in the literature, these methods of EV evaluation and training require many man hours, a high level of clinical skill from the instructors, and considerable cooperation from the patient for optimal results. Even in comprehensive rehabilitation programs, some patients benefit more from one type of training than another⁸ and the instructor may need to use several different techniques⁷ before the goal is reached. In other instances patients learn the general direction in which they should fixate, but do not learn the optimum viewing angle or steadiness of fixation needed for maximum acuity, comfort and ease⁷.

We have observed clinically that individuals with small central scotomas may not need EV training or that patients whose visual system has selected a PRL may only need training to more effectively use that PRL. In other cases patients with extreme head turn have need to replace some of the head turn with EV to properly use telescopic devices. Patients who will benefit from EV training and the specific procedures to use for best results in different clinical scenarios need to be identified.

Although the need to train patients to use alternate areas of retina was clinically recognized many years earlier, only recently have instruments such as the scanning laser ophthalmoscope (SLO) enabled researchers to plot the PRL location, record the size and shape of scotomas surrounding the PRL, and evaluate the patient's ability to use a PRL. The research and development project proposed here will build on that work by developing methods and tools to evaluate EV training. Besides evaluation with the SLO, the use of head/eye tracking systems and self- reports of daily functioning will be used as outcome measures. Thus far, there have been a few supportive studies of EV training, some reporting faster reading speed after EV training, but controversy regarding which area of retina is most effective for reading^12-14, and confirmation that an area of peripheral retina more effective for reading can be established through training^15-17. Before substantive evaluation of cost efficient techniques can be undertaken, however, a comprehensive assessment protocol is needed to fully evaluate the impact of EV training on common daily living tasks, performed both with and without low vision aids.

The SLO and similar devices can be used to determine retinal areas used for EV or measure visual skills with the PRL using stimuli that can be displayed in the instrument. However, the SLO can't be used to evaluate eye position outside of the instrument. To identify the retinal area used for EV when patients are performing activities such as eating or crossing a street, or other everyday visual tasks, an eye tracking system is needed. Eye tracking measures made while the patient performs daily activities could be used to measure the efficacy of EV training.

It is important to combine measures of functional performance in the clinic (i.e., efficacy) with measures of self-report of functioning made after patients return to their homes (i.e., effectiveness). Raasch's review¹⁸ of low vision outcome studies indicates that studies measuring the direct effect of low vision intervention tend to concentrate on measures of efficacy. These measures of task performance are usually part of the process of evaluating training and prescribing for individual patients. They may not be a successful indicator of the overall impact of low vision intervention on functioning in the community¹⁹. Questionnaires with questions sensitive to EV effects could provide us with the means of measuring EV effectiveness.

Specific Aims

The overall objectives of this research and development project are to develop and validate measurement methods and tools that are required to perform outcomes research on eccentric viewing training, to apply those methods and tools in a clinical setting to assess sources of variability in measurements of the effects of EV training, and to perform parametric observational studies that will lead to testable hypotheses for future outcomes research.

Aim 1 is to develop and validate instruments for evaluating patients and measuring the outcome of EV training. There are several types of assessment that must be addressed. First, we must develop methods of measuring eye position before, during, and after EV training to quantify the patient's baseline behavior and determine if EV training produces the prescribed behavior. Incidentally, we will also be able to learn how long it takes for the patient to learn the prescribed behavior.

To achieve aim 1, we must be able to use a head-mounted eye tracking system that does not interfere with the patient's vision while performing everyday activities. The main issue that will be addressed by the proposed research is calibration. To calibrate the eyetracking system, we must compare it to a gold standard. For the proposed studies, the gold standard will be measurements made with a scanning laser ophthalmoscope (SLO).

Clinicians judge patient's viewing behavior by observing the patient's pupil and first Purkinje image. EV is described on a clock dial, with the center corresponding to the optic axis (or foveal line of sight) when the eye is centered in the orbit. EV evaluations and prescriptions are routinely specified with a precision of at least 30o (every hour), and in many cases with a precision of 15o (to the nearest half hour). The question is how accurate and reliable are clinician judgments of EV? A part of objective 1 is to assess EV quantitatively and compare the values to clinician judgments.

Often patients present with head turns that they have adopted as a strategy to assist them with EV. In these cases, one goal of EV training might be to teach patients to EV while maintaining normal head posture. Therefore, we must also develop methods of recording head position relative to the body while the patient is in EV training and when the patient is performing everyday activities.

Eye and head tracking will provide measures of the efficacy of EV training and enable us to measure how well and consistently learned EV skills are used while the patient is performing everyday activities. To measure the effectiveness of EV training, we must assess the patient's functional skills and the patient's perception of his/her functional capability. Therefore, the proposed project will also develop and validate a provider-based performance rating instrument and a patient-based self-assessment questionnaire. These instruments will be validated using analytic methods based on Rasch analysis.

Aim 2 is to evaluate the clinician's prescription of a trained retinal locus (TRL). Clinicians try to determine the retinal locus that has best visual acuity, or gives best visual function in some other way. In interviewing clinicians, it appears that besides visual acuity, they pay attention to the size and shape of scotomas, contrast sensitivity, metamorphopsia, and binocular interference. Therefore, the second aim of the program is to develop and validate methods of perimetrically measuring relevant aspects of visual function. We aim to develop methods of measuring central scotomas, visual acuity, contrast sensitivity, visual distortions, and Panum's area (disparity ranges for binocular fusion) as a function of retinal eccentricity.

Aim 3 is to apply the methods and instruments that we have developed to assess the efficacy and effectiveness of EV training. We must hasten to add that the proposed project is not a clinical trial with the aim of making recommendations regarding EV training. Rather, aim 3 tests the sensitivity of the methods and instruments to changes in EV behavior and to gather observational data that will help us to understand sources of measurement variability. By comparing outcomes to perimetric visual function and clinical measurements, we may be able to generate hypotheses that would be subject to test in a future formal clinical trial of EV training. The knowledge gathered in the proposed project is essential to the planning of a clinical trial.

References

1. Schuchard RA, Naseer S, de Castro K. Characteristics of AMD patients with low vision receiving visual rehabilitation. J Rehabil Res Dev, 1999; Oct:36(4)294-302.

2. Cummings RW, Whittaker SG, Watson GR, Budd JM. Scanning characters and reading with a central scotoma. Am J Optom Physiol Opt, 1985;Dec:62(12)833-43.

3. Timberlake GT, Mainster MA, Peli E, Augliere RA, Essock EA, Arend LE. Reading with a macular scotoma. I. Retinal location of scotoma and fixation area. Invest Ophthalmol Vis Sci, 1986;Jul:27(7)1137-47.

4. Timberlake GT, Peli E, Essock EA, Augliere RA. Reading with a macular scotoma II. Retinal locus for scanning text. Invest Ophthalmol Vis Sci, 1987;Aug:28:1268-74.

5. Schuchard RA, Fletcher DC, Maino J. A scanning laser ophthalmoscope (SLO) low-vision rehabilitation system. Clin Eye Vision Care, 1994;6(3)101-7.

6. Fletcher DC, Schuchard RA. Preferred retinal loci relationship to macular scotomas in a low-vision population. Ophthalmol, 1997;104(4)632-8.

7. Holcomb JG, Goodrich GL. Eccentric viewing training . J Am Optom Assoc, 1976;47(11)1438-43.

8. Goodrich GL, Mehr EB. Eccentric viewing training and low vision aids: current practice and implications of peripheral retinal research. Am J Optom Physiol Opt , 1986;63(2)119-26.

9. Watson G, Jose RT. A training sequence for low vision patients. J Am Optom Assoc, 1976;47(11)1407-15.

10. Backman O, Inde K. Low Vision Training. Malmo: LiberHermods, 1979.

11. Quillman RD. Low Vision Training Manual. Kalamazoo, Michigan: Western Michigan University, 1980.

12. Fine EM, Rubin GS. Reading with simulated scotomas: attending to the right is better than attending to the left.Vision Res, 1999;39;1039-48.

13. Petre KL, Hazel CA, Fine EM, Rubin GS. Reading with eccentric fixation is faster in inferior visual field than in left visual field. Optom Vis Sci, 2000;Jan:77(1)34-9.

14. Lei H, Schuchard RA. Using two preferred retinal loci for different lighting conditions in patients with central scotomas. Invest Ophthalmol Vis Sci, 1997;38(9)1812-8.

15. Frennesson C, Jakobsson P, Nilsson UL. A computer and video display based system for training eccentric viewing in macular degeneration with an absolute central scotoma. Doc Ophthalmol, 1995;91:9-16.

16. Nilsson UL, Frennesson C, Nilsson SEG. Location and stability of a newly established eccentric retinal locus suitable for reading, achieved through training of patients with a dense central scotoma. Opt Vis Sci, 1998;Dec;75(12)873-8.

17. Fletcher DC, Schuchard RA, Watson G. Relative locations of macular scotomas near the PRL: effect on low vision reading. J Rehabil Res Dev, 1999;Oct;36(4) 356-64.

18. Rasch TW, Leat S, Kleinstein R, Bullimore M, Cutter G. Evaluating the value of low vision services. JAOA, 1997;68:287-95.

19. Leat S, Fryer A, Rumney NJ. Outcome of low vision aid provision: the effectiveness of a low vision clinic. Opt Vis Sci, 1994;17:199-206.