Investigating Optical and Neural Causes of Vision Loss

Vision loss has become a major public health problem due to the growth and aging of the
population. Age-related macular degeneration (AMD) is the most common cause of vision loss
in people over 50 years of age. In the United States, over 10 million people have AMD and
over 1.6 million people age 50 and older have late-stage advanced AMD. It is well
established that AMD patients with central vision loss use preferred retinal loci (PRL)
which are peripheral retinal areas adjacent to the fovea for performing daily activities,
such as reading. However, even in healthy eyes, peripheral vision is limited due to reduced
neural sampling density compared to the fovea. Additionally, the function of the peripheral
retina can be further reduced in patients, owing to degenerative disease processes. These
neural substrate losses are coupled with losses in the quality of the optical image on the
retina. Optical imperfections increase with age and off-axis viewing, compared to viewing
along the optical axis of the eye. The combination of these factors plays a significant
role in reducing visual performance of patients with eccentric fixation. The long term goal
of the project is to improve the visual performance of veterans with central vision loss by
development of innovative approaches that will optimize the benefit of vision rehabilitation
techniques. In the current proposal, optical and neural losses will be assessed in AMD
patients with central vision loss using novel techniques. Increased optical losses due to
age and viewing off the optical axis of the eye will be established with wavefront analysis
technology. Increased neural losses due to retinal dysfunction at PRL will be determined
based on measurement of visual acuity with blurred stimuli. Improvement in reading speed
will be evaluated, conditional on neural losses at PRL and/or the stability of PRL, after
compensating for optical losses with our adaptive optics system. The findings will provide
knowledge of PRL function and stability that is beneficial for improving the outcome of
available vision rehabilitation methods that train patients to better use their PRLs. Also,
customized correction of optical imperfections of the eye for effectively improving visual
performance can be developed as an approach for better vision rehabilitation of patients.
Optimizing vision rehabilitation of our veterans will allow them to maintain function and
productivity.

Inclusion Criteria:

Standard inclusion criteria are:

- qualification for entry into the study based on clinical evaluation,

- competence to understand and willingness to sign an informed consent form and
participate in the study,

- pupils that dilate to 5 mm or more.

The inclusion criteria for normal subjects will be:

- corrected visual acuities better than 20/30,

- intraocular pressure less than 21 mm Hg,

- no family history of AMD,

- no history of ophthalmic surgery or neurologic disease,

- no history of diabetes, glaucoma, or a history of elevated intraocular pressure.

The recruitment will ensure that approximately 40 subjects will fall into each of the
three age groups, 50 to 60 years, 61 to 70 years, and 71 years and older. One eye of each
subject will be selected at random to be included in the study.

Exclusion Criteria:

- Ocular opacities that preclude acquiring a clear fundus photograph or refractive
errors greater than 4 diopters.