Flicker Fusion Thresholds Between Young and Old Subjects at Various Luminance Levels

Age-related macular degeneration (AMD) is a chronic, progressive eye disease. AMD is one of
the leading causes of visual impairment and blindness among elderly populations in
economically developed countries . Due to the aging of the population, the incidence and
prevalence of AMD is likely to increase substantially over the next decade, potentially
posing a significant impact on society.

AMD is a complex and progressive degenerative disease, with both genetic and environmental
risk factors. AMD affects the outer retina, retinal pigment epithelium (RPE), Bruch's
membrane, and choroid. The retina is among the most metabolically active tissues in the
body, in part due to rods, which frequently discard their outer segments tips, and the RPE,
which phagocytoses the discarded tips . The retina's metabolism causes accumulation of toxic
by-product by the following: 1. Energy metabolism (oxidative stress); 2. Visual cycle
modulator (lipofuscin); 3. Local inflammation (complement activation). The local
inflammation, and the accumulation of lipofuscin material within the RPE, may lead to drusen
formation, RPE dysfunction, and degeneration of macular rods and cones, finally leading to
the irreversible loss of vision.

AMD occurs in two forms - a non-exudative "dry" form and an exudative "wet" form.
Non-exudative AMD accounts for 80-90% of AMD cases and it involves a diverse phenotype that
may include drusen and/or RPE pigmentation abnormalities. Advanced non-exudative AMD is
characterized by geographic atrophy, which is characterized by the presence of an expanding
region of irreversible RPE and photoreceptor loss in the macula.

At the present time, there are no approved treatments for non-exudative AMD. The clinical
development of therapeutic agents for the treatment of non-exudative AMD is limited by slow
disease progression, unsuitability of commonly used efficacy endpoints such as visual
acuity, and difficulty in identifying those subjects with early stages of disease most
likely to progress. Visual function testing may prove to be useful tools in detecting the
early non-exudative AMD.

In early age-related macular degeneration, outer retinal metabolism is known to be
compromised. The detection of a flickering stimulus imposes a higher metabolic requirement
than does a static stimulus , . Inability to detect a flickering stimuli may identify
earlier stages of disease than the inability to detect static stimuli. Early work by Mayer,
et.al. has shown that AMD subjects experience functional deficits in the mid range of visual
phenomenon most notably at 10HZ and 14Hz. Phipps, et.al. found early AMD subjects to have
larger deficits for flickering than static stimuli . Later work has shown that a flicker
test based on mid-range frequencies has been shown to have effective diagnostic and
reproducibility characteristics relative to other functional tests . In addition to the
diagnostic potential of flicker stimuli, this test has been shown to be predictive of AMD
progression and correlated to AMD severity . Therefore, a flicker test may prove useful in
identifying early dysfunction in macular performance and for assessment treatment in future
interventional clinical trials.

Critical Flicker Fusion (CFF) is a type of flicker test that involves increasing the
frequency of a flashing stimulus until that stimulus appears static to an observer. The
frequency at which critical flicker fusion occurs is recorded as a patient specific endpoint
of visual function. In this study, we will investigate CFF across a wide range of luminance
levels, from photopic to scotopic ranges, in young and old subjects with normal ocular
health. The impact of age on CFF threshold will be the focus of this study, with the primary
objective being to highlight luminance levels where maximum differences between young and
old subjects occur.

Inclusion Criteria:

- Provide written and informed consent;

- Be willing and able to follow all instructions and attend the study visit;

- Must be able to successfully complete all study procedures;

- If female and of childbearing potential, not be pregnant, nursing, or planning a
pregnancy and be willing to submit a pregnancy test at Visit 1 (and exit visit as
applicable) and utilize an acceptable form of birth control for the duration of the
study;

- Be 18 years of age or older

- Have best-corrected distance visual acuity (BCVA) of better or equal to 20/30 in at
least one eye at Visit 1;

- Have best-corrected near visual acuity of better or equal to 20/30 in at least one
eye at Visit 1;

- Have visited an ophthalmologist for an eye exam within 1 year of Visit 1;

Exclusion Criteria:

- Have a history of age-related macular degeneration (exudative and non-exudative),
diabetic retinopathy, retinal detachment, or any chronic retinopathy or retinal
degenerative disease;

- Have had prior retinal vein or artery occlusion, history of macular edema, or optic
neuropathy;

- Have a history of glaucoma or ocular hypertension

- Have visually significant cataracts at Visit 1;

- Have a history of ocular trauma;

- Have a history of photophobia reported at Visit 1;

- Report ocular discomfort of 2 or greater in either eye at Visit 1, or report any
other ocular symptomatology that could in the opinion of the investigator interfere
with study procedures;

- Have active signs or symptoms of conjunctivitis, uveitis, in either eye at the
baseline examination of Visit 1;

- Be currently enrolled in an investigational drug or device study or have used an
investigational drug or device within 7 days of entry into this study;

- Have used contact lenses 24 hours prior to the start of the study or be unwilling to
discontinue wearing for the duration of the study;

- Have a history of uncontrolled systemic disease (e.g. poorly controlled hypertension
or poorly controlled diabetes, a history of status asthmaticus, organ transplant) at
Visit 1;

- Have a history of seizures;

- Be currently taking procyclidine, alprazolam (Xanax), lorazepam (Ativan), Adderall,
or any psychotropic medications;

- Be a woman who is pregnant or nursing an infant

- Have a condition or be in a situation that the investigator feels may put the subject
at significant risk, confound the study results, or interfere significantly with the
subject's participation in the study;