Glaucoma
Top photos: two optic nerves demonstrating "cupping" or excavation indicative of damage due to glaucoma
Bottom photos: two normal optic nerves
What is glaucoma?
Glaucoma is a condition that damages the eye's optic nerve (top photos above) by giving the nerve a cupped and excavated appearance.. Most cases of glaucoma are associated with elevated pressure inside the eye, which is unrelated to a person's blood pressure. Glaucoma is one of the most common causes of irreversible blindness in American adults, with 1.6% of Caucasians and 4.6% of African Americans affected by age 40. This prevalence increases with age, and more than quadruples by age 80.
What causes glaucoma?
Prior injury, inflammation, infection, or surgery can render a patient's eye more susceptible to glaucoma, but the vast majority of cases are genetic in nature. Several genes have been implicated in the development of adult-onset, adolescent-onset, and even congenital-onset glaucoma. Most cases of glaucoma stem from abnormalities in the area of the eye's natural drainage structure, resulting in persistent elevated eye pressures that can cause damage to the optic nerve.
What are the symptoms of glaucoma?
Early optic nerve damage causes no noticeable symptoms, but peripheral vision testing (visual fields) performed in the clinic may detect subtle changes in a patient's ability to detect peripheral visual stimuli. Moderate optic nerve damage causes loss of peripheral vision which may or may not be noticeable, and advanced optic nerve damage causes severe peripheral vision loss that results in tunnel-vision. Total excavation of the optic nerve can occur in end-stage glaucoma, resulting in total blindness.
How is glaucoma diagnosed?
Most cases of glaucoma are diagnosed through identifying a combination of elevated eye pressure, and evidence of optic nerve damage. The optic nerve damage can be visualized through direct eye exam in the clinic if the optic nerve has a "cupped" or excavated appearance, but not all "cupped" optic nerves are glaucomatous. For this reason, ancillary tests, such as peripheral visual field analyzers, are crucial to confirm the diagnosis.
Since glaucoma adversely affects one's peripheral vision prior to any changes in the central vision, formal visual field testing is the only way to reliably detect any early symptoms of glaucoma. Traditional automated visual field examination in clinic has been the mainstay of peripheral vision testing, performed once or twice yearly.
How is glaucoma treated?
Once glaucoma is diagnosed, therapies aim to reduce pressure inside the eye to prevent progression of the disease. Glaucoma cannot be reversed once optic nerve damage has occurred, but further progression can be halted.
Initially, eye drops are used to lower the eye pressure, either by improving fluid outflow from the eye's natural drainage structures, or preventing fluid production. In-office laser therapy can also be used to improve the eye's natural drainage. This type of laser is called "selective laser trabeculoplasty (SLT) and is an entirely different procedure than "LASIK".
If these treatments sufficiently lower the eye pressure and in-clinic examination of visual field and optic nerve health are considered stable, then the disease is considered halted. This scenario occurs in most cases if gluacoma is caught early enough. In severe cases, surgery is required to prevent further vision loss.
Top images: Normal optic nerve (left) and normal result of visual field testing in the clinic (right).
Bottom images: Optic nerve with cupping / excavation suggestive of glaucoma (left). Diagnosis is confirmed with visual field testing (right) in clinic demonstrating inability to detect peripheral visual stimuli (black and gray areas).
Tablet-Based Home Monitoring for Enhanced Glaucoma Screening
Glaucoma is an important cause of irreversible blindness in North America and worldwide. In Americans over the age of 40, the approximate median age-adjusted prevalence is 1.6% of Caucasians and 4.6% of African Americans. This prevalence increases with age, and more than quadruples by age 80. The prevalence of blindness in Caucasians and African Americans with glaucoma is 4% and 8%, respectively.
These statistics, and the associated morbidity and quality of life implications, make the early detection of glaucoma an important public health consideration.
How does the tablet-based app work?
The Melbourne Rapid Fields perimetry application (iPad 3, Apple) tests the patient's visual field at a working distance of 33cm in 2 stages. First, an initial central field test is carried out with 36 peripheral test points while the patient maintains visual attention "fixation" on a target at the center of the screen. In the second stage, four increased peripheral tests are carried out with 30 test points while the patient fixates at each corner of the iPad screen.
The peripheral vision testing stimuli increase in intensity in 7 steps ranging from 0 to 30 decibels (db). Voice-over instructions remind the patients to wear their normal reading glasses, to occlude the other eye with a tissue over the lens, and to maintain the proper 33cm viewing distance from the screen.
The earliest stages of glaucomatous visual field damage tend to occur in the outside rims, usually 10-15 degrees away from the central fixation, in the upper field or toward the nose. Formal visual field machines in the clinic can detect these defects by testing the central 24 to 30 degrees of a patient's visual field. The tablet screen represents 17.4° × 12.9° of visual field at 33 cm; by using the 4 corners as targets, the patient's visual field can be tested out to 34° horizontally and 25° vertically.
Each eye’s visual field is assessed in approximately 4 minutes. A visual field test is reliable only when the patient maintains fixation on the specified target without looking around in other directions. The tablet app assesses fixation through blind-spot monitor method that uses randomly exposed stimuli in a patient's natural blind spot to detect any deviations away from the target that would make the results unreliable.
What are the results of the tablet-based visual field screening and how will it change glaucoma treatment?
In a recently published article in Ophthalmology, researchers from Australia and the UK found that by incorporating tablet-based visual field screening at home on a weekly basis, the amount of visual field loss that would have been detected in 2.5 years with formal in-clinic testing was detected in 0.9 years with the addition of the home app.
This evidence demonstrates that app-based technology can serve as a helpful supplement in the screening of some of our most important blinding diseases, but it does not serve as a replacement for regular follow up with your eye doctor with formal in-clinic testing.
This glaucoma example serves as the perfect benchmark for the intersection between home-based technology and formal clinical evaluation, as the incorporation of one clearly can enhance the other. Using home-based screenings to send real-time clinical data to a physician opens the door to not only improving health care outcomes in established patients, but also improving health care access to potential patients in remote and under-served areas in the United States and abroad.