What Is Low Vision?
Chat Highlights – January 7, 2015
Guest Speaker – Dr. Michael Pro
Lorraine Miller, Editor, Chat Topic Researcher
Moderator: Happy New Year and welcome to our first moderated chat of 2015, “What Is Low Vision?” We are very pleased to have with us Dr. Michael Pro, a glaucoma specialist at Wills. Dr Pro, let’s start with the topic question: What is low vision?
Dr Pro: The definition of legal blindness, according to the Social Security Administration, is 20/200 vision or worse in the better seeing eye or a visual field of less than 20 degrees. Low vision is not an exact medical term with a clear definition but it refers to a condition where the visual function is impaired due to a medical condition. The most common causes in the U.S. are diabetic retinopathy, macular degeneration, and glaucoma.
P: What is a visual field of less than 20 degrees? I have copies of my visual fields. Where do I find this information?
Dr Pro: The visual field requirement was defined on the older Goldmann device. But modern tests can be substituted. There are hash marks on the test printout that indicate the degrees from the central point. You can review this with your glaucoma specialist.
P: What are the symptoms of low vision?
Dr Pro: Symptoms can vary widely. In general, low vision refers to impairment in usual visual function such that common activities or daily living are affected. Reading, navigating an unfamiliar area, and recognizing faces are a few examples.
P: Are red-tipped canes only used by those legally blind or are they also used by those with low vision?
Dr Pro: There is no requirement of legal blindness to get a red tipped cane as far as I am aware. I think they help identify profoundly blind individuals to pedestrians and motorists around them. I think this is a safety issue.
P: Does it benefit the patient if he or she is classified as blind rather than low vision as far as available services are concerned?
Dr Pro: Yes, getting a legal blindness definition can help in obtaining services from federal and state agencies. This can include parking placards or help with transportation services.
P: The Snellen chart jumps from 20/100 to 20/200. Isn’t that a large step in vision to classify a person as having vision to blindness?
Dr Pro: Yes, there are other charts that can record vision in between; for instance, the EDTRS chart. In addition, new digital wall charts may be able to record vision between 20/100 and 20/200. In these instances, vision recorded worse than 20/100 would meet the definition of “legal blindness.” In other words, 20/160 would meet the definition.
P: At what point does a glaucoma specialist discuss low vision with a patient?
Dr Pro: That is a great question. We are confronted daily with patients who have impaired vision. I am often amazed how some patients with very poor vision seem to function without any obvious difficulty and others with seemingly great vision are unhappy. I try to refer to low vision services when the vision falls into the range that we have been discussing.
P: Are there questions I should ask my glaucoma specialist to assess my vision or vision loss?
Dr Pro: Well, it is instructive to ask whether one has a very constricted field as this can affect the ability to safely operate a motor vehicle. Also you can ask what can be done to improve your level of visual functioning. This is where a low vision evaluation can be helpful. A low vision evaluation can determine which devices or behavioral modifications can maximize your visual function. This may include optimizing glasses for particular tasks such as reading, walking, watching TV, and behavioral modification such as deliberate head turning during driving for individuals with good acuity but limited peripheral vision.
P: Apart from some technological aids, are there any clinical ways to mitigate glare or other factors that cause low vision?
Dr Pro: Glare is a common complaint that I hear in my patients with more advanced glaucoma. I think some of this is due to dry eyes. Cataracts may also account for some glare, but some seems to be due to limited vision. I think that amber sunglasses can help, which is a less expensive option, as well as polarized sunglasses, a more expensive choice.
P: How can I find a resource for low vision aids in my community?
Dr Pro: First, I like to direct patients to visit lighthouse.org which is dedicated to low vision services and can provide direction to local resources. Patients can contact city or local social services to find low vision resources. For example, down the street from Wills Eye Hospital is the Associated Services for the Blind & Visually Impaired (asb.org). Finally, there are optometrists who specialize in low vision and they can be located by inquiring about them from your glaucoma doctor or by a Google search.
P: Can a doctor predict how long a person with macular degeneration or glaucoma may retain their sight if their existing visual acuities are around 20/20?
Dr Pro: The answer is determined by review of the visual fields, evaluation of OCT or macular imaging in the case of macular degeneration, and review of the history of glaucoma progression. There is no exact science on this determination but a glaucoma specialist can get a gut sense of the risk of visual worsening based on clinical exam, history, and clinical experience with many other patients.
P: Could you describe some of the training that low vision specialists undertake? Are they optometrists or ophthalmologists?
Dr Pro: They are almost always optometrists. I cannot comment as to their training. I will admit that I was not exposed to low vision training during ophthalmology residency where the focus is more on surgical training and medical management of eye disease.
P: What values determine when a glaucoma patient should stop driving at night? Will you as a specialist advise a patient not to drive based on a visual field? Do you have to report it?
Dr Pro: There is a duty to report individuals who have visual impairment that is determined by individual state regulations. Yes, I do have to discuss driving with my patients and it can be a very difficult discussion.
P: Is degeneration of the optic nerve usually a steady thing or can it halt for a while after some progression?
Dr Pro: By degeneration I think you are referring to on-going damage to the optic nerve due to eye pressure too high for an individual’s eye. This is the process of glaucoma and it can be halted in many cases by reducing the eye pressure to a certain level with drops, lasers, or surgery.
Moderator: Thank you so much, Dr. Pro and our chatters.
Dr. Pro: Thanks to you and all the chatters. Great questions as usual!