O loss of sight, of thee I most complain! Blind among enemies, O worse than chains, dungeon or beggary, or decrepit age! – – John Milton
Our vision is precious to us, yet it is something that we often take for granted. Our ability to get up in the morning, take care of ourselves and go about navigating our daily routines is something to which we rarely give a second thought.
In my practice as an ophthalmologist and a glaucoma specialist, I frequently care for people who have lost, or are losing their eyesight. For many, it is a terrifying and often debilitating experience.
What exactly is LOW VISION?
In conversations with my patients, I commonly find that people do not understand how we quantify a person’s visual acuity. I often get questions like “How blind am I, doc?” when I am determining a patient’s eyeglass prescription. In the United States, eye doctors generally use the Snellen acuity chart to quantify a patient’s vision. From the Snellen chart we get results like the generally understood “20/20” vision or “20/40” vision. 20/20 vision means that a patient, with the best prescription eyewear possible, can see at 20 feet what the average patient can see at 20 feet. If you have a best corrected 20/40 vision, you have worse than average vision – you can see at 20 feet what the average person can see at 40 feet. Eye doctors use the Snellen Chart up to a level of about 20/400. If a patient sees worse that 20/400, We can quantify vision as “Count Fingers,” “Hand Motion” or “Light Perception.” Count Fingers and Hand Motion vision can be further specified as being able to detect the vision at a specific distance i.e. 1 foot. Light Perception vision can be either be with or without the ability to perceive the direction that the light is coming from. A patient with any of the preceding visual acuities, even light perception, would not be described as having “total blindness” by an ophthalmologist. Total blindness would be described as “No Light Perception” or NLP. A patient in the 20/30 to 20/60 range may be describe as near normal vision, or mild vision loss. A patient with a best corrected vision of 20/70 or worse would be described as having “low vision.”
What causes LOW VISION and what are the symptoms?
There are a multitude of diseases that can result in reduced vision. These diseases may affect the entire body and secondarily the eye or may be localized to the eye itself. In the United States, three of the most common disease that result in low vision are MACULAR DEGENERATION, GLAUCOMA, and DIABETIC RETINOPATHY.
Below are some representative images of how a person affected by each of these conditions may see.
A representation of possible outcome of diabetic retinopathy
A representation of possible visual effects of macular degeneration
A representation of possible visual effects of glaucoma
A patient with low vision can have increasing difficulty reading, writing, driving a car. Depending on the degree of vision loss, a patient may lose the ability to function independently. This often puts significant strain on the sufferer and their families.
How is LOW VISION diagnosed and prevented?
Having access to an examination by a qualified eye doctor (Optometrist or Ophthalmologist) is the most important method of diagnosing LOW VISION. Many causes of low vision can be stabilized or improved with accurate diagnosis and treatment. Seeking out a good eye doctor for an annual examination is especially important for those with a family history of VISION LOSS. A personal history of visual changes or the presence of a systemic disease known to cause eye damage (i.e. diabetes) should prompt an immediate eye visit.
What RESOURCES exist for low vision patients?
There are a number of good websites with additional information about the causes, diagnosis and treatment of LOW VISION. I have listed several of them below from the NEI, NIH, American Academy of Ophthalmology, and the Glaucoma Research Foundation. In Tucson, the Southern Arizona Association for the Visually Impaired has been providing outreach and services in our community for over 50 years.
Jason M. Levine, MD