Vision Imperfections
Chat Highlights
July 1, 2009

On Wednesday, July 1, 2009, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Vision Imperfections".

Moderator: Welcome back, Dr Pro. Our topic this evening is Vision Imperfections. This topic was suggested by one of our readers. What are some imperfections, defects or flaws a glaucoma patient might have?

Dr. Pro: OK, I guess the most common "imperfection" is the scotoma (area of relative reduction in the visual field) seen in many glaucoma patients. Now this may be perceived very little at first, especially if the area of reduced visual sensitivity is more peripheral, but, if the damaged area is more central in the visual field, or if the peripheral defect encroaches on the central vision, then the patient may become aware of the defect in his or her vision. Some patients can be frustrated by this, and are aware of this loss centrally.

Other known visual defects in glaucoma patients are a loss of contrast sensitivity. This is more subtle than a person missing part of the visual field. It means that facial recognition can be more difficult, or matching similar objects is hard.

The loss of peripheral vision and the loss of contrast sensitivity can cause glaucoma patients to have difficulty with some basic functions, like navigating in a dim, unfamiliar room, or walking down steps (in persons with inferior field loss).

P: Is a scotoma a blind spot in layman's terms? Can you define peripheral?

Dr. Pro: A blind spot, that's right, but it's not always so absolute; sometimes the vision is just dimmer in the affected part of the visual field.

Peripheral is the vision "out of the corner of your eye." Imagine yourself staring straight ahead at a clock on the wall. While looking at the clock, imagine being able to see a person walking by in a window off to your side; that's your peripheral vision.

P: At what point do you send a patient to a low vision specialist?

Dr. Pro: There is no set time. In general, I send patients who have significant visual field constriction (i.e. less than 10 degrees from center) and/or loss of central acuity (i.e. corrected vision that is less than 20/80).

A low vision exam can be helpful, by introducing visual aids like closed-circuit TV to greatly magnify reading materials, and a low-vision specialist may have the patience and understanding to better refract a person with significant visual impairment.

P: What is a halo and are halos always a sign of trouble?

Dr. Pro: A halo can mean several things. At one level, it can be really worrisome in a glaucoma patient because it can mean that the IOP is suddenly high. A sudden elevation in the IOP can cause corneal edema (swelling caused by retained fluid in the cornea). The edema causes lights to look hazy and have a halo. For this reason we ask patients to come in if they have pain and a halo, the classic scenario is an angle closure attack.

But halos can occur at other more benign times, like in cases of really dry eyes or after surgery, which can also cause temporary corneal edema.

P: What is the difference between a floater and a flasher?

Dr. Pro: A floater is generally perceived as a dark spot, speck, or ring that floats around in front of your vision. It may be more noticeable in certain lighting. A flash is just what it sounds like, a flash of light, like a lightning bolt in the corner of your vision. This usually occurs in only one eye and may be more noticable in the dark. Both can be a sign of retinal problems.

A floater is really common, but new onset floaters can be a sign of a retinal tear. A flash is rarer and more specific for a retinal hole or tear. New floaters and/or flashes needs to be evaluated by your eye doctor ASAP.

P: My Dad described his vision as having a dent in it. He just couldn’t see the pin clearly when he would play golf. Could this have been from macular degeneration or undiagnosed glaucoma?

Dr. Pro: Hard for me to say. Both conditions can affect the vision. Classically glaucoma affects peripheral vision before central vision (But not always!). Macular degeneration affects only central vision. Types of macular degeneration (wet) can cause a distortion of the vision (straight lines may look wavy).

P: Hi Dr. Pro. I've been seeing a fern-like after-image lately when I close my recently operated eye. I had a tube shunt placed in my eye 5 weeks ago. I'm assuming it's all part of the healing process?

Dr. Pro: I have heard various visual distortions after surgery. The most common is a generalized blurriness, often from tight corneal sutures. This resolves as the sutures are removed or dissolve. I wonder if your problem has something to do with the lid kind of pressing on the eye as you blink, maybe the tube has caused an elevation on the eye. I would think this should improve as the eye continues to heal. Obviously talk to your doctor if symptoms worsen, or you have any pain.

P: I recently had a YagPI. Things went well, however, I now have a bright light across center of my vision, like a straight horizontal line, sometime diagonal. Is this some kind of glare that might be normal post laser?

Dr. Pro: This can happen after the PI. I always warn patients that it can happen and is usually temporary. It's probably from light bouncing into the eye at an unusual angle. Certainly let your doctor know about your problem. Flashes in a dark room can be a sign of a retinal problem as I discussed above.

P: Do all glaucoma patients have floaters?

Dr. Pro: No, but floaters are really common in people as they get older, or in people who are more myopic. In fact the majority of people over 80 have floaters. It's a manifestation of the aging eye. A jelly-sticky substance called vitreous fills the inside of the eye. As you age the vitreous liquifies and pulls away from the retina. You may detect the edge of the vitreous as a floater. This is called a posterior vitreous detachment.

P: Are glaucoma patients more prone to cataracts? What does one look for if they think they might have a cataract brewing?

Dr. Pro: Well, there is ample evidence that glaucoma surgery causes or accelerates cataract development. Cataracts may cause a generalized gradual blurring of the vision, or more specific complaints like glare from on-coming headlights or streetlights, difficulty reading, worsened color perception (paintings look dull).

Moderator: Thank you, Dr Pro. Our time is up.

Dr. Pro: Always a pleasure! Good night.

On July 15 , Dr. Myers discussed "Blebitis and Endophthalmitis" in the Chat room. Click here for highlights of that meeting.

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