Glaucoma and Visual Function
Chat Highlights
April 12, 2006

On Wednesday, April 12, 2006, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Glaucoma and Visual Function."

Moderator:  Good evening, Dr. Wilson.  Tonight our topic is Glaucoma and Visual Function. How is visual function assessed?

Dr. Rick Wilson:  Visual function consists of a variety of physical perceptions.  Most of you are aware of the Snellen acuity chart, which starts with the big E at 20/400 vision, has black letters on a bright white background, and is viewed in a dark room.  Clearly, that is not representative of real life, when light may be coming in from many directions, causing glare or washing out the contrast of the letters.  A cataract may also cause glare.

P:  Do your patients often complain about a lack of contrast sensitivity?

Dr. Rick Wilson:   Yes, that's common in glaucoma patients.  My patients tell me they can see things with good light, especially if the things are black on white, but not gray on gray, or if the lighting is poor.

Moderator:   What else is involved in assessing visual function?

Dr. Rick Wilson:   The perception of motion and color.  Many people with glaucoma lose color vision on the blue-yellow axis before they lose it on the red-green axis.  As retinal ganglion cells drop out, the perception of motion can be affected, though this does not seem to be an early change.

P:   The loss of color vision came as a shock to me.  How much damage typically occurs before that happens?

Dr. Rick Wilson:   That varies widely.  The Short-Wavelength Automated Perimetry (SWAP) test is based on blue lights on a yellow background, and is supposed to pick up glaucoma before the white-on-white perimetry.  However, I have patients with advanced glaucoma who do well on color tests.

P:   Why is the blue-yellow visual field test recommended for glaucoma suspects?

Dr. Rick Wilson:   Because it picks up glaucoma damage before the white-on-white perimetry, often by several years.

P:   Last year my visual acuity varied from 20/20 to 20/25 to 20/30.  Why was that?

Dr. Rick Wilson:   The Snellen acuity you speak of can be variable, depending upon how much illumination is washing over the board where the letters appear.  Different rooms may have brighter or dimmer bulbs in the projector, or the lens of the projector may be smudged, making the letters difficult to see.

P:   What causes vision to fluctuate in glaucoma patients?

Dr. Rick Wilson:   Eyedrops disturb the tear film, which causes blurred vision.  If the intraocular pressure is low, the eyelid position on the cornea and the pull of the eye muscles on the eye wall distort the cornea, causing variable vision.  In patients with advanced glaucoma, variable vision is thought to be caused by variation in optic nerve or retinal circulation.

P:   Is acuity the only aspect of vision that can be corrected?

Dr. Rick Wilson:   No.  Snellen acuity is the chief aspect that can be focused with lenses.

P:   How is the perception of motion affected by glaucomatous loss of visual field?  I am wondering if that explains why I am frequently startled to find my son is standing in front of me. It's as if I never see him coming.  Does that sound like a problem with motion perception?

Dr. Rick Wilson:   No, it sounds more like your visual field is constricted, and you don't see him coming in from the side.

Moderator:   What does a "constricted" visual field mean?

Dr. Rick Wilson:   Tunnel vision is the ultimate constricted visual field.  Visual impairment involves a loss of peripheral vision. In other words, the visual field shrinks toward the center.

P:   Does glaucoma with moderate optic nerve damage affect depth perception?

Dr. Rick Wilson:   It can if one eye does not see as clearly in areas as the other.  Both eyes need to see an object clearly to obtain the best stereo vision and depth perception.  [Editor's note:  Stereo vision is visual perception of or exhibition in three dimensions.]

P:   I have glaucoma in my right eye only and have had cataract surgery in that eye only, with an intraocular lens that leaves me with -2 diopter correction.  I have minimal visual field damage in my right eye.  My left eye is myopic by about 4.75 diopters.  When I'm reading in bed in low light without my glasses on, everything seems to get darker and lighter in something like waves.  

Have any of your patients mentioned that happening to them?

Dr. Rick Wilson:   I've heard all kinds of symptoms over the years.  I wonder if you are focusing back and forth between your more-and-less myopic eyes, since they will have trouble focusing together.

P:   Can fluctuating IOPs (intraocular pressure) affect the cornea enough to affect vision?

Dr. Rick Wilson:   If the IOPs are low enough, or if they are high long enough to hurt the lining of the cornea and cause corneal swelling, that could affect vision.

P:   Are the night-vision cells lost at about the same rate as the cells responsible for more complex vision? I have varying "blackouts," too.

Dr. Rick Wilson:   I think so, but I am not sure.  The "blackouts" are worrisome.  Have you told your ophthalmologist?

P:   Yes, thanks.

P:   If the IOP is elevated or fluctuating, doesn't that cause a decrease in visual acuity?

Dr. Rick Wilson:   If your IOP is never less than 12 mm Hg, it has to vary markedly to cause your vision to fluctuate.  It is a symptom of advanced, not early, glaucoma.

P:   Where does damage to the optic nerve start?

Dr. Rick Wilson:   The damage to the optic nerve and retina starts and is most concentrated at 6 to 7 and 11 to 12 o'clock in the right eye and the mirror opposite in the left eye.

P:   If one pupil is larger than the other, can that cause problems with vision?

Dr. Rick Wilson:   Obviously, if the larger pupil does not shrink in response to bright light, glare and sensitivity to bright lights could be a problem.

P:   The first thing in the morning, I have to physically hold and move my left eye to point front and center; otherwise it points far left.  It feels really strange, as if the muscles are slow or not working.  Could Xalatan, Cosopt, or Alphagan cause that?

Dr. Rick Wilson:   You are right; that sounds very strange.  I don't think it is related to your topical medications.

P:   The ink on printed material is not dark enough.  Paint and reflectors on roads at night look old and faded.  Instructions on over-the-counter medicine bottles are too tiny to read.  How much of that is due to glaucoma and how much to being in my Forties?  How am I supposed to figure that out?

Dr. Rick Wilson:   The only way is to ask other people your age who have healthy eyes if they are having trouble seeing what you are having trouble with.  Or take a couple of examples with you when you go to see the doctor.

Moderator:   Dr. Rick, that was the last question.  On behalf of the group, a very big thank you!  Go get some rest.

Dr. Rick Wilson:   Have a great holiday. See you next week.

On April 19, Dr. Wilson discussed "Helping Your Doctor Help You" in the Chat room. Click here for highlights of that meeting.

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