Refractive Concerns
Chat Highlights
November 9, 2009

On Wednesday, November 9, 2009, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Refractive Concerns".

Moderator: Tonight's topic is Refractive Concerns.

P: What is the difference between a refraction and an eye exam?

Dr. Pro: Great topic.

A refraction is a part of a general eye exam. As you know from our chats an eye exam includes a general medical history, an ocular history, medicines and drops listed, and a chief complaint or reason for a visit. The exam includes a vision screen, check of the intraocular pressure, slit lamp exam. Sometimes more involved examinations are done such as a gonioscopy, dilated fundus, etc.

Refraction is the procedure where the patient’s spectacle needs are addressed. This is the part of the exam where the doctor or technician puts a device in front of the patient, and turns knobs while asking, "better one or two." This exam can be partially automated with new equipment.

P: Do glaucoma specialists perform refractions?

Dr. Pro: Many don't, as we tend to focus on glaucoma and leave refraction to optometrists or comprehensive ophthalmologists.

P: As we age, we have more difficulties during a refractive eye exam than we remember in our past. How could we differentiate the normal aging of the eyes from the problems of glaucoma so that every visual imperfection is not blamed on glaucoma?

Dr. Pro: In general we lose the accommodation ability as we age which is the ability to focus at near. This is due to gradual inability of the lens to change its shape as we age, so that after age 40 we start to need reading glasses. Now after about age 60, we start to develop cataracts, which is the gradual opacification of the natural lens. Typically cataracts cause glare, hazy vision, dim vision, and loss of appreciation of color hues. These are the most common refractive problems in the normal aging eye. Rarer causes of refractive errors can be from corneal disease or even retinal disease.

Glaucoma does not usually cause visual defects like these. In fact, early glaucoma is usually asymptomatic. Many times glaucoma causes a subtle peripheral visual field defect that is not very noticeable, and may be compensated by the fellow eye. More advanced glaucoma can cause loss of pattern recognition (recognizing faces) and limitation of ambulation ability.

P: My eyeglasses are doing a poor job for me. I just got them, but I can't read books, street signs, etc. Everything is blurry most of the time. I have NTG and cataracts. The loss of vision has happened rapidly over a period of 10 weeks. Before that my vision was "normal." At least my normal. My doc says I can't have surgery until my glaucoma is stabilized. Is there anything that can help my vision with my glasses?

Dr. Pro: Hard to say. If the visual loss is from the glaucoma then it is usually constant. If the visual loss is from the cataract, then it may be at least partially helped with new glasses as cataracts may cause a change in your refraction as the cataracts mature.

P: What type of difficulty will a patient have during a refraction if their loss from glaucoma is in the center of vision?

Dr. Pro: They can be difficult to refract. For patients like this, there are other refraction techniques such as retinoscopy which are objective (not based on patient input). Also there are eye doctors (mostly optometrists) who are low vision specialists. They work with patients with permanent visual loss to maximize the patient's visual functioning.

P: Can you describe what difficulties a patient will have if contrast is becoming an issue? Can anything be done during the refraction process to help with contrast sensitivity?

Dr. Pro: Ideally the room is dark and the projector has crisp lettering. It is not so much a problem in the exam room, but in the real world where contrast is such an issue—just open a magazine and see where there is type on a colored background.

P: How does a bleb from a trabeculectomy or a shunt effect refraction?

Dr. Pro: Glaucoma surgery can lead to astigmatism. In the case of a trab, tight flap sutures can put the cornea out of round. This can be temporary and once the suture is cut the astigmatism resolves. Sometimes the IOP can be too low post-op which can lead to a refractive change.

P: What are the advantages and disadvantages of an automated refraction?

Dr. Pro: The advantage is that is can speed up the exam process. A technician can perform the automated refraction while the physician examines patients, then the physician can fine-tune the refraction later. The disadvantage is that over-reliance on automation can lead to errors. The machine can be wrong.

P: Does glaucoma cause depth perception problems?

Dr. Pro: It can.

P: Is depth perception needed for a refractive eye exam?

Dr. Pro: No. In fact there is more to depth perception than binocular vision. Monocular patients can perceive depth, especially at distance. They do this with unconscious clues such as length of shadows.

P: Does an astigmatism affect the accuracy of an automated refraction?

Dr. Pro: The automated refraction can accurately pick up astigmatic errors.

P: New high resolution lenses are out in some geographical areas across the United States. What makes them better than the current method of eye correction?

Dr. Pro: I am really not aware of all the changes that take place with lenses in glasses. I am too busy keeping up with advances in glaucoma care! I know that some glasses can be make thinner than before for persons with high refractive errors, due to advances in lens materials.

Moderator: That's all the questions for this evening Dr. Pro. Thank you again. You are very generous to take the time to answer our questions.

Dr. Pro: Thanks everyone. Good night.

On November 18, Dr. Pro discussed "Glaucoma Medications" in the Chat room. Click here for highlights of that meeting.

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