Refractive Surgery in the Glaucoma Patient
Chat Highlights
January 21, 2009

On Wednesday, January 21, 2009, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Refractive Surgery in the Glaucoma Patient".

Moderator: Welcome back to our Chat, Dr. Pro, and chatters. Our topic this evening is “Refractive Surgery in the Glaucoma Patient.” Dr. Pro, can you first explain what refractive surgery is?

Dr. Pro: Refractive surgery is any procedure that aims to correct visual acuity. Implicit is the understanding that refractive surgery is generally performed on otherwise healthy eyes, in persons who desire a reduction or elimination in the need for corrective eyewear or contact lenses. The most common surgeries are laser refractive surgery in which the cornea is modified to improve the vision, such as LASIK or PRK.

P: What are the differences in types of refractive surgery?

Dr. Pro: I mentioned above there are LASIK (laser-assisted in situ keratomileusis) or PRK (photorefractive keratectomy) . These procedures are related in that both utilize a laser to thin the cornea and in that fashion improve the focusing on light on the retina (usually in myopes or nearsighted persons). There are other procedures such as laser techniques to reduce need for reading glasses in presbyopes (most people over 50) but this technique is less common than LASIK or PRK.

P: Are refractive surgeries performed after other eye surgeries?

Dr. Pro: Yes, some doctors will perform LASIK or PRK after cataract surgery. This is becoming more common with the advent of multifocal intraocular lenses, which can allow some patients to see both distant and near after cataract surgery without spectacles. But multifocal lenses are an additional cost in the U.S. and for these demanding patients LASIK after surgery is sometimes used to make sure that the patient does not need glasses after cataract surgery.

P: Why do multifocal intraocular lenses make refractive surgery after cataract surgery more common?

Dr. Pro: They don't make them more common, but they are a cause of increasing patient expectation. Ten years ago patients may have been happy with good vision but needing glasses after cataract surgery; today some patients expect to be completely glasses free after cataract surgery. These persons can receive refractive surgery (LASIK) after successful cataract surgery.

P: Should LASIK be denied to patients with glaucoma?

Dr. Pro: That's a great question! Certainly it depends on the extent of glaucoma and I would not recommend LASIK to persons with advanced disease. But for early to moderate disease it is a bit less clear cut. There are risks to LASIK surgery that could impact a glaucoma patient. For instance, during LASIK there is a moment when the pressure goes as high as 90 mmHg. It is momentary, but it might be too high for an already compromised nerve in a glaucoma patient.

P: How do you define moderate versus advanced glaucoma?

Dr. Pro: There is no definition, but I look at the nerve cupping as well as the extent of visual field loss. I consider anything over a small glaucoma defect to represent moderate glaucoma.

P: Does that mean PRK is better for those with glaucoma?

Dr. Pro: There is some concern that LASIK may be risky due to momentary elevated IOP, so PRK may be better for glaucoma patients.

I'll explain a bit more about LASIK and PRK. As I said both, correct the vision by changing the thickness and shape of the cornea to improve the eye's ability to focus light on the retina.
In LASIK a thin flap is made over most of the cornea. The flap is reflected (folded) over and the laser then ablates the corneal bed a pre-set, individually determined amount.

In PRK there is no flap (and no elevation in the IOP from the device that makes the flap). Instead the outermost layer of the cornea is scraped off and the cornea is ablated with the laser.
Both techniques have similar success, but LASIK is more comfortable because there is no large corneal abrasion.

P: Does the thickness of the cornea come into consideration?

Dr. Pro: Yes, after LASIK or PRK the cornea is thinner by a variable amount. Also the corneal biomechanical properties are changed. Overall this leads to an underestimation of the true IOP by about two to four mmHg after LASIK surgery.

P: Does refractive surgery change treatment of glaucoma?

Dr. Pro: As I mentioned above, the corneal thickness is changed and that may change your treatment regimen. For example, if I have a patient in front of me who is a glaucoma suspect with optic nerve cupping, but normal visual fields and IOP of 14, if that patient had LASIK I might consider the true IOP to be higher, and might then initiate treatment or follow the patient more closely.

P: Do many people with glaucoma undergo refractive surgery to correct earlier damage from glaucoma?

Dr. Pro: No, damage to the visual field from glaucoma is not able to be corrected with surgery. It is permanent. Refractive surgery simply enables people to get rid of glasses or contacts. It generally does not improve the vision more glasses or contacts could.

Moderator: That's the last question for the evening Dr. Pro. It was a very interesting and informative chat. Thank you once again for your time.

Dr. Pro: You are welcome. Good night.

On February 4, Dr. Pro discussed "Laser Iridotomy" in the Chat room. Click here for highlights of that meeting.

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