Follow-up key to safe refractive surgery in glaucoma

Physicians should discuss potential risks, such as IOP spikes, with patients before performing LASIK or PRK, two experts say.

Issue: September 10, 2008

ByErin L. Boyle

Glaucoma patients who undergo LASIK or PRK need careful monitoring of IOP and other parameters to ensure that refractive surgery does not affect the disease, according to two glaucoma specialists.

Although physicians should be cautious when performing refractive surgery on glaucoma suspects and glaucoma patients, the procedures have the potential to improve vision, according to OSN Glaucoma Section Editor Thomas W. Samuelson, MD, and OSN Glaucoma Section Member Richard A. Lewis, MD. They spoke at a glaucoma symposium at the American Society of Cataract and Refractive Surgery meeting about the safety and efficacy of LASIK and PRK procedures in glaucoma suspects and glaucoma patients.

Thomas W. Samuelson

Dr. Samuelson said he often hears the question: “Is glaucoma a contraindication for LASIK?” He said a more accurate inquiry would be: “Should LASIK be denied to patients with glaucoma?”

“My feeling is patients should be presented with all the options, the risks and benefits, and then [they can] make an informed choice,” he said. “I think the choice should include LASIK or PRK, assuming careful execution of the procedure, and probably, most importantly, lots of follow-up.”

Dr. Samuelson does not typically encourage patients with advanced glaucoma to have refractive surgery, but he also said some cases are exceptions. Uncontrolled glaucoma should always be controlled before performing any surgical procedure, he noted.

Glaucoma patients might do best undergoing PRK with topical mitomycin-C because it does not have a flap, suction or interface fluid that would affect IOP or subsequent glaucoma surgery, Dr. Lewis said, adding that advances are still needed to monitor the results of LASIK and PRK for glaucoma patients.

“We would love to have a better tonometer that is independent of corneal thickness, and some day we will have that,” he said. “We’d like to get quality-of-life measures for glaucoma patients, for both before and after LASIK.”

Postoperative monitoring

One of the most important factors for performing successful refractive surgery in glaucoma patients is postoperative monitoring, according to Drs. Samuelson and Lewis. They said IOP fluctuations induced by refractive surgery should be monitored closely.

The first pressure measurement should be taken at least 1 to 2 weeks postop, according to Dr. Samuelson. He said it is vital to measure additional glaucoma parameters postop, including optic disc, nerve fiber layer and visual fields.

Dr. Lewis said refractive surgery can alter other glaucoma parameter measurements, especially when testing contrast sensitivity, and more studies are needed to determine long-term results for contrast sensitivity and structural changes in glaucoma patients who have undergone refractive surgery.

Cornea and refractive surgeons also must place a higher importance on testing IOP and other parameters after surgery, he said.

“If you look at the records of refractive surgeons, seldom do they actually check pressure for the first few months, particularly in the PRK patients. They don’t know what the incidences of glaucoma are because they’re not checking, and when they do check it, they’re often confused by a lot of variables, such as the flap and thinner cornea,” Dr. Lewis said.

Patients

According to Dr. Samuelson, glaucoma patients undergoing refractive surgery fall into two groups: those who electively opt for refractive surgery and those who are medically indicated for surgery.

For glaucoma patients who choose refractive surgery, the visual improvements can help outweigh the risks, especially in younger patients, he said. He outlined the case of a 47-year-old female patient who was a high myope with significant glaucoma in her left eye. The patient also had a cataract in her left eye and was contact lens intolerant.

“After discussing all the options, she wanted to have her refractive error corrected, which is understandable for a 47-year-old high myope,” Dr. Samuelson said. “We did LASIK in the right eye, the one that had normal visual fields, and created a flap in the left eye with no ablation because we were going to take the cataract out 2 days later.”

More than 5 years after the procedures, the patient is 20/20 in both eyes, with thinner central corneal thickness and therefore slightly higher pressure than what registers on the tonometer. Fortunately, her IOP is well-controlled, he said. The patient is satisfied with the outcome and has not had a significant change in her visual fields in that time.

For glaucoma patients who are medically indicated for refractive procedures and contact lens wearers undergoing filtration surgery, the refractive procedure may have the potential to prevent infection by eliminating contact lens wear in patients at increased risk for bleb-related infections, Dr. Samuelson said. Glaucoma surgical intervention introduces the potential for bleb-related endophthalmitis as a life-long risk. Because many younger patients do not want to wear spectacles, contact lens wear can place them at an increased risk for infection.

“In the presence of a bleb, you often have to ask what has more risk: wearing contact lenses or having the refractive error corrected with LASIK or PRK,” he said. “I think, without question, refractive surgery is a safer option in some patients with glaucoma than, say, contact lenses, if performed cautiously and carefully and with proper informed consent.”

Risks

Glaucoma patients undergoing LASIK run the risk of IOP spikes and possible complications from the creation of a flap, Dr. Samuelson said. There are two primary concerns when performing the procedure in glaucoma patients: the risk of the procedure itself and any alteration of postop glaucoma monitoring.

He and colleagues conducted a study that examined the effect of LASIK, with or without brimonidine, on the structural and functional parameters of the optic nerve in 51 patients. They found no direct effect on either the structure or function of the optic nerve from LASIK. However, the study involved patients with normal optic discs and did not examine patients with established optic disc damage.

Although unlikely, it is possible that the high pressures during LASIK, which could spike as high as 80 mm Hg or 90 mm Hg, could further injure a tenuous optic disc. Dr. Samuelson said most studies examining IOP during surgery emphasize the ring pressure and have not focused on when the highest pressures might occur, which could be during the applanation process of the microkeratome or femtosecond laser.

Glaucoma patients must know about the potential for IOP spikes and should be told as part of the prior consent discussion about the procedure, he said.

“My impression is, during that short amount of time, it’s not going to risk injury,” Dr. Samuelson said. “I think you have to tell patients that it’s not known for certain.”

Postop concerns center on complications from the flap. Interface fluid in the flap could lead to low IOP measurements and misdiagnosis of glaucoma, which could be connected to long-term steroid use, Dr. Lewis said.

As IOP rises, fluid is forced into the interface between the flap and cornea. The femtosecond laser appears to reduce those risks with better adhesion of the flap in the stromal bed and reduced interface accumulation, he said.

Differing viewpoints: To perform surgery or not

Richard A. Lewis

Glaucoma and corneal specialists had different opinions concerning whether refractive surgery should be recommended for glaucoma suspects or glaucoma patients, according to an informal poll of electronic mailing lists.

Richard A. Lewis, MD, asked glaucoma experts on the American Glaucoma Society electronic mailing list and corneal surgeons on the KeraNet electronic mailing list if they would recommend keratorefractive surgery for glaucoma suspect eyes. He found that 64% of glaucoma specialists would recommend refractive surgery in glaucoma suspect patients, while 36% responded that they would not.

Cornea specialists, meanwhile, recommended surgery for glaucoma suspect patients more readily, with 74% saying they would recommend surgery and 26% saying they would not.

Dr. Lewis then reworded the question, asking physicians if they would recommend refractive surgery in glaucomatous eyes.

Glaucoma specialists were against recommending refractive surgery to glaucoma patients, with 80% against it and 20% for it.

The corneal specialists, however, had a higher rate of recommending the surgery, with 44% replying that they would recommend it to a glaucoma patient and 56% saying they would not.

Dr. Lewis said the results should be investigated further to determine the reasons for the disparity.

“The question is, why is there a difference between the anterior segment surgeons and the glaucoma specialists in recommending refractive surgery, and how should you personally counsel patients involved?” he said.

For more information:

Richard A. Lewis MD, can be reached at 1515 River Park Drive, Sacramento, CA 95815; 916-649-1515; fax: 916-649-1516; e-mail: rlewiseyemd@yahoo.com.

Thomas W. Samuelson, MD, can be reached at Minnesota Eye Consultants, 701 E. 24th St., Suite 100, Minneapolis, MN 55404; 612-813-3628; fax: 612-813-3656; e-mail: twsamuelson@mneye.com.

Reference:

McCarty TM, Hardten DR, et al. Evaluation of neuroprotective qualities of brimonidine during LASIK. Ophthalmology. 2003;110:1615-1625.

Erin L. Boyle is an OSN Staff Writer who covers all aspects of ophthalmology.