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Systemic evaluation urged before refractive surgical re-treatment
Ophthalmologists must take a holistic approach because there are other factors that may cause refractive error besides the cornea, experts say.
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When considering refractive surgical re-treatment, ophthalmologists must evaluate systemic factors that may trigger sudden, dramatic myopic shifts, according to two practitioners.
 Daniel S. Durrie |
Diabetes may cause transient myopia, requiring surgeons to exercise extreme caution in selecting patients for refractive surgery. In interviews with Ocular Surgery News, OSN Refractive Surgery Section Editor Daniel S. Durrie, MD, and Karin E. Thomas, MD, a U.S. Navy physician, discussed the need to monitor systemic and ocular factors before resorting to refractive enhancement.
Dr. Thomas and colleague David J. Tanzer, MD, addressed medical considerations associated with refractive surgical re-treatment in the Journal of Cataract and Refractive Surgery.
The acute onset of diabetes spurs physiological changes that occur in the lens, Dr. Thomas said.
Several theories exist regarding the refractive changes in diabetes. She said it is believed that sorbitol accumulates in the lens, producing an osmotic gradient, which changes the refractive power of the eye. Myopic changes occur when the blood sugar is elevated; and conversely, hyperopic changes often accompany intensive hypoglycemic therapy.
Performing unnecessary PRK or LASIK in a patient with an elevated blood sugar may lead to hyperopic overcorrection. “In our patient, a re-treatment may have led to ectasia,” Dr. Thomas said.
“When the blood sugar comes down and the lens goes back to its pre-diabetic stage, you’ve thinned out the cornea more after refractive surgery, and you have created a hyperope, which is even worse,” she said. “The patient is even worse than when you started. And you’ve operated on someone you shouldn’t have.”
Regardless of the underlying systemic condition, the lens is often overlooked in favor of the cornea, Dr. Durrie said.
‘Treat the whole patient’
The ophthalmologist must take a holistic approach in evaluating refractive error, Dr. Thomas said.
“We have an optometrist who does our evaluations for re-treatment, but our patients always have to see an ophthalmologist before we do a re-treatment,” she said. “Refractive surgeons are physicians first. One must be aware that there are potential systemic causes for fluctuations in refractive error. Treat the whole patient.”
Systemic and ocular stability alike are critical criteria for re-treatment. Dr. Durrie said.
“Other systemic factors, such as blood sugar or variations in hormonal balance, are certainly important. They need to be stable prior to surgery, especially an enhancement.” he said. “It’s important to have all the factors in your favor. One of them is waiting to make sure that you have a stable refraction. My usual standard is two refractions 2 months apart that don’t change.”
Stable topography is also critical to assessment, Dr. Durrie said.
“When we’re looking at the topography, we’re really looking at the corneal shape, and if we’re going to do refractive surgery, we’re going to change the corneal shape,” he said. “I want that to be stable also.”
It is prudent to wait 6 months or more to re-treat after PRK, he said.
“It’s a bigger procedure to go back and remove the epithelium again, so patients really understand the importance of multiple measurements, multiple office visits,” he said. “You just don’t have to be in a hurry. Certainly, the medical health needs to be looked at.”
A case study
In their paper, Drs. Thomas and Tanzer described the case of a 41-year-old man who underwent successful PRK and had good uncorrected vision for 2 years until he experienced blurred vision while mountain climbing. He was referred for surgical re-treatment with PRK.
An examination showed that the patient had uncorrected visual acuity of 20/70 and near visual acuity of 20/100 in both eyes. The patient reported no medication use or notable medical history. However, he had lost 40 lbs. He was found to have an elevated blood glucose level of 495 mg/dL. He underwent insulin and glucophage therapy. His uncorrected distance visual acuity improved to 20/20 in both eyes 3 months after insulin and glucophage were initiated.
“The diabetes induced a myopic shift,” Dr. Thomas said. “If I had re-treated with laser, that would have been harmful.”
The authors said the patient may have been diabetic before the initial surgery or may have developed diabetes after undergoing the initial PRK. The patient did not present with macular edema or diabetic retinopathy.
Refractive surgical options include conductive keratoplasty, PRK or LASIK with a flap created by mechanical microkeratome or femtosecond laser. However, many concerns remain, the authors said.
“There is a potential risk for poor healing in a diabetic,” they wrote. “Yet some retrospective studies advocate LASIK in diabetic patients without proliferative retinopathy.”
For more information:
- Daniel S. Durrie, MD, can be reached at 5520 College Blvd., Suite 200, Overland Park, KS 66211; 913-491-3330; fax: 913-491-9650; e-mail: ddurrie@durrievision.com.
- Karin E. Thomas, MD, can be reached at Box 555191, Camp Pendleton, CA 92055; e-mail: flykarin@aol.com.
Reference:
- Thomas KE, Tanzer DJ. Medical considerations before refractive surgery retreatment. J Cataract Refract Surg. 2007;33:326-328.
- Matt Hasson is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses on regulatory, legislative and practice management topics.