Not all post-op dry eye is dry eye

Regenerated nerve fibers, which causes symptoms similar to dry eye, may cause problems after refractive surgery

Source: Timo Tervo, M.D.

It’s no surprise that refractive surgery patients often experience dry-eye symptoms post-op.
However, what may be surprising is that not all of these symptoms actually indicate clinical dry eye, said Timo M.T. Tervo, M.D., Helsinki University Eye Hospital, Finland.
“Sore eyes following refractive corneal surgery may also be due to preexisting or acquired dry eye or corneal hypersensitivity,” he said. “In the last case, tear fluid secretion tests are normal.”
Plus, some of these patients may have had previously undiagnosed dry eye in which the symptoms appear more marked after refractive surgery, he said.
Dr. Tervo presented data on dry eye and dry-eye type symptoms at last month’s American Academy of Ophthalmology (AAO) annual meeting in Las Vegas.

Dry eye and refractive surgery

It is commonly thought that dry eye occurs after refractive surgery because of corneal nerve damage, Dr. Tervo said. The damaged nerves can evoke abnormal sensations. This also can trigger hypersensitivity and abnormal nerve morphology in patients with Sjögren’s syndrome, he said.
“Dry eye and the decreased secretion of tears and/or its components are very frequent, if not the most frequent, side effects of refractive surgery,” Dr. Tervo said.
However, recent research shows there is not always a direct correlation between dry eye and refractive surgery.
For example, in one study, patients reported dry-eye symptoms in a questionnaire but did not have signs of dry eye using a test. The same phenomenon occurred in another study in which LASIK patients with more than 10 D reported dry-eye symptoms at two to five years post-op. They tended to have normal sensitivity and a normal Schirmer test result, Dr. Tervo said.
In other studies, LASIK patients that complain of dry-eye symptoms actually have normal corneal mechanical sensitivity, he said.
Dr. Tervo theorized that all dry-eye symptoms patients experience more than a year after refractive surgery may not actually be dry eye; instead, they are caused by aberrantly regenerated nerve fibers in the cornea.
“Early (up to one year) PRK or post-LASIK ‘real’ dry eye is most likely due to impairment of the afferent loop of the cornea—lacrimal glands, reflex arch, and inflammatory mediators,” he said. This subbasal nerve recovery can take two years after PRK and up to five years after LASIK he said.
To better treat symptomatic patients, practitioners must do a better job of managing dry eye before surgery, Dr. Tervo said.
“Management of dry eye improves the accuracy of pre-operative examinations such as refraction and wavefront analysis and the predictability of photoablation,” he said.
Wetting agents, cyclosporine ophthalmic emulsion (Restasis, Allergan, Irvine, Calif.), and punctal occlusion can help with dry-eye treatment before surgery, Dr. Tervo said.

Editors’ note: Dr. Tervo has no financial interests related to his comments.

Contact Information
Tervo: + 358-9-47-16-21-85, timo.tervo@hus.fi