Before performing refractive surgery, ophthalmologists must recognize the signs of dry eye syndrome and choose either PRK or LASIK accordingly.
Baltimore-When performing refractive procedures in patients with dry eyes, ophthalmologists should maximize tear film stability preoperatively and formulate a specific plan that minimizes dry eye postoperatively, said Robert Weinberg, MD, here at the 24th annual Current Concepts in Ophthalmology meeting.
“My particular bias is to do surface ablation in patients with dry eyes. The question is, is there evidence to support that,” began Dr. Weinberg, who is chairman of the Department of Ophthalmology, Johns Hopkins Bayview Medical Center, Baltimore.
Tear dysfunction-or dry eye syndrome-is the most common unwanted sequela of excimer laser correction, he explained. Dry eye syndrome is defined as a disorder of the tear film caused by tear deficiency or excessive tear evaporation that damages the interpalpebral ocular surface and is associated with symptoms of ocular discomfort.
Estimates of dry eye after LASIK range from 69% to 85%, and it is known that in some patients, ocular irritation may persist for 1 to 1.5 years, Dr. Weinberg noted.
Research studies from the Wills Eye Institute, Philadelphia (2008), and the Wilmer Eye Institute, Baltimore (2004), looked at causes of dissatisfaction and seeking consultation after refrctive surgery. Dry eye accounted for about 20% of patient dissatisfaction in both studies.
Is there evidence to suggest that surface ablation or LASIK is better for myopia? Dr. Weinberg reviewed results from six randomized, controlled clinical trials summarized in a Cochrane review that have compared excimer laser surface ablation (PRK) and LASIK for myopia correction.1 For all degrees of myopia, both procedures are equally effective in achieving post-treatment manifest spherical equivalents within ±0.50 D of the desired result. Intraoperative pain was shown to be less with PRK, while postoperative pain was less with LASIK. Visual recovery was faster in patients who underwent LASIK, but final uncorrected visual acuity was equal in both groups.
According to Dr. Weinberg, a careful preoperative evaluation for dry eye will help determine which patients may be at greater risk for developing dry eye postoperatively. A successful preoperative evaluation should include a careful assessment of the eye lids. In addition, tear function, and tear film stability should be maximized preoperatively. Management should include treatment of pre-existing lid disease, the use of cyclosporine 0.05%, and punctal occlusion if necessary, he said.
“We need to be able to recognize, upon preoperative evaluation, the signs of dry eyes. These can include decreased tear meniscus, punctate corneal staining, conjunctival redundancy or conjunctival chalasis (a subtle sign that we need to pay more attention to), irregular corneal surface, increased tear film debris, and inadequate blinking,” said Dr. Weinberg.
In addition, absolute contraindications for refractive surgery include neurotrophic corneas and lid disease, he added.
Currently, it is unknown why dry eye can occur after refractive surgery, continued Dr. Weinberg. Potential reasons can include the following:
decreased corneal sensitivity from prolonged contact lens wear;
goblet cell damage from LASIK suction ring;
changes in corneal curvature resulting in decreased wetting;
severing of corneal nerves resulting in decreased sensation;
decreased sensation reducing the feedback loop to produce tears;
decreased blink rate; and
medicamentosa from postoperative drops.
Researchers of one study showed that tear production, as measured by Schirmer testing, was less following LASIK than after PRK.2 Data from another study showed that patients with low Schirmer test scores had a greater risk of dry eye after LASIK.3
“Since normal tear production depends on corneal sensation, in vivo confocal microscopy of corneal nerves would appear to provide information about differences between PRK and LASIK. In vivo confocal microscopy of corneal nerves shows that there is decreased subbasal nerve density in [patients with] dry eye, and this correlates with Schirmer test results,” said Dr. Weinberg.
In addition, he noted that regeneration of normal nerve density may be faster after PRK than LASIK, but after both procedures, corneal sensitivity eventually returns to normal.4 Further, hinge location was shown to be important to the development of dry eye post-LASIK in one clinical trial, 5but neither flap thickness nor hinge location was shown to affect this in another study.6
Surgeons must then choose between PRK and LASIK, Dr. Weinberg continued.
“PRK would appear to be a better choice in the patient with preoperative dry eye. However, if LASIK is chosen, it is important to prevent epithelial defects and avoid flap drying,” he said.
Postoperatively, after LASIK, aggressive lubrication with nonpreserved tears, topical corticosteroids, punctal occlusion, and topical cyclosporine 0.05% are recommended in the patient with preoperative dry eye, concluded Dr. Weinberg. In patients undergoing PRK, though the problem is less likely, he recommends careful monitoring postoperatively for increased symptoms of dry eye.
Dr. Weinberg has no disclosures.
1. Shortt AJ, Allan BD. Photorefractive keratectomy (PRK) versus laser-assisted in situ keratomileusis (LASIK) for myopia. Cochrane Database Syst Rev. 2006;19:CD005135.
2. Lee JB, Ryu CH, Kim J, Kim EK, Kim HB. Comparison of tear secretion and tear film instability after photorefractive keratectomy and laser in situ keratomileusis. J Cataract Refract Surg. 2000;26:1326-1331.
3. Yu EY, Leung A, Rao S, Lam DS. Effect of laser in situ keratomileusis on tear stability. Ophthalmology. 2000;107:2131-2135.
4. Cruzat A, Pavan-Langston D, Hamrah P. In vivo confocal microscopy of corneal nerves: analysis and clinical correlation. Semin Ophthalmol. 2010;25:171-177.
5. Donnenfeld ED, Solomon K, Perry HD, Doshi SJ, Ehrenhaus M, Solomon R, Biser S. The effect of hinge position on corneal sensation and dry eye after LASIK. Ophthalmology. 2003;110:1023-1029.
6. Mian SI, Li AY, Dutta S, Musch DC, Shtein RM. Dry eyes and corneal sensation after laser in situ keratomileusis with femtosecond laser flap creation. Effect of hinge position, hinge angle, and flap thickness. J Cataract Refract Surg. 2009;35:2092-2098.
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