Perfecting refractive surgery with eye drops

Although refractive procedures are wide-ranging - from refractive laser surgery all the way through to cataract surgery with intraocular lens (IOL) implantation - the sensation of dry eye is common to all.

There is a causal relationship between the sensation of dry eyes and visual acuity. It has been shown that, with ocular surface irregularity or when the eye is kept open for 10–20 seconds, functional visual acuity decreases significantly.¹ Thus the success of refractive surgery, and patient satisfaction, are linked closely to the presence of an optimal ocular surface and a healthy tear film.

The prevalence of dry eye in refractive surgery patients varies from 8.4% in subjects younger than 60 years to 19.0% in those older than 80 years.² This prevalence may, however, be grossly underestimated; recently, Roberts et al. demonstrated that preoperative dry eye is present in 60% of cataract patients, although in some cases this may be asymptomatic; one month after surgery, the rate increases to 87%.³

Preoperatively, the quality of the ocular surface affects the measurement of baseline refraction, the corneal topography and the generation of wavefront data. Corneal, as well as total, aberrations show a statistically significant increase correlating to time after a blink (when pupils are greater than 3.5 mm). After a blink, the gradual increase in optical aberrations associated with the increasingly irregular tear film may cause a progressive reduction in the optical quality of the eye.⁴

A change in corneal topography leads to a decrease of tear film thickness,⁵ with potentially grave consequences: corneal and conjunctival cytologic specimens obtained after cataract surgery have shown the presence of serious squamous metaplasia in the epithelial layer of the globe conjunctiva, especially the lower lid region.⁶

Refractive surgery, and particularly LASIK, leads to loss of corneal innervations, which may affect the reflex loops of the lacrimal and meibomian glands, resulting in decreased aqueous and lipid tear secretion and mucin expression.⁷ In addition to these factors, the application of a microkeratome suction ring induces changes in the perilimbic conjunctiva. In LASIK patients, the mean goblet cell density decreases significantly, from 424±105 cells/mm² preoperatively to 218±99 cells/mm² one month postoperatively.⁸

Because of this combination of factors, dry eye occurs in more than 50% of LASIK surgery patients.⁹ The risk for chronic dryness in LASIK patients is significantly increased among female patients, and those with higher attempted refractive correction and greater ablation depth, as well as the following pre-LASIK variables: increased ocular surface staining, lower tear volume, tear stability, corneal sensation, and dry eye symptoms.

Before a patient is scheduled for a refractive treatment, the clinician's first task should be to improve the ocular surface with eye drops. After this, the postoperative care of an intact tear film is crucial, because surgery will exacerbate pre-existing eye dryness in almost every case.

If eye dryness is not treated effectively, the patient might obtain a poor visual outcome despite the fact that the surgery lacked any other complications: eye dryness leads to reduced Snellen acuity, poor contrast sensitivity, and an increase in higher-order aberrations (HOAs), which in turn cause a reduction in the quality of vision and an increase in night-vision symptoms such as glare and halo. For at least three months after surgery, it is recommended that patients use lubricant drops daily. Case studies have demonstrated that intensive use of lubricant eye drops after LASIK may improve the refractive outcome and alleviate the need for enhancement surgery.¹⁰

In a small pilot study, Dr Starr measured HOAs immediately after the instillation of lubricant eye drops (blink intensive tears; Advanced Medical Optics) and again a few minutes later. He found that HOAs increased immediately after instillation, but then quickly returned to baseline. In a separate study, an anaesthetic was used to suppress the eye's blink response, simulating the compromised ocular surface that can lead to eye dryness. As with the previously cited study, the increase in HOAs decreased significantly after the instillation of the eye drops, but returned almost immediately to the pre-simulation level. The authors concluded that in eyes with a compromised ocular surface, a substantial improvement in the quality of the tear film and vision can be achieved with the use of eye drops.¹¹ In another recent study, blink intensive tears caused less blur and significantly improved patient comfort and quality of vision compared with the control group. Furthermore, recent results from Dr Bucci showed that blink intensive tears caused a significantly improved tear film break-up and fewer instillations.¹²

Based on this evidence, the basis for a perfect refractive surgery - one without pre- and postoperative complications, and with results good enough to satisfy even the increasing demands of patients - is predicated on comprehensive, routine care of the ocular surface.

References1. E. Goto, et al. Am. J. Ophthalmol. 2002 Feb;133(2):181–186.2. S.E. Moss, et al. Arch. Ophthalmol. 2000;118:1264–1268.3. C.W. Roberts and E.R. Elie. Insight 2007;32:14–234. R. Montés-Micó, et al. Ophthalmology 2004 Apr;111(4):758–767.5. P.E. King-Smith, et al. Curr. Eye Res. 2004;29:357–368.6. X.M. Li, et al. Cornea 2007 Oct;26(9 Suppl. 1):16–20.7. J.L. Rodriguez-Prats, et al. J. Refract. Surg. 2007;23(6):559–562.8. R. Ambrósio, et al. J. Refract. Surg. 2008;24:396–407.9. I. Toda. Comp. Ophthalmol. Update. 2007 Mar–Apr;8(2):79–85; discussion 87–89.10. J.M. Albietz, et al. J. Cat. Refract. Surg. 2004 Mar;30(3):675–684.11. C.E. Starr. “Drop can help optimize ocular surface before and after refractive surgery.” Ophthalmology Times, May 1, 2008.12. E. Donnenfeld. “For best results, start with the tear film.” Eurotimes XXVI Report of the ESCRS Berlin, Germany, September 2008, p. 6