Refractive Surgery and the Ocular Surface

Identifying and fixing OSD can lead to optimal refractive surgery outcomes.

BY MITCHELL A. JACKSON, MD

When it comes to achieving optimal refractive surgery outcomes, the bar has been raised. Surgeons know that refractive surgery is no longer considered successful if a patient merely achieves 20/20 vision. Patients expect better than 20/20 vision quantitatively and “high definition” qualitatively.

How we manage patient expectations, correction of the refractive error by an optimized or wavefront laser vision correction and the ocular surface ultimately defines refractive surgery success. After all, the tear film is the most important refracting surface of the eye. Any disruption to it will not only cause poor visual outcomes postoperatively, but also make it difficult to obtain accurate corneal measurements preoperatively — which are critical in determining if a patient is a candidate for refractive surgery in the first place. If the patient is a candidate, we need precise diagnostic readings to achieve the precise visual outcomes — which, again, only occur with a precise reading of the corneal tear film. The tear film is a complex interaction of the environment (Figure 1), the aging process, systemic diseases, medication, osmolarity, inflammatory processes and neuroregulation. Disruptions come under the term ocular surface disease. Here’s how to combat some common threats to the ocular surface and restore it to health.

Ocular Surface Threats

It’s critical to detect and treat ocular surface disease before surgery because disturbances to the tear film typically result in false-positive readings in the patient’s diagnostics. To cite one example: In the corneal topography, OSD can create a pseudokeratoconus-like image in a patient who, it turns out, really doesn’t have keratoconus once the ocular surface is treated.

Ocular surface disease is clinically a crossover of evaporative dry eye (posterior blepharitis, meibomian gland dysfunction [MGD] or lid margin disease), aqueous deficiency (dry eye syndrome), or ocular allergy, or a combination of these. Recognizing which of these disease entities exists or in what combination will help you solve the ocular surface crisis and in turn optimize your refractive surgery outcomes.

► Blepharitis. The anterior form of blepharitis involves the outer lid and typically has acute symptomatology. The posterior form involves the meibomian glands and tends to be chronic, progressive and recurrent in presentation.

► MGD. Like blepharitis, MGD also is divided into two categories. In non-obvious MGD, meibomian gland expression is needed to evaluate the quality and quantity of meibum. In obvious MGD, plugged meibomian glands, gland dropout and inflammation are apparent at the slit lamp. The most common cause of MGD is acne rosacea, seen 50% of the time. Treatment options include anything from warm compresses, lid massage and/or lid scrubs to topical medications such as azithromycin (Azasite, Merck), tobramycin/dexamethasone (Tobradex ST, Alcon Laboratories), tobramycin/loteprednol 0.5% (Zylet, Bausch + Lomb); artificial tears that replace the lipid layer such as Retaine MGD (OcuSoft Inc.), Systane Balance (Alcon), Refresh Optive Advanced (Allergan), and liposome spray; oral doxycycline 50 mg/day; nutritional supplements that offer an anti-inflammatory benefit (Tears Hydrate, OcuSoft; Hydro Eye, ScienceBased Health; and Thera Tears Nutrition, Advanced Vision Research); intraductal meibomian gland probing and expression devices as developed by Steven L. Maskin, MD; and, lastly, the newest technology from Tear Science known as Lipiflow Thermal Pulsation.

Dealing With Dry Eye

There’s a good chance your prospective refractive surgery patient suffers from aqueous deficiency. According to a recent Marketscope survey, there are 23 million dry eye sufferers in the United States age 20 or older. About 12.76 million, or almost 50%, are postmenopausal women over age 50. Other risk factors for dry eye disease include prior corneal refractive surgery, autoimmune diseases with diabetes and thyroid listed as the top two, patients with low blink rate, such as those with Parkinson’s disease and computer vision syndrome, prior cosmetic facial surgery such as blepharoplasty, and contact lens wear. Obviously, a lot of patients will fall under at least one of these headings, so be on the lookout.

The International Delphi Panel through the dry eye workshop (DEWS) committee redefined dry eye as a multifactorial disease of the tears and ocular surface, accompanied by increased osmolarity of the tear film and inflammation of the ocular surface.¹

The abnormal tear film typically has elevated electrolytes as measured by tear osmolarity, decrease in protective enzymes, elevation in inflammatory cytokines and reduction in protective antibodies.

COURTESY: IMITCHELL JACKSON, MD

Figure 1. Tear film ocular

Testing & Treatment

Clinical measures to evaluate dry eye include tear secretion tests such as Schirmer (BST), corneal and conjunctival staining (Figure 2), tear breakup time (TBUT), impression cytology (goblet cell analysis), tear osmolarity (TearLab Osmolarity Test, TearLab, San Diego, Calif.), lipiview analysis (LipiView Ocular Surface Interferometer, Tear Science, Morrisville, N.C.), and patient questionnaires such as the Ocular Surface Disease Index (OSDI) and Standard Patient Evaluation for Eye Dryness (SPEED). Other quick tests such as MMP-9, which correlates well with corneal staining, will be available soon.

Quantifying tear osmolarity is an excellent way to diagnose aqueous deficiency and monitor how efficacious a patient’s treatment is. A tear osmolarity value greater than 300 mOsm/L or a difference more than 8 mOsm/L, or both, are hallmarks of tear film instability. Just as hemoglobin A1C provides a measure of blood sugar in diabetes, so tear osmolarity provides a measure of dry eye severity.

The International Task Force (ITF) created consensus guidelines for diagnostic signs and treatment recommendations.² ITF level 1 reveals conjunctival staining (best seen with lissamine), level 2 adds corneal staining and tear breakup problems, level 3 adds filamentary corneal findings, and level 4 adds conjunctival scarring.

ITF treatment recommendations include topical cyclosporine 0.5% (Restasis, Allergan) for level 2 and above, and only implementing punctual plugs at level 3 and above. Topical cyclosporine is believed to inhibit T cell activation, recruitment of additional T cells, and reduction in cytokine production in the inflammatory process, all part of the disrupted neuroregulation associated with LASIK.^3-5

The recent READY study⁶ revealed continued increased tear production at two years compared to control in patients with chronic dry eye due to ocular inflammation. Because the refractive surgery patient with high visual expectations cannot wait the usual four-to-six weeks for Restasis to have its initial impact, we can utilize topical steroids, such as the newly formulated loteprednol 0.5% gel with only 0.003% BAK (compared to the 0.01% BAK seen in other common topical steroids) during the induction phase for Restasis. Hypotonic artificial tears such as Blink (Abbot Medical Optics) and TheraTears reduce osmolarity⁷ and can also be useful in patients with elevated osmolarity, typically seen after refractive surgery. These drops are important to utilize before and after surgery based on the new DEWS dry eye definition treating inflammation and osmolarity.

The Medication Factor

In addition to taking the previously mentioned risk factors into account, keep in mind that when evaluating a patient for refractive surgery, it is of utmost importance to evaluate the entire patient, not just the eyes. Certain medications such as antihistamines, diuretics, beta-blockers, tricyclic antidepressants, anxiolytics, antispasmodics, hormone replacement agents and birth control pills are among the many therapies that can contribute to dry eye and ultimately affect the refractive surgery outcome.

Obviously some patients cannot stop their medications in anticipation of refractive surgery, but in some circumstances they can switch to something less drying — for example from Claritin-D to Claritin (Schering-Plough) to reduce the severity of dry eye postoperatively. The longer in advance of surgery they can make the switch, the greater the reduction in the risk of dry eye.

COURTESY: WILLIAM TRATTLER, MD, AND PARAG MAJMUDAR, MD

Figure 2. Lissamine green staining revealed mild dry eye that required pretreatment to achieve optimal results.

When It Comes To Allergies

The last piece of the ocular surface disease puzzle is ocular allergy, which can exist alone or in combination with MGD or DES. Patients may have perennial allergies caused by dust mites and/or animal dander or may have seasonal allergies caused by tree, grass and/or ragweed pollens. Most allergy treatments (topical, nasal, inhaled and/or systemic) will have an adverse event of dryness, ocular and salivary dryness being the most common.

Fortunately, the newest method of treating ocular allergy are combination agents. They block H1 receptor activity at the corneal nerve level to prevent itching and stabilize mast cells to prevent the release of histamine and other inflammatory mediators responsible for chemosis, edema, vasodilation and hyperemia. When approaching the refractive surgery patient, avoiding additional dryness while treating ocular allergy is critical so those topical combination agents that have high H1 receptor specificity will avoid the muscarinic side effects of dry eye (Figure 2).

The newest topical combination agents on the market with the most H1 specificity are bepotastine 1.5% or Bepreve (Bausch + Lomb) BID for treatment of itching associated with allergic conjunctivitis and alcaftidine 0.25% (Lastacaft, Allergan) QAM for prevention of itching associated with allergic conjunctivitis, respectively, per their FDA labeling. Thanks to these combination drugs, I see far fewer severe dry eye side effects than previously.

Be Proactive

Refractive surgery patients already come in with high expectations in terms of visual quantity and quality. Achieving 20/20 vision is not sufficient and part of the equation to maximize visual quality is the ocular surface. Ocular surface management requires attention to the lid margin, aqueous status and allergic symptomatology.

The surgeon is responsible to look at the overall patient in terms of systemic diseases and systemic medications that may add risk for dry eye after refractive surgery. For those patients with ocular allergy as a confounding problem, make sure to select therapy that minimizes impact on dry eye exacerbation by choosing a topical agent with H1 receptor selectivity. In the end, achieving optimal refractive surgery outcomes in patients with dry eye and allergy is possible as long as certain protocols are followed. OM

References

1. Schaumberg DA, Gulati A, Mathers WD, et al. Development and validation of a short global dry eye symptom index. Ocul Surf. 2007;5:50-57.

2. Behrens A, Doyle JJ, Stern L, et al. Dysfunctional tear syndrome study group. Dysfunctional tear syndrome: a Delphi approach to treatment recommendations. Cornea. 2006;25:900-907.

3. Kunert KS, Tisdale AS, Stern ME, Smith JA, Gipson IK. Analysis of topical cyclosporine treatment of patients with dry eye syndrome: effect on conjunctival lymphocytes. Arch Ophthalmol. 2000;118:1489-1496.

4. Stern ME, Gao J, Schwalb TA, et al. Conjunctival T-cell subpopulations in Sjogren’s and non-Sjogren’s patients with dry eye. IOVS. 2002;43:2609-2614.

5. Pflugfelder SC, Jones D, Ji Z, Afonso A, Monroy D. Altered cytokine balance in the tear fluid and conjunctiva of patients with Sjögren’s syndrome keratoconjunctivitis sicca. Curr Eye Res. 1999;19:201-211.

6. Rao SN. Reversibility of dry eye deceleration after topical cyclosporine 0.05% withdrawal. J Ocul Pharmacol Ther. 2011;27:603-609.

7. Montani. G. Length of the effect of Blink IntensiveTM on reduction of tear osmolarity. Presented at: British Contact Lens Association Clinical Conference 2009. Manchester, UK; May 28-31.

Dr. Jackson is in private practice and operates laser centers in Lake Villa, III., and Chicago. He also serves as a consultant to Allergan, Bausch & Lomb, Alcon, Abbott AMO and Cyanocon/Ocusoft. His e-mail is mjlaserdoc@msn.com.