The tear film is one of the eye’s most important refracting surfaces. It is refreshed with each blink. If the tear film is not functioning properly and there are dry spots on the cornea, however, a patient may experience fluctuating, suboptimal, blurred vision. Preoperative dry eye disease (DED) can adversely affect outcomes after any refractive surgery. High-quality postoperative vision requires the tear film to function normally.
The American Society of Cataract and Refractive Surgery clinical survey asked eye care professionals what percentage of their patients who underwent LASIK had significantly increased levels of DED, in 2013, the number was 36%.1 In the past decade, there have been some exciting evolutions in the diagnosis and treatment of DED.
THE NEW ERA OF DED
My approach in the new era of DED management is to rely heavily on objective metrics via point-of-care diagnostic testing. These diagnostics include traditional tests like staining the ocular surface with lissamine green and fluorescein, measuring tear breakup time, and occasionally using Schirmer strips as well as newer, more sophisticated tests. These modern tests have greatly enhanced my ability to diagnose and grade the severity of DED and other forms of ocular surface disease. My technicians are trained to identify DED based on suggestive symptoms (validated questionnaires and verbal history), and when these are present, the staff performs the diagnostic tests before any drops or bright lights disrupt the patient’s tear film. Occasionally, DED patients will have neurotrophic corneas and therefore may not have symptoms. For these patients, we rely on clinical signs to drive the diagnostic testing. When symptoms and/or signs are identified, the technician conducts a tear osmolarity test (TearLab) first, followed by the matrix metalloproteinase 9 (MMP-9) test (InflammaDry; Rapid Pathogen Screening). MMP-9 is an inflammatory marker that is elevated in patients with DED.2
These first-line tests have a high sensitivity, specificity, and positive predictive value for DED.2,3 They assess severity and help guide treatment. When test results are negative in otherwise symptomatic patients, we often find other diagnoses such as allergies, corneal basement membrane dystrophies, conjunctivochalasis, and so on that account for the symptoms. Before newer tests became available, many patients were erroneously diagnosed with DED and told to use artificial tears as needed for their symptoms.
If a patient has hyperosmolar tears (eg, a reading of > 308 mOsm/L or an intereye difference of at least 8 mOsm/L), then he or she, by definition, has DED.4 Because the osmolarity number is linearly related to disease severity, as the number increases, so does the severity of the dryness. If the patient also tests positive for MMP-9, then significant levels of ocular surface inflammation are present. In my practice, we then prescribe anti-inflammatory medications. Osmolarity and MMP-9 tests, in conjunction with our traditional metrics, are a good start for any modern practice. Other novel diagnostics such as lipid interferometry, tear film optical coherence tomography, confocal microscopy, noninvasive tear breakup time, lactoferrin, and blood biomarkers can also help to fine-tune diagnostic accuracy and guide treatment. With objective data, I know if DED is present before I walk into the examination room, which ultimately saves me significant chair time. If the patient will undergo refractive surgery (cataract or laser vision correction), then my goal is to normalize the tear film, ocular surface, and diagnostic testing results before proceeding.
Certainly, the effect that DED has on the quality of our preoperative measurements translates to patients’ postoperative satisfaction. Preoperative DED, especially when corneal staining is present, will often lead to inaccurate preoperative measurements such as the refraction and keratometry, topography, and aberrometry readings. The effects of the surgical incisions on the cornea (the LASIK flap and limbal relaxing incisions in cataract surgery) can also worsen DED, which negatively affects patients’ satisfaction. It thus behooves practitioners to identify dryness preoperatively, treat it aggressively, and reverse it prior to recording preoperative measurements for refractive surgeries. Physicians must also continue treatment during the postoperative phase with the assumption that most patients will experience even more dryness afterward.5
DED is widespread in patients seeking laser vision correction and other refractive surgeries. In my practice, it is a common reason patients become contact lens intolerant and seek alternate means of vision correction. As a result, refractive surgeons must have a high suspicion of DED in contact lens wearers. My rule of thumb is not to finalize preoperative measurements or perform surgery until the DED is treated fully. That means tear osmolarity measurements must be normal, the patient must test negative for MMP-9, the tear film must be completely stable in between blinks with a normal tear breakup time, and the corneal epithelium should be smooth. Refractive surgery is a largely elective surgery, so I take the time to treat DED fully before proceeding with final measurements and surgery. Aggressive treatment and close surveillance for worsening should continue throughout the postoperative period and beyond. n
1. ASCRS Clinical Survey 2013. Eyeworld. http://supplements.eyeworld.org/i/203235-ascrs-clinical-survey-2013. Accessed June 26, 2015.
2. Sambursky R, Davitt WF 3rd, Latkany R, et al. Sensitivity and specificity of a point-of-care matrix metalloproteinase 9 immunoassay for diagnosing inflammation related to dry eye. JAMA Ophthalmol. 2013;131(1):24-28.
Christopher E. Starr, MD
• associate professor of ophthalmology at Weill Cornell Medical College in New York
• director of the Refractive Surgery Service, director of ophthalmic education, and director of the Cornea, Cataract, and Refractive Surgery Fellowship at Weill Cornell Medical College
• financial disclosure: consultant to Allergan, Bausch + Lomb, TearLab, Rapid Pathogen Screening, and Shire