Precise Dry Eye Testing is Key to Choosing the Right Lens Implant
By Marguerite McDonald, MD, FACS
For cataract surgeons, choosing the best intraocular lens for an individual patient is one of the most important keys to a successful procedure – and to a satisfied, happy patient. But complicating that lens selection is the likelihood that the patient may also have dry eye – as an estimated 20 percent of patients who undergo cataract surgery do.1
Significant dry eye, and/or blepharitis, can produce effects that lessen the performance and effectiveness of an implanted intraocular lens (IOL). Even those without symptoms initially may develop serious symptoms after being implanted with multifocal (MF) or extended depth of focus (EDOF) lenses. So, it’s imperative that cataract surgeons collect objective data on the quality and stability of the tear film. Yet many don’t.
Instead, many rely on the patient’s description of dry eye symptoms, though 50 percent of patients with clinically significant dry eye have no symptoms, and the results of a slit-lamp exam may be unclear. A few surgeons will augment those findings with a Schirmer’s test, although many shy away from that exam because it is time consuming and its positive predictive value is low.
Both patient history and the slit lamp examination should be regular components of any pre-operative evaluation. But to assure quality outcomes in cataract and refractive surgeries, and to choose the appropriate patients for MF and EDOF IOLs, I recommend a pair of tests that can provide an enormous amount of information about the health of a patient’s tear film:
The HD Analyzer™ made by Visiometrics objectively detects dynamic changes of OSI (Ocular Scatter Index) after blinking, even in clinically asymptomatic patients. This 20-second exam captures in real time the effect of the tear film on a patient’s vision. Using the HD Analyzer, Roger Zaldivar, MD, of Mendosa, Argentina has developed a scale that helps the surgeon determine immediately whether the patient’s ocular surface is healthy enough for a MF or EDOF implanted lens, or whether their surface, even with appropriate treatment, is so unstable that they should have a monofocal IOL.
TearLab’s in-office osmolarity testing also provides information on tear film quality, as patients with dry eye have hyperosmolar tears. The normal patient without dry eye has stable tear osmolarity between 290 and 300 mOsm/L. The two eyes never differ by more than 8 mOsm/L, even when the patient has used oral antihistamines, had a glass of wine, spent several hours on a digital device, or sat on the bow of a speeding motorboat. In other words, patients who don’t have dry eye have tremendous reserve and can easily deal with life’s little desiccating challenges. Their osmolarity doesn’t change, and, is virtually identical in both eyes.
Dry eye patients, however, have little or no reserve. The situations above (or just being awake with eyes open) can cause osmolarity to vary wildly. And when using a digital device of any kind, the normal blink rate of 20 times per minute drops to 3-5 times per minute. So, when osmolarity is above the normal range and/or the patient’s eyes differ by more than 8 mOsm/L, the surgeon should consider that this patient has dry eye that might need treatment before doing the preoperative workup and making his/her IOL selection. Though only 50 percent of dry eye patients have symptoms, any complaints are important red flags that warrant further testing. A surgeon’s greatest fear is that a patient without symptoms will develop them after cataract surgery with implantation of a multifocal or extended depth of focus IOL and become dissatisfied.
Of course, slit lamp exams are still an important part of every pre-operative exam. These often can detect superficial punctate keratitis (SPK), although detection has significant inter-observer differences. In fact, studies have revealed that even fellowship trained ophthalmologists widely differ in their classification of SPK. However, the silt lamp exam remains effective in revealing SPK and a variety of other ocular surface conditions, including exposure keratitis due to lagophthalmos and allergic conjunctivitis, both of which can impact the patient’s satisfaction with a MF or EDOF IOL.
Marguerite McDonald, MD, FACS, with OCLI on Long Island, NY, is clinical professor of Ophthalmology at NYU Langone Medical Center, NY, and clinical professor of Ophthalmology at Tulane University Health Sciences Center, New Orleans, Louisiana.