Preoperative screening may increase surgeon adoption of premium IOLs

Objectively measuring tear film instability can help a surgeon determine a patient's eligibility for a multifocal or EDOF IOL.

Issue: April 10, 2018

ByMarguerite B. McDonald, MD

The adoption of multifocal and extended depth of focus IOLs by American surgeons has been surprisingly slow; it has hovered at approximately 7% for several years. How can this be?

Many experts believe that there are two main reasons. First, there is the fear of the unhappy patient, so unhappy that he or she demands a lens exchange. Second, most cataract surgeons do not perform laser vision correction, so they cannot treat any residual refractive errors. As we know, these premium lenses perform best when the patient is plano (or close to it) for distance.

To avoid having to perform a lens exchange, it is critical to screen patients preoperatively for conditions that would not allow the premium lens to perform as designed. Most surgeons perform topography to rule out subtle corneal dystrophies, such as keratoconus, that would affect the optical performance of the premium lens. They also perform OCTs of the macula to rule out mild macular pathology, such as an epiretinal membrane.

More and more surgeons are evaluating the ocular surface preoperatively, as significant dry eye and/or blepharitis can produce higher-order aberrations that change rapidly, between blinks; these aberrations can profoundly degrade the optical performance of the IOL.

Having said that, most cataract surgeons are not collecting objective data regarding the quality and stability of the tear film. They rely on the patient’s complaints and their slit lamp exam (always important). A very few do Schirmer’s testing, although it is time consuming and its positive predictive value is quite low.

Certainly, if a patient is complaining of dry eye symptoms, this is a red flag. The problem is that half of patients with clinically significant dry eye have no symptoms at all. This asymptomatic group can become quite symptomatic after cataract surgery with a multifocal or extended depth of focus (EDOF) lens, however.

The all-important slit lamp exam can often detect superficial punctate keratitis (SPK), although not reliably, as has been proven in most of the FDA clinical trials that led to the approval (or disapproval) of topical dry eye prescription medications. In other words, even cornea fellowship-trained ophthalmologists differed widely in their classification of SPK. One doctor’s 1+ is another doctor’s 2+ or even 3+. The slit lamp can, however, detect a host of other ocular surface conditions, such as exposure keratitis and allergic conjunctivitis, which can affect multifocal and EDOF outcomes as well.

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There are two tests that objectively analyze the stability of the tear film: the HD Analyzer’s (Visiometrics) dynamic 20-second exam, which captures the effect of tear film on the patient’s quality of vision in real time, and tear osmolarity testing (TearLab).

Using the HD Analyzer, Roger Zaldivar, MD, of Mendoza, Argentina, has developed a scale that helps the surgeon determine immediately whether the patient’s ocular surface is healthy enough for a multifocal or EDOF IOL, or whether the surface — even with appropriate treatment — is still so unstable that a monofocal IOL should be implanted.

Figure 1 shows a seesaw pattern on the left. The vision quality index starts off at zero (an excellent score) but degrades rapidly; the index recovers again after the blink at 10 seconds. Shortly after the blink, the quality index is fairly good but degrades rapidly once again. The score is in the yellow zone, indicating that the patient may need more aggressive ocular surface treatment before he or she receives a multifocal or EDOF IOL. If this is not feasible, this patient may perhaps do best with a monofocal IOL.

On the right in Figure 1, a plateau pattern is seen. The vision quality index is excellent and is stable between blinks. This patient would be — based on tear film stability — a good candidate for a multifocal or EDOF IOL.

Figure 1. The Zaldivar scale: The image on the left shows a seesaw pattern, while the image on the right shows a plateau pattern.

TearLab’s in-office osmolarity testing also provides information on tear film stability. The patient without dry eye has a stable tear osmolarity between 290 mOsm/L 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. Stated differently, normal patients have tremendous reserve and can easily deal with life’s little desiccating challenges. Their osmolarity does not change and is virtually identical in both eyes.

Dry eye patients have little or no reserve. The situations above — or just being awake with eyes open — can cause the osmolarity to swing wildly due to instability, resulting in osmolarity above the normal range and/or the patient’s two eyes differing by more than 8 mOsm/L. This is also invaluable information for the surgeon when selecting an IOL type.

In summary, patients with an unstable tear film should be treated adequately for their ocular surface disease before receiving a multifocal or EDOF IOL. If stability cannot be achieved, perhaps a monofocal IOL would be a better choice.

For more information:
Marguerite B. McDonald, MD, FACS, can be reached at Ophthalmic Consultants of Long Island, 360 Merrick Road, Lynbrook, NY 11563; email: margueritemcdmd@aol.com.

Disclosure: McDonald reports she is a consultant for TearLab but has no relevant financial disclosures for Visiometrics.