Optimizing the Ocular Surface for Refractive Accuracy

Every cataract and refractive surgeon has encountered a patient whose procedure was technically successful but whose outcome fell short of expectations, whether because of dissatisfaction, residual refractive error, or, worst of all, the need for an IOL exchange. The cause is often not the formula, lens, or technique but the ocular surface. Studies have consistently demonstrated that more than 75% of patients presenting for cataract surgery have at least one abnormal tear film parameter and more than half meet the diagnostic criteria for dry eye disease (DED), yet most have not received a diagnosis.¹

The Prospective Health Assessment of Cataract Patients' Ocular Surface (PHACO) study² found corneal staining in 77% of eyes and a tear breakup time of 5 seconds or less in 63%. DED is common and frequently undiagnosed among patients presenting for cataract surgery, and it can undermine surgical outcomes. The reason is straightforward: small errors in keratometry can meaningfully affect IOL power calculations, and the tear film is the eye's most anterior refractive surface. When that surface is irregular or unstable, keratometric measurements obtained with a biometer, topographer, or aberrometer may be unreliable.

Tear Film Instability Compromises Refractive Accuracy

Ahn et al³ demonstrated that patients with high keratometric variability (≥ 0.25 D) had a 45.5% incidence of refractive surprise, defined as a mean absolute error greater than 0.50 D, compared with 17.9% among patients with low variability. Decreased tear breakup time and increased corneal staining were the strongest predictors of keratometric inconsistency. With presbyopia-correcting or toric IOLs, this degree of variability can compromise refractive accuracy and patient satisfaction.

Objective Screening Before Surgical Planning

Ocular surface optimization begins with an objective assessment. In my practice, the Cassini topographer (Cassini Technologies) and iTrace aberrometer (Tracey Technologies) provide useful, often underused screening information. A slit-lamp examination with corneal staining and an assessment of tear osmolarity remain essential components of the evaluation.

Assessing Surface Regularity With Topography

The Cassini uses multicolored LED point-source reflections rather than traditional Placido rings, creating a point-to-point map of the corneal surface and reducing the skew-ray errors associated with ring-based systems.⁴ The device's Surface Regularity Index (SRI) and Surface Asymmetry Index may help identify tear film instability. In patients with DED, SRI and Surface Asymmetry Index values were approximately two to three times higher than those in patients without DED, and an SRI greater than 0.80 had 89% sensitivity and 80% specificity for predicting clinically significant corneal staining.

Scan-to-scan variability can provide an additional warning sign. If three consecutive topographic captures do not align consistently, the tear film may be insufficiently stable for reliable surgical planning.

Separating Corneal and Internal Aberrations

The iTrace aberrometer combines ray-tracing aberrometry with Placido-based corneal topography and can distinguish corneal from internal aberrations.⁵ In eyes with DED, corneal higher-order aberrations (HOAs) have been reported to be 2.3 to 2.7 times greater than those in eyes without DED, whereas internal aberrations remain unchanged. An iTrace measurement showing elevated corneal HOAs and a normal Dysfunctional Lens Index may therefore suggest that the patient's visual symptoms arise primarily from the ocular surface rather than the crystalline lens. This distinction can inform patient counseling and the decision to proceed with surgery or optimize the ocular surface first.

Measurement repeatability also provides useful clinical information. Inconsistent findings across repeated iTrace captures may indicate tear film instability, and an objective scatter index of 1 or greater has been associated with less repeatable measurements.⁶

A Practical Diagnostic Workflow

The practical workflow is straightforward: I obtain ocular surface assessments with both instruments during the initial consultation. If the Cassini shows elevated SRI or Surface Asymmetry Index values or inconsistent maps and the iTrace shows elevated corneal HOAs or scan-to-scan variability, I treat the ocular surface before obtaining final surgical planning measurements.

A Stepwise Treatment Approach

Once DED has been identified, a stepwise treatment protocol should address the underlying pathology, commonly meibomian gland dysfunction (MGD) and evaporative DED in surgical candidates.⁷

Begin With Lid Hygiene

In my practice, lid hygiene is an essential first step. Warm compresses can improve meibomian gland function and increase tear film lipid layer thickness, thereby addressing the evaporative component of DED.

Eom et al⁸ demonstrated in a randomized trial that twice-daily eyelid hygiene for 10 days during the perioperative period prevented the postoperative worsening of meibum quality, blepharitis grade, and ocular symptoms observed in the untreated control group. Preoperative lid scrubs have also been shown to decrease the eyelid microbial load by 58% to 63%, a decrease comparable to that achieved with topical antibiotic prophylaxis. This effect may provide the additional benefit of lowering the risk of postoperative infection.

Escalate Treatment for MGD

For patients with moderate to severe MGD, lid hygiene alone is often insufficient. In-office meibomian gland expression, performed manually or with a device, can evacuate inspissated meibum and improve gland function. Kawagoe et al¹⁰ reported that four intense pulsed light and meibomian gland expression sessions administered at 2-week intervals increased the proportion of eyes within ±0.50 D of the predicted spherical equivalent from 55.4% to 92.9%.

Thermal pulsation with the LipiFlow system (Johnson & Johnson Vision), performed 3 to 5 weeks preoperatively, has also been shown in randomized trials to improve meibomian gland expressibility, tear breakup time, and corneal staining compared with warm compresses, with benefits persisting postoperatively.¹¹

Address Ocular Surface Inflammation

When corneal staining and inflammation are present, topical antiinflammatory therapy may be indicated. Cyclosporine targets the T-cell-mediated inflammation that perpetuates DED.¹²

Hovanesian et al¹³ demonstrated that 28 days of twice-daily cyclosporine 0.09% treatment before cataract surgery decreased the mean absolute prediction error from 0.39 ±0.30 D to 0.33 ±0.25 D. Donnenfeld et al¹⁴ reported that cyclosporine-treated eyes receiving multifocal IOLs achieved better uncorrected distance visual acuity (20/25 vs 20/30), corrected distance visual acuity (20/20 vs 20/25), and contrast sensitivity than eyes treated with artificial tears. Among patients, 57% preferred the cyclosporine-treated eye.

A 2026 study by Biela et al¹⁵ confirmed that ocular surface optimization reduced mean absolute error in patients with DED from 0.39 to 0.27 D, and even patients without DED showed improvement.

Artificial Tears Alone May Be Insufficient

Artificial tears alone may be insufficient to improve measurement reliability. In a randomized trial, Nilsen et al¹⁶ found that 2 weeks of artificial tear use did not significantly improve keratometric variability or refractive accuracy. Meaningful optimization may therefore require treatment directed at the underlying pathology, such as lid hygiene, meibomian gland expression, and antiinflammatory therapy. An oral supplement such as HydroEye (ScienceBased Health), initiated at the start of treatment, may provide long-term improvement in dry eye symptoms and ocular surface health.

(Editor's note: See the sidebar for a summary of current treatment options.)

Repeat Measurements After Stabilization

In my practice, I allow at least 4 weeks for treatment before repeating definitive biometry, although the interval depends on disease severity and the selected therapy.

The rationale is straightforward. Tear film instability can produce inconsistent keratometry, compromise IOL power calculations, and increase the risk of a refractive surprise. I proceed with surgical planning only after repeated Cassini maps align consistently and iTrace measurements demonstrate stable corneal aberrations with minimal scan-to-scan variability. Measurement repeatability is especially important for toric IOL calculations, which depend on an accurate magnitude and axis of astigmatism, and for multifocal and extended depth of focus IOLs, whose performance may be affected by as little as 0.25 to 0.50 D of residual refractive error.

A Foundational Component of the Toolbox

The protocol does not need to be complex. At the initial consultation, I screen surgical candidates with the Cassini and iTrace ocular surface assessment programs and initiate lid hygiene when indicated. I add meibomian gland expression for patients with MGD and topical cyclosporine for those with corneal staining or clinically significant inflammation. After approximately 4 weeks of treatment, I repeat the measurements. Once the scans are consistent and the ocular surface is stable, I proceed with surgical planning.

This approach positions ocular surface optimization not as an afterthought but as a foundational component of the refractive toolbox.