Accurate refractive measurement is foundational to optometric care. Whether prescribing glasses, fitting contact lenses, or planning refractive or cataract surgery, optometrists and ophthalmologists rely on stable, repeatable data. However, one of the most common—and often underrecognized—sources of variability is the tear film. Increasing evidence shows that tear film instability, particularly in the setting of dry eye disease (DED), contributes to higher-order aberrations (HOAs), fluctuating vision, and inconsistent refractive findings.1
Failing to address ocular surface inflammation before finalizing a prescription can lead to inaccurate outcomes, patient dissatisfaction, and costly remakes when patients achieve 20/20 visual acuity in the exam lane but continue to report fluctuating, poor-quality vision in their daily lives. This variability is likely mediated through the induction of higher-order aberrations (HOAs), which degrade retinal image quality and challenge the repeatability of both objective and subjective findings. These discrepancies highlight a critical limitation in traditional refractive paradigms—the assumption of a stable optical interface. Conversely, prioritizing ocular surface and tear film optimization may help restore optical stability and allow for more precise and reproducible refractive measurements while ultimately delivering more consistent visual outcomes and a higher standard of patient care.
The Tear Film as an Optical Surface
The tear film serves as the eye’s most anterior refractive surface and plays a critical role in determining overall optical quality. In a perfect scenario, an intact tear film provides a smooth, uniform interface that minimizes light scatter and supports precise focusing of light onto the retina. Its contribution is not trivial; even subtle disruptions in tear film integrity can lead to measurable changes in optical performance.2
In the presence of irregular tear film instability, the localized breakup may introduce rapid changes in surface tension and thickness, which lead to microfluctuations in corneal curvature and refractive power. These changes occur over seconds, particularly between blinks, and effectively transform the ocular surface into a temporally unstable refractive medium.3 The dynamic nature of tear film instability shows that the challenge extends beyond surface irregularity because the irregularity itself is in constant flux.2,3
Inflammation as the Underlying Mechanism
Tear film instability is largely driven by chronic ocular surface inflammation. Inflammatory mediators disrupt lacrimal and meibomian gland function, alter tear composition, and compromise epithelial integrity, leading to an unstable tear film that degrades rapidly.¹ This creates a self-perpetuating cycle in which inflammation further destabilizes the tear film, and tear film instability, in turn, amplifies surface stress and inflammation. From an optical standpoint, the result is a consistently irregular refractive interface. Importantly, this cycle highlights that tear film instability is not simply a mechanical issue but one that is rooted in underlying biochemical dysfunction and requires treatment strategies that address inflammation, not just tear supplementation.
Higher-Order Aberrations and Dynamic Optical Degradation
From a wavefront perspective, tear film instability is a significant driver of HOAs. Unlike lower-order aberrations, HOAs (such as spherical aberration, coma, and trefoil) represent complex distortions in the optical wavefront that cannot be corrected with conventional lenses.
Wavefront aberrometry has demonstrated that HOAs increase progressively during the interblink interval. Immediately following a blink, the tear film is relatively smooth, and aberrations are minimized. As evaporation and breakup occur, localized irregularities emerge, resulting in increased wavefront error and degraded retinal image quality.
These optical changes are not merely theoretical; they manifest as real-world visual symptoms. Patients frequently experience transient clarity immediately after blinking, with rapid deterioration in visual quality thereafter. These symptoms highlight a critical limitation of conventional testing: Visual acuity alone is an incomplete measure of functional vision in the presence of ocular surface disease.
Refractive Variability in Clinical Practice
The impact of tear film instability becomes particularly evident during refractive assessment. Both objective and subjective measurements rely on the assumption of a stable optical system, but that assumption is frequently violated in patients with ocular surface dysfunction.
Autorefraction may yield inconsistent results across repeated measurements, with fluctuations in sphere, cylinder, and axis. These variations are often dismissed as instrument noise, but may sometimes more accurately reflect true optical instability. Subjective refraction is one way to help confirm these fluctuations, but treating the ocular surface and repeating the measurements can also provide a better idea of the problem to differentiate between instrument noise and true instability.
Similarly, subjective refraction can become a moving target. Patients may struggle to provide consistent responses. Their preferences may shift rapidly and endpoints remain elusive. The familiar difficulty of “1 or 2” comparisons in these patients is not a matter of indecision, but rather a manifestation of real-time changes in retinal image quality.
Corneal measurements are equally affected. Keratometry and topography depend on a smooth tear film to generate the most accurate data. In its absence, distorted mires and irregular astigmatic patterns are not uncommon, and they reduce the reliability of measurements used for spectacle prescriptions, contact lens fitting, and surgical planning.
The Consequences of Prescribing Without Surface Optimization
Proceeding with a refraction in the presence of untreated ocular surface disease introduces significant risk. Because the optical system is unstable, any measurement obtained represents only a transient state rather than a reliable measurement. Prescriptions obtained under these conditions are therefore more likely to be inaccurate or poorly tolerated.
Clinically, these faulty measurements often manifest as patient dissatisfaction. They may return with complaints that their new glasses “don’t feel right” or that their vision remains inconsistent. Remakes become necessary and increase both cost and chair time. More subtly, repeated prescription changes can erode patient confidence and create the perception of clinical imprecision.
In an era where patients expect immediate and consistent visual clarity, these outcomes are increasingly problematic.
Ocular Surface Optimization as a Refractive Strategy
Stabilizing the ocular surface before prescribing or measuring refraction transforms outcomes. A smooth, stable tear film reduces HOAs, improves repeatability of both objective and subjective measurements, and enhances corneal assessment reliability. The result is more accurate prescriptions, consistent vision, and higher patient satisfaction as well as reduced remakes and follow-up visits.
This principle also extends directly to surgical care. In LASIK and cataract surgery, tear film instability compromises keratometry, topography, wavefront analysis, and biometry.4 Even small fluctuations can alter IOL power calculations or ablation profiles, which increase the risk of refractive surprise.4 Like spectacle and contact lens wearers, surgical patients receiving premium IOLs or specialty contact lenses have high expectations for visual performance, and even subtle optical imperfections can lead to dissatisfaction if the tear film is not optimized first. Therefore, we want to establish a stable, reliable optical interface as soon as possible to ensure both surgical precision and predictable visual outcomes.
In short: Stabilize the tear film, and every measurement—from glasses to surgery—becomes more accurate, reliable, and repeatable.
Clinical Integration and Patient Communication
Incorporating ocular surface optimization into routine care requires a small shift in clinical mindset. Rather than viewing dry eye as a secondary concern, it must be recognized as a primary determinant of refractive accuracy. This begins with identifying signs of tear film instability, particularly in patients with fluctuating responses or inconsistent measurements.
Equally important is patient education. Explaining the role of the tear film in visual quality helps patients understand why treatment may be necessary before prescribing glasses. Framing the tear film as part of the eye’s functional system—rather than merely a source of comfort—can improve both compliance and expectations.
In some cases, delaying the final prescription until the ocular surface is stabilized is the most appropriate course of action. Although this may initially seem counterintuitive, it ultimately leads to more reliable outcomes and fewer downstream complications.
The Bottom Line
Tear film instability is a significant and often underrecognized contributor to HOAs and refractive variability. In the presence of ocular surface inflammation, the eye’s most anterior refractive surface becomes unreliable and undermines the accuracy of both objective and subjective measurements.
Prescribing glasses without addressing these issues frequently results in inaccurate prescriptions, increased remakes, and diminished patient satisfaction. However, optimizing the ocular surface prior to refraction stabilizes the optical system, enhances measurement precision, and improves visual outcomes.
For the modern optometrist, this represents a necessary evolution in clinical practice. Refraction cannot be separated from ocular surface health, and the most accurate prescriptions are those that are derived from a stable optical foundation.
Optimize the surface first. The best refraction will follow.
References
- Jones L, Craig JP, Markoulli M, et al. TFOS DEWS III: management and therapy. Am J Ophthalmol. 2025;279:289-386. doi:10.1016/j.ajo.2025.05.039
- Willcox MDP, Argüeso P, Georgiev GA, et al. TFOS DEWS II tear film report. Ocul Surf. 2017;15(3):366-403.
- Jiang Y, Chen X, Gao Y, et al. Impact of tear film stability on corneal refractive power measurement and surgical planning for cataract. Adv Ophthalmol Pract Res. 2025;5(2):100-106.
- Lacmanović Lončar V, Mikulić D, Aljinović-Vučić V, Vatavuk Z, Petric Vicković I. Impact of dry eye disease and lipid-containing artificial tears on keratometric reproducibility and intraocular lens calculation in cataract patients. Medicina (Kaunas). 2026;62(1):179. doi:10.3390/medicina62010179
