Traditionally, refraction in optometric circles has focused on correcting lower-order aberrations (LOAs), namely defocus and regular astigmatism. These second-order aberrations account for most refractive error encountered in primary eye care and are effectively managed with spectacles and conventional contact lenses. Indeed, when ocular optics are regular and the ocular surface is stable, correcting LOAs typically yields excellent high-contrast visual acuity. However, visual acuity alone does not fully capture visual quality, particularly in patients who report glare, halos, ghosting, or poor night vision. As patient expectations for visual quality continue to rise, clinicians are increasingly challenged by visual complaints that persist despite accurate correction of LOAs. In many of these cases, higher-order aberrations (HOAs) play a significant role.
HOAs include coma, trefoil, spherical aberration, and other complex distortions that cannot be corrected with standard spherocylindrical lenses (Figure 1). HOAs are often elevated after refractive surgery or in patients who have otherwise irregular corneas, such as in keratoconus, corneal scarring, ocular surface disease, dry eye disease, or decentered optics. Importantly, patients with significant HOAs may still achieve 20/20 acuity while experiencing substantial degradation in contrast sensitivity and visual clarity, which leads to frustration for both patient and clinician.
When Traditional Refraction Falls Short
A key clinical challenge is that traditional refraction is largely insensitive to HOAs. I routinely see this in my practice: Patients in a specialty contact lens will continually respond that subjective refractions appear “better” with increased cylinder correction. Clearly, the amount of cylinder present in the overrefraction fails to correlate with what one would expect when comparing to the expected amount of residual cylinder. In almost every situation, this is the result of HOAs (usually coma).
Further, wavefront aberrometry can identify elevated HOAs, but its routine application in clinical practice remains limited, and treatment options are not always straightforward. As a result, clinicians must recognize when visual complaints are unlikely to be resolved through additional sphere or cylinder refinements.
The Critical Role of Contact Lens Selection
Soft contact lenses generally conform to the underlying corneal shape and therefore provide minimal reduction of corneal HOAs. In some cases, lens decentration, tear film instability, or multifocal optics may further influence aberration profiles. In contrast, rigid gas permeable and scleral lenses can mask corneal irregularities by creating a new, smooth anterior refracting surface that often results in meaningful reductions in corneal HOAs and improved subjective visual quality (see Figure 2).
We also now possess the ability to incorporate HOA-correcting optics into scleral lens designs. When stabilized, these designs can result in significantly improved visual outcomes for patients.
Presbyopia Management
Multifocal contact lenses intentionally introduce controlled aberrations to extend depth of focus. Although this strategy improves functional vision at multiple distances, it may reduce contrast sensitivity or increase dysphotopsias, particularly in patients with preexisting elevated HOAs. Proper patient selection and expectation setting are essential for success.
When you incorporate an understanding of lower- and higher-order aberrations into everyday practice, you can better identify the root cause of visual dissatisfaction, select appropriate lens modalities, and communicate realistic outcomes. Ultimately, recognizing when visual quality is limited by factors beyond traditional refraction can lead to improved patient satisfaction and more efficient clinical decision-making.OM
