Refractive Focus

Keratoconus: Many Perspectives, a Common Goal

BY JASON MARSACK, PHD

I would like to start this edition of Refractive Focus with a quick exercise. To complete this exercise, I am going to ask you to please clear your mind of as many distractions as possible. Allow your existing thoughts to fade into the background. For just a moment, focus solely on the following task: I am going to say a word (or, more accurately, as this is a print journal, you are going to read a word), and I want you to think of the first word or phrase that comes to your mind.

Are you ready?

The word is keratoconus.

The first word or phrase that comes to your mind is... ________________

My Perspective

When I think of keratoconus, typically one of four thoughts comes to mind. Those thoughts are (in order of frequency): “contact lens,” “reduced vision,” “optical aberration,” and “patient satisfaction.” These associations make sense for me, given that I spend a lot of my time thinking about how “contact lenses” help to mitigate the “reduced vision” associated with keratoconus that is caused by “optical aberration” in the hopes of improving “patient satisfaction.”

Keratoconus Defined

While the terms that I associate with keratoconus align well with my own research interests, they do reveal my own rather limited consideration of keratoconus. In fact, the words/phrases that I most associate with keratoconus might truly be more closely associated with the consequence of having the disease rather than associated with the disease mechanism itself.

When pressed to identify a definition for keratoconus, I tend to lean on the following definition, which can be found in Cornea Fundamentals, Diagnosis and Management. Vol. 1:

“Keratoconus is a clinical term used to describe a condition in which the cornea assumes a conical shape because of thinning and protrusion. The process is non-inflammatory. Cellular infiltration and vascularization do not occur. It is usually bilateral and, although it involves the central two-thirds of the cornea, the apex of the cornea is usually centered just below the visual axis. This disease process results in mild to marked impairment of visual function,” (Feder and Gan, 2011).

This definition references the optical and visual consequence of keratoconus that I tend to consider. Contact lenses are the mainstay of correction for keratoconus; their use reduces optical aberration, severity of visual disturbances, and the overall burden of the disease. Given the often debilitating level of both lower-order (sphere, cylinder) and higher-order (coma, etc.) aberration that can present with keratoconus and the ability of current clinically available contact lenses to partially mask higher-order aberration, we would be justified in considering contact lenses as nothing short of amazing—I certainly do.

Current contact lens technology provides good visual performance for a substantial segment of the keratoconus population and dramatically reduces the burden of the disease. However (and somewhat obviously), these benefits are only realized for keratoconus patients when the lenses are worn. Said differently, patients who have keratoconus have the potential to experience the visual burden of their disease every time they remove their lenses. This is likely felt most acutely by individuals who experience limited wear time or in cases in which spectacles are not particularly effective.

Clinical and Laboratory-Based Investigation of Keratoconus

The definition cited previously also references other aspects of keratoconus beyond optics and vision, and indeed, there are a vast number of clinical and research questions posed by this disease. Keratoconus is being examined from an impressive number of different vantage points in the clinical and research communities. A search of pubmed.com with the keyword “keratoconus” returns 426 matches for the calendar year of 2015 alone (U.S. National Library of Medicine).

Figure 1. A word cloud created in Wordle representing words in the titles of manuscripts related to keratoconus that were published in the literature over the last five years. The image conveys a rich, diverse research space associated with many varied aspects of this disease.
COURTESY OF AVSL: THE ASSOCIATION OF VISION SCIENCE LIBRARIANS

And these reports are dedicated to a diverse cross section of questions related to keratoconus. For instance, the 2015 literature contains reports on (to name but a few active areas of research, among many others):

• Novel treatment strategies (a notable number pertaining to the resurgent scleral contact lens)

• Development of subjective patient assessment tools (related to, among other aspects of the disease, visual performance and quality of life)

• Methods to halt the progression of the disease (notably, corneal cross-linking)

• Keratoplasty methods (several different modalities are under investigation)

• Longitudinal evaluation of the disease and its treatment strategies

• Novel instrumentation as well as novel use of existing instrumentation (including imaging, microscopy, and topography)

• Mathematical modeling of data

• Methods for disease detection and severity indexing, classification, and assessment of surgical and clinical techniques

• Increased understanding pertaining to the origins of the disease

• Genetic characterization

• Epidemiologically oriented studies

• Disease management

• Comorbidity of keratoconus and other diseases

• Identification of disease risk factors

• Treatment outcome measures

• Studies related to pathology, anatomy, biometry, biomechanics, cell biology, and drug delivery

Conclusion

If you now revisit the word association activity that we completed earlier, the area that you most associate with keratoconus is likely an active area of research pertaining to this disease. When simply considering the range of clinical and research topics related to keratoconus, we can be awed by the breadth of effort being expended to understand and manage this disease.

And while keratoconus is a complex disease process with many consequences for both clinicians and patients, it is clear that one common goal of these activities is to reduce the burden of the disease for the individual patients who suffer from it. CLS

For references, please visit www.clspectrum.com/references and click on document #243.

Dr. Marsack completed a PhD in Physiological Optics and Vision Science at The University of Houston, College of Optometry, where he is currently a member of the faculty. He is affiliated with the Visual Optics Institute and The Ocular Surface Institute. His research interests include optical aberration of the eye, custom and pseudo-custom correction of optical aberration, visual performance and optically-based metrics predictive of visual performance.