Eye care providers need to look beyond visual acuity in screening for keratoconus.
Most people with keratoconus (KC) have myopic astigmatism. As the disease progresses, the myopia and/or astigmatism may increase over months and years and as it becomes even more advanced, the patient will lose best-corrected visual acuity. Often, it is worsening vision or the inability to correct the patient to 20/20 that leads to the initial referral to a cornea specialist or a contact lens specialist.
By contrast, the conventional wisdom is that we really don’t expect to see KC in an emmetrope or even in a low ametrope. However, there are patients with frank keratoconus who actually have reasonably good vision without correction or who can achieve 20/20 vision with a simple soft contact lens or spectacle correction. If these patients undergo topography/tomography imaging, the cone will be clearly visible even though there might otherwise not have been any other red flags.
For example, an 18-year-old low myope who had good vision in his habitual glasses that had been prescribed elsewhere presented with viral conjunctivitis with 2+ injection and follicles in both eyes. He was started on a topical steroid OU. One week later he returned, complaining of a reduction in vision. Upon examination, visual acuity was reduced to only 20/60 OD and 20/40 OS with his current glasses. Since he had developed subepithelial infiltrates, corneal topography was performed and, surprisingly, revealed keratoconus in both eyes (Figure 1). There was no family history and no prior suspicion of keratoconus. The steroid was continued and the infiltrates resolved. After repeat imaging that demonstrated progression, he underwent cross-linking in both eyes a few months later.
In another case, a 28-year-old male patient was referred for a keratoconus evaluation in the right eye because of decreasing vision and Vogt striae upon slit lamp examination. We confirmed that the right eye (Figure 2a) had significant keratoconus and scheduled cross-linking. Interestingly, however, the fellow eye also had keratoconus (Figure 2), despite seeing 20/20 uncorrected. If keratoconus in the right eye manifested and progressed at a similar pace as in the left eye, this patient would likely not have gone in for an eye exam, which would have deferred the diagnosis of keratoconus even further.
We know that keratoconus is a bilateral disease that can present asymmetrically so it is not surprising to find early KC in the fellow asymptomatic eye of a patient undergoing cross-linking in the worse eye. However, cases like these demonstrate that 1 or both eyes could very well have good uncorrected or best-corrected vision and still have not just a suspicious topography, but obvious keratoconus. This may be more likely when the cone or area of irregular astigmatism is outside the visual axis. If the patient has inferior steepening, for example, anterior corneal topography may show an obviously keratoconic cornea, even while the central vision remains unaffected. An eye like the 1 shown in Figure 2b can be just on the brink of significant vision loss if the cone is allowed to progress further and encroach on the visual axis.
In most primary eye care practices, it may not be practical to do a topography exam on every patient. But clinicians should be aware that 20/20 vision and a normal slit lamp exam do not rule out corneal disease and should continue to have a healthy suspicion of KC regardless of refractive status.
One should be on the lookout for subtle signs and symptoms or aspects of the patient history that predispose to KC. One such subtle symptom is a complaint of ghosting in a patient who corrects to 20/20 on the eye chart but seems dissatisfied with their vision. Patients with KC may also see 20/20 in the office but complain that they have trouble driving at night. When the pupil expands in dim light, the more peripheral irregular astigmatism of an inferior cone can have a much larger impact on visual acuity or quality of vision.
The reason it is so important to pay attention to these red flags is that early detection of progressive keratoconus can lead to intervention with cross-linking to slow or halt further progression of the disease. A 20/20 eye can be cross-linked, in our opinion. In fact, it is ideal to cross-link with the FDA-approved iLink cross-linking platform as soon as progression has been identified—before there is irreversible vision loss.
Complete care for patients with progressive keratoconus demands collaboration among primary eye care providers, cornea specialists with access to advanced imaging and iLink cross-linking, and contact lens specialists who can correct or rehabilitate vision with a wide range of lens modalities. It is imperative that optometrists and ophthalmologists work together and actively seek out other doctors they know and trust to share in the responsibilities of caring for patients with keratoconus.