Eye care providers must look beyond visual acuity in screening for disease.
Most patients 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. It is often 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 don’t expect to see KC in an emmetrope or even in a low ametrope. However, there are patients with frank KC who 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 patient with 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. Because he had developed subepithelial infiltrates, corneal topography was performed and surprisingly revealed
KC in both eyes (Figure 1A-B). There was no family history and no prior suspicion of KC. 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 KC evaluation in the right eye due to decreasing vision and Vogt striae upon slit lamp examination. We confirmed that the right eye (Figure 2A) had significant KC and scheduled cross-linking. Interestingly, however, the fellow eye also had KC (Figure 2B) despite seeing 20/20 uncorrected. If KC in the right eye manifested and progressed at a similar pace as the left eye, this patient would likely not have gone in for an eye exam, which would have deferred the diagnosis of KC even further.
We know KC 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 only a suspicious topography but also obvious KC. 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 obvious keratoconic cornea even while the central vision remains unaffected. An eye like the one 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. However, clinicians should be aware that 20/20 vision and a normal slit lamp exam does 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 KC 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 fact, it is ideal to cross-link with the FDA-approved iLink cross-linking platform as soon as progression has been identified and before there is irreversible vision loss.
Complete care for patients with progressive KC 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 KC.