However, diagnosing keratoconus in its early stages is more difficult, requiring a thorough case history, a search for visual and refractive clues and the use of instrumentation. Often, keratoconus patients have had several spectacle prescriptions in a short period, and none has provided satisfactory vision correction. Refractions are often variable and inconsistent. Keratoconus patients often report monocular diplopia or polyopia and complain of distortion rather than blur at both distance and near vision. Some report halos around lights and photophobia.
Many objective signs are present in keratoconus.
Retinoscopy shows a scissoring reflex. The keratometer also aids diagnosis. The initial keratometric sign of keratoconus is absence of parallelism and inclination of the mires. These can easily be missed in mild or early cases. As the cornea advances, the mires appear smaller.