Keratoconus is a condition that weakens the cornea, causing it to thin and bulge forward into an irregular cone-like shape. The cornea provides most of the focussing power of the eye. Therefore, any irregularities to its shape will cause vision to be blurred. Common symptoms of keratoconus include: multiple images, streaking of lights and haloes. Vision is usually most affected in low light conditions such as night time. This is because the pupil is larger in low light conditions and therefore exposes more of the irregular cornea. Patients with keratoconus usually have high degrees of myopia and astigmatism that is not correctable with ordinary spectacles.