A schematic diagram showing change in cornea Corneal topographer, used for mapping the surface curvature of the cornea Prior to any physical examination, the diagnosis of<unk>  frequently begins with an ophthalmologist's or optometrist's assessment of the person's medical history, particularly the chief complaint and other visual symptoms, the presence of any history of ocular disease or injury that might affect vision, and the presence of any family history of ocular disease. An eye chart, such as a standard Snellen chart of progressively smaller letters, is then used to determine the person's visual acuity. The eye examination may proceed to measurement of the localized curvature of the cornea with a manual keratometer, with detection of irregular astigmatism suggesting a possibility of<unk> . Severe cases can exceed the instrument's measuring ability. A further indication can be provided by retinoscopy, in which a light beam is focused on the person's retina and the reflection, or reflex, observed as the examiner tilts the light source back and forth.<unk>  is amongst the ophthalmic conditions that exhibit a scissor reflex action of two bands moving toward and away from each other like the blades of a pair of scissors. If<unk>  is suspected, the ophthalmologist or optometrist will search for other characteristic findings of the disease by means of slit lamp examination of the cornea. An advanced case is usually readily apparent to the examiner, and can provide for an unambiguous diagnosis prior to more specialized testing. Under close examination, a ring of yellow-brown to olive-green pigmentation known as a Fleischer ring can be observed in around half of keratoconic eyes. The Fleischer ring, caused by deposition of the iron oxide hemosiderin within the corneal epithelium, is subtle and may not be readily detectable in all cases, but becomes more evident when viewed under a cobalt blue filter. Similarly, around 50% of subjects exhibit Vogt's striae, fine stress lines within the cornea caused by stretching and thinning. The striae temporarily disappear while slight pressure is applied to the eyeball. A highly pronounced cone can create a V-shaped indentation in the lower eyelid when the person's gaze is directed downwards, known as Munson's sign. Other clinical signs of<unk>  will normally have presented themselves long before Munson's sign becomes apparent, and so this finding, though a classic sign of the disease, tends not to be of primary diagnostic importance. A handheld keratoscope, sometimes known as "Placido's disk", can provide a simple noninvasive visualization of the surface of the cornea by projecting a series of concentric rings of light onto the cornea. A more definitive diagnosis can be obtained using corneal topography, in which an automated instrument projects the illuminated pattern onto the cornea and determines its topography from analysis of the digital image. The topographical map indicates any distortions or scarring in the cornea, with<unk>  revealed by a characteristic steepening of curvature that is usually below the centerline of the eye. The technique can record a snapshot of the degree and extent of the deformation as a benchmark for assessing its rate of progression. It is of particular value in detecting the disorder in its early stages when other signs have not yet presented. Stages Corneal topography showing stage II<unk>  Once<unk>  has been diagnosed, its degree may be classified by several metrics: * The steepness of greatest curvature from 'mild' ( 52 D); * The morphology of the cone: 'nipple' (small: 5 mm and near-central), 'oval' (larger, below-center and often sagging), or 'globus' (more than 75% of cornea affected); * The corneal thickness from mild (> 506 μm) to advanced ( 53.00 D * Pachymetry 200 to 400 µm Stage 4 * Refraction not measurable * K-reading > 55.00 D * Central scars * Pachymetry ≤ 200 µm Stage is determined if one of the characteristics applies. Corneal thickness is the thinnest measured spot of the cornea.
Keratoconus
Pellucid marginal degeneration
Pinguecula
Corpora arenacea
Epiblepharon
Ecamsule
Enamel pearl
Vitreous bulge