Examination of cornea
Loupe and lens examination or preferably slit-lamp biomicroscopy may be a must to delineate corneal lesions. While examining the cornea, a note of following points should be made:
i. Size. The anterior surface of normal cornea is
elliptical with a mean horizontal diameter of 11.7 mm and vertical diameter of 11 mm. Abnormalities of corneal size can be:
_ Microcornea, when the anterior horizontal diameter is a smaller amount than 10 mm. it's going to occur isolated or as a neighborhood of microphthalmos.
_ Corneal size also decreases in patients with phthisis bulbi.
_ Megalocornea is labelled when the horizontal diameter is quite 13 mm. Common causes are congenital megalocornea and buphthalmos.
ii Shape (curvature). Normal cornea is sort of a watch glass with a consistent posterior curve in its central area.
In addition to biomicroscopy, keratometry and corneal topography is required to verify changes in corneal curvature. Abnormalities of corneal shape are:
_
Keratoglobus. it's an ectatic condition during which cornea becomes thin and bulges out sort of a globe.
_
Keratoconus. it's an ectatic condition during which cornea becomes cone shaped.
_ Cornea plana i.e., flat curvature of cornea which can occur in patients with severe hypotony and phthisis bulbi and infrequently as a birth defect .
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iii.
Surface. Smoothness of corneal surface is disturbed thanks to abrasions, ulceration, ectatic scars and facets. Changes in smoothness of surface are often detected by slit-lamp biomicroscopy, window reflex test and Placido’s disc.
Placido’s keratoscopic disc it's a disc painted with alternating black and white circles. it's going to be wont to assess the smoothness and curvature of corneal surface.
Normally, on rummaging through the opening within the centre of disc a consistent sharp image of the circles is seen on the cornea. Irregularities within the corneal surface cause distortion of the circles
iv.Sheen. Normal cornea may be a bright shining structure. Sheen of corneal surface is lost in ‘dry eye’ conditions. A loss of the traditional polish of the corneal surface causes loss within the sharpness of the outline of the image of circles on Placido’s disc test.
v. Transparency of cornea is lost in corneal oedema, opacity, ulceration, dystrophies, degenerations, vascularization and thanks to deposits within the cornea.
Examination for corneal ulcer.
Once corneal ulcer is suspected, a radical biomicroscopic examination before and after fluorescein staining should be performed to notice the location , size, shape, depth, floor and edges of the corneal ulcer.
Examination for corneal opacity
is best through with the assistance of a slit-lamp. Note the amount , site, size, shape, density (nebular, macular or leucomatous) and surface of the opacity.
vi. Corneal vascularization.
The cornea is an avascular structure but its vascularization may occur in many diseases. When vessels are present, a particular note of their position, whether superficial or deep and their distribution whether localised, general, or peripheral should be made.
Differences between superificial and deep
vascularization of cornea.
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vii. Corneal sensations.
Cornea may be a very sensitive structure, being richly supplied by the nerves The sensitivity of cornea is diminished in many affections of the cornea, viz., herpetic keratitis, neuroparalytic keratitis, leprosy, DM , trigeminal block for post-herpetic neuralgia and absolute glaucoma.
To test the corneal sensations,
patient is asked to seem ahead; the examiner touches the corneal surface with a fine twisted cotton (which is brought from the side to avoid menace reflex) and observes the blinking response. Normally, there's a brisk reflex closure of lids.
Always compare the effect thereupon on the other side. the precise qualitative measurement of corneal sensations is formed with the assistance of an aesthesiometer.
viii. Back of cornea should be examined for keratic precipitates (KPs) which are cellular deposits and a symbol of anterior uveitis.
KPs are often of various types like fine, pigmented, or mutton fat.
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ix.
Corneal endothelium.
it's examined with specular microscope which allows a transparent morphological study of endothelial cells including photographic documentation.
The cell density of endothelium is around 3000 cells/mm2 in young adults, which decreases with advancing age.