2. DEFINITION
• KERATOCONUS
• It is a clinical entity characterized by noninflammatory and noninfective,
progressive, bilateral thinning of the cornea with ectasia of conical shape.
• This is mostly bilateral condition, girls between 15- 20 years affected more,
overall incidence rate estimated to be 0.15 to 0.20 percent.
• It manifests by adolescence, resulting in considerable visual impairment owing to
the development of high degree irregular myopic astigmatism.
4. ETIOLOGY
• Definite etiology is unknown.
• 95% of patients do not show evidence of specific hereditary pattern. Pattern of inheritance is
variable.
• Several theories have been put forward to explain the etiology of keratoconus.
• ENZYME THEORY Alteration in the levels of following enzymes have been noted: Increased
level of epithelial lysosomal enzymes. Decreased level of alpha-1 proteinase inhibitor in the
epithelium. Decreased levels of glucose-6 phosphate dehydrogenase in the epithelium.
• CONNECTIVE TISSUE ABNORMALITY THEORY There is association of keratoconus with some
connective tissue disorders.
• EYE RUBBING Habitual eye rubbing in some diseases like vernal catarrh, Down syndrome and
poorly sighted patients of Leber’s tapetoretinal degeneration are associated with keratoconus.
7. CLINICAL FEATURES
• Gradual decrease in vision, photophobia, monocular diplopia or monocular
polyopia.
• Severe photophobia and watering is seen in cases of hydrops.
• There is conical protrusion of the cornea with central thinning and the apex
of the cone is usually directed inferonasally.
8. SIGNS
• Munson’s sign is a V-shaped conformation of the lower
lid produced by the ectatic cornea in downgaze.
• Rizzuti’s sign is a sharply focused beam of light near the nasal limbus, produced
by lateral illumination of the cornea in patients with advanced keratoconus.
• Retinoscopy shows a scissoring reflex.
• On direct ophthalmoscopy It is called a Charleux oil droplet reflex
9. SLIT LAMP EXAMINATION
Prominent corneal nerves
Fleischer's Ring - yellow-brown to olive-green ring of pigment which may or may not completely surround the
base of the cone.
• Formed when hemosiderin (iron) pigment is deposited deep in the epithelium.
• Locating this may be made easier by using a cobalt filter.
Lines of Vogt: Small and brushlike lines, generally vertical but they can be oblique.
Found in the deep layers of the stroma. Disappear when gentle pressure is exerted on the globe through the lid.
10. Corneal Hydrops: Corneal hydrops occurs in advanced cases, when Descemet's
membrane ruptures, aqueous flows into the cornea. report a sudden loss of vision
and a visible white spot on the Cornea
Corneal Scarring: Sub-epithelial corneal scarring,
may occur as keratoconus progresses because of ruptures in
Bowman's membrane which is then filled with connective tissue.
Deep opacity of the cornea are also common in keratoconus.
11. INVESTIGATIONS
PACHYMETRY
• Thinning in the inferior quadrant can be diagnostic of keratoconus.
• Central or paracentral corneal thickness of less than 450 µm is abnormal.
• If the reading decreases by nearly 20 µm on successive pachymetric readings, it is suspicious
of keratoconus.
Corneal topography
• Provides a color coded map of the corneal surface. meridians
• Steep curvatures are marked orange or red
• Flat curvature in blue or violet
• Normal curvatures in green or yellow
13. 1. GLASSES- Spectacles can provide acceptable vision for patients in very early stages, and they are
especially appropriate for those who achieve 20/40 or better visual acuity.
2. CONTACT LENSES- In early stages, a Toric soft lens may be sufficient for correcting myopia and
regular astigmatism. However, as the diseases progresses, such lenses are no longer capable of
correcting the refractive error, and there is need for special lenses such as Rose K, hybrid lenses,
piggy back, or scleral lenses.
3. COLLAGEN CROSS LINKING - This method relies on the interaction between UVA at a wavelength
of 370 nm and topical riboflavin (vitamin B) for 30 min. The main effect of CXL is that it prevents
disease progression through the formation of chemical bonds among collagen fibrils.. Increases
rigidity of corneal collagen and thus reduces the likelihood of further ectasia.
14. 4. CAIRS- Corneal Allogenic Intrastromal Ring Segments or “CAIRS” is
the next progression of intracorneal ring segment surgery and was
first described in 2017. The procedure begins with harvesting a ring of corneal
tissue from a donor graft. Channels are then formed in the patient’s cornea with a laser and the
stromal ring segments are then threaded into the channels.
5. Deep Anterior Lamellar Keratoplasty -Partial corneal transplant.
The cornea is removed to the depth of posterior stroma, and the donor button is
sutured in place.
6. Penetrating Keratoplasty- In this procedure, the keratoconic cornea is prepared by removing the
central area of the cornea, and a full-thickness corneal button is sutured in its place. Usually trephines
between 8.0-8.5 mm are used.
15. DIFFERENTIAL DIAGNOSIS
1. KERATOGLOBUS-
This is due to thinning of periphery of the cornea which gradually progresses towards
the centre.
It is present at or soon after birth. So it is thought to be a developmental anomaly.
Perforation can occur in this condition with minimal ocular trauma.
2. PELLUCID MARGINAL DEGENERATION-
Bilateral peripheral corneal ectatic disorder
characterized by a band of thinning of 1-2 mm width typically in the inferior cornea.
Maximum corneal protrusion occurs superior to the area of thinning.
There is no other abnormality and it occurs in 2nd to 5th decade.
