KERATOCONUS

Keratoconus

1. KERATOCONUS Dr Preethi Naveen Senior consultant Cornea and refractive surgery Academic director Medical director- dr. Agarwal’s eye bank

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.

3. staging Keratoconus is classified into four stages by Amsler Krumeich et al. STAGE 1- Eccentric corneal steepness -Myopia and/or astigmatism < 5D , Corneal radius ≤ 48D , Vogt’s striae - no corneal scar STAGE 2 – Myopia and/or astigmatism > 5D < 8D , Corneal radius ≤ 53 D , No corneal scar , Corneal thickness ≥ 400 µm STAGE 3 – Myopia and/or astigmatism > 8D < 10D , Corneal radius > 53D , No corneal scar , Corneal thickness 300-400 µm STAGE 4 – Refractive error not measurable , Corneal radius > 55D , Corneal scar/perforation , Corneal thickness upto 300 µm

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.

5. ASSOCIATIONS SYSTEMIC DISEASES Connective tissue and mesodermal dysplasia Marfan’s syndrome Ehlers-Danlos syndrome Osteogenesis imperfecta Congenital hip dysplasia Oculodento digital syndrome Rieger’s syndrome Crouzon’s syndrome Floppy eyelid syndrome Down syndrome Turners syndrome Atopic dermatitis

6.  ASSOCIATED OCULAR DISORDERS Retinitis pigmentosa Lebers congenital amaurosis Blue sclerae Congenital cataract Aniridia Retinopathy of prematurity Fuchs dystrophy Posterior polymorphous dystrophy Granular and lattice dystrophy ALLERGIC CONDITIONS Spring catarrh Asthma

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

12. management Glasses Contact lenses Collagen cross linking Intracorneal rings (CAIRS) Deep anterior lamellar Keratoplasty Penetrating Keratoplasty

13. 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.  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. 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. . I ncreases 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 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.

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