Ophthalmology/Diseases of Cornea

Introduction to Cornea The cornea is a transparent, avascular, watch-glass like structure. It forms anterior 1/6th of the outer fibrous coat of eyeball. Functions Major refracting medium Protects intraocular contents Applied Physiology Corneal Transparency It is due to the following factors: Peculiar arrangement of corneal lamellae (Lattice Theory of Maurice) Avascularity Relative state of dehydration maintained by barrier effects of epithelium and endothelium and active bicarbonate pump of endothelium Source of Nutrients Solutes enter the cornea by: Simple diffusion through aqueous humor Active transport through aqueous humor Diffusion from perilimbal capillaries Oxygen directly enters from the air via an active process of epithelium Congenital Anomalies Megalocornea When the horizontal diameter of cornea is of adult size at birth or 13mm or greater after the age of 2 years. Microcornea When the horizontal diameter is less than 10mm since birth. Cornea Plana Bilaterally the cornea is comparatively flat in this condition. Congenital Cloudy Cornea Cloudiness in the cornea since birth due to generally Sclerocornea Tears in Descemet's membrane Ulcer Metabolic conditions Posterior Corneal Defect Endothelial dystrophy Dermoids Inflammatory Conditions The inflammation of cornea is called keratitis. Morphological Classification A. Ulcerative Keratitis (corneal ulcer) Depending on location Central Peripheral Depending on purulence Purulent Corneal Ulcer (suppurative) Non-Purulent Corneal Ulcer (non-suppurative) Depending on hypopoyon Simple Corneal Ulcer Hypopyon Corneal Ulcer Depending on Depth Superficial Deep Impending perforation Perforated Depending on Slough fornmation Non-Sloughing Corneal Ulcer Sloughing Corneal Ulcer B. Non-Ulcerative Keratitis Superficial keratitis Diffuse superficial keratitis Superficial Punctate Keratitis (SPK) Deep Keratitis Non-suppurative Interstitial Disciform Sclerosing Keratitis Profunda Suppurative Central Corneal Posterior Corneal Etiological Classification Infective keratitis Bacterial Viral Fungal Chlamydial Protozoal Spirochaetal Allergic Keratitis Phlyctenular keratitis Vernal keratitis Atopic keratitis Trophic Keratitis Exposure keratitis Neuroparalytic keratitis Keratomalacia Atheromatous Ulcer Associated with diseases of skin and mucous membrane Associated with systemic collagen vascular disorders Traumatic keratitis Idiopathic keratitis Mooren's Corneal Ulcer Superior limbic keratoconjunctivitis Thygseon's superficial punctate keratitis Degenerative Disorders It happens when normal corneal cells undergo some degenerative changes due to age or some pathological conditions. Classification A.Etiological Classification Age related degenerations Arcus senilitis Vogt's white limbal girdle Hassal-Henle bodies Mosaic degeneration Pathological degenerations Fatty degeneration Amyloidosis Calcific degeneration Salzmann's nodular degeneration Furrow degeneration Spheroidal degeneration Pellucid marginal degeneration Terrien's marginal degeneration Mooren's ulcer Corneal Dystrophies These are inherited disorders in which the cells have some inborn defects due to which cornea becomes hazy with the passage of time. There is no associated systemic pathology. Classification Anterior Dystrophies Epithelial basement membrane dystrophy Reis-Buckler's Dystrophy Meesman's Dystrophy Recurrent Corneal Erosion Syndrome Stocker-Holt Dystrophy Stromal Dystrophies Lattice Dystrophy Crystalline Dystrophy (Schnyder's) Granular Dystrophy (Groenouw's type I) Macular Dystrophy (Groenouw's type II) Posterior Dystrophies Cornea Gutta Fuch's late hereditary endothelial dystrophy Posterior polymorphous dystrophy (of Schlichting) Congenital hereditary endothelial dystrophy (CHED) Ectatic Conditions Keratconus: is a non-inflammatory, mostly bilateral, ectatic condition of cornea in it's axial part. Keratoglobus: It is a familial and hereditary bilateral congenital disorder characterized by thinning and hemispherical protrusion of the entire cornea. Keratoconus Posterior: Extremely rare condition. Cone-like bulging of posterior surface of cornea occurs. Abnormalities in transparency of cornea Any condition that alters corneal transparency leads to loss of vision. The most common causes of loss of corneal transparency are: Corneal Oedema Drying of Cornea Depositions on Cornea Inflammations of Cornea Corneal Degenerations Dystrophies of cornea Vascularization of cornea Scarring of Cornea Corneal Opacities This term is typically used for the loss of transarency of cornea due to scarring. Causes: Developemental Anomalies Following birth trauma Healed Corneal wounds Healed Corneal Ulcers Corneal Oedema Normal water content of cornea is 78%. If it becomes greater than this, central thickness increases and transparency reduces.slit lamp examination shows hazy cornea. Causes: Raised IOP Endothelial damage Epithelial damage one drop of glycerine clears the hazy appearance of the cornea Vasclarization of Cornea Normally the cornea has only small capillary loops in the periphery for about 1mm. It can be invaded by vessels leading to irritation and decreased corneal transpaency.