Examination of cornea

Few highlights of points to be kept in mind while examining the cornea

1. EXAMINATION OF THE CORNEA - Dr. Akshay Nayak

2. Anatomy in brief Dimensions of cornea- 1] Anterior surface is elliptical with horizontal diameter 11.75mm and vertical diameter 11mm 2]Posterior surface is circular with average diameter 11.5mm 3]Thickness of cornea in the centre is 0.52mm and at periphery is 0.67mm 4]Anterior radius of curvature is 7.8mm and Posterior is 6.5mm 5]Refractive power is 43+ D 6]Refractive index is 1.37

3. Histology Epithelium- 50-90microns, 5-6 layers Entire epithelium replaced in 6-8 days. i ]Basal layer-tall columnar,germinal layer; ii]wing cells;iii ] flattened cells-zonulae occludentes,microvilii Bowmans Layer 8-14microns Condensed superficial part of stroma Does not regenerate. Stroma(substantia propria ) 0.5mm Collagen fibrils(lamellae) Lamellae are parallel to each other. Cells- keratocytes , macrophages,histiocytes etc

4. Descemet’s membrane(posterior elastic lamina) Represents basement membrane of the endothelium from which it is produced. 10-12microns Can regenerate In the periphery, ends at the anterior limit of trabecular meshwork as Schwalbe’s line. Endothelium Flat polygonal. 6000 cells/mm2 at birth---2400-3000cells/mm2 in young adults Corneal decompensation occurs when counts <500cells/mm2 Pump mechanism. BLOOD SUPPLY-Anterior ciliary vessels NERVE SUPPLY- Long ciliary nerve

5. EXAMINATION OF CORNEA-POINTS TO NOTE VISUAL ACUITY!! EXAMINATION OF CORNEA PROPER UNDER FOLLOWING HEADINGS- SHAPE SIZE CURVATURE THICKNESS TRANSPARENCY SENSATION VASCULARISATION DEPOSITS ENCROACHMENT FROM LIMBUS

6. EXAMINATION OF CORNEA Methods of examination of cornea Examination under torch light Examination under focal illumination- Listers lamp Handheld slit lamp Focal illumination with magnification Corneal loupe

7. 2. SLIT LAMP BIOMICROSCOPY Direct illumination- 1]diffuse, 2]narrow beam ,3]optical section-narrow beam gives linear cut of the cornea without illuminating surrounding. In this mode various levels of cornea available for inspection.

8. Direct illumination….. 4]Specular Reflection-uses principle of reflection of light. Specular microscopy is a specialised biomicroscopy to examine corneal endothelium. Indirect illumination- enhances contrast during visualisation of defects at various levels of cornea. Retro illumination and Sclerotic scatter

9. WHAT TO SEE ON SLIT LAMP?- EPITHELIUM- 1]EROSIONS(GREY WHITE)- superior—tarsal fb, concretions,Superior limbal keratopathy etc ; inferior— lagophthalmos , trichiasis entropion etc ; interpalpebral – uv light,welding exposure etc 2]ULCER- breach in continuity, grey white, surrounded by infiltration 3]OEDEMA- bullae– acute congestive glaucoma,trauma , after surgery, keratoconus 4]FILAMENTS- peeled off epithelium attached to cornea– recurrent idiopathic corneal erosion, keratoconjunctivitis sicca etc 5]PUNCTATE EPITHELIAL KERATITIS

10. STAINING OF CORNEA Fluorescein and rose Bengal resemble each other in structure, available as dark crystals, soluble in water and used as 1pc drops Fluoroscein stains the damaged epithelium bright green. Rose Bengal stains devitalised cornea and conjunctival epithelium.

11. Opacities Fully healed opacities do not stain.

12. Bowman’s membrane- deposits- Calcium Hemosiderin Copper Iron Stroma Oedema- may be associated with infiltrate and seen in disciform keratitis,fuch’s dystrophy etc Infiltrates-leucocytes in stroma through either limbal blood vessels or via epithelial break Vascularisation- Superficial(pannus)-trachoma, leprosy, spring catarrh, contact lens use,lagopthalmos , trichiasis , ectropion, chemical burns etc Deep (due to entry of anterior ciliary vessels)- interstitial keratitis, chemical burns etc

13. Descemets membrane- Breaks –congenital glaucoma,trauma , keratoconus. Split- trauma, surgical complication Folds- soft eye Endothelium- KP,vascularisations , fibrin deposits KERATOMETRY Principle of image formation by a convex mirror. Anterior surface of cornea acts as convex mirror. Curvature is measured in millimetres or dioptre Formula --- D=[n-1]/r ; D is refractive power of cornea, n is refractive index and r is radius of curvature

14. PACHYMETER Optical pachymeter is attached to slit lamp Ultrasonic pachymeter is most commonly used device. KERATOSCOPY AND CORNEAL TOPOGRAPHY Cornea acts as a convex mirror and any change in its surface will produce a change in shape of image. Window reflex First purkinje image- small erect virtual, anterior surface of cornea, moves with movement of light—principle of any keratoscope

15. Keratoscopy …… 4.PLACIDO DISK 10INCHES DIAMETER Central peephole has a +2D sphere lens attached to relax accommodation of observer. Normal cornea will have concentric rings spaced at regular intervals

16. Klein keratoscope Photokeratoscope Examine 55pc , whereas keratometers only examine 8pc of corneal surface Gives a a visual display photo or a video display It is used to follow progressive keratoconus,radial keratometry result, postsurgical astigmatism

17. Other procedures CORNEAL SCRAPING EXAMINATION OF TEAR FILM OCULAR ADNEXA IOP SYSTEMIC EXAMINATION

18. interpretation Shape- elliptical in hypotony , quadrilateral in phthisis Size- horizontal diameter more than 13mm – megalocornea Curvature- cornea is more curved vertically due to pressure of lids. increased- keratoconus decreased- cornea plana,perforation of globe irregular- pterygium,keratoconus Thickness –increased— disciform keratitis, corneal leucoma decreased-keratoconus, buphthalmos , pellucid degeneration

19. Transparency—check for any opacity- position,number,shape,staining , vascularisation,iris incarceration and deposits

20. Etiology of opacities- Congenital Trauma Infection Inflamation -interstitial keratitis and discifrom keratitis Allergy- phlycten , spring catarrh Degenerations Dystrophy Encroachment Deposits- Hudson stahli line,fleischers ring, kayser Fleischer ring, tattoo,foreign body Staining Vascularisation Incarceration

21. Testing sensation Should be done prior to instilling an anesthetic agent and before schirmer test. If anesthetic is used , postpone by 24hrs Diminished sensations in- herpes simplex and zoster, leprosy,scar,degenerations , dystrophies, involvement of 5 th nerve, C-P angle tumor etc Bilateral loss is rare – leprosy, herpes simplex, opacity Vascularisation

22. Causes of superficial vascualrisation -trachoma, leprosy,phlycten,riboflavin deficiency, mooren ulcer Deep- interstitial keratitis , disciform keratitis Intercorneal –superficial vessels encroaching under lamellar keratoplasty Retrocorneal - epithelial down growth, neo vascularisation of iris, intraocular tumor

23. Corneal fistula If perforation is in central cornea, iris fails to plug it, wound remains open, acqueos leaks, cornea flattens, absence of AC and soft eye resulting in corneal fistula. Lined by corneal epithelium Predisposing factors- corneal perforation in case of widely dilated pupil, which does not constrict eg use of atropine for long,large iridectomy,coloboma , aniridia etc Fistula is surrounded by a zone of infiltrates which appears white.

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