Cornea and ocular surface anatomy and physiology

Dr Laurie Sullivan 2013 laurence.sullivan@gmnail.com

Cornea and Ocular Surface Anatomy, Physiology and Immunology

Why is there a cake on this slide?

Lamellar Structure - Cornea

Tear film

• Structure

• Function

Conjunctiva

Conjunctiva anatomy

1. Epithelium

2. Substantia propria (vascular stroma)

a) Lymphoid layer (superficial)

b) Fibrous layer (deep)

Conjunctiva anatomy

Substantia propria layers

a) “lymphoid layer”– Superficial, thin– Diffusely distributed lymphocytes– Contain mast cells

b) “fibrous layer”• Deep, thicker• Contains vessels, lymphatics and nerves• Attachments: tarsal plate & limbus• Mast cells: predominantly in perilimbal &

tarsal lymphoid layer

Cornea

Corneal Anatomy and PhysiologyThe cornea is a transparent, avascular structure. It consists of 5 layers :

A – Anterior Epithelium: Non-keratinised stratified squamous epithelium. Cells migrate from the basal layer upwards and from the periphery to the centre. Barrier and optical function. Tear film.B – Bowman's membrane condensed stroma - structuralC – Stroma: Connective tissue layer, type 1 collagen. Keratocytes (fibroblasts). Anterior compact, posterior spongy.D – Descemet's Membrane barrierE – Endothelium: Actively pumps water and ions from the stroma to produce corneal dehydration and transparency. If damaged, these cells do not regenerate (can slide) and corneal decompensation occurs where the cornea becomes white and cloudy

Confocal microscopy

Figure 1. Heidelberg Retina Tomograph 2 Rostock Cornea Module confocal images of central cornea (23-year-old woman) showing (A) an epithelial wing cell layer, (B) an epithelial basal cell layer below the epithelial wing cell layer, and (C) less reflective fibrous structures at the level of Bowman’s layer compared with subbasal nerves (arrowheads). In some images, the structures appear to form nodes (arrow). D–F, Images of the polymorphic structures (K-structures; arrows) with subbasal nerve plexus (arrowheads). Dark shadows always accompany these fibers. These structures are 5 to 15 μm in diameter and appear to consist of bundles of filaments. Bars, 100 μm.

Epithelium

Limbus

Immunology

• Langerhan’s cells in epithelium = macrophages (antigen presenting cells APCs)

• Present Ag to lymphocytes

Bowmans

• Structure

• Function

Stroma

Ultrastructure - collagen

Collagen triple helix with crosslinks form microfibrils

Collagen microfibrils lined up and cross- linked form collagen fibrils

(A) SEM of an adult human corneal keratocyte (K) showing the complex dendritic morphology of the cell body and processes. (B) Light micrographs of keratocyte network in the feline. Keratocytes are connected by broad cellular processes (open arrows) extending from main cell body which contains nucleus (arrows).

Corneal Innervation

• Trigeminal nerve (CN V) - Ophthalmic Branch (CN V1) - Long Ciliary nerves

• Sub epithelial nerve plexus

(A) A stromal nerve surrounded by a keratocyte in a keratoconus patient.

(B,C) CGRP positive nerve fibres in the subbasal plexus. (D,F) SP positive nerve fibres. Penetration of a stromal nerve fibre bundle through the Bowman's layer ( ) and establishment of ∗nerve leashes of the subbasal plexus is shown in (B) (arrows). The whole mount preparation shown in (C) illustrates the parallel running CGRP-positive nerve bundles of the subbasal plexus. The cross section in (D) illustrates SP-immunoreactive nerve fibre bundles in a 60 μm thick frozen section. Tangential view of SP-positive beaded intraepithelial nerve terminals are shown in a whole mount preparation (F). (E) Schematic drawing on the architecture of nerve bundles in the subbasal plexus (arrow) containing a mixed population of straight and beaded fibres. Only the beaded fibres bifurcate from the bundle and turn upwards into the epithelium. Bar: A, 1 μm; B; 25 μm; C, 1 mm; D, 25 μm; F, 10 μm.

Subbasal nerve plexus in a 6 mm diameter central button from a 61 year-old left cornea. For clarity, only the largest diameter subbasal nerve fibers have been illustrated. Individual subbasal nerves follow straight or curvilinear trajectories and converge on an imaginary center, or vortex (asterisk), located approximately 2.5 mm inferonasal to the corneal apex.

What conditions are associated with corneal hypoaesthesia?

• HSV• HZO• Stroke/CVA• Orbital tumours / trauma / surgery• Chronic corneal inflammation and scarring• Corneal surgery / trauma / contact lens• PRP

Dry eye/neurotrophic keratitis in a patient, who underwent an uneventful LASIK procedure 5 days earlier. The patient was treated with topical lubricants and wetting agents, and recovered completely. A:fluorescein staining reveals confluent epithelial surface lesions. The flap margins can also be observed. B: biomicroscopical image on the same eye.

Descemet’s Membrane

Endothelium

• Structure

• Function

Endothelial Pump

Pathology

Corneal infections. A. Slit-lamp photograph of the cornea with Acanthamoeba keratitis. Subepithelial opacities and numerous radial keratoneuritis lesions. B. In the epithelial basal cell layer, numerous highly reflective, high-contrast round-shaped particles 10-20μm in diameter suggestive of Acanthamoeba cysts were detected by in vivo laser confocal microscopy. (Bar=50μm) C. Direct examination of the epithelial scraping with Parker ink-potassium hydroxide shows Acanthamoeba cysts. Note that the cysts have double walls with characteristic wrinkled outer wall. (Bar=10μm) D. Slit-lamp photograph of the cornea with Aspergillus keratitis. Severe corneal ulcer was observed. E. In the stormal layer, numerous highly reflective, high-contrast branching filaments suggestive of Aspergillus hyphae were detected by in vivo laser confocal microscopy. (Bar=50μm) F. scrapingrevealed Aspergillushyphae

Cornea and ocular surface anatomy and physiology

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