Sclera, episclera, limbus

Question 1

Anatomy of sclera

Answer 1

Elastic fibres and fibroblasts dispersed among collagen I bundles

Anterior ciliary areties anastomose with superficial vascular plexus (superficial sclera )

Scleral venous plexus (mid-sclera) anastomoses with AAP (deep)

Question 2

How thick is the sclera ?

Answer 2

Dog 0.3 -0.4 mm posterior pole

0. 12-0.2 mm equator
1. 6mm limbus

Cat 0.13 - 0.6mm posterior pole

0. 09-0.2 equator
1. 1mm limbus

Question 3

Anatomy of episclera

Answer 3

Loosely adherent to the sclera, coalesces with Tenon’s fascia.
Highly vascular, fibroelestic structure consisting of collagen, fibroblast, melanocytes, proteoglycans and glycoprotein

Question 4

Anatomy of limbus

Answer 4

Transition zone between cornea, sclera, epithelia of conjunctiva and cornea.
1mm wide, pigmented area encircling cornea containing melanocytes a d epithelial stem cells.

Question 5

Developmental abnormalities of sclera

Answer 5

Thin sclera, dermoid, congenital staphyloma, sclerocornea

Question 6

Staphyloma of sclera

Answer 6

Thinning and protrusion of the fibrous tunic lined with uveal tissue.
Posterior more common,associated with CEA + MOD.
May resemble melanoma if at limbus.
Most static, no treatment. If >3mm scleral autograft or xenograft, intestinal submucosa
Multifocal in cystic eye

Question 7

Sclerocornea

Answer 7

Congenital absence of limbal anlage
Peripheral or total scleratisation
Corneal curvature less than scleral curvature
Intraocular malformations are common

Question 8

Acquired inflammatory conditions of episclera/sclera

Answer 8

Episcleritis ( simple, nodular)
Nodular episclerokeratitis 
Scleritis
Subconjunctival granuloma 
Abscess 
Ulcerative limbal keratitis 
Neoplasia 
Ocular melanosis 
Trauma

Question 9

Other names for nodular episclerokeratitis

Answer 9

nodular granulomatous episcleroker.
Ocular/ophthalmic nodular faciitis 
Fibrous histiocytoma
Idiopathic granulomatous disease
Limbal granuloma
Proliferative episclerokeratitis 
Proliferative keratoconjunctivtis

Question 10

NGE

Answer 10

Frequently in Collie and Shetland Sheepdog.
Simgle or multiple raised nodules composed of histiocytes, plasma cells and lymphocytes infiltrate episclera and corneal stroma. May be present on eyelids, 3rd, lip commisure or iris.

Question 11

Treatment of NGE

Answer 11

Sx, cryo, cct, beta irradiation,

steroids (p.o, topical, intralesional) azathioprine, tetracycline, niacinamide, cyclophosphamide.

Question 12

Types of scleritis

Answer 12

Anterior /posterior

Necrotizing granulomatous / non-necrotizing granulomatous scleritis

Question 13

Anterior scleritis

Answer 13

Ant non- nec gr scleritis most common form
Usually no nodules but if present then immobile
Painful
Deep and superficial episcleral vasculature congestion
Red/purple sclera
+/- Corneal infiltrate

Question 14

Posterior scleritis

Answer 14

Diff diagnosis
Concurrent retinal detachment, uveitis. U/s hyperechoic + thickened sclera and intraconal anterior orbital hyperechogenicity

Question 15

Limbal melanocytoma/epibulbar melanocytoma

Answer 15

From limbal melanocytes
Extends to perilimbal sclera and cornea bulbar conjunctiva moves freely over mass
Gonioscopy - focal appositional angle closure
Rapid growth in young, slow in old dogs

Question 16

Differentials for limbal melanocytoma

Answer 16

Anterior uveal melanoma with extrascleral extension
Limbal melanoma
Staphyloma

Question 17

Ocular melanosis

Answer 17

Middle age Cairn terrier

Melanocyte in episclera and ica

Question 18

Other neoplasia of limbus

Answer 18

Fibrosarcoma, scc, schwannoma, haemangioma, haemangiosarcoma, lymphoma

Question 19

Acquired scleral thinning

Answer 19

Trans-scleral laser cyclophotocoagulation

Glaucoma