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Flashcards in opthamology Deck (194)
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What are external hordeolum?

styes - young dogs, may have single or multiple abscesses caused by suppurative infection of the glands of zeiss or moll. treatment is the same as for meibomianitis.


What is chalazion?

Obstruction of the tarsal gland secretions by a blocked duct can cause the gland to rupture, liberating its content within the eyelid substance, visible through the palpebral conjunctiva as a firm spherical, yellow lipogranuloma. If Occular surface irritation is present then treat by incising into the lesion with a blade, under general anaesthesia and curetting out the contents, followed by topical antibiotics for 7-10 days.


What happens to the eyelids after trauma?

Marked oedema comon. repair carefully without undue delay, ensuring good apposition at the lid margins. minimal debridement is required because of the good vascular supply to the lids. if laceration is extensive then repair in two layres, ensuring the deeper layer does not go full thickness through the conjunctiva where it will abrade the cornea.


Describe eyelid neoplasias

Most lid tumours occur in old dogs and are benign in behaviour. tarsal gland adenomas are most common followed by melanomas. they grow slowly but may abrade the cornea or bleed. The lid margin should be closed first and the figure of 8 suture is a neat way of taking the knot of the first suture away from the lid margin.


What is the third eyelid?

The third eyelid is a large fold of conjunctiva supported internaly by a T shaped cartilage. the base of the cartilage is surrounded byt he nictitans gland, which produces 40% of the aqeous component f the preocular tear film. The third eyelid is important in the distribution of the tear film. it is swept across the eye when the lids are closed in blining. the TEL is devoid of muscle in the dog, so its position is determined by the size and position of the globe. In the cat - movement can be both active and passive.


Describe prolapse of the nictitans gland

Appears acutely as a smooth pink swelling at the medial canthus. the mass is seen to protrude from behind the leading edge of the membrane. Thought to result from a weakness in the connective tissue attachment between the gland and the peroorbital tissue. Unacceptably high risk of dry eye if gland is excised. Surgical replacement should therefore be attempted. Pocket eye technique and anterior anchoring technique useful.


What is scrolling of the third eyelid?

Also known as eversion or kinking of the cartilage, thee straight stem of cartilage kinks, forcing the membrane to fold outwards so that the leading edge no longer contacts the cornea. may have some Occular discharge and conjunctivitis. treatment is by excising the kinked portion of the cartilage from the deep surface of the membrane.


What is plasma cell infiltration of the third eyelid?

Affects GSD and collie types, with bilateral depigmentation of the membrane, a pink/red fleshy infiltrate and rough irregular surface. The infiltrate consists of plasma cells and lymphocytes and is often concurrent with chronic superficial keratitis. Despite its appearance there is usually minimal disconfort. Treatment is with topical corticosteroids frequently initially reducing to a maintenance dose.


How do foreign bodies affect the third eyelid?

The deep surface is an occasional site for a foreign body that may be easily missed. the clinical signs are acute and marked discomfort, frequently with corneal damage opposite the foreign body. sedation and topical anaesthesia usually required to identify and remove it.


What conditions may cause third eyelid protrusion?

REtrobulbar space occupying lesions with exopthalmos eg extraconal abscess or tumour. REtraction of the globe with enopthalmos. Micropthalmos or phthisis bulbi - reduction in orbital contents. Dehydration, cachexia, masticatory muscle atrophy. alteration to nervous control- horners syndrome.


Describe the clinical anatomy of the conjunctiva

It is a thin mucous membrane. it extends from the lid margins where it is continuous with the epidermis to the limbus where it meets the cornea epithelium. It lines the inner surface of the upper and lower lids, reflected forwards at the fornixes as the bulbar conjunctiva over the globe. it is mobile, has a good blood supply and heals rapidly. The conjunctiva contains goblet cells, contributing the mucous fraction of the tear film and lymphoid follicles.


What is conjunctivitis?

The whole conjunctiva becomes diffusely reddened with a variable amount of discharge. In significant bacterial infections the discharge has a typically purulent apearance. Interpretation of bacterial culture complicated by he fact conjunctiva is not sterile and has a wide range of bacteria. Mostly commensals recovered eg streptococci, staphylococci, occasional gram -ves.


How does bacterial conjunctivitis occur?

The majority of cases are secondary to causes such as an eyelid mass, eyelid irregularity or foreign body. primary bacterial conjunctivitis is less common, acute and self limiting. in both situations a mucopurulent Occular discharge occurs in the presence of increased or normal tear production. Infection frequently wth staph or other gram positives. Fusidic acid has god activity against gram positives - apply once or twice daily.


What is opthalmia neonatorum?

Infection within the conjunctival sac before the eyelids are opened (usually at 10-14 days) will cause swelling of the eyelids, sometimes with a small amount of pus escaping at the medial canthus. this must be treated promptly to avoid corneal ulceration and penetration. the lids should be opened along their line of fusion digitally or with blunt ended scissors. after culture the occular surface should be irrigated with sterile saline and the infection treated with broad spectrum, topical antibiotic ointment and frequent application of occular lubricants.


What is ectropion?

Can cause a mild conjunctivitis due to exposure. Lid shortening can be considered in the worst affected cases, otherwise client education only.


How does distemper affect the eyes?

A purulent Occular discharge may accompany the other signs of the disease. Treatment is symptomatic, check tear production as the virus attacks the lacrimal gland, possibly leading to corneal damage. A chorioretinitis may also be present.


What is follicular conjunctivitis?

Hypertrophy of the lymphoid follicles scattered on the bulbar surface of the Nictitans and the conjunctival forniixes, occurs with chronic antigenic stimulation. The condition is poorly understood, but clinical signs are usually mild, occurring most often in dogs <18 months old. Most cases respond to treatment with saline irrigation and symptomatic use of topical steroids. Non responsive cases may improve following mechanical debridement of follicles following topical anaesthesia using a dry gauze placed over a cotton bud.


How does allergy affect the conjunctiva?

Conjunctiva and lids may be involved in local allergic reactions or generalised atopy. the finding of a single eosinophil on conjunctival cytology is considered diagnostic of an allergic process, although plasma cells and lymphocytes are more common. Intermittent use of topical steroids may be required. (alternatively topical antihistamines or mast cell stabilisers may be required). Immediate hypersensitivity reactions are occasionally encountered with rapid and dramatic chemosis (conjunctival oedema). These are usually self limiting once the dog is no longer in contact with the allergen and most respond well to a single parenteral dose of short acting corticosteroids.


What is chronic conjunctivitis?

A low to medium grade mucopurulent chronic conjunctivitis is sometimes seen as part of a generalised problem in association with marginal tear production, seborrhoea, pyoderma, otitis externa, ectropion etc, particularly in cocker spaniels. treatment is symptomatic with a view to control rather than cure. Topical cyclosporin ointment can make a considerable difference in those cases where tear production is marginal.


Describe the canine lacrimal system?

The lacrimal system consists of 3 components - secretory - glandular production of the lipid, aqueous and mucus layers of the preocular tear film. Distributory - movements of the eyelids and nictitans distribute the tear film over the Occular surface. Drainage - drainage of tears to the nasal cavity via the nasolacrimal syste.


What is keratoconjnctivitis sicca?

A common condition in the dog resulting from a deficiency in the aqueous portion of the tear film produced by the lacrimal and nictitans glands. Causes are immune mediated destruction of lacrimal tissue, with progressive loss. Seen in westies, cocker and CKCS, shih tzu and lhaso apso. Also caused by endocrine diseases (hypothyroidism, diabetes mellitus, hyperadrenocorticism) or drug induced - sulphadiazine (Widely used in sulphonamide antibiotic, found in tribrissen) and sulphasalazine may cause acute dry eye in the dog. The cornea may be ulcerated. drugs should be discontinued. damage may be temporary or permanent Viral adenitis - inflammatory destruction of lacrimal tissue in distemper. Unilateral KCS is less common. Causes include excision or uncorrected prolapse of the TEL, topical atropine, congenital abscence or hypoplasia of lacrimal tissue, neurological deficits, orbital disease.


What are the clinical signs of keratoconjunctivitis Sicca?

Conjunctivitis, mucopurulent discharge characteristically tenaceous, lustreless cornea with more advanced disease, variable degrees of corneal neovascularisation and pigmentation. Test with schirmer tear test strips - The mean normal STT is around 21mm in the dog. Values of 13-15mm should be interpreted on the basis of the occular surface appearance and level of discomfort. Treated with tear replacement - lubrithal gel, lacrilube, hylashield or tear stimulation with topical 0.2 cyclosporine ointment. Tacrolimus or pimecrolimus can be used if cyclosporine response is inadequate. Oral pilocarpine may be used in neurogenic cases with denervation hypersensitiviity. Surgical parotid duct transposition used to be performed frequently but now reserved for refractory cases - may be deposition of irritant calcium crystals on the cornea.


How can epiphora be investigated?

Epiphora is overflow tears due to poor drainage. Check with fluorescein instilled into both eyes and observe external nares for passage of fluorescein. Lack of dye does not necessarily mean that drainage is inadequate as false negatives are common. Nasolacrimal cannulation - can be performed under topical anaesthesia and a sedation in many dogs, upper punctum is cannulated with a lacrimal cannula and a syringe containing 5ml of saline. Saline should appear at the lower punctum or at the nares when the lower punctum is occluded by gentle digital pressure. Dacryocystorhinography - 0.1-1.0ml positive contrast used to delineate the nasolacrimal system.


What is a congenital imperforate puncta?

Produces epiphora in young animals frmo about 8 weeks of age. the duct system is present but the punctum is occluded by a thin covering of conjunctiva. The diagnosis is made by direct disualisation, confirmed by flushing. The saline will form a bleb at the site of occlusion. The covering membrane can be simply surgically excised.


How should lacerations of the nasolacrimal duct be treated?

Acute lacerations should be treated by cannulation of teh caniculis with monofilament nylon, over which a fine polypropylene tube is passed. the cannula should be left in place for 14 days until the wound has healed.


What is dacryocystisis?

Inflammation of the lacrimal sac (usually plus inflammation of the duct and canaliculi) most often due to a foreign body such as a grass seed. Flushing of the system from the upper punctum may allow the foreign body to be grasped at the lower punctum. Retrieval from the lacrimal sac is less straightforward but the lacrimal sac can be incised from a conjunctival approach using probes or plastic cannulae to identify site of incision. repeated flushing and systemic and topical antibiotics usually needed to prevent occlusion of the duct.


Describe the anatomy of the cornea?

The corneo scleral coat is the outermost fibrous coat o the eye. The cornea is a transparent continuation of the sclera, the junction is termed the limbus. The cornea relies on the aqueous and tear film for nourishment and cleansing and the third eyelid and lids for protection from the external environment. the cornea consists of 5 layers.


Describe the 5 layers of the cornea

A) anterior outer epithelium - continuous with the conjunctival epithelium at the limbus. Non keratinised, stratified squamous epithelium with rapid turnover of cells. Basement membrane produced by deepest layer of epithelial cells. Hemidessmosomes attach the basal cells to the thin basement membrane, which in turn anchors the epithelium to the stroma. Connective tissue stroma - 90% of corneal thickness, composed of collagen lamellae, separated by ground substance and fibroblasts. D) Descemets membrane - the basement membrane of the underlying endothelium produced throughout life, elastic and fairly strong, does not stain with fluorescein. Endothelium - the deepest layer, important for maintaining corneal dehydration. The cornea is avascular, deriving its nutrition from the aqueous perilimbal capillaries and the tear film. The corneal reflex is the reflection of the light in the cornea.


The normal cornea is transparent. Pacities in the cornea take the form of what?

2) cells infiltrating the cornea or depposited on the endothelium
3) blood vessels - distinguish superficial vessels from deep vessels (deep are darker red, dont cross limbus, straight like hedges)
4) pigment
5) disorganised collagen


What is a corneal dermoid?

A congenital mass of hairy skin on the cornea, usually at the lateral limbus. The hairs on the dermoid can irritate the corneal surface. The mass is removed by superficial keratectomy, incising in clear cornea and following a superficial plane of dissection under the mass.