Module 7 Flashcards
(34 cards)
The Uveal Tract - iris
Anterior - iris and ciliary body. Posterior - choroid.
Iris is the diaphragm between anterior and posterior chambers. Narrow darker pupillary zone, wider paler peripheral zone. Iris collarette is the junction between them.
Embryology: mesenchyme and neuroectoderm. Neuroectoderm covers the back of the pupillary membrane (mesenchyme) and these fuse to become the iris with an opening in the centre.
Histology: stroma, nerves, blood vessels and muscle. Anterior border - fibroblasts and uveal melanocytes overlying loose stroma. Sphincter is in the stroma encircling the pupillary zone. Particles up to 200um can pass through the tissue spaces. Posterior to stroma, 2x epithelium, which forms blood-aqueous barrier. Anterior non-pigmented epithelium –> dilator muscle, continuous with pigmented ciliary epithelium (–>RPE). Posterior pigmented epithelium is continuous with non-pigmented ciliary epithelium (–> neurosensory retina)
Uveal tract - iris
Blood supply: major arterial circle - raise tortuous line around the periphery. Long posterior ciliary arteries enter at 9 and 3 o’clock positions. Venous drainage via tortuous radial vessels, empty into anterior choroidal veins and vortex veins.
Nerve supply: sensory - trigeminal - enter via iris root and terminate naked in stroma. Sphincter muscle - mainly parasympathetic, CN III, from ciliary ganglion via short ciliary nerves -> constriction. The dilator muscle single layer of radially oriented fibres, mostly sympathetic supply. Derived from superior cervical ganglion and via posterior ciliary nerves.
Iris colour: colour is determined by melanocytes in the stroma, brown = dense pigmentation, blue = less pigmentation, albino pink - no pigment but red glow from fundus reflected through iris
Iris shape: pupillary margin - pigmented epithelium extend around pupil - ectropion uveae. Shape varies in species and is a result of different patterns of constrictor muscle arrangement.
Ciliary body
Posterior to iris, anterior to the choroid.
Functions: secretion of aqueous, nourishing the lens, muscle for accommodation, supporting the zonular fibres and forming part of the vitreous face.
Histology: thin stroma, muscles, blood vessels. Two layered epithelium, inner/vitreal non-pigmented epithelium–> neuroretina. Non-pigmentary epithelium secretes aqueous. Outer/scleral side is pigmented epithelium, extension of RPE. Adhesion complexes between the two layers closes the gap.
Ciliary body –> triangular in shape, anterior = pars plicata, posterior = pars plana. Pars plicata surface has multiple folds; ciliary processes formed from anterior cup. ^SA for aqueous production. Ciliary processes also anchor suspensory zonular fibres of the lens. Most anterior portion of ciliary body is the ciliary cleft of the iridocorneal angle.
Choroid
Between retina and sclera.
Bruch's membrane - lies next to RPE Choriocapillaris Tapetum Stroma & large vessels Suprachoroid
Congenital conditions of the uveal tract
Aniridia - very rare, absence of iris. Iris coloboma - partial absence of tissue or holes.
Persistent pupillary membranes (PPMs) - remnants of the anterior portion of mesodermal, vascular membranes which surround developing lens in utero. Membrane regresses after birth. PPM = web-like strands iris-iris, iris-lens, iris-cornea. Focal opacities. iris from collarette, synechiae arise from pupil margin or periphery. Inherited in the Basenji.
Uveitis in dogs and cats
Inflammation or the uveal tract, in part or whole.
Iritis = anterior uveitis - just iris
Iridocyclitis = iris and anterior ciliary body (most common)
Pars planitis = inflammation of posterior ciliary body
Choroiditis = inflammation of the choroid - posterior uveitis often chorioretinitis
Endophthalmitis = inflammation of the entire globe
Uveitis signs
CS acute uveitis:
pain - photophobia, blepharospasm, inc lacrimation
miosis - or sluggish PLR
Aqueous flare - +/- keratitic precipitates and debris. BAB breakdown
Hypopyon - cellular material leaked into anterior chamber
Corneal oedema
Iris swelling - vessels changes and stromal oedema, iris dull looking
rubeosis iridis - vascular congestion and neovascularisation of the anterior iris face.
Episcleral vascular congestion - dark, straight, distended vessels perpendicular to limbus
Peripheral corneal deep neovascularisation - short, brush-like vessels arising from limbus
Hypotony - drop in IOP, reduced aqueous due to inflammation of ciliary epithelium
Hyphaema - haemorrhage in the anterior chamber
Active chorioretinitis - effusion and vascular changes +/- choroidal haemorrhage
Retinal detachment
optic neuritis
Causes of uveitis
Many possible causes but frequently dx is idiopathic as no cause is found
Non-infectious:
- Reflex/neurological: following corneal insult, transient and mild. mediated by CN V. Tx: cycloplegic mydriatic agents
- Immune mediated: perpetuation and recurrence of uveitis may be associated with immune mediate disease, may be part of uveodermatological syndrome (autoimmune destruction of melanocytes –> eye and skin symptoms)
- Lens induced: phacoclastic; sudden release of antigenic lens proteins as a result of trauma leading to very intense uveitis and phacolytic; slow release of lens protein as a result of hypermature cataracts leading to low grade uveitis.
- Neoplastic: primary and secondary, neoplastic cells induced inflammatory response
- Trauma: penetrating or blunt. Infection, IO haemorrhage, and glacuoma may complicate this.
- Other: blood and lipid in the anterior chamber –> nonspecific uveitis
Infectious causes of uveitis
Viral: CAV-1, or a reaction to a vaccination with live CAV-1. Sight hounds particularly susceptible. Corneal oedema - blue eye, Arthus (type IV DHP) reaction. Uncommon as use CAV-2 in vaccs now.
Cats - generalised viral disease, FeLV, FIV, and FIP is a common cause of uveitis.
Bacterial: primary - following trauma/sx infection (pasteurella multocida), or secondary due to blood-ocular barrier breakdown due generalised bacteraemia (borreliosis - lyme dz, leptospirosis, brucellosis). Also septicaemia e.g. staphylococcal toxins in pyometra
Protozoal: Toxoplasma cats>dogs. Dx: rising titre over 3-4 weeks. IgG and IgM should be measured.
Leishmaniasis and Ehrlichosis are seen abroad, see in rescue or travelling pets.
Parasitic: migrating parasites are a rare cause - toxacariasis, canine filariasis, A. vasorum, IO deptera larvae.
Fungal: tropical countries - yeast, fungal, algae. Posterior uveitits. Causes - blastomycoci, crypotococcosis, coccidiomycosis, geotrichosis, histoplasmosis.
Chronic uveitis - severe IO signs that can be sight threatening
CS: Iris rests, synechiae, iris bombe, darkened iris, glaucoma, cataract, lens luxation, phthisis bulbi, post inflammatory retinopathy
Chronic uveitis - severe IO signs that can be sight threatening
Dx and work up
CS: Iris rests, synechiae, iris bombe, darkened iris, glaucoma, cataract, lens luxation, phthisis bulbi, post inflammatory retinopathy
Dx: bilateral = systemic problem, one eye may be affected before the other
1- pupil: size, shape, reaction to light
2- light across anterior chamber in a few directions, estimate depth of chamber, depth will be shallower if iris is swollen, deeper if lens has ruptured
3- narrow beam or small circle to assess for aqueous flare
4- transillumination to differentiate masses from cysts
5- tonometry
6- gonioscopy may be useful, especially fellow eye
Work up
1 - PE
2- haemamtology and biochemistry
3- platelets, serum electrophoresis, lipoprotein analysis and autoantibody tests
4- seroligical tests (2 samples 2-3 weeks apart), CAV, borrelosis (lymes), lepto, brucellosis, toxoplasmosis. Cat - FeLV, FIV and coronavirus is always advised.
5- BM and LNs
6- US, x-rays, MRI to work up neoplasia/systemic dz
7- aqueous/vitreous samples - referral
8 - if severe and secondary glaucoma - enucleation and histopathology
Tx of uveitis
1 - Specific cause if found
2 - systemic antibiotics for bacterial dz, clindamycin in cases of toxoplasma, doxycycline for borreliosis (lymes)
3- symptomatic treatment - anti-inflammatories and mydriatics
4 - care with CCS, if infection suspected then must be covered with ABs. Also care corneal ulceration.
5- mydriatics caution if secondary glaucoma is a risk.
Medical tx uveitis in cats and dogs
CCS:
- topical; prednisolone acetate, dexamethasone
- systemic; prednisolone
NSAIDs:
- topical; ketorolac, flurbiprophen sodium, diclofenac sodium, bromfenac
- systemic; meloxicam and many other
Mydriatrics:
- topical; atropine, cyclopentolate hydrochloride, tropicamide, phenylephrine
Others:
- systemic; azothiaprine, ciclosporin
Other acquired uveal conditions
Iris atrophy: senile change, thinning iris, more common in toy breeds
Uveal cysts: pigmented, well-circumscribed, arise from posterior surface of iris, fixed or free floating, do not usually cause a clinical problem. Transilluminate. May rupture. Multiple iridociliary cysts may lead to glaucoma and IO haemorrhage (Great Dane, Golden Retrievers)
Anterior uveal neoplasia: relatively common. Should always be considered in refractory glaucoma and uveitis cases.
Anterior uveal melanoma: usually pigmented (not always) mass, from iris or ciliary body. Can see diffuse iris involvement - iris thickening (as seen in DIM in cats - more likely malignant cf. dogs). In dogs usually benign but local invasion –> enucleation rather than concern regarding metastasis. Laser photocoagulation may be used to slow growth.
Ciliary body adenoma/adenocarcinoma: pinkish, protrude from behind pupil. Enucleation is curative is most cases.
Metastatic neoplasia: lymphoma most common secondary neoplasia affecting the eye. Solitary mass or generalised uveal tract inflammation. Multiple myeloma and systemic histiocytosis also possible. Mammary and pulmonary adenocarcinoma also reported.
Iris pigment changes in the cat
Benign melanosis - discrete foci - common and normal
Hyperpigmentation and melanocytes and increase in size - ageing phenomenon
When confined to anterior surface they are of no concern
Histo only way to dx melanoma
Examine sequentially - taking photos
Cause for concerns: deeper stromal involvement, pigment shedding, change in texture, dyscoria, glaucoma.
LN bx also an option
The lens
Anatomy and embryology: capsule, epithelium, lens fibres. Nucleus and cortex, anterior and posterior.
Zonules from ciliary processes insert onto the lens capsule, anterior and posterior to the equator. Ciliary body muscle contract = alters lens shape = dynamic accommodation.
Vitreous attached at the mid-periphery, hyaloideocapsular ligament.
Lens develops from thickening of surface ectoderm. Lens vesicle forms day 25. Primary lens fibres differentiate from posterior epithelium. Induced by retina. Forming nucleus. Posterior lens capsule very thin in adult, no epithelial cells in this region.
Anterior lens capsule - actively dividing epithelial cells, at equator start to elongate forming secondary fibres, an arm into anterior and arm into posterior. Nucleus compressed throughout life due to generation of new secondary fibres.
Anterior lens capsule produced by anterior epithelium and gets thicker throughout life.
Close examination - can see suture lines, where tips of fibres meet, posteriorly inverted Y (Mercedes) and anteriorly upright Y
Lens nutrition - hyaloid artery, traverses vitreous, and later the tunica vasculosa lentis a perilenticular vascular network of mesenchymal origin. Adult lens relies on aqueous for oxygen, nutrients and waste removal.
Disorders: congenital and acquired.
Congenital lens anomalies
Genetic or exogenous factors. Lens development crucial for IO embryogenesis and so lens anomalies often present as part of MODs.
Aphakia - absence of
microphakia - small, alone or as part of MODs e.g. microphthalmia, cataracts, PHPV
Lenticonus - abnormal shape
Coloboma - an area fails to form, usually equator, resulting in notch
Congenital lens anomalies
Capsular cataracts associated with PPM: remnants of embryonic vasculature arising from iris. If insert onto lens capsule may be associated with capsular or subcapsule cataracts. May also see other defects; MODs
Persistent hyperplastic primary vitreous (PHPV) and persistent hyperplastic tunica vasculosa lentis (PHTVL): embryonic vascular network that may persist into adult life. fibrovascular plaque is present on the posterior lens surface and involves the lens capsule. +/- lens abnormalities. Persistent hyaloid vasculature may be present. May be blind. Bloods vessels differentiate from regular cataract. Can occur spontaneously but inherited in Staffies and Dobies.
Congenital cataracts
Cataracts
Opacity in the lens or it capsule
Pathological changes: increase in the amount of insoluble lens protein, alteration in the proportion of different lens crystallins, breakdown in the normal metabolic pathways, increase in lens hydration.
Deposition of lens protein, disruption of fibres, loss of transparency.
Examination of lens: mydriasis, distant direct ophthalmoscopy, magnification, slit-lap biomicroscopy.
Cataracts classification
Classification:
1) Position: capsular, subcapsular, nuclear, cortical, axial, anterior and posterior polar, equatorial
2) Stage: incipient (cotton woolly, inherited in GSD), immature, mature (tapetal reflex absent), hypermature including morgagnian (leaking protein)
3) age of animal: congenital, developmental/juvenile, senile
4) aeitology: inherited, secondary to ocular disease, traumatic, metabolic, toxic or dietary
Cataracts ddx
1 - Nuclear sclerosis: a common misdiagnosis, compression of nucleus results in loss of hydration to lens nucleus. greying of nucleus. Distant direct ophthalmoscopy - denser nucleus appears as a circle within the lens against tapetal reflection. No effect on vision, can still examine fundus.
2- temporary developmental lens opacities: seen in puppies a few weeks of age. Arrow-tip opacities at the equatorial end of suture lines. Disappear in a few weeks
Inherited cataracts
Examples:
1 - congenital cataracts: with microphthalmos and MODs. Proven inherited in the Miniature Schnauzer. Breed-related incidences in English cocker spaniel, Golden retriever, WHWT. Searching nystagmus is common, mostly non-progressive. Mydriasis may help by allowing light through cortex.
2- early developing cataracts: Boston terrier, Frenchies, Staffies. Incidence is now low.
3 - Posterior polar subcapsular cataract (PPS): commonest inherited cataract seen in adult dogs. The retriever breed, Siberian Husky, Munsterlander are affected. Bilateral. Develops at posterior suture lines, triangular. No noticeable effect on vision. Progression minimal, 5% affected dogs may be candidates for sx. Do not confused Mittendorf’s dot for this.
4- Inherited cataract in the American Cocker: variable age of onset, progressive or stationary, unilateral or bilateral. Any cataract in this breed is generally considered inherited.
Secondary cataracts
Generalised Progressive Retinal Atrophy (GPRA): may be presenting sign in ECS and miniature poodles, cataracts formation secondary to GPRA. Bilateral in breeds at known risk for GPRA. Toxic products from retina –> cataract. Hx is giveaway - night blindness prior to milky look
Antierior uveitis and glaucoma: alter composition of aqueous, unsurpisingly induces cataracts. Hypermature and rapidly developing. Hyper-mature or rapidly developing cataracts –> uveitis. so cataracts can induce uveitis and vice versa
Trauma: blunt and penetrating. Blunt - uveitis –> lens damage. Small perfs will seal but will see cataracts formation. Uveitis results from sudden release of lens protein with large tear in capsule. Sx indicated to remove lens, prognosis still guarded. Also seen in DM
Metabolic cataracts: hyperglycaemia due to poor diabetic control, glucose –> lens capsule, saturates pathways and aldose reductase –> sorbitol. Too large to leave lens, accumulates and increases osmotic pressure. Disruption of fibres, vacuolation, cataract. Can rupture due to increase in size (labradors). Sx removal carrier good prognosis, providing animal is stabilised. Chronic phacolytic uveitis common, so early sx advised. If ruptures then emergency sx to save eye.
Toxic or dietary: cataract formation orphaned puppies or kittens fed appropriate milk subs. Also various drugs/toxins that are cataractogenic. Radiation tx for malignancies can induce cataract.
Senile cataract: cause under debate. Free radical damage and changes in aldose reductase metabolism implicated. Very common in dogs
Feline cataracts
Congenital: uni or bi, persian and BSH, nuclear. Presumed autosomal recessive. Also isolated cases with no apparent breed incidence or aetiology.
Cataract uncommon in the cat and is almost always secondary
Causes of secondary:
- post-inflammatory (uveitis) - most common, synechiae seen also
- traumatic - penetrating FBs involving lens capsule. Extent and progression of traumatic cataracts is variable in the cat, adhesions to iris usually seen
- metabolic - diabetic cataract rare in cats, slower onset cf. dogs. Young diabetic cats
Nutritional - arginine deficiency, young cats. Bilateral. Especially following hand-rearing from birth.
Senile nuclear sclerosis - more advanced age cf. dog, dogs tends to be noted 6-7 years, cats not until 10 years
Management of cataract similar to dog, sx is only possible tx. Cats cope well with blindness and not performed as frequently. Less IO inflammation and glaucoma post op, despite the fact cataract often secondary to uveitis in cats!!!
