Module 7

Question 1

The Uveal Tract - iris

Answer 1

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)

Question 2

Uveal tract - iris

Answer 2

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.

Question 3

Ciliary body

Answer 3

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.

Question 4

Choroid

Answer 4

Between retina and sclera.

Bruch's membrane - lies next to RPE
Choriocapillaris
Tapetum
Stroma & large vessels
Suprachoroid

Question 5

Congenital conditions of the uveal tract

Answer 5

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.

Question 6

Uveitis in dogs and cats

Answer 6

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

Question 7

Uveitis signs

Answer 7

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

Question 8

Causes of uveitis

Answer 8

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

Question 9

Infectious causes of uveitis

Answer 9

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.

Question 10

Chronic uveitis - severe IO signs that can be sight threatening

Answer 10

CS: Iris rests, synechiae, iris bombe, darkened iris, glaucoma, cataract, lens luxation, phthisis bulbi, post inflammatory retinopathy

Question 10

Chronic uveitis - severe IO signs that can be sight threatening
Dx and work up

Answer 10

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

Question 11

Tx of uveitis

Answer 11

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.

Question 12

Medical tx uveitis in cats and dogs

Answer 12

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

Question 13

Other acquired uveal conditions

Answer 13

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.

Question 14

Iris pigment changes in the cat

Answer 14

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

Question 15

The lens

Answer 15

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.

Question 16

Congenital lens anomalies

Answer 16

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

Question 17

Congenital lens anomalies

Answer 17

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

Question 18

Cataracts

Answer 18

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.

Question 19

Cataracts classification

Answer 19

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

Question 20

Cataracts ddx

Answer 20

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

Question 21

Inherited cataracts

Answer 21

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.

Question 22

Secondary cataracts

Answer 22

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

Question 23

Feline cataracts

Answer 23

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!!!

Question 24

Assessment of cataract pt.

Answer 24

Suitability for sx: suitability of the eye, pt. client expectations, finance, compliance

Ocular assessment for cataract sx should include: ophthalmic exam, ocular US, electroretinography, +/- gonioscopy.

Assess: type of cataract, extension, progression, capsular involvement. Earlier sx more favourable - do not leave to “ripen”, usually cataracts progressed quite considerably before being presented for sx with veterinary pts cf. human. Hypermature = higher risk of complication.

Retinal dz must be excluded with indirect ophthalmoscopy if possible, electroretinography if not. PLR not adequate as not test of vision. Absence of PLR is a not a clear indicator of retinal dz either, may be iris atrophy or something else

Factors that increase sx complications: lens-induced uveitis, posterior keratoconus or PHPV, capsular plaques, hypermature cataracts, instability, lens capsule rupture, KCS, PLA/goniodysgensis, vitreal degeneration, corneal disease

The presence of any above does not automatically stop surgery but means there are additional risks which will impact success rate.

Question 25

Suitability of pt for sx

Answer 25

Age, general health, temperament

Old age is not a contraindication but pt should she determined as in good condition prior to sx. May take longer to recover from GA.

PAP, screen for renal dz and cardiac dz.

Other systemic dz: DM, HAC, atopy. Adequate management of these conditions must be achieved else outcome may be compromised.

Patient temperament is important for peri and post op care. O needs to be able to medicate the pt.

Question 26

Client counselling

Answer 26

Education:

• success rates
• method of sx
• one or both eyes at same time
• complications need to be explained
• post-op expectations
• estimates as cost £££
• compliance big factor in success
• compliance improved by: education and communication, verbal and written instructions, manageable medication protocol

Question 27

Medication for cataract sx

Answer 27

Pre-operative medication:

• achieve and maintain IO mydriasis
• stabilise the blood-aqueous barrier
• reduce surgically induced inflammation
• Atropine, 12 and 2 hours prior to sx; mydriasis and cycloplegia. Avoid atropine in KCS
• phenylephrine 2 hours prior to sx: enhances mydriasis with atropine. May sting.
• Alternatively inject intracameral adrenaline at beginning of sx
• topical NSAID 4x q30mins 2 hours prior to sx; prevents prostaglandin mediated miosis and BAB breakdown.
• Antibiotics; value unclear, aseptic prep with 1in10 for skin with 3 minutes contact time and 1in50 copious flushing IO.
• IO irrigating fluid solutions; BSS or BSS plus, commercially available products that maintain corneal endothelial health, however, Hartman’s with bicarb, adrenaline and heparin is a good substitute.
• viscoelastic substances; various available described by their properties (viscosity, pseudoelasticity, elasticity, adhesiveness, cohesiveness). Create and maintain spaces. Most commonly used: sodium hyaluronate, chondroitin sulphate, methycellulose.

Question 28

Phacoemulsification

Answer 28

Method of choice. 3.2mm incision made into cornea. Blue dye injected to outline the anterior lens capsule. Phaco handpiece is used to fragment and remove the lens. I/a irrigate aspirate handpiece, a blunt handpiece, used to ensure damage to thin posterior lens is less likely. Artificial lens is inserted. Viscoelastic is used at various stages of the procedure and is removed on completion. Wound is closed and globe re-inflated

Post op:

• antibiosis; topical +/- systemic, broad spectrum e.g. ofloxacin, drop. 7 days but longer for diabetics, KCS, poor healing
• analgesia; systemic NSAID
• anti-inflammatory; topical steroids, 4-6x daily. topical NSAID sometimes as well or instead for DM, continues for 2-3 months before tapered off although some may need life long
• mydriatics; tropicamide 1-4 weeks following surgery to stabilise BAB and reduce synechiae

Question 29

Lens luxation

Answer 29

Lens zonules breakdown and dislocation of lens, primary or secondary
Underlying cause determined to influence tx
Lendectomy tx of choice for primary luxation. Secondary has less favourable prognosis.
Cats with secondary lens luxation from chronic uveitis - sx beneficial if cataracts as will restore vision and ongoing uveitis stimulation.

Primary: terrier breeds and border collies. Sudden onset painful eye. Young to middle aged. Episcleral congestion, corneal oedema, deepened anterior chamber and aphakic crescent. IOP ^. Examine other eye as bilateral so may show iridodonesis or strands of vitreous protruding.

• Recessive but heterozygous have increased risk but older than homozygous
• Analgesia!!!
• Prognosis better if removed early as success rate less if glaucoma is present

Question 30

Lens luxation 2

Answer 30

Management of acute glaucoma with lens luxation:

• osmotic diuretics; acute cases with pressure >50mmHg, rapidly reduce IOP.
• Mannitol 1-2g/kg over 30 mins
• Carbonic anhydrase inhibitors; decrease aqueous production, independent of their diuretic effect, reduce IOP 50%
• Dorzolamide and Brinzolamide

Surgery for lens luxation:

• pre-op: short acting mydriatic (tropicamide), if a posterior or if implant planned after extraction.
• Anti-inflammatories as per cataract sx and attempt to drop IOP
• intracapsular lens extraction: lateral canthotomy, 170* incision, grooved with blade and entered with blade, then completed with corneal scissors. Cornea held with colibri forceps and lens extracted with lens loop. vitrectomy. Cornea closed with 8/0 vicryl. Anterior chamber re-inflated with BSS
• subluxated lenses can be removed by phaco and vitrectomy.

Question 31

Lens luxation 3

Answer 31

Complications: glaucoma (chronic) or even up to several years following sx. Lifelong medication required. Retinal detachment not uncommon through loss of attachment at the ora ciliaris retinae –> rhegmatogenous detachment

Question 32

Secondary lens luxation

Answer 32

• Glaucoma - globe enlargement, rupture of zonules – >luxation. aphakic crescent at the edge of the pupil and the equator. Important to determine what came first - lens luxation or glaucoma!!!
• Cataract formation
• trauma
• uveitis

Question 33

Lens luxation in the cat

Answer 33

Unilateral or bilateral less frequent than dogs.
Congenital (with microphakia) is rare
Secondary - most commonly with uveitis, trauma and glaucoma also leads to dislocation.
Aged cats due to zonular degeneration
Anterior lens luxation and posterior luxation is unusual
Glaucoma may occur secondary to lens luxation but not as acutely as in the dog.
Removal of lens indicated if secondary glaucoma or if cataracts affecting vision. Uveitis needs to be addressed.