Module 14 Flashcards
Approach to ophtho exam
- Hx - husbandry!!
- Hands off exam - may or may not be useful - may be helpful to assess vision
*Tear production - if unilateral can use other eye as reference, or may need to use cage mate. 4 techniques
1) STT - may be used as normal if palpebral fissure >5mm,
2) modified STT - cutting STT strips into thinner strips, may be some literature with this technique but perhaps sequential reading in same animal may be most useful,
3) phenol red threat test (PRTT) - tears change thread from yellow to red measured for 15 or 60s and then measured in mm.
4) endodontic absorbent paper point tear test (PPTT) - 0.3mm distal diameter, inserted into fornix for 60s, wetted portion is bent and then measured.
Rabbits RR STT 5+/-3mm/min, PRTT 24 +/4mm/15s
Birds RR STT 5+/-3mm/min, PRTT 22 +/4mm/15s
*Vision testing and ocular reflexes - menace not reliable in most, dazzle can be useful in detecting intact visual pathway,
dilation for fundic exam - tropicamide/atropine useful in mammals, although slower if binding to melanin.
Reptiles and birds - striated muscle under voluntary control, curariform drugs needed (non-polarising muscle relaxants) - rocuronium at 0.2-0.4mg/eye, caution as OD would result in paralysis of other muscles including respiratory with poss devastating consequences
- Direct ophthalmoscopy (distant then close) - 0D for fundus, 10D for lens and iris, 20D cornea.
- Slit lamp exam (adnexa, eyelids, conj, puncta, corneal layers, anterior chamber, iris, lens, anterior vitreous) - unlikely rewarding to achieve sections of thin cornea but excellent on circular light function
- Indirect ophthalmoscopy - 30-90D typically required. as D increases, the lens needs to be closer to the eye.
- sample collection
- fluorescein
*tonometry - tonopen with LA may be used in some with a large enough cornea, tonovet is easier and probe tip is 2mm, tonolab has tips 1mm.
Rabbit RR 13+/6
Owl 11+/-4
Raptors 20+/-4
*general CE
*additional tests - ocular US useful if opaque ocular media. >10mhz will be required.
High quality digital camera with macro lens is invaluable. 100mm macro on DSLR.
Restraint - many are not used to handling. An experienced animal handler is invaluable. Chemical restraint may well be required.
Evolution of the eye
Homo sapiens - 200K years ago. Great apes 14 million years ago. Cats 30 million years ago.
Early eye was an eye spot, directed towards or away from light, as seen in algae.
The eye spot then progressed into a pit of bulge as it evolved. Invaginated (pit) started to move towards a camera-style eye. Bulge design led to compound eyes.
600M years ago - paired eyes
150M years ago mammals began to thrive
Monotremes (lay eggs) - oldest living relative of early mammals, eyes are more like reptile eyes.
Marsupial eyes became more complex
Placental mammals bring us to modern day. Most have two visual pigments, ancestors have 4. Most have red and blue wavelengths.
Old world monkeys have three photopigments, an example of re-evolution, New-world monkeys did not re-evolve this third pigment
Human eyes:
pinnacle of evolution, lost rectractor bulbi and nictitans gland. Three photopigments (shrimp have 16!!). Lack striated muscle so pupil dilation and accommodation not under voluntary control. Our photoreceptors are backwards and light has to travel through whole retina before they reach photoreceptors.
Our six EOmuscles are unlike any other striated muscle, work endlessly without fatigue.
110M photoreceptors, 10M cones, and 100M rods.
1/3 of brain devoted to vision. Birds and reptiles process a lot in the retina.
Eyes function in >9orders of magnitude.
Comparative anatomy - Rabbits
Large field of view, almost 360degrees, only 10-35 degrees of binocular vision, poor visual acuity but good motion detection. Green and blue wavelengths, 5% photoreceptors are cones. Eyes very prominent but prone to damage.
Upper and lower lids, nictitans membrane.
Blink infrequently - 1-2x per minute, as little as 10-12x/minute
NL systemic - one punctum and one duct - deep in ventromedial conjunctival fornix, duct follows tortuous route with several sudden points of constriction, passes close to molar and incisor teeth.
STT readings 5.3+/-2.96/min, range 1-15mm/min, tear film osmolarity 300-305mOsm/l, TFBUT 20s.
Cornea large, 30% globe, thinner 355um. Endothelial cells have ability to regenerate following injury, adjacent cells divide.
Merangiotic fundus - retinal bloods vessels only present in horizontal streak each either side of ONH. ONH located dorsally to midline so rabbit needs to be elevated for fundoscopy. ONH has deep physiological cup and lamina cribrosa is poorly developed meaning ONH cupping occurs rapidly in glaucoma.
Rabbits do not have a tapetum.
Closed orbit - large retrobulbar venous plexus.
Lacrimal gland + accessory gland (infraorbital, retro-orbital and orbital lobes)
TEL gland - superficial and deep portions (deep also called Hardarian gland)
Comparative anatomy - birds
Lids are thin, even transparent.
Lower lid contains fibroelastic tarsal plate and no meibomian glands
Conj similar to other species
TEL drawn from dorsonasal aspect by contraction of pyramidalis muscle (tendon loops over optic nerve, through sling formed by quadratus muscle), innervated by VI
no TEL gland
lacrimal gland is present inferotemporal to globe and Hardarian gland posterior to sclera, near base of TEL but not part of it
EOmuscles thin and poorly developed, head movements instead.
Two lacrimal puncta.
Avian orbit large and incomplete, paranasal sinuses (infraorbital especially) impact globes due to close proximity.
Thin cornea, Bowman’s layer underneath the epithelium.
Iris musculature is striated muscle, somewhat under voluntary control.
Crystalline lens, surrounding capsule has an annular pad at its equator - nutritional function.
Retina is non-tapetal and avascular. choroid supplies retina. pecten - heavily pigmented, pleated, vascular structure - projects from ONH into vitreous.
Rods and cones present, the latter with oil droplets to filter out light.
Area centralis +/- one or more fovea.
100% nerve fibre decussate at the optic chiasm so no consensual PLR
Comparative anatomy - Reptiles
Reptilia - five orders
Lizards, chelonians, crocodilians and tuatara have similar eyes
Snakes lost of of the reptilian anatomy as they evolved
In most except snake: upper and lower lids, lower more mobile. Crocs have bony tarsal plate in upper lid, chameleons move their lids with their eyes. Lacrimal and harderian glands secrete tears. Lacrimal gland functions as an extrarenal site of salt excretion in marine chelonians. NL duct absent in chelonians.
With the exception of lizard, EOmuscles are poorly developed except the retractor bulbi.
Slit pupils tend to be nocturnal, round pupils tend to be inactive at night.
Lizards and chelonians - hyaline cartilage in the posterior portion of their globes, scleral ossicles anteriorly
Lens in lizards and crocs is soft and pliable, equatorial pad
To accommodate most apply pressure to lens equator via contraction of ciliary body
Iris vasc - two arteries entering laterally and ventrally.
Ciliary body and iris sphincter are striated, curariform drugs required for mydriasis
Retina is avascular in all species.
Lizards - conus papillaris, derived from hyaloid
Crocs - retinal tapetum - guanine crystals
Lizards and tuatara have fovea
Snakes and a few others: vascular spectacle that covers the cornea, space between is the subspectacular space. Prior to shedding the spectacle becomes cloudy and blind during this time.
Snakes cannot be treated topically
Snakes have no scleral ossicles or cartilage
Accommodation is via forward movement of the lens, by increased pressure of vitreous
Snakes have a conus during development but mostly regresses
Common diseases - RABBITS
Orbital dz:
- Orbital plexus - caution during enucleation, subconj approach required
- periodic bilateral exophthalmos - thymic mass around jugular impacts venous return and venous orbital sinus becomes engorged, especially if stressed, dramatic exophthmos
- Retrobulbar abscess - tooth root abscess, Pasteurella. Tx: extractions or exenteration. Unlike other animals cannot drain through oral cavity.
- Orbital glands - TEL glands may prolapse. Replacement is via pocket as in dogs.
Adnexal dz:
*conjunctival overgrowth - “pseudopterygium”, conj at limbus spreads across, but does not adhere to, the cornea. Tx: radial incisions and suture conj to sclera. Ciclopsorin topically has been suggested
*conjunctivitis - consider husbandry - overhead feed racks etc., distinguish from dacryo. Staphs and Pasteurella species most common.
Myxoma virus causing oedematous swellings at lids, conj, mouth, anus and genitals.
*Blepharitis - Treponema cuniculi. “rabbit syphilis”. Transmission to neonates by infected genitals of mother, lesions similar to myxo, definitive diagnosis by ID of spirochete on cytology. Parenteral penicillins. ddx: staphylococcal infections, SCC
*Nasolacrimal duct abnormalities - dacryocystitis, older bunnies with dental dz, purulent ocular disch, swollen medial canthal area, medial canthal dermatitis. Flushing, dental tx, long term systemic ABs may be requried
*Entropion - simple sx in some cases, but if blepharitis then difficult, tx underlying dz before sx
Corneal dz:
- ulcerative keratitis - bedding related, will heal in 7 days. non-healing superficial ulcers - loose epithelial edges, debridement required in first instance. grid or diamond burr if no progress but care - thin cornea!! INI consider keratectomy and send for histo
- KCS - rare in rabbits, ciclosporin can be effective. Rabbits txed with TMPS should have their tear production recorded, as has been shown to have an affect
- eosinophilic keratitis - as in cats, rabbit eosinophils can be difficult to distinguish from heterophils. Tx: steroids or ciclosporin topically
Intraocular dz:
- glaucoma - hereditary dz in NZ white. Goniodysgenesis. Rarely show sign of discomfort but likely due to prey species. Often secondary to uveitis. Medical mx and sx rarely effective
- Uveitis - white, vascularised inflammatory lesions in their irises. Were thought to be abscesses caused by Pasteurella but now believe lens rupture and lens-induced uveitis secondary to E. cuniculi.
- cataracts - can appear spontaneously, congenitally or hereditary. E. cuniculi also from vertical transmission from other to offspring. Tx of choice is rapid lens removal.
Common diseases - BIRDS
Orbital dz:
- infraorbital and periocular sinusitis - exophthalmos, strabismus initially. Chronicity - sinus collapses resulting in enophthalmos. Abscessation is semi-solid in birds –> fibrosis. Flushing and sx debridement required.
- microphthalmos/anophthalmos - persistent conjunctivitis may be a concurrent problem, possibly inherited component.
- cryptophthlmos - constriction of eyelid aperture, following head trauma or inflammation but may be inherited, sx is unrewarding.
Adnexal dz:
- Poxviral blepharitis - CS differ according to strain. Pigeons - eyelid swelling and growths, psittacines - mild blepharitis, lid oedema and epiphora. Preventing self trauma is key to resolution.
- Hypovitaminosis A - Vit A deficiency may lead to periocular and conjunctival swelling. Systemic signs with white plaques in and around the mouth, breathing problems, sneezing, crusted nares. Exclusive high energy diet (sunflower seeds) may provoke deficiency. management = supplementation - oral beta-carotene
- knemidokoptes - scaly leg and scaly beak. The mite burrows into the skin and provokes proliferative reaction. Tx - ivermectin
- Eyelid neoplasia - rare, lymphosarcoma and chondrosarcoma are reported
- conjunctivitis - 1) FB/infectious 2) manifestation of periocular dz, 3) manifestation of systemic dz. Pigeons - one eyed cold caused by mycoplasma, chlamydophila or salmonella
- cockatiel conjunctivitis - severe, profound chemosis, no causative agent has been found but response to chlortetracycline.
Corneal dz:
- ulceration - trauma primarily, superficial non-healing ulcers in older birds.
- amazon parrot keratitis and mynah bird keratitis - transient, stress/trauma induced. Self-limiting
Uveal dz:
*uveitis - as other species, can be secondary to systemic dz, ocular trauma most common and lens-induced. Tx: topical steroids or NSAIDs and mydriatics if poss although hard to achieve as curariform e.g. vecuronium would be required frequently
Lens:
- cataract - age related, trauma, inherited (Norwich canary). Sx an option if used to regular handling, due to post op care.
- lens luxation - aphakic crescent, trauma or cataract related.
Retinal dz:
*trauma related mostly, also toxoplasmosis and excessive sunlight reported in owls but possible is just variation of the norm
Horner’s syndrome:
*only ptosis as iris is under voluntary control so no miosis is seen. Globe is not mobile in orbit either. Phenylephrine can be used to alleviate the ptosis and confirm dx. Trauma is most likely cause
Common diseases - REPTILES
Adnexal dz:
- hypovitaminosis A in - chelonians, mild eyelid oedema to markedly chemotic conjunctiva. +/- resp problems. Oral supplementation but may be insufficient, weekly IM injections may be required
- blepharitis - viral dz (caiman pox) may also affect the eyelid. Herpesvirus; proliferative and ulcerative skin lesions in sea turtles.
- conjunctivitis - pet reptiles can be a sign of septicaemia, chlamydophila reported in reptiles. irritation from bedding
- periocular masses - firm swellings that gradually increase in size, most are gram -ve bacterial or fungal infections. semi-solid. resection UGA is usually required and histopath.
- dacryocystitis - fluorescein passage test (jones test) may aid dz. NL flushing with topical and systemic ABs.
Spectacle:
- opacity - normal before ecdysis, but can occur following trauma or due to bullous spectaculopathy
- retained spectacle - raised opaque plaque. likely due to underlying ill health or husbandry. Infection with mite ophionyssus natrics also. Must not remove by force as whole spectacle may be removed resulting in marked keratitis.
- tx: increase humidity, damp cotton wool used to encourage removal of tissue, if still will not come away then UGA and with operating microscope the spectacle should be remove carefully.
- bullous spectaculopathy - NL obstruction, subspectacular fluid build up of tear fluid. (diff from glaucoma where whole globe is enlarged). If due to infectious dz process then is actually subspectacular abscess. Tx: short term needle drainage or UGA a ventral triangle of spectacle excised to allow drainage
- subspectacular abscessation - abscess between cornea and spectacle as a result of infection of NL duct. Yellow mass in ventral subspectacular space. Tx: excision of triangle of spectacle, copious flushing will be required
Cornea:
- ulceration - mostly trauma, and inv as per other species
- corneal opacification - post-traumatic fibrosis. corneal deposits of lipid, calcium or protein. After hibernation chelonians may have a dense white corneal lesion, suggested to be a proteinaceous deposit. Diet assessment required but may not disappear even when balanced.
Uvea:
*Uveitis - rare in reptiles. most associated with systemic gram -ve infections (pseudomonas). Dx: blood culture, haematology and biochemistry. Tx: broad spectrum Abs pending culture. Topical anti-inflammatories
Cataracts:
*pathogenesis unclear in reptiles. Diet, trauma, environment, inherited etc, but also post hibernation!! Sx in larger reptiles possible
Glaucoma:
*rare. tonometers not useful in snakes! Can differentiate form megaglobus by presence of vision.
Microphthalmos/anophthalmos:
*congenital defects seen if incubation too high
ocular toxicology
Toxicology speciality evaluating effects of drugs and devices on ocular tissue via all routes of administration.
Lab animal ophtho exam plays an important roles in studies evaluating impact of drug/devices.
Ophthalmologists must therefore be aware of:
1) what is normal for the species
2) common spontaneous abnormalities for that species/age/breed/strain
Ocular toxicology:
1) ocular effects when eye is the target organ and applied to eye
2) systemic effect associated with drug applied to eye
3) ocular effects from a drug given systemically
Minimum: slit lamp exam and indirect (20, 30 or 40D lens +/- tropicamide).
Depending on study more advanced exam may be required; tonometry, pachymetry, photography, fluorescein angiography, ERG, specular microscopy, optical coherence tomography. Lesions graded and recorded (Hackett-McDonald ocular scoring system)
Animals with pre-existing pathology should be eliminated. Animal examined during study, at end of study and into a recovery phase. Examiner masked to tx and dose. Examiner must interpret findings wrt species, age, study design, pretest data, drug evaluated, dose group.
Animals used: dogs - beagles, rats (several strains), mice, rabbits, swine, some primates (rhesus and cynomolgus monkeys)
Orbital blood sampling common from rats, can have undesired consequences: exophthalmos, corneal rupture, exposure keratitis, retinal degeneration, hyphaema, cataracts, phthisis bulbi.
A large number of animals are assessed, examiner performs slit lamp exam and indirect ophtho within seconds, 300-350 rats/mice examined per hour! 2-3 animal handlers are needed per examiner and someone entering data, 1-2 people working ahead dilating pupils.
