Herp Ophthalmology Flashcards
What reptile taxa have a parietal eye?
Describe its anatomy and function?
Parietal Eye (3rd eye, median eye or pineal accessory apparatus)
- Squamata & Rhynnchocephalia, absent in crocodilians
- Overlying scales show degrees of transparency (cornea like) in tuatara
- Lacertilla- prominant parietal eye
- Always has neurological input & contain a primitive retina (fewer, but large ganglia)
- Function is a mystery; but relationsihp b/w parietal eye & pineal body (produces melatonin & seritonin)
- Dosimeter
- Hormone production & thermoregulation
- Compass (orientation lost when covered with nail varnish)
- Iguana
- Absent in nocturnal lizards, exceptions are teiids and some geckos
Which taxa all have normal palpebral fissures?
Which taxa may have spectacles?
Which eyelid is usuallly the mobile one?
Eyelids
- Functional with normal palpebral fissures
- Chelonia & Crocodilia
- Immobile and fused eyelids (spectacle) with no palpebral fissures
- Squamates (covered later)
- Most reptiles- upper eyelid less mobile
- Lower eyelid moves up to cover most of globe
- Lacertidae, Teiidae, Scincidae…. (some lower eye-lids are transparent) - so can still see when eyes are closed or protection from substrate
- Tarsal plate in lower lid offering support
- If unsure about mobile eye-lids; look for nictitating membrane (indicates mobile)
- Most have 3rd eyelid
- Lower eyelid moves up to cover most of globe
- Crocodilian- more like people with movable upper eye-lid
- Third eye-lid semi transparent with cart plate
- Aged gators…calcium or salt deposits can make 3rd eye-lid opaque
- Third eye-lid semi transparent with cart plate
Describe the anatomy of the spectacle in reptiles.
What species have them?
What is the subspectacular space filled with?
Spectacles (brille, eyecap, eye scale, watchglass, goggle)
- Eye-lids fused as a transparent membrane over globe
- Squamates- tertiary specticle (named by embiologic development)
- Highly vascular (although can’t see this unless inflamed)
- *Not part of or attached to the cornea*
- Subspectacular space that separates cornea from spectacle
- Also intraconjunctival space
- Lubricated by Harderian gland
- Retractor bulbi & bursalis are absent
- Also intraconjunctival space
- Subspectacular space that separates cornea from spectacle
Describe the lacrimal system of reptile eyes.
- What taxa have them?
- Where is the harderian gland located?
- What about the lacrimal and conjunctival glands?
- What taxa lacks nasolacrimal ducts?
- How is the nasolacrimal system tested for patency in reptiles?
Describe the anatomy of the globe in reptile eyes.
- What structures give support to the globe? What taxa lack them?
- What taxa has the most well developed ocular muscles? How much can they move their eyes?
- What is the average IOP like?
Describe the corneal anatomy of reptiles.
Describe the uveal tract of reptiles.
- What muscle type is present in the iris?
- How is mydriasis induced?
- What are the typical pupil shapes of reptile irises?
Describe the lens anatomy of reptile eyes.
- How does the shape of the lens differ from fish and amphibians?
- How is accomodation accomplished within different orders?
Lacrimal System
- Most Sauria & Chelonia have
- Harderian gland in orbitonasal region (medial); assoc with 3rd eyelid-oily
- Can have salt secreting cells & immunocompetent cells
- Lacrimal gland in orbitotemporal region (lateral); assoc with lids- watery
- Conjunctival glands usually assoc. With upper eyelid
- Harderian gland in orbitonasal region (medial); assoc with 3rd eyelid-oily
- Nasolacrimal duct is absent in all Chelonia
Testing Patency of Nasolacrimal System
- Fluoroscein stain in palpebral fissure; Squamates 0.05mls 30g nedle into subspectacular space
- Rostral to jacobson’s organ should be examined for signs of patency in squamates
- Normal for tears to be running down face in chelonians
Globe
- Spherical in most reptiles
- Scleral ossicles- when present, compactly placed and overlap
- Serve to maintain convenx of globe
- Absent in crocs
- Snakes have an elongated along visual axis (no ossicles or cartilage)
- Chameleons- well developed ocular muscles
- 180 degrees in horizontal plane and 90 degress in vertical plane
- IOP- lower than mammals, 6mmHg and some torts avg 14mmHg
Cornea
- Thin and no Bowman’s membrane
- Squamates- only single layer
- Decement’s membrane is present in most lizards, except some geckos
- Cholesterol crystals- normal age change or high polysat fat diet
Anterior Chamber & Uveal tract
- Well-developed sphincter- striated; resilient to mydriatics
- 2 way to induce mydriasis- general anesthes or with intracameral inj of neromuscular blocking agents (not work topically or in subspectacular space)
- Voluntary control and no consensual PLRs
- Nocturnal (slit) & diurnal (round); except Heloderma are round & nocturnal
- Stenopeic openings in Gekkonidae (pin holes that open when pupils shut)
Lens & Accommodation
- Annular pad, allows lens to connect to ciliary body, usually by zonular fibers
- Differences within orders
- Reptile lens is flatter than fish and amphibs & soft
- Snakes- lens moves back and forwards with IOP (cool)
Describe the retina and visual tract of reptile eyes.
What is the retinal vasculature like?
What structure supplies the retina and posterior chamber? How does it differ in crocodilians and snakes compared to lizards?
What taxa have well developed fovea?
What taxa has tapetum lucidum?
Pit organs in snakes are inervated by what nerve?
Retina & Visual Tracts
- Avascular retina
- Lizards have the conus papillaris (like the avian pecten)
- Reduced to a glial pad in crocs
- Reduced more in alligators to layer of melanocytes
- Snakes have membrana vasculosa retinae
- Reduced to a glial pad in crocs
- 5 primary cell types
- Photoreceptors,Outer segment, Inner segment, Nuclear and connecting fibers, Synaptic pedicles
- Rods and cones
- Area centralis or fovea-cones are smaller and more densely packed (only some species)
- Amyda (only turts to have fovea)
- Absent in crocs
- Absent in nocturnal
- Crocs have tapetum- guanine crystals
- Pit organs- infared- inervated by trigeminal nerve
Describe the common diseases of reptile eyelids.
What is a common nutirtional cause of blepharoedema and blepharitis?
What viruses can produce neoplasia of the eyelids?
- Eyelid Trauma
- Red-eared sliders in feeding frenzy
- Blepharoedema and blepharitis
- Hypovit A- most common problem that affects ocular adnexa
- Eyelid Neoplasia
- Viral neoplasia- fibropapilloma, papillomata, poxvirus
Describe the diseases of the spectacle of reptilian eyes.
What is the most serious sequelae of losing the spectacle?
Infections of the spectacle come from what source?
What parasites affect the spectacle?
What are the causes of subspectacular abscesses?
What is the most common ocular problem of snakes?
What causes pseudobupthalmia?
- Abrasions and Ulcers of Spectacle (not confused with corneal ulcer)
- Loss of Spectacle
- Serious- dessication to cornea
- Infection of the Spectacle: Bacterial and Fungal
- Dermal origin (even though transparent)
- Subspectacular Abscess
- Common and due to
- Ascending infx from oral cavity via nasolacrimal ducts
- Septicemia via hemotagenous (bilat)
- Penetrating trauma
- Sequela to conjunctivitis
- Common and due to
- Parasites affecting Spectacle
- Mites- Ophionyssus
- Retained Spectacle
- Most common ocular problem of snakes
- Most commonly from dry environment or dehydration
- Denting specticle is pathognomonic
- Pseudobuphthalmos
- Blockage of nasolacrimal system- snakes and geckos
Describe the ocular diseases of reptiles.
What is an important cause of deratoconjunctivitis sicca?
What is the most common congenital abnormality?
What is an important cause of exophthalmia?
What are some causes of keratitis in reptiles?
What are some sequelae to exposure to freezing temperatures?
- Keratoconjunctivitis Sicca (Dry Eye)
- Vit A deficiency
- Congenital Abnormalities of the Globe
- Microopthalmia is most common, particularly in snakes
- Exopthalmos
- Ultrasound with 10-20 MHz or greater probe
- Orbital varix (path enlargement of 1 or more venous channels)
- Hypertension secondary to renal disease
- Infection of the Globe
- Conjunctivitis (substrate, infectious)
- Corneal Disease
- Keratitis
- Excessive UV; viral (herpes)
- Uveitis
- Hyphema and hypopyn often present after exposure to freezing temps in chelonians
- Cataracts
- Torts secondary to freezing episodes; changes reversible
- Retinal Disease- Vit A & freezing
- Therapeutics- None licenses in reptiles
Describe the procedures performed on reptilian eyelids and spectacles.
What is the most common surgery on reptilian eyelids?
When is aspectalculectomy performed?
How is pseudobupthalmos treated?
How do address spectacle avulsion?
Eyelid Repair
- Usually traumatic injuries; lower eye-lid is most important for protection of the eye in most reptiles
Spectacle Debridement and Spectalculectomy
- Spectacle (being skin) is an ideal area for surgical approach
- Treatment & obtaining cytology -resolving a subspectacle abscess
- Spectaculotomy- small wedge resection- usually lateral quadrant; 25-30% can be removed
- Be careful not to remove too much, will result in excessive loss of tear film & dessication of cornea
Pseudobuphthalmos
- Distension of the subspectacle space with fluid
- Temp fistula is required to allow drainage
- Doesn’t sound like the author recommends a wedge resection here (has been done)
- Treat the blocked nasolacrimal duct or create a new drainage canal (conjunctivoralostomy)
- New canal- formed b/w medial aspect of inferior fornix of subspectacular space and mouth emerging b/w palatine nad maxillary teeth
- With 22 or 18g needle, place 0.625 mm silicon tube sutured in place for up to 6 weeks
- New canal- formed b/w medial aspect of inferior fornix of subspectacular space and mouth emerging b/w palatine nad maxillary teeth
Spectacle Avulsion
- Loss of spectacle = loss of tear film & dessication of cornea
- Use mucosal graft or commercially avialable amniotic membrane sutured to remnants of spectacle edge
What are retained eye caps in leopard geckos? What causes them and how are they removed?
Describe corneal repair in reptiles?
How are corneal plaques removed?
Describe cataract surgery in reptiles? What is different? What suture causes corneal abscesses?
What are the indications for enucleation in reptiles?
Gecko Retained ‘Eye Caps”
- Unique to geckos, usually 2ndary infection or hypovit A and low environmental humidity
- Removal with care and lubricate
Corneal Repair- Simple interrupted sutures of 8-10/0 suture Or Steribone or vetbond
- Conjunctival graft if not in apposition
- 3rd eye lid flap (although may apply pressure to the globe and potentiate corneal rupture)
Corneal Plaque (Keratitis Removal)
- Tx: Removal of plaque and topical atb therapy
- Use of 27g needle to gently lift off cornea; perhaps pretreat with ATBs
- If very adhered, superfiical keratectomy and realize that there will be a resulting ulcer
Cataract Surgery
- Life impacted by vision loss
- Lens is soft, less ultrasound (phacoemulsification) and more irrigation/aspiration; not always need to repair cornea
- Vicryl has been reported to cause focal abscesses in cornea
Enucleation
- Glaucomatous eyes
- Snakes- spectacle removed too; optic blood vessels sealed with hemostatic pressure and wound allowed to granulate in over 4 weeks.
