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Ophthalmology Part 1 IVSA Standing Committee of Veterinary Education
Tapetum lucidum
Anterior segment Diseases Uveitis Uveitis is inflammation of the uveal tract. The uveal tract consists of the Iris, Ciliary body and choroid. Uveitis can be localized to the anterior or posterior segment of the eye. Anterior- Iris Posterior- Ciliary body and choroid Uveitis is caused often by systemic disease, including: toxaemia, bacteraemia, FeLV, FIV, toxoplasma, neospora, trauma, pyometra. Inflammation of the uveal tract causes breakdown of the blood aqueous barrier and subsequent extravasation of fluid and proteins. 1. In Acute cases, clinical signs are: Red eye (conjunctival hypereamia/ episcleral injection), conjunctivitis, miosis, blepharospasm, changes in colour of the iris, decreased intraocular pressure due to decreased aqueous production, aqueous flare, hyphema, photophobia, hypopyon, posterior synechiae. 2. Chronic cases, clinical signs are: Cataracts, hyperpigmentation of iris, keratitic precipitates, synechia, retinal degeneration, corneal vascularization, secondary glaucoma Treatment: •
Prednisolone is an steroid and caused immunosuppression
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Atropine is used as it alters the drainage angle to increase fluid loss in the anterior chamber of eye. If you need a touch up on your eye anatomy, then there is a revision page at the end of this leaflet!
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What is reflex uveitis?
Drainage angle
A stimulus to the corneal nerve (a branch of trigeminal nerve) sends noxious stimulation along the nerve axon as it courses back to the Ciliary ganglion, but on its way it sends a branch to the Ciliary body. The Ciliary body stimulation causes irritation and releases autocoids, which facilitates breakdown of blood aqueous barrier and causes uveitis. Cataracts Increased opacity of the lens. A cataract is when the lens becomes cloudy. Causes: Diabetes mellitus (as sorbitol enters the lens and osmotic fluid effect), uveitis, nutrition, trauma, retinal degeneration such as Primary retinal atrophy in Poodles, congenital from iatrogenic causes or diseases such as Bovine Viral diarrhoea virus (BVD). Clinical signs: Photophobia, blind/double vision, change in colour vision Diagnosis: -
Distant and close direct eye exam to see posterior segment of eye after pupil dilator eye drops given. Dazzle reflex will show if animal is blind.
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Glaucoma risk assessment to see IOP and drainage angle
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Ultrasound to see lens
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Electroretinogram (ERG) shows function of cones and rods
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Purkinje fibres (P3 most posterior part)
Treatment: -
Phacolensectomy/ phacoemulsification- involves the replacement of the cloudy lens with an artificial plastic lens.
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Immunosuppressants
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Improve eye health
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MAYLOREM 2016 THE IPSUMS Glaucoma
High intraocular pressure (>35mmHg) and often bilateral. It can cause enlarged eyeball size (buphthalmia). Primary- Abnormal development of drainage (goniodysgenesis) Secondary- Blockage of drainage from lens luxation, uveitis, neoplasia, trauma. Breed predispositions including (Jack Russel Terriers, Collie) Clinical signs: Buphthalmia, uveitis, corneal oedema, episcleral injection Diagnosis: Measure intraocular pressure with tonometry, clinical signs, gonioscopy (close direct ophthalmoscopy to see drainage angle) Treatment: Conservative- carbonic anhydrase inhibitor, beta blocker, prostaglandins (increase outflow of fluid), anti-inflammatory (Timolol), across sclera inject gentamycin Surgery- cryosurgery, endoscopic cyclophotocoagulation (obliterate Ciliary body), glaucoma shunt Lens luxation: Zonular fibres that hold the lens in place are weak in this case, which predisposes the lens to movement and subluxation (movement to abnormal location). There is a long-term glaucoma risk Treatment: •
Phacolensectomy
Posterior segment Diseases Retinal lesions can be either: Perivascular cuffing, hypertension, pigmentation (e.g. equine pigmentary retinopathy), retinal folds (general primary retinal atrophy in Poodles/Cocker Spaniels), retinotoxic agents (Ivermectin-Collies, Enrofloxacin-Cats) All causes can lead to retinal detachment with colibomas (holes in 6’oclock position) and increased reflection of tapetum lucidum
Optic nerve problems include: pseudopapilloedema, papilloedema, optic neuritis caused by septicaemia or CNS infection. These can lead to negative dazzle reflex, dilated nonresponsive pupil Fundic vasculature- trauma, hypertension, lipaemia Choroidal- chorioretinitis, hypertension
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MAYLOREM 2016 IPSUMS THE How to perform an ophthalmic exam:
1. History- Take a detailed history from owner about recent trauma, medication history and previous diseases. 2. Distance examination of both eyes and neuro-ophthalmic exam (menace response, palpebral reflex, corneal reflex). 3. Schirmer Tear test (normal range is 15-25mm) and corneoconjunctival sampling (take a swab between lower eyelid and conjunctiva) and send it for culture and PCR. Fluorescein eye drops can be used to assess corneal integrity (to make corneal ulcers more noticeable) as well as ‘tear break up time’ which should be approximately 20 seconds. 4. Adnexa and anterior segment exam 5. Intraocular pressure measurement and pupil dilatation with tropicamide or atropine. Tonometry or a schiotz-tonomoter can be used to measure IOP, which normal range is 10-20mmHg. 6. Lens and posterior segment exam after pupil dilatation with a 20D condensing lens Orbit (eye globe) 1. Exopthalmos (protrusion of the eye). Clinical signs- ocular pain, episcleral injection, strabismus, lagophthalmos and secondary keratitis, protrusion of third eyelid and decreased ocular motility Causes: Ø Globe proptosis- this can be treated with eye lubcrication, tarsorrhaphy, lateral canthotomy or enucleation Ø Retrobulbar abscess/cellulitis leads to eyeball protrusion- treat with drainage and antibiotics and systemic non-storoidal drugs (NSAIDs) Ø Temporal/Massester myositis leads to increase in type 2M antibodies and creatinine phosphokinase Ø Extraocular polymyositis causes bilateral exophthalmos but no third eyelid protrusion. Treat with corticosteroids and azathioprine Ø Neoplasia Ø Cysts, traumatic lesions, granuloma 2. Exophthalmos Causes: Ø Decreased globe size Ø Decreased orbital content from low muscle mass or fat Ø Ocular pain can lead to contraction of the retractor bulbi muscle Ø Horner syndrome 4
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Eye Anatomy
http://www.peteducation.com/ article.cfm?c=2+2083&aid=1596
• Iris: regulates the amount of light that enters the eye. It forms the coloured, visible part of the eye in front of the lens. Light enters through a central opening called the pupil. • Pupil: the circular opening in the centre of the iris through which light passes into the lens of the eye. The iris controls widening and narrowing (dilation and constriction) of the pupil. • Cornea: the transparent circular part of the front of the eyeball. It refracts the light entering the eye onto the lens, which then focuses it onto the retina. The cornea contains no blood vessels and is extremely sensitive to pain.
• Lens: a transparent structure situated behind the pupil. It is enclosed in a thin transparent capsule and helps to refract incoming light and focus it onto the retina. • Choroid: the middle layer of the eye between the retina and the sclera. It also contains a pigment that absorbs excess light so preventing blurring of vision. • Ciliary body: the part of the eye that connects the choroid to the iris. • Retina: a light sensitive layer that lines the interior of the eye. It is composed of light sensitive cells known as rods and cones. • Tapetum lucidum- lies immediately behind the retina and allows reflection of visible light back to the retina, to increase light quality of image. It contributes to superior night vision in animals and causes the eyes to shine at night when illuminated. • Fovea: forms a small indentation at the centre of the macula and is the area with the greatest concentration of cone cells. When the eye is directed at an object, the part of the image that is focused on the fovea is the image most accurately registered by the brain. • Optic disc: the visible (when the eye is examined) portion of the optic nerve, also found on the retina. The optic disc identifies the start of the optic nerve where messages from cone and rod cells leave the eye via nerve fibres to the optic centre of the brain. This area is also known as the 'blind spot’. • Optic nerve: leaves the eye at the optic disc and transfers all the visual information to the brain. • Sclera: the white part of the eye, a tough covering with which the cornea forms the external protective coat of the eye. • Rod cells are one of the two types of light-sensitive cells in the retina of the eye, which are necessary for seeing in dim light. Cone cells are the second type of light sensitive cells in the retina of the eye. They function best in bright light and are essential for acute vision (receiving a sharp accurate image). It is thought that there are three types of cones, each sensitive to the wavelength of a different primary colour – red, green or blue. Other colours are seen as combinations of these primary colours.
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IVSA SCoVE hope you enjoyed this short but useful leaflet on Ophthalmology. Next edition will talk about corneal, eyelid and tear production problems that occur in animals. SCoVE is here to help and support you on your veterinary educational journey. We always appreciate feedback and if you would like us to produce more leaflets on other topics then please do not hesitate to contact us via our Facebook Page! We also have the IVSA VET Education Forum group on Facebook to connect with students globally and to share and support one another on educational material. Good wishes from SCoVE Committee!