Veterinary Ophthalmology

Transcription

1 Veterinary Ophthalmology Eyelids Protect the eye Provides part of and spreads the tear film Regulates the amount of light that enters the eye Clears foreign material Third Eyelid Protects the cornea by removing foreign material Only moves passively in the dog Third Eyelid Contains the gland of the third eyelid Helps to spread the tear film Can move actively in the cat Tear Film Outer lipid layer Meibomian glands Middle aqueous layer Lacrimal gland=65% Gland of third eyelid=35% Inner mucin layer Goblet cells of conjunctiva Conjunctiva Palpebral Bulbar Third eyelid 1

2 Cornea More than just a windshield! Accounts for 70% of the focusing power of the dog and cat Only.5 mm thick! Cornea Cornea Three layers thick Epithelium 5-6 cell layers thick Stroma Lamallae of collagen Endothelium and Descetmet s membrane 1 cell layer thick Anterior Chamber Fluid filled space between the cornea and iris Can fill with pus, blood or tumor 2

3 Aqueous Humor Produced by glands in the ciliary body Provides nutrition and O2 to the lens and cornea Provides the fluid support for the eye (IOP) color of the eye The color in dogs is simply different amounts of pigment cells-not different pigments Controls amount of light entering the eye Iris Pupil Pupil Shapes Empty space in the center of iris Can be different shapes Dog= circle Cat= vertical oval Horse= horizontal oval Iridocorneal Angle A sieve-like mesh at the junction between the cornea and the iris i 360 degrees Drains the aqueous humor from the eye Lens Behind the iris 30% of focus power in the eye Location of cataracts 3

4 Anchored by the zonules that extend to the lens from the ciliary body Zonules pull on lens to change it s shape in accomodation Lens Lens Many layers to lens much like an onion Nucleus Cortex Capsule Jello-like material that fills the back of the eye Holds the retina in place against the back of the eye Vitreous Retina The film in the eye 10 cell layers that transmit images to the optic nerve and then to the brain Tapetum No tapetum Human and pigs Tapetum Fibrosum Horses and cows Tapetum Cellulosum Dogs and cats Tapetum 4

5 Gross Fundus Animal Retinas Questions??? History What does your doctor need to know? History- Signalment History Age Breed Sex Weight Indoor/outdoor Other health issues Known trauma Other meds How long has the problem been going on? What treatment have you been giving if any? Have the treatments helped? 5

6 Color? Character? Constant? Irritating? History-Discharge History Painful Squinting rubbing Color Red Green/orange Cloudy/white History-Vision problems How well can they see? Is the vision different in dark vs. light? If loss: sudden or gradual? Any other systemic problems? BAR Orbit Enophthalmos Exopthalmos Eye Position Straight Strabismus Pre-examination 3 Rules in Order of Testing Ophthalmic Examination Tests Schirmer tear test is ALWAYS first!!!!!! 6

7 3 Rules in Order of Testing Schirmer tear test is ALWAYS first!!!!!! Don t do ANY other tests before STT!! 3 Rules in Order of Testing Schirmer tear test is ALWAYS first!!!!!! Don t do ANY other tests before STT!! Don t forget the STT at the beginning!!!! Schirmer Tear Test 1 minute Insert notch between the lower eyelid and cornea mm = normal < 15 mm = dry eye <10 mm = too dry Culture Acquire prior to putting any dye in the eye Swab the lower conjunctival fornix Wash eye well first Sample the site affected Cytology Flourescein stain Stains exposed stroma Will not stain the corneal epithelium Stains tear 7

8 Cornea Three layers thick Epithelium 5-6 cell layers thick Stroma Lamallae of collagen Endothelium and Descetmet s membrane 1 cell layer thick 44 Stains sick epithelial cells Rose Bengal Biomicroscopy Slit lamp examination Pathognemonic staining of Herpes virus dendritic ulcers Magnification 10x or 16x Biomicroscopy Indentation Tonometry Depth of cornea Anterior chamber Layers of lens Consistency of vitreous 48 8

9 Applanation Tonometry Applanation Tonometers *Imbert-Fick Law* Goldmann, Perkins, Mackay-Marg, Pneumatonograph Tono Pen XL +/-Topical Anesthesia Learning curve Takes 3-6 measurements OK with some corneal disease and contact lens, but can give falsely low readings too 1990 study* underestimates IOPs > 40 mmhg and overestimates IOPs < 20 mmhg Rebound Tonometry Electromagnetic probe 1 mm diameter tip False readings in face of corneal disease 6 measurements No topical anesthesia Canine Normal IOP Values /- 4.0 (TP) Knollinger et al /-3.1 (TV) 12.9+/- 2.7 (TP). Feline /- 5.6 (TP) Equine (Gelatt 4) Knollinger et al /-5.9 (TV) /- 5.9 (TP). Canadian Beaver* Ketamine sedation (TP) Harbor seals/sea lions 8-18mmHg** Rabbits*** 17.9+/-2.11 (pneumotonograph) New Zealand White Rabbits under GA - Perkins BEST!! Chinchilla /- 5.8 Koi Fish**** 4.9 mmhg (1-11) (TV) Indirect Biomicroscopy Fundic examination Large field of view 3D picture with head loops 51 Indirect Biomicroscopy Transilluminator and lens Hold lens close to the patient s eye Hold transilluminator next to your eye Direct Biomicroscopy Ophthalmoscope Small view but very magnified 9

10 Indirect vs. Direct 3x 15x Allows examination of the iridocorneal angle Gonioscopy Vision in Animals Does my dog see in color or black and white? Sensitivity to Light More rods than cones Tapetum reflects light Minimum threshold for light Cats-6 times lower than humans Dogs somewhere inbetween 66 inches Visual Perspective 34 inches Visual Perspective Average human Great Dane 10

11 8 inches Visual Perspective Visual Acuity Myopia Shih tzu Emmetropia Hyperopia Visual Acuity Ability to see details separately & in focus Optical Retinal Visual pathway interpretation Color Vision in Dogs Canine 20/50 to 20/140 (mean 20/75) Feline 20/100 to 20/200 Horse 20/30 Cattle 20/240 to 20/ Thanks for coming!!!!! 11