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A technician's role in the ophthalmic examination (Proceedings)

Article

What makes up the eye?

What makes up the eye?

     • Adnexa (lids), Precorneal Tear Film, Cornea, Anterior chamber, Iris, Lens, Vitreous, Fundus

Eyelids

     • Protect the eye

     • Provide part of and spreads the tear film

     • Regulate the amount of light that enters the eye

     • Clear foreign material

Third eyelid

     • Protects the cornea by removing foreign material

     • Contains the gland of the third eyelid

     • Helps to spread the tear film

     • Only moves passively in the dog

     • Can move actively in the cat

Tear film

     • Outer lipid layer created by the meibomian glands

     • Middle aqueous layer created by the lacrimal gland (65%) and gland of third eyelid (35%)

     • Inner mucin layer created by the coblet cells of conjunctiva

Conjunctiva:

     • Palpebral

     • Bulbar

     • Third eyelid

Cornea

     • More than just a windshield!

     • Accounts for 70% of the focusing power of the dog and cat

     • Only 0.5 mm thick

     • Layers: Epithelium, Stroma, Endothelium and Descetmet's membrane

Anterior chamber

     • Fluid filled space between the cornea and iris

     • Can fill with pus, blood, fat, protein, cells, or tumor

Aqueous humor

     • Produced by glands in the ciliary body

     • Provides nutrition and oxygen to the lens and cornea

     • Provides the fluid support for the eye (IOP)

Iris

     • "color" of the eye

     • The color in dogs is simply different amounts of pigment cells-not different pigments

Pupil

     • Empty space in the center of iris

     • Can be different shapes

     • Controls amount of light entering the eye

     • Shape: Dog – circle, Cat - vertical oval, Horse - horizontal oval

Lens

     • Behind the iris

     • 30% of focus power in the eye

     • Lens is where cataracts occur

     • The lens is anchored by the zonules that extend to the lens from the ciliary body

     • Zonules pull on lens to change its shape in accomodation

Vitreous

     • Jello-like material that fills the back of the eye

     • Holds the retina in place against the back of the eye

Retina

     • The "film" in the eye

     • 10 cell layers that transmit images to the optic nerve and then to the brain

     • Dogs and cats have a tapetum

     • No tapetum: Human and pigs

     • Tapetum Fibrosum: Horses and cows

     • Tapetum Cellulosum: Dogs and cats

History

     • What does your doctor need to know?

     • Signalment, Age, Breed, Sex, Weight, Indoor/outdoor, Other health issues, Known trauma, Other meds

Signalment:

     • Glaucoma in Cockers, Bassets

     • KCS in Cockers, Bulldogs, Pugs, Lhasas, Shih Tzu

     • Retinal degeneration in Poodles, Labs

     • Indolent corneal ulcerations in Boxers, Retrievers

History

     • What did you notice first? How long has the problem been going on? What treatment have you been giving if any? When did the treatment start?

Discharge

     • Color? Character? Constant?

Pain

     • Squinting, Rubbing, Lethargic

     • Color of the eye: Red, Green/orange, Cloudy/white

Vision problems

     • How well can they see? Is the vision different in dark vs. light? Are they bumping into things? If loss: sudden or gradual? Any other systemic problems?

Set your doctor up for success

     • Quiet dark room, Comfortable exam space, Stool or chair, You the technician!

Equipment

     • Gather equipment and proceed to a low lit area

     • Bright light source

     • Schirmer tear strips

     • Fluorescein stain

     • Proparacaine

     • Tono-Pen/Tono-Vet

     • Head loops

     • Direct ophthalmoscope or lens

Ophthalmic examination tests

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

     • Performing: Do not touch the notched end with your fingers. If you like to fold them, do it PRIOR to removing from the plastic package. Always perform test on BOTH eyes.

Dog

     • 15-25 mm = normal

     • 10-15 mm = suspect

     • <10 mm = too dry

Culture

     • Ask your doctor if culture is a possibility, Acquire prior to putting any drops in the eye

     • Can culture: Cornea, Discharge, Lower conjunctival fornix

Fluorescein stain

     • Stains exposed stroma

     • Will not stain the intact corneal epithelium

Rose bengal

     • Stains "sick" epithelial cells, Shows unhealthy tear film, Pathognomonic staining of Herpes virus "dendritic ulcers"

Cytology

     • Wash eye well first, Sample the site affected

Intraocular pressure

     • Tonopen: Applanation tonometry

     • TonoVet: Rebound Tonometer

     • Schiotz: Indentation tonometry

     • Normal IOP: 15-25mmHg

     • Low= uveitis

     • High= glaucoma

Indirect biomicroscopy for fundic examination

     • Large field of view

     • 3D picture with head loops

     • How to : Transilluminator and lens, Hold lens close to the patient's eye, Hold transilluminator next to your eye

Direct biomicroscopy

     • Small view but very magnified

Sensitivity to light

     • Dogs and cats have more rods than cones. Their tapetum reflects light

     • Minimum threshold for light: Cats- 6 times lower than humans, Dogs – somewhere in between

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