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 THE OPHTHALMIC EXAMINATION
Tips to get dogs and cats to hold eyes open:
- bounce gently if a small animal
- lean gently over the edge of a table, they will think they are falling and open eye and often pull down the third eyelid
- topical anesthetic
- lid block to decrease blepharospasm - rarely needed, use 2-3 ml of lidocaine, terminal fibers of the auriculopalpebral nerve, use a 25guage 1-inch needle, insert 2 cm lateral to the lateral canthus, then direct medially along dorsal orbital rim, then along ventral orbital rim, provides some anesthesia as well.
Equipment for Eye Examination in General Practice:
- Schirmer Tear Test Strips
- Fluorescein Dye Strips (avoid prepared drops, as they can easily become contaminated if the bottle is not used up in a day or two)
- Proparicaine -refrigerate, don't give to clients to administer to patients at home, toxic to epithelium
- Eye Wash, to clean off debris
- Light source:
- Welch Allyn transilluminator (Welch Allyn rechargeable handle, cat. no. 71000 with Finoff ocular transilluminator, cat. no. 41100) - or -
- Welch Allyn Halogen Penlight (cat no. 7660)
- Cobalt Tip for viewing fluorescein dye
- Direct Ophthalmoscope
- 20 Diopter Lens - for indirect ophthalmoscopy - Welch Allyn (cat. no. 12300) about $60.00
- Forceps to Examine Third Eyelid - Von Graeffe, or Adson's Delicate Tissue Forceps
- #15 Blades for conjunctival scrape - use blunt end
- Sterile Q-tips, or cellulose sponges
- nasolacrimal cannula or IV catheter for nasolacrimal flushing
- Tropicamide 1% Solution - for pupil dilation
- Magnification
- Culturettes - Minitip
The order in which you do the steps in an eye exam is very important:
- avoid putting topical anesthetic in before culture or before Schirmer Tear Test, but must go in before tonometry
- avoid dilating pupil prior to tonometry as it can increase IOP
- always get Pupillary Light Responses prior to dilating pupil
Proper order to do an eye exam:
- History - Vision testing - Pupillary Light Response - Culture if needed - Schirmer Tear Test - Topical Anesthesia - Tonometry - Examination of Adnexal Structures - Examination of Anterior Chamber - Dilate Pupil with Tropicamide - Examination of Lens - Examination of Vitreous, Retina and Optic Nerve
Vision Testing
- menace response (not effective puppies or kittens), make sure animal can blink
- cotton balls
- maze tests
- placing response
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- Pupillary Light Responses
- to evaluate pupil size, stand at arms length and look through the direct ophthalmoscope (set at zero diopters)
- remember that a positive pupillary light response does not indicate the animal can see, cortically blind animals will have a normal pupillary light response
- fearful animals will have widely dilated, poorly responsive pupils, however this can be overcome with use of a strong light
Schirmer Tear Test
- do prior to administration of topical anesthetic
- Strip should contact cornea
- should be at least 15mm/min in dogs, may be less in cats and still be normal
- remember there are three layers to the tear film, and Schirmer only measures the middle layer or aqueous layer, deficiency of the mucin layer (inner) or the lipid layer (outer) may also cause corneal irritation and opacity
Eyelids:
- evaluate ability of dog to blink
- look for distichiasis, trichiasis, ectopic cilia
- eyelid tumors, blepharitis
- entropion, ectropion
- are both nasolacrimal punctae present?
Nasolacrimal Flush:
- use 22 gauge Teflon catheter if you don't have a metal cannula
- use sterile saline or LR for flush, or eye wash (sterile buffered saline)
- avoid causing bleeding which can result in scarring and adhesions
- use syringe, or sterile bulb syringe
Nictitans:
- look behind with forceps, all the way to the fornix
- look for follicles on both surfaces, foreign bodies
Fluorescein dye:
- does it flow to both nares?
- rinse well
- use cobalt light attachment to the transilluminator (Welch Allyn)
- use to measure "tear breakup time": apply fluorescein, allow animal to blink, then hold eyelids open until the fluorescent layer begins to break up, average time between the first blink and appearance of first dry spot is about 15-25 seconds
- use for Seidel test, test if a deep ulcer is leaking - touch spot with dry fluorescein strip, do not flush, spot will be orange, press cornea gently with moistened swab, if there is a leak a tiny green spot appears due to dilution of the dye
- fluorescein does wash out of clothing with soap and water!
Schiotz Tonometry:
- use topical anesthetic (use proparicaine, avoid tetracaine)
- always stain with fluorescein after to make sure you have not caused an ulcer
- clean the tonometer after each use
- zero the tonometer before each use
- you need 3 people: one to hold dog with head up, second to hold tonometer on cornea, third to read scale
- most common mistake is sticky dirty tonometer, or not having foot plate rest evenly on cornea
- plus or minus 2 rule: with the 5 gram weight normal intraocular pressure is 5 plus or minus 2 i.e. between 3 and 7 on the scale, with the 7.5 gm weight normal would be 5.5 to 9.5
- let the tonometer rest lightly on the cornea, do not press
- tonometer must be vertical and entirely on cornea
Examination of Anterior Chamber:
- aqueous flare: looks like dust particles in the air of a movie theater in projector beam
- evaluation for aqueous flare not accurate without slit lamp biomicroscope
- some ophthalmoscopes have a slit beam which can give you a rough idea, or shine a transilluminator across the eye at close range
- may see iris cysts - look like brown floating balloons, can be transilluminted
- look for posterior or anterior synechia
- look for persistent pupillary membranes
- look for iris atrophy
- use the direct ophthalmoscope to examine the anterior chamber, settings of 12+ to 15+ will usually put the iris and associated structures in focus
Examination of Lens:
- examine in a dark room, may want to dilate pupil with tropicamide
- stand at arms length and hold penlight or ophthalmoscope light, look for bright tapetal reflex, should be equal in each eye
- nuclear sclerosis - tapetal reflex will be present
- cataract - tapetal reflex will not be present
- vacuoles in lens can indicate impending onset of cataract
- refer for cataract surgery at first sign of cataract
Dilation of the Pupil:
- For dilation do not use atropine, lasts up to 10 days!, use short-acting mydriatic: tropicamide 1%
- dilation of pupil can cause glaucoma
Examination of Fundus
Indirect Ophthalmoscopy:
- most animals can be examined in a dark room without dilation
- image is upside down and backwards
- view is of a large area of the retina at lower magnification than direct
- use a 20 diopter lens and a strong light source
Direct Ophthalmoscopy:
- only small area of retina is viewed
- high magnification ( 17 - 20 X)
- face is right next to animal
- image is right side up
Technique - Indirect Ophthalmoscopy
- a dark room is essential
- 20 minutes before examination, dilate pupils with one drop of 1% tropicamide
- technician holds animal at arm's length
- light source should be held at the right or left temple of examiner
- hold lens with thumb and forefinger and touch animal's forehead with remaining fingers
- obtain tapetal reflex before placing lens in front of animal's eye
- lens should be 4-6 cm in front of animal's cornea
- move lens as needed to keep fundus in focus
- lens must remain perpendicular to light beam
- to move around the fundus move your eye, lens and light source together as if they were connected by a straight line
- to view optic disc in most dogs look slightly up, i.e. your head must be below the dog's
- remember that what you see is upside down and backwards
- when you lose the view of the fundus, take away the lens and find the tapetal reflex again before replacing the lens in front of the eye again
Technique - Direct Ophthalmoscopy
- Dilate pupils with tropicamide
- Use a darkened room
- Restrain animal, muzzle if necessary
- use right eye to examine patient's right eye, and left to examine patient's left
- start with lens dial at zero and hold ophthalmoscope 20 inches from patient's eyes
- bring ophthalmoscope to about 1 inch from animal's eye until retina is in focus
- there is a dial with viewing lenses from -25 to +40 diopters, usually 0 will be in focus on the retina, if a lesion is in focus at -5 diopters the lesion is depressed behind the retina, if it is in focus at +5 diopters it is anterior to the retina
- there is usually a variety of apertures, small pupil, large pupil, a fixation aperture, a slit beam, and a cobalt filter
- there is usually a switch with three choices of filters, red free light (a green dot), no filter, or crossed linear polarizing filter (decreases glare from cornea)
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ANESTHESIA AT ANIMAL EYE CARE
Surgery is performed under general anesthesia and we are proud of our anesthetic protocols and monitoring systems. The anesthetics are state-of-the-art medications that are used routinely in human hospitals. The safest possible anesthetics are used in each patient using preoperative blood work and other test results to guide our choices. Pulse rate, blood oxygen saturation, blood pressure, and the electrocardiogram are monitored continually throughout the surgery by a technician who is assigned to monitor your pet during the entire surgery. Intravenous fluids are given during anesthesia, and for our diabetic patients, intraoperative and preoperative blood glucose measurements are repeatedly tested to insure that blood glucose levels remain in a safe range.
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OPHTHALMOLOGY WEB LINKS
Veterinary Ophthalmology Information Centre
Mammal Eye
Research in veterinary and comparative ophthalmology
OPHTHALMOLOGY ORGANIZATIONS and PRACTICES SITES
American College of Veterinary Ophthalmologists
American Society of Veterinary Ophthalmology
American Academy of Ophthalmology
Association for Research in Vision and Ophthalmology
Massachusetts Eye and Ear Infirmary
BREEDING and GENETICS SITES
Institute for genetic disease control (GDC)
American Kennel Club
Canine Eye Registration Foundation (CERF)
Optigen
Testing for Inherited Eye Diseases of Purebred Dogs
SPECIAL INTEREST SITES
BlindDogs.com
This is good site for owners that have blind dogs or dogs that are going blind.
PetCareBooks.com
This site offers a few books about blind dogs.
PepeDog.com
These owners have designed and are marketing a hoop on a harness that can be used to help blind dogs move around more confidently in familiar and even unfamiliar environments.
Angelvest
Another site demonstrating a vest with a hoop that can be used to help blind dogs move around more confidently in familiar and even unfamiliar environments.
Doggles
Doggles are sunglasses made for dogs. They can protect the eyes from trauma, reduce glare, or relieve light sensitivity.
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