A good ocular examination begins with a complete medical history. The saying goes that the eyes are the window to the soul – to the ophthalmologist they are often a window to illness elsewhere in the body. The general medical history should be scrutinized starting with signalment and work/play/housing environments.
• Basic Equipment to have on Hand
• A focal light source (halogen Finoff transilluminator)
• A direct ophthalmoscope or a indirect ophthalmoscopy lens
• Loupe for Magnification
• Serrated Thumb Forcep
• Schirmer Tear Test Strips
• Fluorescein strips
• Rose Bengal strips
• A Kimura spatula or a #10 blade
• Glass Slides
• Sterile cotton tipped swabs
• Culture Swabs and transport media
• Tropicamide 1%
• 23g IV catheter
• Digital camera
A good ocular examination begins with a complete medical history. The saying goes that the eyes are the window to the soul – to the ophthalmologist they are often a window to illness elsewhere in the body. The general medical history should be scrutinized starting with signalment and work/play/housing environments. Travel history can be important when considering some infectious diseases that have different geographic occurrences. Many Arizona snowbirds have returned to the Midwest bringing with them pets with Valley Fever (coccidiomycosis) which is endemic in the Southwestern US. A vaccine and deworming history can also be integral in finding answers to the problems at hand. Other clinical signs not thought to be directly related to the ocular condition may be very important to an accurate diagnosis. Ie, skin lesions or GI signs with can accompany ocular histoplasmosis. When assessing the primary ocular complaint, onset of signs, duration of and response or lack of response treatments as well as current medications should be considered.
The best restraint for an ocular exam is normally the least amount necessary. Sedation will often make the examination more difficult by causing protrusion of the third eyelid (TEL), enophthalmos, and rolling down of the globe in the orbit. The TEL is often a formidable obstacle to getting a good exam done even without sedation. Dogs will utilize the retractor bulbi muscles to pull the globe caudally causing TEL elevation, while cats have a direct mechanism to raise the TEL. Keeping the animal alert, positioning them over the edge of a table or making noises to attract their attention will often help to keep the TEL in its normal position. There are times that proparicaine and a serrated thumb forceps or a cotton swab will be required to move the lid out of the field of view. A systematic exam and short periods of exposure to the bright light of the exam will allow for the most affective and complete exam.
First the head should be examined with limited restraint. For animals that have been treated chronically, or animals that are painful, even the thought of head restraint will cause blepharospasm and will make examination difficult. Using a focal light source, look for normal facial conformation and symmetry. The size of each palpebral fissure, the size of each globe and the position of each globe should be assessed and compared. Often times, one eye can act as your normal, so always assess both eyes. Viewing the patient straight on, from both sides and from above will help in determining symmetry and normal versus abnormal findings. Manually palpate the orbital rims, the muscles of mastication, and the globes themselves through a closed lid. Repeated gentle manual comparison of intraocular pressures through closed lids will eventually give you a good idea of which eyes are hard and which are soft even before you get a good look at the eye itself. Additionally, as you handle and manipulate the head it can be done in such a manner than many dogs begin to relax and enjoy the rubs and scratches. I will normally wait to assess retropulsion of each globe until the end of the examination as it can be disconcerting to both the patient and the owners. Finally the gross exam should include assessment of ocular discharge, lid abnormalities, dermatologic lesions, alopecia and erythema.
Moving systematically, from a broad to more a more concentrated focus and from outside to inside; the palpebral, third eyelid and bulbar conjunctiva are next. Appropriate restraint of the head will allow for a closer and magnified examination. The conjuctiva can be normal, pale, hyperemic, or chemotic and could contain masses, hyperplastic follicles, ulcerations or hemorrhages. A commonly skipped structure in the ocular exam is the limbus: it should be visible, complete and free of distortions or masses. In cases of episcleritis, the limbus can be completely obscured by cellular infiltrate that migrates from the episclera over the limbus into the cornea. The cornea should have an excellent luster and be free of irregularities and opacities. The anterior chamber, iris, pupils and lens can also be assessed grossly and with magnification. The use of retroillumination can help to highlight flare in the anterior chamber, dyscoria or atrophy of the iris, and opacities of the lens. Focus on the fundic reflex and then use that reflected light to examine the other ocular structures. Ophthalmoscopes have a slit beam setting which can be very helpful in identifying aqueous flare or determining the depth at which a lesion is occurring in the cornea or lens. Fundic examination via direct or indirect ophthalmoscopy will illucidate any vitreal or retinal pathology.
Most patients that I examine have a basic ocular assessment consisting of a complete ocular exam as well as a Schirmer Tear Test (STT), a Fluoroscein stain test, and Tonometry measurement. STT results not only identify aqueous tear deficiencies, but can also can identify an increase in tearing (>25mm/wetting minute) secondary to conjunctivitis or corneal irritation.
Fluoroscein stain is not just for ulcers anymore. It can be used to assess tear film breakup time (TFBUT) which measures the stability of the tear film and can help to diagnose qualitative tear film deficiencies. The TFBUT is the time that it takes for black spots for lines to appear in a film of fluorescein stain after a blink occurs (normally ~20 seconds). In affected animals, the TFBUTs are accelerated to 5 seconds or less. TFBUTs are also accelerated by corneal surface abnormalities. Qualitative tear deficiencies result in corneal pathology secondary to rapid evaporation of the aqueous tear film. These conditions can be treated, providing increased comfort and improved corneal health. Fluoroscein stain can also be used to detect leakage of aqueous from descemetoceles (Seidel Test). With the application of a concentrated drop of stain to the cornea the stain will appear yellow/orange in color. If aqueous is leaking the stain will stream changing color from yellow to green and the stain is diluted by the leaking aqueous. The patency of the Nasolacrimal apparatus can be assessed with fluorescein stain (Jones test). The dye should appear at the nares or in the mouth within 5 minutes of its application. Some dogs will repeatedly raise their head and lick their nose during the exam in protest of the restraint. In these cases gentle pressure down on the muzzle will allow for assessment of the Jones test. False negative results often occur in brachycephalic breeds when the stain drains caudally into the nasopharynx rather than through the external nares. Examination of the caudal tongue and pharynx can confirm passage of the dye in these animals.
Intraocular pressure measurements (IOPs) are by far one of the most difficult diagnostic tests to acquire accurately. I find the rebound tonometer (Tonovet) to be much easier to use with practice than the applantation tonometer (Tonopen). With either instrument an accurate measurement all starts with appropriate restraint. Struggling or the application of pressure on the chest, neck, or eye of the patient will falsely elevate the intraocular pressures. Glaucoma is a bilateral disease, but it rarely affects both eyes at the same time. If both eyes are showing elevated IOPs, stop, regroup and try again. Collars should be loose about the neck and restraint of the head should be at the occiput and under the mandible or at the occiput and around the muzzle. If a cloth muzzle is being used, it can cause compression of the globe and falsely increase the IOP. If marked blepharospasm is present, sometimes the repeated application of proparicaine can be helpful. When holding the lids open, attempt to place pressure only on the orbital bones and not the globe itself. Hold the lids open only as much as is necessary to get the necessary measurements.
Cultures and Cytology
Treatment of all corneal stromal ulcers can benefit from collecting cytology samples and by obtaining bacterial culture and antibiotic sensitivities. Cytology and gram stain results are often available within 24 hours of collection and can help in guiding antibiotic selection. Although culture results are not immediate, they can still be helpful in guiding treatment choices. Culture samples should be taken prior to the application of fluorescein and if possible prior to the application of proparicaine, both have preservatives that can inhibit culture growth. Cytology samples can be collected with a Kimura spatula, the blunt end of a #10 blade or with a pre-moistened cotton swab.
I highly recommend purchasing or designing an ocular examination form. Consistent documentation of ocular findings, especially in a multi-doctor practice makes for a higher quality of patient care and service. Having the form also supports examination of the entire eye from the lids through the globe and into the orbit. Digital photography is also a highly useful tool for the documentation of ocular pathology and for tracking changes in ocular conditions. Digital photos are invaluable in providing conformation that the feline iris melanosis has not progressed significantly or to make a case that surgery is necessary as the melanosis worsens.