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First ask yourself “where is it” not “what is it”. Ophthalmic Examination – PART 1 Elizabeth A. Giuliano DVM, MS, DACVO Associate Professor, University of Missouri Columbia, MO, USA Overview of the Issue Ocular examinations can sometimes be intimidating when the practitioner is unsure of the diagnosis. The goal of this lecture will be to help review techniques useful in the localization of an ocular lesion, thereby helping to narrow down the possible differential diagnosis and further hone the diagnostic work-up. Emphasis will be placed on the anterior segment examination. Objectives of the Presentation 1. Provide an overview to the basic instrumentation, supplies and diagnostic pharmaceuticals required for a complete ophthalmic exam 2. Discuss the key components of the “minimum ophthalmic data base” 3. Provide helpful tips to ensure success in performing the complete ophthalmology exam Key Clinical Diagnostic Points Minimal equipment is necessary to perform a complete ophthalmic exam Always strive to acquire the “minimum ophthalmic data base” to best diagnose and treat your ophthalmic patients. Rarely, an aspect of the complete ophthalmic exam will be forfeited (example: tonometry should not be performed on an eye with a descemetocele due to risk of globe rupture). Components of the minimum ophthalmic data base include: menace response, direct and consensual pupillary light reflex, palpebral reflex, Schirmer tear test, fluorescein stain, and tonometry Additional diagnostics typically performed in an awake patient include: conjunctival / corneal cytology and/or culture and sensitivity, conjunctival biopsy, and nasolacrimal flush. Basic Instrumentation A thorough ophthalmic examination may be performed with a minimum of diagnostic instrumentation. The most basic instruments/equipment necessary for the small animal practitioner include: - magnifying source – (e.g. Optivisor loupe) - power source – (e.g. Welch-Allyn (W-A) 3.5V halogen handle) - focused light source – (e.g. Welch-Allyn Finoff transilluminator) - direct ophthalmoscope head - attaches to W-A 3.5V handle or PanOptic - 28-20 diopter condensing lens - tonometer (e.g.:Tonopen or Tonovet) - nasolacrimal cannula (or small catheter with stylet removed can be used) - thumb forceps - Instruments for cytology: scraping blade - spatula or surgical blade (clip-on end) or microbrushes More Advanced Ophthalmic Equipment -handheld slit lamp (e.g. SL-15) -binocular indirect ophthalmoscope -operating microscope -high resolution ocular ultrasound Supplies and Diagnostic Pharmaceuticals Consumable materials that should be readily available are: - Schirmer tear test (STT) strips - sterile fluorescein strips - culturette swabs (mini-tip) - cotton swabs - sterile eye wash irrigating fluid or sterile saline - dilating agent - 1% tropicamide (Mydriacyl) - topical anesthetic solution - 0.5% proparacaine (e.g.Alcaine) Components of the Anterior Segment Ocular Exam The eye is unique in that most of its structures can be visualized and clinicopathologic diagnoses frequently are possible from the complete ophthalmic exam. You will need to have a basic knowledge of gross and histologic anatomy of the eye and orbit in order to make a diagnosis and provide a prognosis. Minimal equipment is necessary to perform a complete ophthalmic exam. The practitioner is encouraged to always strive to acquire the “minimum ophthalmic data base” to best diagnose and treat his/her ophthalmic patients. Rarely, an aspect of the complete ophthalmic exam will be forfeited (example: tonometry should not be performed on an eye with a descemetocele due to risk of globe rupture). Components of the minimum ophthalmic data base include: menace response, direct and consensual pupillary light reflex, palpebral reflex, Schirmer tear test, fluorescein stain, and tonometry. Additional diagnostics typically performed in an awake patient include: conjunctival / corneal cytology and/or culture and sensitivity, conjunctival biopsy, and nasolacrimal flush. The adnexa and ocular anterior segment can be thoroughly examined in a lighted room with the aid of an examining light and source of magnification, such as the Opti-Visor loupe with dial adjustable headband. The ocular posterior segment can best be evaluated by ophthalmoscopy in a darkened room. Always examine both eyes even if only one seems abnormal. If the eye is painful to the patient and there is danger of injuring the eye during examination, or if the eye cannot be thoroughly examined, judicious use of chemical restraint is recommended. As with any other problem, a history is important to properly interpret your physical exam findings. This should include establishing how long the client has had the patient. Establish when and under what circumstances vision became impaired or ocular problems began. The appearance of the eye, as perceived by the client, may give valuable clues as to what came first when dealing with an entity such as cataract. I frequently like to begin my ophthalmic examination by asking the client simply “what first made you think your pet was having an eye problem?” Other questions might include: Does the patient see better under any particular lighting arrangement? What type of lifestyle does your pet have (e.g. indoor only, agility performer, etc) Did the patient's vision loss correspond with rearrangement of household items or visiting an unfamiliar environment? Has there been a change in the general health of the patient? Additional questions should be tailored to fit the particular situation at hand. I recommend examining all patients initially from a distance. This will help the practitioner determine if the problem is unilateral or bilateral (if it is an externally visible problem). Observe the relationship of the globe to the orbit and eyelids, and to the other globe. Ask yourself the following questions: What is the size of the eye - small, normal or enlarged? What is the position of the eye - protruding or sunken into the orbit? Is there a difference between the axes of the two eyes? Any evidence of periorbital swelling? Is there any ocular discharge and if so, what is the character of the discharge (serous, mucoid, sanguineous)? Use of a Transilluminator The transilluminator powered by a 3.5V handle is used to closely inspect extraocular structures including the lacrimal caruncle, the nasolacrimal puncta, the leading edge of the third eyelids, the meibomian glands, and the limbus of each eye. Conjunctival vessels are differentiated from episcleral (ciliary) vessels. Translucency of the cornea is determined. Intraocular structures in the anterior segment of the eye may also be examined. The light is directed obliquely across the anterior portion of the globe and the depth and clarity of the anterior chamber is noted. The color and surface contour of the iris and the size and symmetry of the pupillary openings are observed. Direct and consensual pupillary responses are tested. Recall that the use of dilating agents will invalidate pupillary responses for several hours. You may localize intraocular opacities by considering the posterior area of the lens nucleus as the center of rotation of the eye. If an opacity appears to move with or in the same direction of eye movement, then it is rostral or in front of the posterior area of the lens nucleus. If an opacity appears to move against or in the opposite direction of eye movement, then it is caudal or behind the posterior area of the lens nucleus. If an opacity does not appear to move when the eye moves, then it is in the nuclear area. Direct the light through the pupils and observe the fundic reflexes. The presence and color of tapetum will determine the color of the fundus reflex. The lenses are normally translucent and allow reflected light to fill the pupil spaces. In most animals the tapetal reflection is gold or blue-green. In atapetal animals the reflection is red or dull grayish-blue. Opacities are frequently detectable by this technique which is referred to as retroillumination. A partial or complete absence of a fundus reflex indicates opacification involving one or more portions of the normally transparent parts of the eye. Pupillary Light Reflex The direct pupillary response is done by simply shining a bright light into each eye. I find it best to perform this test under standard exam room lighting (i.e., not with the lights off) in order to also evaluate symmetry of the pupils without the complication that darkness would inject through reduction of parasympathetic tone. However, it may be difficult to determine the response in the non-stimulated eye because exam room lighting reflects off the cornea preventing adequate visualization of the pupil. You can overcome this by one of the following methods: (1) Dim or extinguish the exam room lights and stand back far enough so that you can see both pupils via the fundus reflection when you look through the direct ophthalmoscope set at ‘0’ diopters. Have an assistant shine a light first in one then the other eye while you observe the response in the non-illuminated eye. (2) A more simple method does not require an assistant or extinguishing of exam room lights. First establish that each eye has a direct response. Then shine your light in the right eye. When the pupil constricts (or after a second or two, if the pupil does not constrict), quickly swing your light to the left eye. If there had been a constriction on the left side, the left pupil should still be in a constricted state if you have swung the light quickly enough to the left eye. (If you were not quite quick enough, the left pupil will be slightly dilated and will, if normal, constrict directly in response to your light.) Repeat the procedure for the left eye. This is termed the swinging flashlight test. It is useful in identifying unilateral pupillomotor problems. For example, if you are going from the right pupil to the left pupil and the left pupil dilates rather than remaining constricted, this indicates a defect in the left eye’s afferent branch of the pupillary light response pathway. Other “tips” when performing a PLR: allow the patient to relax as much as possible. High sympathetic tone can alter normal PLR results. Secondly, remember that prolonged bright light stimulation into an eye is uncomfortable. Perform this test quickly and give your patients a few seconds “rest” between direct PLR testing. Corneal/Palpebral Reflex This reflex involves trigeminal (fifth; sensory) and facial (seventh; motor) nerves - any painful stimulus to or touching of cornea or eyelids leads to reflex closure of palpebral fissure through action of orbicularis oculi muscle. Menace response You may see this sometimes referred to as the “blink reflex” and it involves optic (second; afferent) and facial (seventh; motor) nerves. It is a “learned response” such that the patient responds to sudden stimulation of visual system (such as foreign body moving toward eye) by closure of palpebral fissure and sometimes, turning of head away from the stimulus. It is learned, and therefore more appropriately referred to as a response (not a reflex). Schirmer Tear Test The Schirmer tear test I (STT) is a method of measuring basal and reflex tear production in animals when deficient tear volume (aqueous component) is suspected. It is performed by inserting a sterile filter paper strip into the lower, middle conjunctival fornix of each eye. The strip is inserted and left in place for 60 seconds, then removed and the length of the filter paper that has been moistened by the tear fluid is measured on a mm scale. Normal values for dogs are 15 mm/min or greater while normal values in cats may be considerably less, possibly as low as 5 mm/min. STT measurements should be made at the beginning of the examination prior to application of topical agents or to any manipulation of ocular tissues. Conjunctival-Corneal Cultures & Cytology Cultures of the ocular surface are necessary for definitive diagnosis of severe, chronic, or nonresponsive infections. For conjunctival culture, the lower eyelid is everted and a sterile cotton or rayon-tipped swab in applied to the ventral fornix in front of the third eyelid. To insure adequate tissue contact the swab tip is gently pressed against the conjunctiva and rotated so as to slightly elevate the conjunctival tissue. The swab is then removed and inserted into the transport tube which contains an ampule of transport media. The ampule is ruptured and the sample is sent to the laboratory as soon as possible. Some specimens may be refrigerated depending upon the type of culture, i.e., the organism suspected. For corneal cultures, the swab is applied to the margin of the ulcerated or necrotic lesion. Ideally, cultures should be taken prior to instillation of topical agents, including topical anesthetic. However, in cases of corneal ulcers, one drop of topical anesthesia will aid patient compliance and has been shown to have minimal effects on culture results. Contamination is avoided by being cautious not to touch the skin or hair with the swab tip. Cytologic evaluation of ocular surface cells may be quite helpful in making a definitive diagnosis in cases of inflammatory or neoplastic lesions. For cytology, spatula collection or use of cytologic microbrushes are two commonly used techniques for removal of surface cells at affected sites. Samples for conjunctival or corneal cytology are collected after discharges are cleansed from the eye and topical anesthetic has been instilled. Several drops of topical anesthetic solution are instilled over a 2-minute period (e.g., 1 drop every 30 seconds). Platinum spatulas are specifically designed for ocular use, however, less expensive spatulas, such as pharmaceutical or chemical spatulas or the blunt, snap-on end of a surgical blade, may also be used. Scrapings are collected by placing the spatula or blade (blunt end) perpendicular to the surface, by pressing firmly against the tissue, and then pulling along the surface. Samples collected from scrapings should be gently blotted onto glass slides and air dried. A minimum of three slides should be prepared, one for a modified Wright's stain, one for a Gram's stain, and the remaining one for special staining if needed. Cytologic findings of greatest diagnostic interest are the presence of inflammatory or neoplastic cells or the presence of microorganisms. Fluorescein Staining Fluorescein dye is used diagnostically in veterinary ophthalmology for a number of reasons. The most common and important reason for placing fluorescein stain onto the eye is to detect a corneal ulcer. Recall that the corneal stroma is hydrophilic and, therefore, the water soluble fluorescein has a marked affinity for exposed stromal tissue. An area of positive staining will be noted by a bright yellow-gold appearance under room light conditions or using a focal white light. A cobalt blue filter on the tip of a hand-held transilluminator or an ultraviolet (UV) light will excite the fluorescein and any area of positive staining will appear bright green. Keep in mind that fluorescein does not stain epithelial surfaces or Descemet's membrane. Fluorescein may also be used to determine patency of the nasolacrimal (NL) drainage ducts (Jones test). Open the package of an individually wrapped, single, fluorescein strip and withdraw the sterile strip. Place a drop of diluent (sterile eye wash or sterile saline) onto the end of a sterile, individually packaged, fluorescein strip. As a bolus of stained fluid pools on the end of the strip, instill one drop of stain into each eye. Do not allow the strip to touch the surface of the cornea, or you may cause a corneal ulcer. Apply a cotton swab to the medial canthus, lower the animal's head slightly and flush the eye with diluent. Gently blot the medial canthus with a cotton swab to remove excess fluid. The eye is scanned with a focused light (with or without a cobalt filter or UV light). A short time later, usually in 3-5 minutes, the nares are inspected using the focused light to determine if fluorescein has passed through the nasolacrimal ducts. If dye has not drained into the nostrils by 5-10 minutes after instillation, obstruction of the duct is suspected and NL irrigation may be indicated. Nasolacrimal Irrigation An irrigating cannula, attached to a 3cc or 5cc syringe containing sterile eye wash or saline, is inserted into the upper and then lower punctal openings of each eye following administration of topical anesthesia. Shortly after fluid is injected into the ducts it should be seen flowing from the nostrils indicating patency of the drainage system. If fluid flows without resistance but is not observed exiting the nares, drainage into the nasopharynx is probable and the animal is observed for swallowing. If resistance is encountered to attempts at irrigation, an obstruction is probably present. Continued gentle pressure may flush out minor obstructions. Excessive pressure should be avoided so that the duct system is not further damaged. When the puncta are imperforate in dogs, retrograde irrigation may be attempted from the nasal opening. However, this is difficult to achieve especially in small dogs or cats. Tonometry Intraocular pressure measurement, or tonometry, is important for diagnosing glaucoma (elevated pressure) and uveitis (low pressure) and in assessing response to therapy when treating these conditions. In small animals, the hand-held Schiotz tonometer provides an effective and affordable means of measuring the intraocular pressure, however is rarely used for various reasons. Applanation tonometry (Tonopen) provides accurate and reproducible intraocular pressure readings in veterinary patients and is becoming increasingly used in general practice. Applanation tonometers have several advantages over the Schiotz tonometer. They are highly accurate, their readings are less affected by corneal disease, they can be used to measure intraocular pressure in vertically as well as horizontally positioned corneas, and are very easy to use, making them the instrument of choice for measuring intraocular pressure in domestic animals. The TonoVet is a newer, handheld veterinary tonometer which allows measurement typically without anesthetic. With TonoVet, a very light probe is used to make momentary contact with the cornea. Ophthalmoscopy – see also notes on Exam Part 2 Either direct or indirect ophthalmoscopy may be used to examine the posterior portion of the eye, i.e., the vitreous and fundus. The monocular direct ophthalmoscope is routinely available for use in general practice for examining the back of the eye. Pharmacologic pupillary dilatation is needed to adequately examine all intraocular structures deep to the iris (recall, pharmacologic dilation is contra-indicated in patients with glaucoma). Generally, 1% tropicamide is used in in most species for routine mydriasis; it is a synthetic atropine derivative and acts by blocking the use of acetylcholine, therefore blocks parasympathetic action and pupil dilates due to sympathetic tone. The pupil dilates in about 15 minutes in small animals, (20-25 minutes in large animals) and will remain dilated for approximately 4-8 hours. There are dials on the direct ophthalmoscope head piece – one dial will control the size and shape of the light beam and another will control the focal point of the light beam. The horizontal dial is set to project a large circular white light beam and the vertical dial is adjusted to focus on the structure(s) of interest, (e.g., start at 0 for viewing the fundus). By adjusting the focusing distance of the direct ophthalmoscope, the examiner may use the instrument to examine all visible intraocular structures. Its most common use is in examination of the posterior portion of the globe. When the vertical dial is set on 0, subtracting diopters (i.e.,-1,2,-3, etc.) moves the focal point away from the viewer. Conversely, when diopters are added (e.g., +1,+2,+3, etc.) the focal distance is brought closer to the viewer. The vitreous should be in focus when the diopter dial is set between +6 to 0 for most animals and the fundus is in focus between 0 and -2 diopters. Note: if the examiner normally wears corrective eyewear, and removes his/her glasses when performing direct ophthalmoscopy, the refractive power of the examiner will need to be adjusted for (thus, the diopter power needed to achieve focus for various ocular structures may vary slightly from person to person). Indirect ophthalmoscopy involves using a focused light and a condensing lens (typically 20-28 diopters in small animal) to view the fundus. A head-mounted light source combined with a set of prisms may be used and provides the viewer with a binocular view. A hand-held light may also be used. A Finoff transilluminator is recommended as a focal light source for performing monocular indirect ophthalmoscopy. The vitreous is examined for congenital remnants (retained hyaloid structures) and other opacities (degenerative materials, hemorrhage or exudates). Examination of the fundus involves studying the optic disc (papilla), retinal vessels, tapetal fundus (tapetum), and nontapetal fundus (nontapetum). Fundus examination should begin by identifying the optic disc and by evaluating its size and shape. In dogs and ruminants, a beige, irregular, fluffy margin to the optic disc is a frequent finding indicating lipid covering (myelination) of the nerve fibers (axons) entering the optic nerve. In cats, because of less myelin, the disc margin is usually sharper and more distinct. The shape, location, and vascular pattern of the optic disc and the appearance of the fundus vary considerably among species and individual animals. In dogs the disc may be round or irregular and may occur in the colored (tapetum), dark (nontapetal), or junctional area. Three or four veins return to the disc in dogs and frequently join together (anastomose) in the central area of the nerve. In cats, the disc is smaller than in dogs and is characteristically circular. The veins enter the disc at the periphery and no anastomosis occurs in cats. Fewer retinal arterioles are seen in cats as compared to dogs. The tapetum, the upper, brightly-colored portion of the fundus, is usually triangular in dogs and cats. The color of the fundus is quite variable from animal to animal and generally reflects the tapetal color with yellow, green, or blue-green most commonly noted. The tapetum may be incomplete or totally absent in animals with light haircoat color (color dilution or subalbinism). Affected animals may have a blue or blue-brown iris and may lack full fundus pigmentation. Atapetal areas of the fundus may appear orange or red reflecting the deeper vasculature of the eye. The nontapetum is usually brown or black, however, reddish, or light gray nontapetal areas are often seen in color-dilute animals. Abnormal funduscopic findings of the optic disc include a small disc (hypoplasia; micropapilla), elevation (papilledema), depression (cupping), degeneration (atrophy), and vascular changes (e.g., congestion, attenuation, or hemorrhages). The tapetal fundus is evaluated for clarity, coloration, pigmentation, and integrity of the retinal vessels. The nontapetal fundus is studied primarily for uniformity of pigmentation. Both tapetal and nontapetal areas are assessed for retinal elevations or detachments, hemorrhages, degenerations, disorganization (dysplasia), or sclera defects (colobomata). Summary Including 5 KEY “TAKE HOME” POINTS: When presented with any ophthalmic abnormality, concern for the patient’s vision and ocular comfort should guide the practitioner’s diagnostic and therapeutic plan The patient should be examined first at a distance, and then at eye level. A room with controlled lighting is ideal for the small animal ophthalmic exam. At a minimum, a room that can be completely darkened to permit accurate examination of intraocular structures is essential. The complete ophthalmic exam with its “minimal ophthalmic data” should be acquired during all ophthalmic examinations, almost without exception. Components of the minimum ophthalmic data base include: menace response, direct and consensual pupillary light reflex, palpebral reflex, Schirmer tear test, fluorescein stain, and tonometry Additional ocular diagnostic procedures routinely performed by the general practitioner include nasolacrimal flushing, conjunctival/corneal swabs for cytology and culture, and conjunctival biopsy. Key Drug Drug Class Tropicamide Parasympatho -lytic, short-acting mydriatic Proparacaine Depolarizing topical ocular anesthetic Dose Range N/A Frequency Route N/A 1 drop References available upon request 1 drop Indications Topically to To achieve pupillary corneal dilation in a surface normotensive eye for complete posterior segment examination Topically to Prior to tonometry or corneal ocular cytology surface