Adnexa

Lacrimal and Nasolacrimal Systems

The lacrimal system consists of the orbital lacrimal gland, the gland of the third eyelid, the accessory glands of Krause and Wolfring, the glands of Zeis, the tarsal glands, and the nasolacrimal duct system.^1–3 The lacrimal gland lies in the dorsolateral wall of the orbit. The lacrimal gland is innervated by the lacrimal nerve (branch of the ophthalmic branch of the trigeminal nerve) and parasympathetic fibers from the facial nerve nucleus and, to a lesser extent, by sympathetic nerve fibers.⁴ Two large and four to five small excretory ducts originate from the central surface of the lacrimal gland in both sheep and goats.⁵ The lacrimal fluid drains into the dorsal fornix of the conjunctival sac and mixes with the secretions of the accessory glands.³ The tarsal glands and, to a small extent, the glands of Zeis produce the outer lipid layer of the precorneal tear film. The orbital lacrimal gland and the gland of the third eyelid produce more than 90% of the middle aqueous component of the precorneal tear film, with a minor contribution from the accessory glands of Krause and Wolfring. The inner mucin layer is produced by the conjunctival goblet cells.¹ The three layers of the precorneal tear film are continuously spread across the eye’s surface by the eyelids and nictitating membrane during blinking. Unlike cattle, sheep and goats have lysozyme, an antibacterial enzyme, in their tears.⁶ Excess tear film pools in the lacrimal lake at the medial canthus. Mechanical pumping action draws the tear fluid into the superior and inferior lacrimal puncta located on the palpebral conjunctiva, just inside the edge of the eyelid and medial to the last tarsal gland.¹ The superior and inferior lacrimal puncta continue as the superior and inferior canaliculi. The canaliculi coalesce at the nasolacrimal sac located in the lacrimal fossa of the lacrimal bone.¹ The lacrimal sac empties into the nasolacrimal duct, which initially continues rostrally through the osseous lacrimal canal and the osseous lacrimal groove of the maxilla. It then parallels the mucous membrane of the middle meatus and opens on the nasal mucous membrane at the junction of pigmented and nonpigmented skin.⁵

Globe

The globe (bulbus oculi) is nearly spherical in shape. The average anterior-to-posterior axis of the globe in sheep is 26.85 mm¹ and in goats is 24.24 mm.⁷ The globe is composed of three tunics, or coats: the fibrous, vascular, and nervous tunics. The external fibrous tunic is made up of dense collagenous connective tissue that resists the eye’s internal pressure and gives the globe its round shape. The fibrous tunic is composed of the cornea and sclera, which coalesce at the corneoscleral junction or limbus. The middle vascular tunic is composed of the uvea, which includes the iris, ciliary body, and choroid. The inner nervous tunic includes the retina and optic nerve. The three tunics surround the clear intraocular media: the aqueous humor, lens, and vitreous humor.

Fibrous Tunic

Vascular Tunic (Tunica Vasculosa Oculi)

The vascular tunic is composed of the iris, ciliary body, and choroid. These structures are highly vascularized and usually are pigmented.

Neural Tunic

The neural tunic includes the retina and optic nerve, both derivatives of the forebrain. The retina and optic nerve are the only portions of the brain that can be seen on a physical examination, so observations of these structures can provide clinical information about the animal’s physical status. The retinal blood vessels and, to a small extent, the vitreous provide nutrition for the inner layers of the retina. The inner layer of the choroid (choriocapillaris) provides the outer layers of the retina with nutrients. The retinal metabolic rate is one of the highest in the body, and therefore if either the retinal or choroidal vasculature is even marginally compromised, the retina can become ischemic.¹

The retina has 10 layers, the outermost of which is the retinal pigmented epithelium (RPE), and nine inner histologic layers, known as the sensory retina, which include the clinically important photoreceptors and ganglion cells. The RPE is a single layer of cells between the sensory retina and the choriocapillaris. It is nonpigmented in the superior half of the fundus, allowing exposure of the tapetum to light. The RPE has tight interepithelial junctions that form the major portion of the blood-retina barrier, and it removes photoreceptor metabolic waste products.

The photoreceptors include the rods and cones. Rods function in dim light vision. Cones function in bright light and are involved with color recognition and visual acuity. The retina in all ungulates is primarily composed of rods. The rod-to-cone ratio for sheep is 30:1 to 40:1.¹¹ No rod-to-cone ratio has been reported for goats. Both sheep and goats have two types of cones, allowing these animals dichromatic color vision.¹ When stimulated by light, the photoreceptors initiate the electrical impulse through the other layers of the sensory retina eventually reaching the ganglion cells. The axons of the ganglion cells make up the optic nerve (cranial nerve II), which then carries the impulse to the optic tracts, optic radiation, and finally the visual cortex of the brain. The area centralis of the retina is the area of maximal cone density, and the visual streak is the area of maximal ganglion cell density. The central retina of sheep is similar to that of other mammals, with an area centralis and a single visual streak. Goats have an area centralis and two visual streaks—a horizontal streak and a vertical streak.¹² Sheep and goat retinas have a holangiotic vascular pattern with very prominent vessels, as is typical of ruminants. The term holangiotic means that all quadrants of the retina are vascularized with vessels extending from the optic nerve to the periphery. Sheep retinas have three or four pairs of vessels (artery and vein) in the dorsal, ventral, ventronasal, and ventrotemporal quadrants; and an additional five to eight arterioles and venules radiating from the nasal and temporal portion of the optic disk. Paired vessels may wrap around each other, especially the larger, dorsal vessels. Occasionally the superior arteriole and venule wrap around each other. Goat retinas have three to six arteries (one to three dorsal and two or three ventral) and two or three retinal veins. The dorsal (tapetal) fundus appears more vascularized than the nontapetal fundus owing to the more numerous vessels branching across the tapetum.¹³

The tapetal fundus is triangular, can be yellow to bluish-purple, and is stippled with the stars of Winslow (end-on choroidal capillaries). The dorsomedial tapetal fundus has more pigment than the other sections. The nontapetal fundus is pigmented owing to presence of pigmentation in the RPE cells in this region. In sheep, the optic disk is located within the nontapetal fundus just ventral to the tapetal-nontapetal junction; in goats, it usually is located in the tapetal fundus just above the tapetal-nontapetal junction. Sheep have a kidney bean–shaped optic disk; goats have a rounder optic disk surrounded by a ring of pigment.¹⁴ The small dark depression in the center of the optic disc is the physiologic cup or pit.

The optic nerve is located ventrolateral to the posterior pole of the globe. It is myelinated in all species; in sheep and goats the myelin is maintained as the fibers enter the globe through the sclera. Herbivores, including sheep and goats, exhibit more than 80% decussation at the optic chiasm to form the optic tracts. Each optic tract is composed of pupillary and visual fibers. The pupillary fibers travel to the pretectal nucleus to control the pupillary light reflex (described in detail further on), whereas the visual fibers travel to the lateral geniculate nucleus and then to the visual cortex for visual perception.

Clear Intraocular Media

Preliminary Considerations

Although special instrumentation and proper restraint are necessary, routine eye examination is not excessively time-consuming and promotes not only familiarity with variations of normal eye appearance but also an appreciation of the variety of ocular lesions encountered in different small ruminant species and breeds. An ophthalmic examination is strongly indicated for all sheep and goats exhibiting obvious or primary ocular or periorbital symptoms. It also should be included as a key component of a routine physical examination and whenever systemic disease is present,¹ because the overall appearance of the eyes may reflect the general condition of the animal. Information obtained from an eye examination can be helpful in differentiating among many systemic diseases, leading to a more precise diagnosis and institution of a tailored treatment regimen.

It is imperative to document historical findings, clinical signs and interpretation, final diagnosis, treatment administered, and progression of the condition. Record keeping is invaluable, especially in the management of complicated eye diseases or with patients unresponsive to treatment. Unfortunately, such scenarios are not always anticipated, so every case should be well documented from the very beginning.² Special forms are helpful in organizing the examination process, allowing efficient recording of all observations in a user-friendly manner (Figure 14-1). Drawing and labeling a diagram of the lesions will facilitate objective evaluation of progress over time.

Figure 14-1 Ophthalmology examination form.

Getting the History

A thorough ophthalmic history begins with ascertaining the animal’s signalment including age, breed, gender, pregnancy status, and presenting ophthalmic problem. Owners and caretakers should be interviewed about initial signs and symptoms such as presence of ocular pain (blepharospasm, apparent photophobia or epiphora); nature of ocular discharge, if present; change in color or size of the eye(s); visual status in bright versus dim light; and behavioral changes (e.g., isolation from the rest of the flock). Other factors to identify include the duration of the ocular condition, its progression (improving, same, or worsening), and whether it is worse on one side or the same on both sides. Investigate if related (in case of hereditary conditions) and unrelated herd mates also are affected with similar clinical signs. Inquire information about treatment administered and whether it changed the appearance, pain or vision status of the affected eye(s). Next, ask about the environment in which the sheep or goats are housed (e.g., indoor (bedding type, air quality), outdoor (pasture, dry lot, stocking density), exposure to temperature extremes or potential hazards, present and previous diet, vaccination and deworming status including products used and dates, recent or past diseases diagnosed in the flock, existence of previous eye problems, medical therapy administered, response to treatment, and intended use of the animal. Ocular changes can be clues to an animal’s health status, so questions concerning the animal’s ophthalmic problems should be accompanied by inquiries about the animal’s physical condition. The examiner should avoid asking so-called leading questions that may induce the owner to overinterpret observed clinical signs.

Initial Vision Assessment

After taking the history, the examiner should observe the animal’s movements in a small area before beginning the ophthalmic examination. The animal should be encouraged to maneuver around obstacles in bright and dim light. Because sheep and goats have laterally placed eyes, unilateral blindness is less likely to be compensated for by the contralateral eye. An animal often turns its head in an attempt to see in front of it when visual acuity is compromised on one side. If the examiner still harbors doubts concerning vision, each eye can be covered individually for better assessment.

During initial inspection and before restraint, the head carriage, appearance and symmetry of the face, the eyes and periocular region should be first examined from a distance in normal ambient light for obvious gross abnormalities. More specifically, periocular swelling or alopecia, palpebral fissure size, ocular or nasal discharge or dryness, redness or other color changes, corneal clarity and moistness, and size and position (enophthalmia, exophthalmia, strabismus) of the globes in their respective orbit should be noted.^1,3 In most cases, enophthalmia is associated with moderate to severe dehydration, but sunken-appearing eyeballs also may reflect loss of periorbital fat in animals with overall poor body condition. During this initial assessment, the animal’s temperament and requisite methods of restraint also are determined.¹

Instruments and Supplies for Ophthalmic Examination

Ophthalmologic instruments and supplies should be placed in a portable box or carry-on tote for easy access on field calls. In a hospital setting, the ophthalmic box should be located in a designated area of the examination room, readily available for use. Instruments and supplies recommended for small ruminant ophthalmic examination are listed in Box 14-1.

Restraint for Eye Examination

The ophthalmic examination ideally is conducted in dim ambient light, preferably in a darkened room or stall. If this is not feasible, a blanket or dark cloth can be used to cover the animal’s head during examination to evaluate the ocular condition.³ In most small ruminants, this evaluation can be performed using manual restraint of the animal in a standing posture; in sheep, “sitting” the animal on its rump is an alternative means of restraint. Depending on the species, size, and temperament of the animal, placing it in a chute, stand, or crate and application of halter can contribute to optimal immobilization. Use of a simple rope halter helps limit head movement and allows for safe and expedient completion of the task. If the eye is painful, topical proparacaine 0.5% can be used to eliminate superficial (corneal and conjunctival) pain, thereby facilitating the examination. Swabbing for subsequent culture and Schirmer tear testing, if indicated, should be performed before instillation of a topical anesthetic. An auriculopalpebral nerve block may be required for examination of patients exhibiting severe blepharospasm not alleviated by topical anesthetic.

Chemical restraint usually is not necessary but may be needed in noncooperative patients or in animals that must be completely immobilized for more delicate procedures. In such instances, xylaxine (0.05 to 0.1 mg/kg IV, IM), or butorphanol (0.05 to 0.1 mg/kg IV) alone or combined with diazepam (0.05 to 0.2 mg/kg IV) can be administered. Higher dosage or combined sedation is likely to lead to recumbency. This outcome should be anticipated and prepared for ahead of time. It is prudent to have tolazoline (1 to 2 mg/kg IM) or yohimbine (0.125 mg/kg IV) available for reversing the effects of xylazine if necessary. Assessment of the neurophthalmic reflexes (palpebral, corneal, menace) must be performed before auriculopalpebral nerve block and chemical sedation, because the effects of these techniques may interfere with the animal’s true response.

Assessment of Neurophthalmic Reflexes

Before touching the head, the examiner should assess the eyes for symmetry in size and position, note the presence of abnormal ocular discharge, observe the eyelids as they pass over the ocular surface, and record any rubbing, blepharospasm, or other abnormalities. The menace response can be used to evaluate the optic nerve (cranial nerve II) and facial nerve (cranial nerve VII) for presence of vision and ability to blink, respectively. This is an acquired response and therefore may not occur in normal lambs and goat kids younger than 2 weeks of age. In this age group, vision can be better evaluated by observing the animal’s ability to maneuver around obstacles in an enclosed area. After checking for the menace response, the palpebral reflex should be tested to confirm the presence of the ability to blink and to assess the completeness of the blink. The palpebral reflex test is performed by touching the skin around the eye. This test assesses the trigeminal nerve (cranial nerve V) and facial nerve (cranial nerve VII).

Both pupils should be assessed for size, shape, and symmetry under both light and dark conditions without direct stimulation. Shining a focal bright light source into one eye allows assessment of the pupillary light reflex (PLR). After the response from the stimulated eye is observed, the contralateral eye should be quickly assessed for the consensual pupillary response. The consensual pupillary response is slower and more incomplete than that in the stimulated eye because of unequal crossover of the optic nerve fibers at the optic chiasm. The PLR is a subcortical response that requires normal function of the retina, optic nerve (cranial nerve II), midbrain, oculomotor nerve (cranial nerve III), and iris sphincter muscle. Cortically blind animals have a normal PLR. The dazzle response assesses the visual pathway between the optic nerve and the midbrain. A very bright light source directed toward the eye usually causes a bilateral blink or turning of the head away from the light stimulus. This is a subcortical response that reaches the rostral colliculus and also stimulates the facial nucleus to cause the blink reflex.

Detailed Ophthalmic Evaluation

Abnormalities of the orbit can be assessed by palpation of the bones of the orbital rim for fractures and asymmetry or by skull radiography. Difficulty in retropulsing the globe (with the eyelids closed) may indicate a retrobulbar space-occupying mass or other orbital disease. Difficulty or pain on opening of mouth may indicate inflammatory orbital disease. Retrobulbar neoplasia usually does not cause pain on opening of the mouth. The involved orbit or globe should always be compared with the contralateral side. The eyelids should be evaluated for entropion or ectropion, complete closure of the palpebral fissures, increased wetness or ocular discharge on the hair adjacent to the eyelid margins, and distichiasis or trichiasis.

The nictitans can be examined by pulling the lower eyelid down and retropulsing the globe. The nictitans will sweep across the corneal surface. To examine the bulbar aspect of the nictitans, after application of topical anesthetic (proparacaine 0.5% or lidocaine 2%) over the surface of the nictitans and cornea, the nictitans is elevated by retropulsing the globe, and the margin of the nictitans is grasped with Graefe or dressing forceps and pulled up and then out.

The patency of the nasolacrimal apparatus can be assessed by determining whether fluorescein dye passes from the lacrimal lake to the nares after it is placed on the globe and flushed with saline solution. If fluorescein dye is not evident at one or both nares, the examiner can use a 22- or 23-gauge cannula attached to a 6-mL syringe filled with sterile saline solution to flush the nasolacrimal ducts in an orthograde direction. This procedure is performed by first applying topical anesthetic (0.5% proparacaine) to the globe and puncta. The distal blunt end of the cannula is inserted into the superior puncta, and saline solution is injected until fluid is seen exiting the inferior puncta. The cannula is then inserted into the inferior puncta, and again, saline solution is gently injected until fluid is seen exiting the distal naris in this case.

The conjunctiva should not be hyperemic, thickened, or edematous (indicating chemosis). Examination for hemorrhage, foreign bodies (especially beneath the nictitating membrane), and lymphoid follicle hyperplasia is indicated. Samples from the conjunctiva for culture and sensitivity testing, cytologic analysis, immunofluorescent antibody (IFA) testing, polymerase chain reaction (PCR) assay, and biopsy can be obtained in physically restrained animals after the application of topical anesthetic solution. Fluorescein dye should not be applied before sample collection for IFA testing because it may cause a false-positive result.⁴

The cornea is examined with a focal light source for clarity. A bluish hue is indicative of edema, white opacities may indicate scarring, a yellow-white color is often associated with white blood cell infiltrate, and red is consistent with neovascularization. Corneal edema can result from injury to the superficial corneal epithelium or corneal endothelium. Corneal ulcers manifest with focal corneal edema and uptake of dye on fluorescein staining. Any pathologic process involving the cornea warrants use of this staining procedure for visualization, because fluorescein is a hydrophilic dye that binds to exposed corneal stroma but not epithelium or Descemet’s membrane.

The slit beam of a direct ophthalmoscope can be used to assess the depth of a corneal ulcer by how deeply the beam is projected on the ulcer. If the ulcer is deep and fluorescein dye uptake is not evident, a descemetocele is likely. With a perforated corneal ulcer, aqueous humor may be seen draining from the perforation, or the iris or fibrin may occlude the perforation. Such ulcers should not be manipulated, and minimal diagnostic testing should be performed, because surgical intervention is the treatment of choice.

The anterior chamber is evaluated for clarity and depth. Damage to the blood-aqueous barrier allows protein and cells into the aqueous humor, creating turbidity or the Tyndall effect (aqueous flare). The slit beam or the smallest circle on a direct ophthalmoscope can be used to identify aqueous flare. The beam of light is focused directly on the cornea, which is then observed at 90 degrees to the direction of the beam as it passes through the anterior chamber. The light should not be visible passing through the anterior chamber. Aqueous flare is seen when protein and cells absorb light and the light beam is visible passing through the aqueous humor. A shallow anterior chamber can be caused by a perforating corneal injury, anterior lens subluxation, intumescent cataract, iris mass, or iris bombé, characterized by a 360-degree posterior synechia (resulting in complete adherence of the pupil to the lens), with the peripheral iris bowing forward. A deep anterior chamber can be caused by buphthalmia (enlargement of the globe from glaucoma), posterior lens luxation, or hypermature resorbing cataract.⁵

The iris is examined for abnormal color and thickness, and the pupil is examined for abnormal shape (dyscoria), miosis, or mydriasis inconsistent with the level of ambient light. Dyscoria can result from synechiae or a mass caudal to or within the iris. Pupil size should be examined in both bright and dim light, and the examiner should determine direct and consensual PLRs. The color and thickness of the iris should be compared with those on the contralateral side; increased iridal thickness may be obvious in the presence of cellular infiltrate and with anterior uveitis. The granula iridica should be examined for size and symmetry, because severe acute or chronic uveitis can cause them to atrophy.

Intraocular pressure (IOP) in most species is between 15 and 25 mm Hg. The average IOP reported in Corriedale sheep was 10.61 ± 1.4 mm Hg (range, 9 to 13 mm Hg) as measured using a Perkins applanation tonometer.⁶ The average intraocular pressure in caprine species has been reported at 7.9 to 11.8 mm Hg (range, 6 to 14 mm Hg) using a Tonovet rebound tonometer and 10.8 mm Hg (range, 8 to 14 mm Hg) using a Tonopen applanation tonometer in Pygmy goats.⁷ In Angora goats, mean IOP was reported at 13.9 mm Hg (range, 8 to 20 mm Hg) using a Tonopen applanation tonometer.⁸ The most common tonometers used in veterinary medicine are the Tonopen applanation tonometer and the Tonovet rebound tonometer. Both are easy to use in sheep and goats. With the Tonopen, topical anesthesia is required before the examiner gently touches the cornea several times to obtain a computer-averaged pressure reading. The Tonovet does not require topical anesthesia but has a more precise requirement for head position so that the tonometer probe is parallel to the ground. The probe assesses IOP at the corneal surface several times for a computer-averaged pressure reading, but the examiner does not have to touch the cornea directly. Proper technique is critical for accurate IOP readings. The examiner must avoid any pressure on the globe by placing a finger on the dorsal orbital rim and on the ventral orbital rim to stretch the eyelids open. The person restraining the animal must avoid holding the neck, because any pressure on the jugular veins will increase IOP. A high reading is consistent with glaucoma. The lens, vitreous, and fundus are best evaluated through a dilated pupil. The pupil should be dilated with a short-acting topical parasympatholytic such as 1% tropicamide. Time to effect for tropicamide is 10 to 20 minutes, and the effect lasts between 4 and 8 hours.⁵ The lens should be evaluated for position and clarity. Nuclear sclerosis is a normal aging change that does not preclude evaluation of the fundus but must be differentiated from cataract. It will appear as a bilaterally symmetric, homogeneous, slight grayness to the center (nucleus) of the lens.

A fundic examination can be performed by either direct or indirect ophthalmoscopy. Direct ophthalmoscopy is performed at a distance of 2 to 3 cm from the patient’s eye. The large circle is used when the pupil is dilated, and the smaller circles are used when the pupil is not dilated. The instrument is set at either 0 or the red (negative diopter) 2 to begin the examination. The numbers are sequentially changed to bring a lesion into focus depending on its location. If a lesion is posterior to the plane of the fundus, it will be in focus at a more negative diopter setting; a lesion anterior to the plane of the fundus will be in focus at a more positive (green) diopter setting. The disadvantages of direct ophthalmoscopy include the small field of view (approximately 2% of the entire fundus), difficulty in examining the peripheral fundus, and limited ability to see through any opacification of the clear media. The advantages of direct ophthalmoscopy include greater magnification and the ability to alter the dioptric strength of the ophthalmoscope.⁵

Indirect ophthalmoscopy requires use of a focal light source, such as the Finnoff transilluminator, to be held adjacent to one of the examiner’s eyes and an indirect lens (held at arm’s length) positioned 2 to 4 cm in front of the patient’s eye after the tapetal reflex has been identified. A relatively inexpensive, 20- to 30-diopter, ophthalmic indirect lens is effective. The image seen is virtual but is inverted and reversed. The advantages of indirect ophthalmoscopy include a larger field of view (approximately 40% of the entire fundus depending on the strength of the lens), which allows the peripheral fundus to be examined more completely; stereopsis (use of both of the examiner’s eyes) for depth perception; and the ability to see through mild to moderate opacification of the clear ocular media. Disadvantages include the need for a relatively dilated pupil. Examination in a darkened room along with use of a dimmed light source often allows fundic evaluation without dilation in herbivores through their horizontally oval pupils. Another limitation of indirect ophthalmoscopy is that it requires practice for the examiner to become proficient with the technique. In examining the fundus by indirect ophthalmoscopy, movement of the examiner’s head should follow in the direction that is to be visualized within the fundus. The examiner should have a pattern for examining the fundus beginning with the optic nerve, dividing the fundus into quadrants, and examining each one by evaluating the vessels and color of the tapetal and nontapetal fundi (Figures 14-2 and 14-3).

Figure 14-2 Normal fundus of a sheep.

(Courtesy Dr. Paige Evans, Leesburg, Virginia/Annapolis, Maryland.)

Figure 14-3 Normal fundus of a goat.

(Courtesy Dr. John Mould, Marlbrook, Leominster, United Kingdom.)

Auriculopalpebral Nerve Block

The auriculopalpebral nerve is a branch of the facial nerve and provides motor function to the eyelids. It can be palpated along the dorsal margin of the zygomatic arch. Local anesthesia of the auriculopalpebral nerve results in flaccid eyelids, which facilitates manipulations of the lid and examination of the cornea and conjunctiva, especially in a painful eye. When combined with topical anesthesia (0.5% proparacaine), local anesthesia helps with removal of foreign bodies, cytology, flushing the lacrimal puncta, and subconjunctival injections. The auriculopalpebral nerve block is performed by first palpating the nerve over the zygomatic arch and then tenting the skin over the nerve to insert a 22- or 25-gauge needle to the hub. A 3-mL syringe with 2% lidocaine is then attached, and 2 to 3 mL of lidocaine is infiltrated subcutaneously around the nerve.⁹ Local anesthesia of the eyelids may be accomplished with up to 4 to 5 mL of anesthetic infiltrated into each eyelid quadrant. In small ruminants, the amount of lidocaine 2% used for local anesthetic purposes should remain below the toxic dose (5 mg/kg).

Corneoconjunctival Bacterial Culture

For investigation of suspected bacterial infection of the eyes, specimens obtained by swab of the conjunctiva, cornea, or third eyelid may be cultured to isolate and identify the microorganism(s). Aerobic bacterial cultures are valuable for the diagnosis of infectious keratoconjunctivitis in small ruminants. Antibiotic susceptibility testing of bacteria isolated should be used as a guide for therapy.

Reports describing the normal conjunctival flora of sheep and goats are scarce. In clinically normal sheep, 60% of eye swabs were negative for bacterial growth.¹⁰ In sheep, the most commonly isolated bacteria were similar to Branhamella ovis (previously Neisseria ovis) and were recovered in low numbers. Other frequently isolated organisms were Micrococcus and Streptococcus species. Less common isolates included Corynebacterium, Acinetobacter, Bacillus, Staphylococcus, Pseudomonas, Moraxella, Escherichia coli, and Pasteurella.^1,10,11 Moraxella bovis is not a cause of infectious keratoconjunctivitis in goats.¹¹ However, conflicting reports indicate the possible pathogenicity of Moraxella in ovine keratoconjunctivitis.^12,13

Technique

After gentle retraction of the upper and lower eyelids, the affected conjunctiva or cornea selected area is swabbed using a standard tip or micro tip bacterial culturette (e.g., Copan Transystem swab or BBL CultureSwab, respectively, both made by Copan Diagnostics, Inc., Corona, California). Care should be taken to avoid contamination from the palpebral margins. The sample should immediately be placed in the transport tube or plated onto an appropriate growth medium. Corneoconjunctival swabbing ideally should be performed before application of topical anesthetic or fluorescein stain to the eyes. Topical anesthetic solutions have been reported to have antibacterial effects.¹ Once collected, the sample is submitted to a veterinary microbiology laboratory, with care taken to specify appropriate culture conditions (especially with Mycoplasma spp.) for the presumptive clinical diagnosis. Anaerobic bacteria and fungi are rare ocular pathogens in sheep and goats.¹¹ Fungal cultures usually can be obtained using standard culturettes; however, scraping the tissue with a sterile Kimura cytology spatula and placing the sample directly onto fungal culture media may provide even better results.¹¹

Corneoconjunctival Cytology

Conjunctival cytologic evaluation is valuable for the diagnosis of infectious keratoconjunctivitis. Corneal cytologic examination is useful in characterizing cellular infiltrates such as for bacteria, fungi, and type of inflammatory cells. Cell samples obtained from conjunctival scraping also can be submitted for PCR testing. Before the procedure is undertaken, the cornea and conjunctiva should be anesthetized with topical 0.5% proparacaine; an auriculopalpebral nerve block may be beneficial. If conjunctival follicles are present, these areas should be avoided to obtain a more representative sample. Cytologic samples are obtained either by gently scraping the tissue with a spatula or by using a cytobrush (e.g., Care Express Products, Inc., Cary, Illinois) or regular-size Microbrush (Microbrush International, www.microbrush.com), which is simply rolled over the affected tissue. The cytobrush is inexpensive and very easy to use and creates slides with evenly distributed cells with little crush artifact. Cytologic samples should be very gently rolled or smeared onto a slide and allowed to dry somewhat for 1 or 2 minutes before staining with Diff-Quick or Wright’s or Gram’s stain.^11,13,14 At least one slide should always be left unstained for submission to a veterinary clinical pathologist if required. Viral, mycoplasmal, or chlamydial organisms are poorly identified by Gram staining.¹¹

Healthy conjunctiva is characterized cytologically by numerous epithelial cells, occasional lymphocytes, and rare neutrophils. Intracytoplasmic melanin granules may be observed in dark-faced breeds and can be mistaken for bacteria or chlamydial elementary bodies. Goblet cells are more common in animals with subacute to chronic keratoconjunctivitis but can be a normal finding in corneal or conjunctival cytologic preparations. Neutrophils are the predominant cell type seen in acute conjunctivitis, especially of bacterial or viral origin. A few mononuclear cells, multiple bacteria, and degenerating epithelial cells also should be present. Lymphocytes and plasma cells are more typical to chronic infection. Presence of small numbers of eosinophils in otherwise normal sheep probably indicates a local reaction to environmental irritants.¹⁵

Nasolacrimal Flushing

Signs of nasolacrimal duct obstruction may include moderate to severe epiphora (wet face appearance) that persists for days to weeks or accumulation of mucus or purulent material, in the absence of obvious ocular lesions or mild conjunctivitis, especially medially. Presumptive diagnosis is made on the basis of delayed or absent passage of fluorescein stain from the lacrimal puncta to the nasal punctum. For normograde flushing of the nasolacrimal duct, after application of topical anesthetic (0.5% proparacaine or 2% lidocaine) a 5-mL syringe is filled with buffered saline or eyewash solution, and a nasolacrimal canula or blunted, smooth 20- or 22-gauge stainless steel hypodermic needle is used to canulate the dorsal and ventral lacrimal puncta, near the medial canthus.¹ Fluorescein stain can be added to the irrigating solution to aid visualization of the fluid passage. In larger patients, a small canine urinary catheter or 3.5F flexible polypropylene catheter (e.g., Tom Cat Catheter, Sherwood Medical Industries, Inc., St. Louis, Missouri) may be used for normograde and retrograde flushing. In ruminants, the nasal orifice of the nasolacrimal duct is located caudolateral to the alar fold.

Imperforate lacrimal puncta, congenital atresia of the nasal puncta, or agenesis of the distal nasolacrimal duct should be suspected in young animals presented with bilateral nasolacrimal duct obstruction. Surgical intervention and management should follow published guidelines for small animals.³

Imaging Techniques

Retrobulbar Needle Aspiration

Retrobulbar aspiration is indicated in patients showing progressive exophthalmia. For differentiation of space-occupying mass in the retrobulbar space, aspirated material is submitted for cytologic examination and bacterial culture. The material required and landmarks for needle insertion are similar to those described for the Peterson eye block. Use of ultrasound imaging to guide needle placement usually will yield better diagnostic results.

Cleaning the Eyes and Periocular Tissues

Proper cleaning of the eyes often is done inadequately, usually owing to a lack of a suitable eyewash bottle.² A 6- or 8-ounce plastic goosenecked bottle that produces a sizable stream of buffered saline to the eye is an inexpensive choice for this purpose. Commercially available eyewash squirt-type bottles also can be used. In all cases, the examiner must avoid aiming the stream at the cornea and holding the bottle tip too close to the eye surface, because either may lead to damage of the cornea if the animal moves suddenly. Likewise, the tip should not touch any ocular or periocular tissues, tears, mucus, exudate, or blood owing to the risk of aspirating contaminated fluids back into the eyewash bottle. Mucoid or purulent ocular discharge can be wiped off from the conjunctiva or lid margins with a dry gauze pad or lightly moistened cotton ball. Care must be taken to avoid abrasion of the cornea during this process.

In preparing periocular tissues before surgery (e.g., tarsorrhaphy, eyelid laceration repair, third eyelid flap), it is crucial to ensure protection of and avoid irritation or damage to the eyes. Application of sterile artificial tear ointment helps protect the cornea. Hair removal near the eyes requires particular care and should be done using sharp clipper blades. Repeated lavage using eyewash solution or buffered sterile saline is warranted after clipping to ensure that all hair particles are removed from the eye surface, conjunctival sac, and bulbar conjunctiva of the third eyelid. Povidone-iodine solution (10% solution in sterile saline) is an acceptable detergent for periocular skin preparation. Chlorexidine solutions or scrubs are very irritating to the eye and should be avoided.

Topical Medications

Administration of topical eye medications in small ruminants is relatively easy to accomplish when proper restraint has been obtained but can be challenging in a noncooperative patient. In most cases, ophthalmic ointments and solutions can be applied to the eye surface directly from the tube or bottle. An alternative method of application is by use of a clean gloved fingertip to smear a ½- to 1-inch strip of ointment across the medial canthus or one of the lid margins.² Use of ophthalmic ointments should be avoided if a deep corneal ulcer or corneal perforation is suspected, because such preparations are very irritating to intraocular structures. Liquid medications are administered using one hand below the mandible to direct the patient’s nose upward while the thumb holds the lower lid open. The upper eyelid is retracted with the back of the second hand as it rests on the patient’s head while holding the medication at a distance of 2 to 4 cm from the eye surface. A single drop is then instilled. The purpose of placing the hand on the animal’s head is to allow for simultaneous movement with the animal’s head and decrease the likelihood of contamination or iatrogenically induced ocular trauma from contact of the bottle with the patient’s eye.

The choice of topical eye medication formulation should be based on the specific ocular disease present, product availability, patient demeanor, and ease of treatment for the caretaker. Several ophthalmic medications, either solutions or ointments, are commercially available. Topical ointments have a contact time with the eye of no more than 20 minutes, and solutions even less. Ointments are appropriate for eyelid, conjunctival, and corneal disease with no threat of perforation; however, many owners find ointments more difficult to administer, and their use requires a closer proximity to the eye, risking accidental contact with ocular structures. Solutions can be used for eyelid, nasolacrimal, conjunctival, corneal, and anterior intraocular disease. Systemic therapy is required for posterior intraocular disease (chorioretinitis), retrobulbar or orbital disease, severe blepharitis, and severe dacryocystitis. Frequency of topical treatment depends on the disease and severity of disease being treated. A septic corneal ulcer should be treated every 2 to 4 hours; however, prophylactic treatment of a superficial, noninfected corneal ulcer can be every 6 to 8 hours. Anticollagenase drugs for melting corneal ulcers usually are recommended every 1 to 2 hours. In a mild case of uveitis, one dose of atropine may provide mydriasis for several days, whereas in a severe case of uveitis atropine may be required every 6 hours.

Powdered preparations, sprays, insecticides, mastitis preparations, or injectable antibiotics are, in most cases, very irritating to the eyes because of either the carrier type or an acidic or alkaline pH and should be avoided.

Subpalpebral Ocular Lavage System

For safe and reliable delivery of ophthalmic solutions, a single-hole subpalpebral ocular lavage system (SPL) can be a valuable means of providing topical ocular therapy, especially in a patient with severe ocular disease requiring medication as often as every hour,² or with a very painful eye in which direct manipulation and treatment of the eye can be expected to be difficult. The lavage apparatus is commercially available (Eye Lavage Kit, Mila International, Inc., Erlanger, Kentucky) or can be easily fabricated from polyethylene tubing. Homemade fabrication of an SPL entails cutting a 90-cm-long piece of #190 polyethylene tubing and creating a footplate flange by warming the tube extremity over a match flame until it is softened and then pressing it gently against the flat surface of a scalpel blade.¹⁷

The patient can be sedated before placement of an SPL, if necessary. An auriculopalpebral nerve block as previously described will ease the procedure. The skin at the exit point of the needle tip, in the area of the dorsal to dorsolateral orbital rim, is aseptically prepared and locally anesthetized by infiltrating 2 mL of 2% lidocaine subcutaneously at the site the needle will exit. Using a 22-gauge needle hub (obtained by breaking off the needle while leaving the hub attached), 2 mL of 2% lidocaine is sprayed into and across the dorsal conjunctival fornix. The lavage tubing is secured into a hubless needle. The needle-tubing unit is held in one sterilely gloved hand; the needle tip securely positioned along the veterinarian’s index finger. Before insertion in the palpebral fissure, the veterinarian’s hand is turned such that the index fingernail lies between the cornea and the needle.¹⁷ The operator’s opposite hand should lift the upper eyelid away from the cornea. The finger and needle are then pushed dorsolaterally through the palpebral conjunctiva of the upper eyelid until the needle is touching the inside of the orbital rim. Once properly positioned, the needle is fully inserted through the upper eyelid, just rostral to the orbital rim, and the lid is released. The tubing is gently pulled through until the footplate reaches its destination in the dorsal conjunctival fornix. An alternative placement in the lower, medial conjunctival fornix between the eyelid and nictitans has been described in the horse.¹⁸

Waterproof “butterfly” tape is placed around the tube and sutured to the skin at the lavage exit point from the upper eyelid, to prevent retrograde movement of tubing and footplate and potential damage to the cornea. A 20-gauge, 2-inch intravenous catheter is carefully inserted in the extremity of the polyethylene tubing and then occluded with an injection cap. To avoid tubing damage, the stylet should be retracted 2 to 3 mm from the catheter tip during placement. Additional butterfly suture units are placed along the length of the tubing as needed. To prevent breaks, the remaining free portion of the tubing and catheter is folded (not bent), taped along a wooden tongue depressor or similar light plastic device, and secured to the animal’s halter or dorsum. A regular halter must be left in place until the ocular condition is improved enough to warrant removal of the SPL.

Once the SPL is in place, the dead space in the tubing is measured by slowly injecting eyewash through the system and measuring the amount injected as soon as it is seen coming out the eye. This is the volume of air that should be used to push medication through the tubing. Excessive air pushed through the tubing blows on the cornea, which is uncomfortable for the patient. For each treatment, 0.1 mL of ophthalmic solution is administered through the injection cap of the subpalpebral lavage system.

Medications should be given individually as combining some drugs cause precipitates in the tubing¹⁹ and risks diluting the effectiveness of medications. Minor lid swelling can be expected within 48 hours after SPL placement. The swelling must be differentiated with migration of the footplate subconjunctivally which occurs more commonly with small home-made footplate. Tearing in the lavage tubing as well as loss of the injection cap also can occur. A tubular stockinette can be placed and fitted around the head of the patient to protect the tubing from getting caught on objects and subsequently torn. Improper placement of the lavage system or loosening of the butterfly sutures can result in corneal ulceration as a consequence of rubbing of the footplate on the cornea. It is therefore essential to check for and correct such technical problems: loose tubing should be tightened and an improperly placed SPL must be removed promptly.