SAOphthalmicAtlas&Guide
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The third eyelid, nasolacrimal system, |
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and precorneal tear film |
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Please see Chapter 3 for images of the third eyelid, nasolacrimal system, and precorneal tear film.
1 Third eyelid
○○Also referred to as the nictitating membrane or nictitans.
○○A thin band of tissue located in the ventromedial orbit in cats and dogs.
○○The third eyelid “blinks” across the ocular surface.
■■Direction of movement is diagonal, from ventromedially within the orbit in a dorsolateral direction.
■■In dogs, movement of the third eyelid across the eye is passive, occurring when the eye is retracted into the orbit.
■■In the cat, smooth muscle may contribute to movement.
○○Components
■■Cartilage.
□□T-shaped, with the horizontal portion of the cartilage along the leading edge of the third eyelid and the vertical cartilage perpendicular to this.
■■Lymphoid tissue, particularly on the bulbar surface of the third eyelid.
■■Glandular tissue (gland of the third eyelid), located at the base of the third eyelid.
■■Conjunctiva overlying the anterior and bulbar surfaces.
○○Functions of the third eyelid
■■Physical protection of the ocular surface.
■■Formation of the precorneal tear film.
□□Up to 50% of the aqueous component of the tears is produced by the gland of the third eyelid.
■■Distribution of the precorneal tear film across the ocular surface (occurs each time the third eyelid sweeps across the ocular surface).
■■Removal of debris from the ocular surface (by sweeping across the ocular surface).
■■Immunologic protection to the ocular surface (lymphoid tissue).
○○Diseases of the third eyelid may appear as changes to the third eyelid itself or as surface ocular inflammation secondary to compromised function.
■■Changes to the third eyelid itself include the following:
□□Elevation of the third eyelid
□□Swelling or thickening of the third eyelid (Figure 3.1)
□□Hyperemia of the conjunctiva overlying the third eyelid
□□Depigmentation of the third eyelid (Figure 3.1)
■■Clinical signs resulting from altered third eyelid function include the following:
□□Conjunctival hyperemia (Figure 4.2)
□□Superficial corneal vascularization (Figure 5.1)
□□Corneal edema (Figure 5.5)
□□Corneal fibrosis (Figure 5.8)
□□Corneal melanosis (Figure 5.6)
□□A dry or roughened appearance to the cornea (Figure 5.1) 2 The nasolacrimal drainage apparatus
○○For each eye, components are as mentioned below:
■■An orbital lacrimal gland and the gland of the third eyelid
□□These glands produce the aqueous component of the precorneal tear film.
■■Lacrimal puncta (Figure 2.1)
□□One punctum is located in the dorsal eyelid and one is in the ventral eyelid; each is approximately 2 mm from the medial canthus.
□□These are the entry points to the nasolacrimal canaliculi.
■■Nasolacrimal canaliculi
□□Extending from each of the puncta, the canaliculi merge to form the nasolacrimal sac, which is a dilated entrance to the nasolacrimal duct.
■■Nasolacrimal duct
□□Extends from the lacrimal bone, through the maxillary bone, into the nasal mucosa, to exit within the nasal cavity.
□□Terminates at the nasal punctum within the nasal cavity.
■■Nasal punctum
□□A small hole in the nasal mucosa that is the exit point of the nasolacrimal drainage apparatus
□□Located approximately 10 mm proximal to the opening of the corresponding nare, on the floor of the nasal cavity.
Small Animal Ophthalmic Atlas and Guide, First Edition. Christine C. Lim.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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○○Functions of the nasolacrimal drainage system:
■■Production of the aqueous precorneal tear film (by the orbital and third eyelid glands).
■■Nutrition and oxygenation of the ocular surface (by the precorneal tear film).
■■Immune protection of the ocular surface (antimicrobial substances are dissolved within the precorneal tear film.)
■■Lubrication of the ocular surface (by tears).
■■Disposal of wastes (during each blink, older tears are pushed into the lacrimal puncta.)
○○Clinical signs of obstruction of the nasolacrimal apparatus
include epiphora or other ocular discharge (mucoid and mucopurulent).
3 The precorneal tear film
○○Made up of three main components, which are as follows:
■■Mucin
□□Produced by conjunctival goblet cells (see page 91).
□□Functions of mucin:
——Adheres tears to the cornea.
——Smooths irregularities of the corneal surface.
——Binds particulate matter for disposal.
——Stabilizes the tear film to prevent early evaporation.
■■Aqueous
□□Produced by the third eyelid gland and the orbital lacrimal gland.
□□Functions:
——Hydrates the ocular surface.
——Lubricates movement of eyelids across the ocular surface.
——Immunologic functions (dissolved antimicrobial substances within the aqueous tears).
——Nutrition to the cornea.
——Removal of waste from the ocular surface.
■■Lipid
□□Produced by Meibomian glands.
□□Function: to prevent early evaporation of the precorneal tear film.
——Tear film deficiency or dysfunction increases friction between the eyelids and the cornea and promotes drying of the cornea. Therefore, clinical signs of tear film deficiency and dysfunction are compatible with clinical signs of ocular surface inflammation, including the following:
■■Blepharospasm
■■Conjunctival hyperemia
■■Superficial corneal vascularization (Figure 5.1)
■■Corneal edema
■■Corneal fibrosis
■■Corneal melanosis
■■A dry, roughened corneal surface (Figure 5.1)
■■Mucoid or mucopurulent ocular discharge (Figure 5.1) Disorders of the third eyelid, nasolacrimal system, and pre corneal tear film can alter the production, distribution, and
removal of tears. This affects protection, nourishment, and hydration of the eye, which is why disorders of these structures can have a significant impact on corneal and conjunctival health. Effects range from mild to marked surface ocular irritation and inflammation (superficial keratitis, conjunctivitis, and keratoconjunctivitis) (see Chapters 13 and 14) and can even include corneal ulceration (see pages 105 to 112).
Diseases of the third eyelid and lacrimal
system
Third eyelid gland prolapse (“cherry eye”)
What it is
•Displacement of the gland of the third eyelid from its normal position in the ventromedial orbit.
Predisposed individuals
•Third eyelid gland prolapse occurs in young animals, usually manifesting by 1–2 years of age.
○○Third eyelid neoplasia should be ruled out when older animals present with apparent third eyelid gland prolapse.
•This occurs most often in dogs.
○○Third eyelid gland prolapse is seen most often in brachycephalic dogs and dogs with excessive facial skin (e.g., mastiff, Newfoundland, and St. Bernard).
•Prolapse of the third eyelid gland is uncommon in cats.
○○Burmese are affected most often.
•Individuals with eversion of the third eyelid cartilage (Figure 3.2) are predisposed to development of third eyelid gland prolapse.
○○The vertical portion of the third eyelid cartilage bends and causes the third eyelid to fold on itself.
○○This encourages third eyelid gland prolapse by placing abnormal forces on the gland and tissues surrounding it.
○○Predisposed breeds include the great Dane, Newfoundland, and German shorthaired pointer.
Defining characteristics
•A swollen, pink round mass (the gland of the third eyelid) is seen at the medial canthus, anterior to the eye (Figure 3.3).
○○The surface of the gland overall is relatively smooth.
•The leading edge of the third eyelid is ventral to the prolapsed gland and may or may not be visible (Figure 3.4).
•Conjunctivitis is usually present, ranging from mild to marked.
○○Conjunctival hyperemia
○○Chemosis
○○Mucoid ocular discharge
•Cartilage eversion, if present, may or may not be visible on initial examination.
○○A very swollen third eyelid gland can hide the bend in the cartilage.
Chapter 12 The third eyelid, nasolacrimal system, and precorneal tear film 85
Clinical significance
•A prolapsed gland is inflamed and uncomfortable.
•Chronic inflammation leads to fibrosis of the glandular tissue.
○○Chronic fibrosis decreases the amount of functional glandular tissue, predisposing to KCS.
•In older animals, a prolapsed third eyelid gland may be a symptom of orbital neoplasia.
Diagnosis
• The diagnosis is based on clinical appearance.
Treatment
•The goals are to reduce inflammation of the third eyelid gland, to replace the gland in the orbit, to maintain the gland in this position, and to minimize the effects of gland prolapse on surface ocular hydration.
•Anti-inflammatory therapy should be employed preoperatively and postoperatively.
○○Improves patient comfort.
○○Reduces gland swelling, facilitating its repositioning.
○○Decreases postsurgical inflammation.
○○Use both ophthalmically applied and systemically administered drugs.
■■For example, prednisolone acetate 1% ophthalmic suspension or dexamethasone (available as a 0.1% solution, 0.05% ointment, or in combination with neomycin and polymyxin B in both ointment and suspension forms) applied to the affected eye three to four times daily prior to surgery and for 7–14 days postoperatively. □□ Do not use if corneal ulceration is present.
■■For example, oral veterinary-labeled NSAIDs at the labeled dose prior to surgery and for 7–10 days postoperatively.
•Tear film replacement.
○○Corneal exposure, keratitis, or corneal ulceration can occur when the prolapsed gland prevents full eyelid closure.
○○Chronic conjunctivitis leads to instability and premature evaporation of the precorneal tear film, causing cornea drying, development of keratitis, and a predisposition to corneal ulceration.
•A prolapsed third eyelid gland, in the absence of concurrent neoplastic disease, should not be excised.
○○Excision is an unacceptable treatment that greatly increases the potential for development of KCS.
•The gland should be replaced to its original position within the ventromedial orbit.
○○Specific surgical techniques are numerous and published elsewhere. Most involve either tacking the gland down (e.g., to the orbital periosteum) with nonabsorbable suture or tucking the gland into a pocket created in the conjunctiva.
•Third eyelid cartilage eversion should be corrected at the time of third eyelid gland replacement.
○○Various techniques are published elsewhere and involve resection of the bent portion of the cartilage or use of cautery to alter the shape of the cartilage.
Prognosis
•For prolapse of short duration, the prognosis for replacement of the gland is good.
○○The prognosis is guarded when the gland has been chronically prolapsed because recurrence is more likely.
○○The prognosis is guarded for patients that have undergone previous surgical attempts at gland replacement because recurrence is more likely.
•Recurrence is the most common complication.
○○Recurrence is more likely to occur in breeds that are predisposed to gland prolapse.
•Surgery should be repeated if the prolapse recurs.
•In some cases, surgery may have to be repeated several times.
○○Individuals experiencing multiple prolapses should be referred to a veterinary ophthalmologist for treatment.
•Dogs with third eyelid gland prolapse are at risk of KCS even with successful replacement of the gland.
○○The risk of KCS is higher when gland prolapse is more chronic or when multiple surgeries have been performed, in part due to the large amount of scar tissue that develops.
○○The STT values should be monitored for several months following gland replacement.
○○Therapy for KCS should be initiated if the STT values fall below 15 mm/min (see pages 102 to 103).
Third eyelid neoplasia
What it is
•Neoplasms arising from the third eyelid or metastasizing to the third eyelid.
Predisposed individuals
•Dogs and cats of any age, breed, or sex can develop third eyelid neoplasia.
Defining characteristics
•Superficial neoplasms are usually small, raised masses arising from the conjunctiva of the anterior or bulbar surfaces of the third eyelid (Figure 3.5).
•Neoplasms of the gland of the third eyelid may initially appear as a prolapse of the third eyelid gland.
•Because of their location, neoplasms of the gland may not present for evaluation until they are quite large.
•These are often fleshy orbital masses located anterior to the eye but posterior to the third eyelid (Figure 3.6).
•Although these originate from the ventromedial orbit, this can be difficult to determine when the tumor is large.
Clinical significance
•Small, benign, superficial neoplasms are often clinically insignificant (see pages 95 and 96 for conjunctival neoplasia).
•Malignant neoplasms can be locally invasive.
•Third eyelid neoplasms can also be a part of a larger, systemic neoplastic process.
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•Many different third eyelid neoplasms have been reported.
○○Some malignant and/or invasive neoplasms include adenocarcinoma (Wilcock & Peiffer, 1988), lymphoma (Hong et al., 2011; Newkirk & Rohrbach, 2009), melanoma (Schobert et al., 2010), and squamous cell carcinoma (Lavach & Snyder, 1984).
○○Some benign neoplasms include papilloma, hemangioma/ hemangiosarcoma (Pirie & Dubielzig, 2006; Pirie et al., 2006), and extramedullary plasmacytoma (Perlmann et al., 2009).
Diagnosis
•The diagnosis of third eyelid neoplasia is made by visualizing a mass on the anterior or bulbar surface of the third eyelid, a diffuse thickening of the third eyelid and/or third eyelid gland, or a mass arising from the third eyelid gland.
○○Masses arising from the gland of the third eyelid tend to be significantly larger and more inflamed than a gland that is simply prolapsed.
○○Masses arising from the gland of the third eyelid tend to appear much more irregular in texture or shape when compared with a gland that is simply prolapsed.
•Histopathology is required to diagnose the type of neoplasm affecting the third eyelid.
○○Small conjunctival masses can be removed completely and submitted as excisional biopsy samples. The technique for excision of small masses is listed below:
■■A cotton swab is saturated with proparacaine 0.5% ophthalmic solution or 2% lidocaine jelly and held over the biopsy site for 1 min. This provides anesthesia to the conjunctival surface.
■■Small forceps, such as Bishop Harmon forceps, are used to grasp the conjunctiva adjacent to the mass. The forceps are pulled up to tent the conjunctiva, elevating the mass and some normal surrounding conjunctiva.
■■At the base of the tent, where the conjunctiva attaches to the surface of the third eyelid and below the level of the mass, the conjunctiva is snipped with tenotomy scissors.
■■The sample is placed onto a flat surface such as a tongue depressor, a piece of paper, or the inside of a tissue cassette to keep it flat and maintain orientation.
■■The sample with the tongue depressor/paper/tissue cassette is then placed into 10% neutral buffered formalin and submitted for histopathology.
○○For larger masses, incisional biopsies can be performed before attempting complete removal.
•Advanced imaging, such as an MRI or a CT, is recommended for larger masses, especially those involving the gland, prior to pursuing removal.
○○Imaging helps to determine the extent of the mass within the orbit and whether more aggressive surgery or adjunctive therapies are required.
Treatment
•The goal of treatment is to completely remove the neoplasm while minimizing damage to adjacent structures.
•For small conjunctival masses:
○○ If histopathology indicates a benign lesion and complete removal, then the excisional biopsy is adequate therapy.
○○If histopathology indicates a benign lesion and incomplete removal, options include the following:
■■Monitoring for regrowth.
■■Adjunctive therapy at the site of mass removal.
■■Resection of a larger area of conjunctiva to remove any remaining neoplastic tissue.
○○If histopathology indicates a malignant lesion, monitoring for regrowth, adjunctive therapy, and further resection (including removal of the third eyelid) are all options.
■■Which option to choose is influenced by tumor type, whether the resection was complete or incomplete, and imaging that indicates tumor extent.
■■Rule out metastatic disease (e.g., thoracic radiographs or CT, abdominal ultrasound or CT, and lymph node aspirates).
•For larger masses where incisional biopsy was used to obtain a diagnosis, the treatment depends on the tumor type.
○○Further surgical resection to obtain clean margins can include third eyelid removal, exenteration, or more invasive surgery that may require referral.
○○Adjunctive therapies such as radiation therapy, chemotherapy, or a combination of these may be required instead of or in addition to surgical excision.
Prognosis
•The prognosis is very good following removal of benign neoplasms.
•For malignant neoplasms, such as adenocarcinoma, the prognosis is good if the tumor is confined to the third eyelid and excision is complete.
•If obtaining clean margins at removal is challenging, then prognosis for malignant neoplasms is guarded.
○○If clean margins have not been obtained, recurrence is likely and prognosis for overall survival depends on the tumor type (this determines behavior and responsiveness to other therapies.)
Additional information
•Prolapse of the third eyelid gland is a disease of young animals (usually the first 1–2 years of life). If this condition is diagnosed in older animals, third eyelid neoplasia should be suspected and diagnostics pursued.
•KCS can occur following third eyelid removal. Periodic monitoring of the STT values is recommended so that if KCS develops, it is diagnosed and treated early.
Chapter 12 The third eyelid, nasolacrimal system, and precorneal tear film 87
Nasolacrimal duct obstruction
What it is
•Blockage at any point along the nasolacrimal drainage system that prevents flow of tears from the conjunctival sac into the nasal cavity.
•The blockage may be due to a physical impairment of drainage (e.g., foreign material trapped within the nasolacrimal duct).
•The blockage can also be a result of conformation (e.g., ventromedial entropion causing misalignment of the punctum with the ocular surface such that tears are unable to enter the nasolacrimal duct).
Predisposed individuals
•Brachycephalic individuals are predisposed to nasolacrimal duct blockage as a result of ventromedial entropion that is part of their conformation (see pages 62 and 63 for discussion of brachycephalic ocular syndrome).
•Hunting dogs and other highly active, outdoor dogs have a higher likelihood of developing nasolacrimal duct obstruction following entrapment of foreign material within the duct.
Defining characteristics
•Epiphora and tear staining near the medial canthus of the affected eye.
○○If dacryocystitis is present, there may also be mucoid or mucopurulent discharge arising from the nasolacrimal puncta.
•If the obstruction is due to eyelid conformation, entropion of the medial aspect of the ventral eyelid is visible.
Clinical significance
•Clinical significance depends on both the amount of facial moisture resulting from the nasolacrimal duct blockage and the underlying cause of the obstruction.
•Mild periocular wetness may not cause clinical problems, but as periocular moisture increases, the risk of dermatitis rises.
•Potential causes of obstruction:
○○Punctal atresia
■■Congenital absence of the puncta.
○○Imperforate punctum
■■A congenital defect where a thin layer of conjunctiva occludes the punctal opening.
○○Obstruction of the nasolacrimal punctum secondary to conformational entropion.
■■Common in brachycephalic individuals.
○○Nasolacrimal duct atresia
■■Congenital absence of all or a portion of the nasolacrimal duct.
○○Foreign body obstruction
○○Dacryocystitis
■■Swelling of the nasolacrimal drainage apparatus can occlude the nasolacrimal duct.
○○Scar tissue
■■Scarring following conjunctivitis can result in stenosis or occlusion of the puncta.
■■Scarring following dacryocystitis can result in stenosis or occlusion of the nasolacrimal duct.
○○Neoplasia
■■Neoplasia of the surrounding skull structures can cause obstruction.
○○Trauma
■■For example, the nasolacrimal drainage system components can be damaged with eyelid laceration or skull fractures.
•In many cases, the cause of the nasolacrimal duct obstruction cannot be identified.
○○Clinical significance then depends on the degree of epiphora and periocular moisture (mentioned earlier) and whether this is causing discomfort to the patient.
•Regardless of underlying cause, many pet owners, particularly those with white dogs, find epiphora esthetically objectionable.
Diagnosis
•Diagnostics are aimed at (1) confirming obstruction and (2) determining the underlying cause of obstruction.
1. Confirming obstruction
•Jones test
○○A positive Jones test occurs when fluorescein placed into the conjunctival sac is visualized at the ipsilateral nostril or in the mouth (Figures 3.7 and 3.8).
■■This usually occurs within two minutes of fluorescein placement into the conjunctival sac.
○○A positive Jones test rules out nasolacrimal duct obstruction.
○○The Jones test is negative if fluorescein fails to appear at the nostril or in the mouth (Figure 3.8).
○○A negative Jones test supports conformational or physical obstruction of the duct.
•Nasolacrimal duct flush
○○Should be performed when the Jones test is negative.
•For obstructions secondary to physical obstruction, attempts at flushing the nasolacrimal ducts are either difficult (resistance encountered during attempts at flushing) or unsuccessful.
•For conformational obstructions, the Jones test is negative but the nasolacrimal duct is easily flushed.
2. Determining the cause of obstruction
•Visualization of eyelid puncta can rule out obstructions at this level.
•Imaging.
○○Indicated when nasolacrimal duct flushing is unsuccessful.
○○Dental radiographs may identify any maxillary or tooth root lesions contributing to obstruction.
○○Skull radiographs with contrast injected into nasolacrimal duct.
■■Can identify bony lesions contributing to obstruction.
■■Can identify the site of obstruction, dilations within the nasolacrimal duct, or perforation of the nasolacrimal duct.
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○○Computed tomography with contrast injected into nasolacrimal duct.
■■Can identify bony lesions contributing to obstruction.
■■Can identify the site of obstruction, dilations within the nasolacrimal duct, nature of obstruction, perforation of the nasolacrimal duct, or other physical alterations of the nasolacrimal duct.
■■Image quality and level of detail visible is superior to those of radiographs.
■■Indicated when previous tests have not identified the nature of the obstruction.
•Cytology and culture and sensitivity of any discharge are also recommended to identify infectious components.
Treatment
•The main goal of treatment is to reestablish patency of the nasolacrimal duct.
•Treatment must therefore address the underlying cause of obstruction.
○○Punctal and nasolacrimal duct atresia are addressed surgically, and referral is advised.
■■Treatment usually involves creating alternative drainage pathways.
○○Imperforate punctum
■■Flushing of the nasolacrimal duct through the other, patent punctum can result in a visible conjunctival bulge where the imperforate punctum is present.
■■If this bulge is visible, the conjunctiva can be carefully snipped with small scissors to open up the punctum.
■■Ophthalmically applied corticosteroid suspensions (e.g., prednisolone acetate or dexamethasone) are applied to the conjunctival sac two to four times daily for 7–10 days to inhibit scarring and reocclusion of the punctum.
○○Conformation can be improved surgically by repairing ventromedial entropion.
○○Foreign body obstruction requires referral for surgical removal.
○○Dacryocystitis should be treated with systemic veterinarylabeled NSAIDs and ophthalmically applied antibiotics (chosen according to cytology and culture and sensitivity).
○○Treatment for neoplasia is based on the type of neoplasia present and extensiveness of the neoplasm.
○○Following repair of skull fractures or eyelid lacerations, and for cases of obstruction secondary to scarring, the patient may require referral for surgical reconstruction of the nasolacrimal duct.
Prognosis
•Prognosis depends on the underlying cause.
•The prognosis is good for removing the obstruction when it is secondary to conformation, imperforate punctum, or dacryocystitis.
•The prognosis is fair for establishing and maintaining patency when surgery is required to reconstruct a new drainage pathway.
•Postoperative scarring can lead to future obstructions.
Additional information
•In many cases, pet owners seek treatment because the epiphora and tear staining are bothersome. In many cases, especially when epiphora is due to conformation, tearing can only be reduced, but not completely eliminated, by treatment.
○○Managing expectations is important.
•Perform the Jones test on one eye at a time, with several minutes between each eye.
○○This way, if fluorescein appears in the mouth instead of at the nares, one can determine from which side the fluorescein emerged (and therefore which side is patent).
Tear film disorders—KCS
•Because many of the clinical signs of KCS are corneal changes, this condition is discussed in Chapter 14.
•Please see pages 101 to 103 in Chapter 14.
Qualitative tear film abnormality
What it is
•An abnormality of the lipid or mucin portion of the precorneal tear film resulting in instability of the precorneal tear film, premature evaporation of the precorneal tear film, and ocular surface irritation.
Predisposed individuals
•Cats and dogs with active or recent conjunctivitis are likely to have a mucin deficiency of the precorneal tear film.
○○Inflammation of the conjunctiva leads to atrophy of the conjunctival goblet cells (Johnson et al., 1990; Lim et al., 2009; Moore & Collier 1990).
•Cats and dogs with blepharitis are likely to have abnormalities of the lipid portion of the tear film.
○○Inflamed Meibomian glands produce abnormal lipid products (Nelson et al., 2011).
Defining characteristics
•Clinical signs are consistent with those of surface ocular irritation, which are as follows:
○○Blepharospasm
○○Mucoid ocular discharge
○○Conjunctival hyperemia
○○Superficial corneal vascularization
•The tear production, as measured by the STT, is usually within normal limits.
Clinical significance
•Although the aqueous component of the precorneal tear film is adequate, premature evaporation of the tear film leads to drying of the corneal surface.
Chapter 12 The third eyelid, nasolacrimal system, and precorneal tear film 89
•The chronic irritation resulting from a dry corneal surface is uncomfortable.
•The chronic irritation resulting from a dry corneal surface predisposes to keratoconjunctivitis and even corneal ulceration.
•Underlying causes of blepharitis and conjunctivitis may be present and, if so, should be treated (see pages 80 to 81 and 91 to 95 in Chapters 11 and 13).
•Mucin deficiency can result from conjunctivitis, but can also perpetuate conjunctivitis after the original cause of inflammation has resolved.
○○Treatment of the mucin deficiency is then needed to decrease conjunctival inflammation.
•Mucin deficiency can persist for weeks after clinically visible signs of conjunctivitis have resolved (Lim et al., 2009).
Diagnosis
•When active blepharitis is present, an abnormality of the lipid portion of the tear film should be assumed.
•When active conjunctivitis is present, mucin deficiency should be assumed.
•While meibometry exists and can be used to assess tear film lipids, it is not available for the practice setting.
•Goblet cell atrophy can be diagnosed by conjunctival biopsy.
○○See page 96 in Chapter 13 for technique.
•The tear film breakup time (TFBUT) is an assessment of tear film stability and is considered an indirect measure of the mucin content of the precorneal tear film. It is less invasive to perform than conjunctival biopsy.
○○This is a measurement of how long the tears remain as a stable film over the cornea.
○○Therefore, a shorter TFBUT means the tear film is less stable (evaporates early), while a longer TFBUT indicates a very stable tear film (it remains as an intact film over the cornea.)
○○Normal TFBUT for cats ranges from approximately 12 to 21 seconds (Cullen et al., 2005).
○○Normal TFBUT for dogs ranges from approximately 15 to 20 seconds (Moore et al., 1987).
○○Qualitative tear film deficiency is diagnosed when the TFBUT is shorter than the reference range and clinical signs of surface ocular disease are present.
○○Technique for TFBUT:
■■This test should be performed in a darkened room, as for the ophthalmic examination. It requires the use of a slit lamp for magnification and cobalt blue light, a stopwatch or other method of timing, fluorescein stain, and at least one assistant to restrain the pet and control the timer. Timing begins when the tears are first spread over the cornea and ends when the first sign of evaporation (visible as a break in the tear film) is seen.
■■Place a drop of concentrated fluorescein solution into the conjunctival sac, then close the eye.
■■Position the slit lamp and the timer so that they are ready for use. Timing will begin when the eyelids are opened.
■■With the slit lamp in place, open the eyelids and observe the dorsolateral corneal surface (this is where timing begins.) Continue to observe the cornea until the first sign of evaporation is seen.
■■The corneal surface will initially appear green due to the fluorescein in the tear film that covers the corneal surface. Eventually, a black spot will appear within the tear film. This represents the first spot of evaporation within the precorneal tear film. This is when timing ends.
Treatment
•If active conjunctivitis is present, it should be treated as per the discussion on pages 92 to 95 in Chapter 13.
○○Ophthalmically applied CsA (Optimmune®) is a good choice for treating the qualitative tear film deficiency associated with conjunctivitis because it increases mucin stores within the conjunctiva (Moore et al., 2001).
○○Application of mucinomimetic tear film replacements will also reduce corneal drying and irritation.
○○Hyaluronan 0.15, 0.25, or 0.30% (I-Drop®Vet) is a mucinomimetic tear film replacement.
■■Hyaluronan has superior corneal retention time when compared with other lacrimomimetics (Snibson et al., 1992).
■■Preservative-free formulations are preferred over multi-dose vials because ophthalmic preservatives can be toxic to the epithelial surface (especially with frequent application).
■■Administer two to four times daily (or more, if preserva- tive-free formulation is used) and continue for 3–4 weeks beyond resolution of clinical signs.
•If active blepharitis is present, it should be treated as per the discussion on pages 80 and 81 in Chapter 11.
○○Application of tear film substitutes that mimic the lipid portion of the tears will reduce corneal irritation and discomfort.
○○These are generally available as ophthalmic ointments.
○○The ingredients that mimic lipid include petrolatum, lanolin, and mineral oil.
○○Administer two to four times daily during active blepharitis.
Prognosis
•Following resolution of the original inflammatory insult (blepharitis and conjunctivitis), the prognosis for resolution of the qualitative tear film abnormality is very good.
○○Because recovery of the goblet cells is delayed, resolution of mucin deficiency lags behind resolution of clinical conjunctivitis.
Other third eyelid disorders—pannus
Please see pages 104 to 105 in Chapter 14.
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References
Cullen, CL, et al. 2005. Tear film breakup times in young healthy cats before and after anesthesia. Veterinary Ophthalmology. 8(3): 159–165.
Hong, IH, et al. 2011. Mucosa-associated lymphoid tissue lymphoma of the third eyelid conjunctiva in a dog. Veterinary Ophthalmology. 14(1):61–65.
Johnson, BW, et al. 1990. Effects of inflammation and aqueous tear film deficiency on conjunctival morphology and ocular mucus composition in cats. American Journal of Veterinary Research. 51:820–824.
Lavach, JD & Snyder, SP. 1984. Squamous cell carcinoma of the third eyelid in a dog. Journal of the American Veterinary Medical Association. 184(8):975–976.
Lim, CC, et al. 2009. Effects of feline herpesvirus type 1 on tear film break-up time, Schirmer tear test results, and conjunctival goblet cell density in experimentally infected cats. American Journal of Veterinary Research. 70(3):394–403.
Moore, CP & Collier, LL. 1990. Ocular surface disease associated with loss of conjunctival goblet cells in dogs. Journal of the American Animal Hospital Association. 26(5):458–466.
Moore, CP, et al. 1987. Density and distribution of canine conjunctival goblet cells. Investigative Ophthalmology and Visual Science. 28(12): 1925–1932.
Moore, CP, et al. 2001. Effect of cyclosporine on conjunctival mucin in a canine keratoconjunctivitis sicca model. Investigative Ophthalmology and Visual Science. 42(3):653–659.
Nelson, JD, et al. 2011. The international workshop on meibomian gland dysfunction: report of the definition and classification subcommittee. Investigative Ophthalmology and Visual Science. 52(4): 1930–1937.
Newkirk, KM & Rohrbach, BW. 2009. A retrospective study of eyelid tumors from 43 cats. Veterinary Pathology. 46(5):916–927.
Perlmann, E, et al. 2009. Extramedullary plasmacytoma of the third eyelid gland in a dog. Veterinary Ophthalmology. 12(2):102–105.
Pirie, CG & Dubielzig, RR. 2006. Feline conjunctival hemangioma and hemangiosarcoma: a retrospective evaluation of eight cases (1993–2004). Veterinary Ophthalmology. 9(4):227–231.
Pirie, CG, et al. 2006. Canine conjunctival hemangioma and hemangiosarcoma: a retrospective evaluation of 108 cases (1989–2004).
Veterinary Ophthalmology. 9(4):215–226.
Schobert, CS, et al. 2010. Feline conjunctival melanoma: histopathological characteristics and clinical outcomes. Veterinary Ophthalmology. 13(1):43–46.
Snibson, GR, et al. 1992. Ocular surface residence times of artificial tear solutions. Cornea. 11(4):288–293.
Wilcock, B & Peiffer, R. 1988. Adenocarcinoma of the gland of the third eyelid in seven dogs. Journal of the American Veterinary Medical Association. 193(12):1549–1550.
13 Conjunctiva
Please see Chapter 4 for images of the conjunctiva.
•The conjunctiva covers the external ocular surface, except for the cornea (Figure 4.1).
○○The conjunctiva overlying the sclera is referred to as the bulbar conjunctiva.
○○The conjunctiva that lines the inner surfaces of the eyelids is referred to as the palpebral conjunctiva.
○○The dorsal conjunctival fornix is the area at which the dorsal palpebral and the dorsal bulbar conjunctiva merge, and the ventral conjunctival fornix is the area at which the ventral palpebral and the ventral bulbar conjunctiva merge.
○○The conjunctiva also covers the anterior and posterior surfaces of the third eyelid.
•Components of the conjunctiva include the following:
○○Blood vessels
○○Nerves
○○Lymphoid tissue
○○Lymphatic vessels
○○Goblet cells
○○Fibrous tissue
○○Melanocytes
•Various microbes inhabit the conjunctival surface in health.
○○The population consists of a mixture of Gram-positive and Gram-negative bacteria, with greater numbers of Grampositive aerobes (Gerding & Kakoma, 1990).
○○Staphylococcus spp. predominate (Gerding & Kakoma, 1990).
○○Other bacteria that have been found in the healthy conjunctival sac include Streptococcus spp., Corynebacterium spp., Bacillus spp., Neisseria spp., and Pseudomonas spp. (Gerding & Kakoma, 1990)
○○Chlamyophila felis has been recovered from the conjunctival sacs of normal cats (Low et al., 2007).
○○Mycoplasma spp. have been recovered from the conjunctival sacs of normal cats and dogs (Campbell et al., 1973; Rosendal, 1973).
○○Fungal organisms are occasionally isolated from the conjunctival sacs of healthy dogs and cats (Samuelson et al., 1984).
•Functions of the conjunctiva:
○○Conjunctival goblet cells produce the mucous component of the precorneal tear film.
■■Mucin stabilizes the precorneal tear film and prevents early evaporation.
■■Goblet cells are most highly concentrated in the ventromedial conjunctival fornix.
○○Immunologic protection to the ocular surface.
■■By the conjunctiva-associated lymphoid tissue.
○○Allows movement of the eye while minimizing friction between it and the eyelids.
•Signs of conjunctival disease include the following:
○○Ocular discharge: mucoid, serous, sanguineous, or purulent.
○○Conjunctival hyperemia (Figures 4.2 and 4.3)
○○Chemosis (Figures 4.3 and 4.4)
○○Conjunctival lymphoid follicle formation (Figure 4.5)
○○Thickening of the conjunctiva (Figure 4.6)
○○Mass formation on the conjunctiva (Figure 4.7)
○○Subconjunctival hemorrhage (Figure 4.8)
Diseases of conjunctiva
Canine conjunctivitis
What it is
• Conjunctivitis refers to the inflammation of the conjunctiva.
Predisposed individuals
• Dogs of any age, breed, or sex can develop conjunctivitis.
Defining characteristics
•Clinical signs of conjunctivitis that are consistently present include the following:
○○Ocular discharge, usually mucoid
○○Conjunctival hyperemia (Figures 4.2 and 4.3)
•Signs of conjunctivitis that are variably present include the following:
○○Chemosis (Figures 4.3 and 4.4)
Small Animal Ophthalmic Atlas and Guide, First Edition. Christine C. Lim.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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○○Conjunctival lymphoid follicle formation (Figures 4.5 and 4.9)
○○Hemorrhage (Figure 4.8)
○○Conjunctival thickening (Figure 4.6)
•Neoplastic conjunctivitis tends to have one of two appearances:
○○Diffuse thickening of the conjunctiva (Figure 4.6).
○○Mass lesions elevated from the conjunctival surface (Figures 4.7 and 4.10).
Clinical significance
•Conjunctivitis is irritating and causes patient discomfort.
•Chronic conjunctivitis leads to goblet cell atrophy, mucin deficiency in the precorneal tear film (qualitative tear film abnormality or deficiency, see pages 88 and 89), and instability of the precorneal tear film.
○○Instability of the precorneal tear film is associated with early evaporation of tears. This in turn dries the ocular surface in spite of adequate or even excessive tear production.
○○Tear film instability perpetuates further ocular surface irritation and inflammation, even if the inciting cause of conjunctivitis is no longer present.
•Canine conjunctivitis tends to be noninfectious in etiology.
•Conjunctivitis has many potential causes. Some include the following:
○○Idiopathic
○○Immune-mediated
■■Atopy (Pena et al., 2008)
■■Follicular conjunctivitis in young dogs (Pena et al., 2008)
□□This is thought to be due to an immature immune system
■■KCS (see page 101 to 103) (Kaswan & Salisbury, 1990)
■■Pannus or chronic superficial keratitis (see pages 104 and 105) (Bedford & Longstaffe, 1979)
■■Neoplastic (see pages 95 and 96 for conjunctival neoplasia)
○○Trauma
■■Including entropion, aberrant hairs (distichiae, ectopic cilia, and trichiasis), and eyelid masses
Diagnosis
• Diagnosis is two-part and involves the (1) diagnosis of conjunctivitis and (2) diagnosis of the underlying cause.
1 Conjunctivitis is diagnosed by observation of clinical signs as aforementioned.
2 Determining the underlying cause of conjunctivitis requires careful ophthalmic examination and, often, additional diagnostic testing.
•Ophthalmic examination will rule out eyelid abnormalities such as entropion, aberrant hairs (distichiae, ectopic cilia, trichiasis), eyelid masses.
•The STT will determine if low aqueous tear production (see pages 101 to 103 for KCS) is contributing to conjunctivitis.
•The tear film breakup time (TFBUT) can identify if a qualitative tear film abnormality is present. (See pages 88 and 89 in Chapter 12.)
•In the absence of eyelid and precorneal tear film abnormalities, the underlying cause of conjunctivitis is often not definitively identified.
•Conjunctival culture is often of limited utility.
○○Bacteria can be cultured from the conjunctiva of dogs and cats without ocular disease.
○○Primary bacterial conjunctivitis is rare in dogs.
■■Bacterial overgrowth can occur secondary to other etiologies such as KCS.
•Cytology of conjunctival scrapings can be nondiagnostic, but also can be more informative than culture.
○○A diagnosis of atopic conjunctivitis in dogs can be supported by changes in cells visualized on cytology.
○○Neoplastic cells can be identified by cytology.
•Histopathologic evaluation of a conjunctival sample is often the most useful diagnostic test.
○○Indicated for severe conjunctivitis, when neoplasia is suspected, or when conjunctivitis is unresponsive to therapy.
○○See page 96 under conjunctival neoplasia for technique of conjunctival biopsy.
○○In dogs, lymphoplasmacytic conjunctivitis without an obvious etiology is a very common diagnosis.
○○Histopathology is very useful for ruling out the uncommon and potentially more serious causes of conjunctivitis.
Treatment
•The goal of treatment is to eliminate conjunctival inflammation.
•Treatmentcanbedividedinto(1)nonspecificanti-inflammatory therapy, (2) therapy directed at the underlying cause of conjunctivitis (if identified), and (3) supplementation of the precorneal tear film.
1 Anti-inflammatory therapy
○○This is indicated whether or not the underlying cause is identified.
○○Anti-inflammatory therapy involves ophthalmically applied corticosteroids, CsA, or a combination of these drugs.
■■Corticosteroids
□□Prednisolone acetate ophthalmic suspension 1% or dexamethasone (0.1% ophthalmic solution or 0.05% ophthalmic ointment or, if antibiotics needed, in combination with neomycin and polymyxin B in both ointment and suspension forms).
□□Do not use when infectious etiologies are suspected.
□□Do not use in the presence of corneal ulceration.
□□Dose: one drop of suspension/solution or 1/4″ strip of ointment applied to the affected eye two to four times daily, as determined by the severity of inflammation. As clinical signs improve, the dose should be gradually tapered.
□□Improvement is usually noted within 1–2 weeks of starting treatment.