Ординатура / Офтальмология / Английские материалы / Small Animal Ophthalmology Secrets_Riis_2002
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Corneal Dystrophies |
Figure 6. This endothelial dystrophy caused so much edema centrally that the cornea bulged forward (keratoconus). Also present are multiple blis- ter-like areas (bullous keratopathy). Some resolution was obtained by the use of hyperosmotic ointments.
amination of the eye for the presence of signs of anterior uveitis (i.e., conjunctival hyperemia, aqueous flare, miosis), or lens luxation (lens in the anterior chamber, deep anterior chamber if the lens has luxated posteriorly). Specular microscopy may reveal a decreased number of endothelial celis, but this is not usually available in a clinical setting.
Examination tip: Globe digital pressure applied through the lids will temporarily cause hypertension within the globe to increase the density of the corneal edema if endothelial degeneration is present).
22.What is the treatment for endothelial dystrophy?
There is no treatment for the disease itself. The loss of endothelial cells is permanent. The
secondary corneal edema can be treated using hypertonic solutions or ointments (2.5-5% NaCI ointments). Corneal ulcers associated with the corneal edema will often behave as indolent ulcers and may need to be treated as such (see Chapter 7). Thermokeratoplasty may be beneficial in advanced stages of the disease. Penetrating keratoplasty is the treatment of choice in human beings. Its use in veterinary ophthalmology is limited, mainly because of donor cornea availability.
23.What is posterior polymorphous dystrophy and in which breed of dog does this occur? This is a focal dysfunction of corneal endothelial cells resulting in multifocal posterior
corneal opacities. This has been reported in the American cocker spaniel.
BIBLIOGRAPHY
1.Cooley PL, Dice PF: Corneal dystrophy in the dog and cat. Vet Clin North Am Small Anim Pract 20:681-692,1990.
2.Crispin SM, Barnett KC: Dystrophy, degeneration and infiltration of the canine cornea. J Small Anim Pract 24:63-83, 1983.
3.Ekins MB, Waring GO, Harris RR: Oval lipid corneal opacities in beagles. Part II: Natural history over four years and study of tear function. JAm Anim Hosp Assoc 16:601-605, 1980.
4.Genetics Committee, American College of Veterinary Ophthalmologists: Ocular Disorders Presumed to be Inherited in Purebred Dogs, 3rd ed. city, ACVO, 1999.
5.Linton LL, Moore CP, Collier LL: Bilateral lipid keratopathy in a boxer dog: Cholesterol analyses and dietary management. Prog Vet Comp OphthalmoI3(l):9-14, 1993.
6.MacMillan AD, Waring GO, Spangler WL, et al: Crystalline corneal opacities in the Siberian husky. J Am Vet Med Assoc 175:829-832, 1979.
7.Ward DA, Martin CL, Weiser I: Band keratopathy associated with hyperadrenocorticism in the dog. J Am Anim Hosp Assoc 25:583-586, 1989.
8.Waring GO, MacMillan A, Reveles P: Inheritance of crystalline corneal dystrophy in Siberian huskies. J Am Anim Hosp Assoc 22:655-658, 1986.
9.Waring GO, Muggli PM, MacMillan A: Oval corneal opacities in beagles. J Am Anim Hosp Assoc 13:204-208, 1977.
10.Whitley RD, Gilger BC: Diseases of the canine cornea and sclera. In Gellatt K (ed): Veterinary Ophthalmology, 3rd ed. Baltimore, Lippincott Williams & Wilkins, 1999, pp 635-674.
7. CORNEAL EROSIONS (INDOLENT ULCERS)
Alexandra van derWoerdt, D.V.M., M.S.
1. What is an indolent ulcer?
An indolent ulcer is a nonhealing superficial corneal ulcer or erosion with nonadherent epithelial edges.
2.Name a few other terms that are used to describe an indolent ulcer.
Boxer ulcer Recurrent erosion
Refractory corneal ulcer Rodent ulcer
3.In how many days does an uncomplicated ulcer usually heal?
An uncomplicated corneal ulcer should heal within 3-5 days. Erosions are called persistent
if they have been present for more than 14 days.
4.In which species have indolent ulcers been reported?
Dogs, cats, and horses.
5.What breeds of dogs most commonly develop indolent ulcers and at what age?
The boxer is the breed in which this condition has been most extensively studied. Other
breeds that appear to be predisposed include the Australian cattle dog, Boston terrier, English springer spaniel, golden retriever, Labrador retriever, miniature poodle, miniature schnauzer, and Welsh corgi. The average age of affected dogs is approximately 9 years.
6.Describe the histopathologic abnormalities in a cornea with an indolent corneal ulcer.
Ultrastructural examination of affected corneas has revealed abnormalities in the basal cell-
basement membrane complex with a lack of hemidesmosomes and a thickened and irregular corneal epithelial basement membrane. A thin superficial acellular zone of hyalin collagen, which may act as a barrier to epithelial adhesion, has also been shown to be present in affected areas.
7.What are the most common complaints of owners of dogs with an indolent ulcer?
Dogs with an indolent corneal ulcer usually present with the complaints of redness of the eye,
chronic discharge from the eye, and mild blepharospasm. If the dog has already been treated by another veterinarian, owners may indicate a lack of response to treatment with topical antibiotic ointment or solution with or without atropine. A dog with an indolent corneal ulcer may show surprisingly little discomfort considering the size of the ulcer.
8. How are indolent ulcers diagnosed?
An indolent ulcer is diagnosed by clinical signs and exclusion of other etiologies of a nonhealing superficial ulcer. The tear production should be measured using a Schirmer tear test to rule out keratoconjunctivitis sicca (KCS). A careful examination of the conjunctiva and eyelids should be performed looking for the presence of distichiae or ectopic ciliae. The conjunctival cul-de-sac should be inspected for the presence of a foreign body. After application of a topical anesthetic, the loose epithelium can easily be removed from the edges of the ulcer using a dry cotton swab.
9.List the most common ophthalmic abnormalities in an eye with an indolent ulcer.
Ophthalmic examination may reveal the following abnormalities: Mild blepharospasm
Mild epiphora
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Corneal Erosions (Indolent Ulcers) |
Conjunctival hyperemia
Superficial corneal ulcer with redundant epithelial edges
A reflex miosis of the pupil usually does not occur in dogs with an indolent ulcer, and the pupil is usually of normal size. Fluorescein stain may migrate under the loose epithelial edges. In general, indolent ulcers are superficial and do not involve the stroma, and there is no cellular infiltration into the ulcer. Cytology may be normal or show nonseptic inflammation (Figs. 1-3).
Figure 1. Corneal erosion showing the irregular edges of the epithelial exfoliation.
Figure 2. A corneal erosion showing the roughened epithelium at the edges of a fluorescein-stained lesion. Note the stain is positive beyond the edges of the loosened epithelium. Once the loose epithelium is removed, the original erosion is made considerably larger.
10.What is the differential diagnosis of an indolent ulcer?
Other causes of nonhealing ulcers include:
Decreased tear production |
Exposure keratitis |
Goblet cell deficiency |
Lagophthalmos |
Distichiae |
Neurotrophic keratitis |
Ectopic ciliae |
Presence of a foreign body |
Other eyelid abnormalities (e.g., |
Infection |
entropion, eyelid tumors) |
|
Endothelial cell degeneration with secondary corneal edema predisposes the cornea to the development of bullous keratopathy (blisters), which may progress to superficial corneal ulcers.
11.What additional diagnostic tests should be performed?
Tear production should be measured. The conjunctival cul-de-sac should be carefully inspected
for the presence of abnormal hairs or foreign bodies. Evaluate a thyroid panel. Approximately 44%
Corneal Erosions (Indolent Ulcers) |
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Figure 3. An erosion stained with fluorescein showing the stain uptake under the visible edges of the lesion.
of the erosions evaluated in boxers also had hypothyroidism. Supplemental thyroxine decreased healing time and prevented either recurrence or the opposite eye from developing an erosion.
12.How is an indolent ulcer treated?
The loose epithelium needs to be debrided using dry cotton swabs after application of topical
anesthetic to the cornea. After debriding the cornea, the resulting ulcer is usually significant larger than the original ulcer. Aftercare consists of topical antibiotic solution or ointment three to four times a day with or without topical atropine. (Therapy tip: Keep in mind that some antibiotics, especially the "rnycins," inhibit epithelial mitosis and cell migration-so don't over medicate).
Additional procedures that can aid in healing of these ulcers include a grid keratotomy using a 25-gauge needle or punctate keratotomy using a 20-gauge needle and placement of a soft contact lens or collagen shield. The dog may experience some discomfort after these procedures, which can be treated with an oral nonsteroidal anti-inflammatory drug (NSAID) such as buffered aspirin at a dose of 10 mg/kg/body weight once or twice daily.
Additional medications that have been used to aid in healing include 5% NaCI ointment or solution if significant corneal edema is present, autogenous plasma or serum, fibronectin, aprotinin, epidermal growth factor, and polysulfated glycosaminoglycans. Ophthalmic tissue adhesives and superficial keratectomies have also been used in the management of these lesions (Figs. 4 and 5).
An Elizabethan collar is indicated if excessive rubbing of the eye occurs.
13. Describe the mechanism of action of aprotinin in treatment of an indolent ulcer.
Aprotonin inhibits the enzymes (chymo)trypsin, plasmin, and kallikrein. Excessive plasmin levels have been shown to be present in animals with persistent corneal erosions.
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Corneal Erosions (Indolent Ulcers) |
Figure 4. A central ulcer being strengthened by tissue adhesive (N- butylcyanoacrylate). Note that the adhesive should be a thin overlay allowed to extend to the edges of the erosion.
Figure 5. Tissue adhesive in place over an erosion. Approximately 2-3 weeks are required for healing and rejection of the glue.
14.Why do polysulfated glycosaminoglycans have a beneficial effect on healing in some dogs with an indolent ulcer?
Polysulfated glycosaminoglycans act by inhibiting protease activity. The proteolytic activity of lacrimal fluid in eyes with an indolent ulcer has been shown to be significantly higher in a high percentage of affected dogs than the proteolytic activity of lacrimal fluid of normal eyes.
15.Explain the beneficial effect of epidermal growth factor on healing of indolent ulcers.
Epidermal growth factor (EGF) stimulates mitosis in the corneal epithelium. Topical appli-
cation of EGF resulted in resolution of an indolent ulcer in 8 out of 10 affected dogs witbin 2 weeks, compared to 2 out of 10 dogs treated with a placebo.
16.How is grid keratotomy performed?
Topical anesthetic is applied to the cornea, and the abnormal epithelium is removed using a
dry cotton swab. A 25-gauge needle is used to make multiple superficial microincisions (scratches) into the cornea in a grid pattern, 1-2 mm apart. The grid should cover the entire ulcer and extend a few millimeter into normal cornea.
Corneal Erosions (Indolent Ulcers) |
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17.What is a punctate keratotomy?
Punctate keratotomies can be performed with a 20-gauge needle or a Yag laser. Prepare the
surface as with the grid procedure. The objective is to disrupt the exposed stroma by superficially fracturing the collagen. The needle technique superficially penetrates the stroma from a 45-60° angle then exits the stroma at 90°. This produces a ticking sound. Each site leaves a stellate white abrasion, which serves as an anchor site for migrating epithelium to adhere onto. The entire area should be treated. Once healed, these punctate sites become imperceptible except on slit lamp examination (Fig. 6).
18.Which surgical procedures have been used in the management of indolent ulcers?
Chemical cauterization, temporary tarsorrhaphy, nictitans and conjunctival flap procedures
and superficial lamellar keratectomy have all been reported in the management of indolent ulcers. A nictitans flap was found to have no beneficial effect in one study. A superficial keratectomy may be highly beneficial in refractory cases, with the disadvantage of requiring specialized equipment and general anesthesia.
19.What is the reported success rate of debridement with a cotton swab only?
In one large retrospective study, 84% of indolent ulcers healed with one or more debridement
procedures of the cornea in an average of 23.4 ± 11.1 days. Sixteen percent needed additional surgical procedures to heal.
Figure 6. Punctate keratotomy procedure.
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Corneal Erosions (Indolent Ulcers) |
20.What is the reported success rate of debridement followed by grid keratotomy?
In one large retrospective study, all ulcers treated with debridement and grid keratotomy
healed, although 17% of cases required more than one procedure. Average healing time was 13.4 ::!:: 5.1 days. Similar findings were obtained with punctate keratotomy.
21.What is the reported success rate of superficial keratectomy?
In one large retrospective study, all ulcers treated with superficial keratectomy healed with
one treatment in an average of 9.3 ::!:: 3.9 days.
22. Explain the mechanism through which grid keratotomy and superficial keratectomy encourage healing of an indolent ulcer.
Abnormal hyalin collagen is present in the corneal stroma in the area of an indolent ulcer that acts as a barrier to epithelial adhesion. Both grid keratotomy and superficial keratotomy will disrupt this barrier, allowing migrating corneal epithelial cells to be exposed to the subepithelial type I collagen. This will lead to a more effective attachment between the epithelium and the stroma.
23.Why might an ulcer appear to be healed but then recur?
The epithelium may migrate over the ulcer bed but fail to properly attach to the underlying
basement membrane and stroma. This may give the impression that the ulcer has healed, but the weak epithelium will quickly retract from the stroma creating the impression of a recurrence when in fact the original ulcer has never healed properly.
24.What can be done to prevent these ulcers from recurring?
There has been little information reported in the literature regarding prevention of indolent
corneal ulcers. Application of a lubricating ophthalmic ointment twice daily may help to protect the cornea from environmental irritants and may help to decrease the forces applied to the corneal epithelium by the eyelids during normal blinking.
25.What infectious agent may be associated with indolent ulcers in cats?
Geographic corneal ulcers associated with feline herpes virus type I may behave as indolent
corneal ulcers.
26.Is the treatment of an indolent ulcer the same for dogs and cats?
No. The use of a grid keratotomy has been associated with the development of a corneal se-
questrum in cats. Repeated debridement of the cornea using a cotton tipped applicator is indicated in the treatment of a nonhealing ulcer in the cat. Antiviral therapy is indicated when herpes virus is suspected to be an etiologic factor.
BIBLIOGRAPHY
I. Champagne ES, Munger RJ: Multiple punctate keratotomy for the treatment of recurrent epithelial erosions in dogs. J Am Anim Hosp Assoc 28:213-216, 1992.
2.Chavkin M, Riis RC: Management of persistent corneal erosion in a boxer dog. Cornell Vet 80:347-356, 1990.
3.Cook C, Wilcox B: A clinical and histological study of canine persistent superficial corneal ulcers. Proc
Am Coil VetOphthalmoI26:139, 1995.
4.Cooley PL, Wyman M: Indolent-like corneal ulcers in 3 horses. J Am Vet Med Assoc 188:295-297, 1986.
5.Gelatt KN, Samuelson DA: Recurrent corneal erosions and epithelial dystrophy in the boxer dog. J Am Anim Hosp Assoc 18:453-460, 1982.
6.Kirschner SE, Niyo Y, Betts DM: Idiopathic persistent corneal erosions: Clinical and pathological findings in 18 dogs. J Am Anim Hosp Assoc 25:84-90,1989.
7.Kirschner SE: Persistent corneal ulcers: What to do when ulcers won't heal. Vet Clin N Am Small Anim Pract 20(3):627-642, 1990.
8.Kirschner SE, Brazzell RK, Stern ME, et al: The use of topical epidermal growth factor for treatment of nonhealing corneal erosions in dogs. J Am Anim Hosp Assoc 27:449-452,1991.
Corneal Erosions (Indolent Ulcers) |
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9. La Croix NC, van der Woerdt A, Olivero D: Nonhealing corneal ulcers in cats: 29 cases. Proc Am Coli Vet OphthalmoI30:84, 1999.
10. Miller WW: Using polysulfated glycosaminoglycan to treat persistent corneal erosions in dogs. Vet Med 9\ :916-922, 1996.
I I. Morgan RV, Abrams KL: A comparison of six different therapies for persistent corneal erosions in dogs and cats. Vet Comp OphthalmoI4:38--43, 1994.
12.Pickett JP: Treating persistent corneal erosions with a crosshatch keratotomy technique. Vet Med 90:561-572, \995.
13.Stanley RG. Hardman C. Johnson BW: Results of grid keratotomy, superficial keratectomy and debridement for the management of persistent corneal erosions in 92 dogs. Vet Ophthalmol 1:233-238, 1998.
14.Willeford KO, Miller WW, Abrams KL, et al: Modulation of proteolytic activity associated with persistent corneal ulcers in dogs. Vet Ophthalmol 1:5-8, 1998.
8. FELINE CORNEAL SEQUESTRUM
Ronald C. Riis, D.V.M, M.S.
1.What is unique about feline corneal sequestrum?
It is a keratopathy seen predominantly in the feline species.
2.What other names have been given to this condition? Corneal mummification
Corneal nigrum Corneal necrosis Necrotizing keratitis Corneal sequestrum.
3.What are the characteristic clinical signs?
A dark brown-to-black spot in the central or paracentral cornea. Depending on chronicity, the cornea mayor may not have neovascularization. The surface of the sequestrum has no epithelium. Fluorescein stain does not light up sequestra, only around the sequestra. Sequestra usually present with minor blepharospasm and little mucopurulent discharge but with brownish tears. They are usually initially unilateral with the opposite eye at high risk. Recurrence is also possible. The highest incidence of occurrence of sequestra is found in brachycephalic cats (Figs. 1-4).
Figure 1. Central corneal sequestrum with associated diffuse corneal edema. Fluorescein stain is positive only around the pigment.
4. What is the etiology of these sequestra?
Corneal sequestra have not been reproduced in experimental studies. Prolonged exposure of the central cornea from causes such as neuroparalytic or neurotrophic conditions and sicca have been suggested. Sequestrum following a bout of rhinotracheitis (FVH-l) has been reported clinically and experimentally; polymerase chain reaction (PCR) herpesvirus DNA have been found in keratectomized samples.
5. What is the treatment for sequestra?
Removal by superficial keratectomy is recommended. It is difficult to judge the depth of the sequestrum prior to surgery. Therefore, the keratectomy may begin as a superficial procedure and end with a more radical procedure if the majority of the corneal thickness has to be removed. Because more radical procedures involve many options, it is much easier to keratectomize small, superficial sequestra than to wait and see if the cornea will vascularize to reject the sequestrum.
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Feline Corneal Sequestrum |
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Figure 2. Large superficial sequestrum that was not noted by owner; however, the dark discharge was a complaint.
Figure 3. Large superficial and deep sequestrum present for 6 months. Note the neovascularization and scarring. Surgical keratectomy required a free Tenon's grafts to support the compromised cornea.
Figure 4. Sequestrum that was finally extruded after 9 months. Note the damage to the cornea generated by months of reaction as evidenced by neovascularization and scarring.