CORTICOSTEROIDS, TOPICAL (OPHTHALMIC)
(see also Antibiotic & Corticosteroid Combinations)
Indications/Dosages/Precautions - Topical corticosteroids are used to treat diseases of the eye involvingthe conjunctiva, sclera, cornea, and anterior chamber. Penetration of topically applied corticosteroids intothe eyelids is poor as is penetration to the posterior segment of the eye. Corticosteroid-responsiveconditions affecting these areas are usually managed with systemically administered agents (with orwithout adjunctive topically applied medications).
Conjunctivitis in animals is often treated symptomatically, particularly during the first occurrence of thecondition for any particular patient. Antibiotic agents with hydrocortisone or dexamethasone, or antibioticagents alone initially, are used for conjunctivitis in the dog and the horse. Allergic and eosinophilicconjunctivitis are rare diagnoses in the cat. Topically applied corticosteroids should not be used to treatconjunctivitis in cats. Herpes virus is the most common feline conjunctival pathogen and topically appliedsteroids can induce prolonged disease, steroid dependency and corneal complications including ulcerativekeratitis and/or corneal sequestrum formation.
Inflammatory conditions of the canine sclera and episclera include episcleritis, scleritis, nodulargranulomatous episclerokeratitis, Collie granuloma and others. Potency and penetration of corticosteroidagents is important in the management of these conditions. Dexamethasone sodium phosphate ointment isoften employed and the relatively reduced penetration of the fibrous ocular tunics of this medicationcompared with that of 1% prednisolone acetate ophthalmic suspension is made up for by increasedcontact time of the ointment form of this drug and by the increased potency of dexamethasone (30Xcortisone) relative to prednisolone (4-5X cortisone). Dexamethasone products alone (without antibiotics)are becoming increasingly scarce in the marketplace and because of this, dexamethasone is often used incombination with an antibiotic for availability reasons only. Four times daily treatment is often the initialfrequency with tapering paralleled to clinical response. Topical treatment is often used followingsubconjunctival injection of corticosteroid agents into or adjacent to the lesion (if focal). Systemic steroidtreatment is usually not necessary.
Nonulcerative inflammatory conditions of the cornea of animals include chronic superficial keratitis(pannus) of the German Shepherd and other breeds, eosinophilic keratitis of the cat and certain, oftenpoorly understood, keratopathies of the equine, including Onchocerca related keratitis. German Shepherdpannus may be better managed using cyclosporine ophthalmic solution or ointment with or withoutconcurrent topical steroids initially followed by long term management with cyclosporine ophthalmicalone (see cyclosporine ophthalmic). Eosinophilic keratitis is often treated with subconjunctivalcorticosteroids in addition to topical 0.1% dexamethasone ophthalmic ointment or solution or 1%prednisolone acetate ophthalmic suspension 4 times daily, tapering the dosage frequency based on clinicalresponse. Recent research reveals that eosinophilic keratitis may be an unusual immune response to latentfeline herpes virus in the corneal stroma, calling into question the value of topical steroids in themanagement of a disease with an infectious etiology. Equine keratopathies are treated with 0.1%dexamethasone ointment 4 times daily with tapering of the treatment frequency based on the clinicalresponse.
Corticosteroids are also used to manage anterior uveal inflammatory disease of companion animals. Insmall animals, 1% prednisolone acetate ophthalmic suspension is generally used for this purpose becauseof superior penetration into the anterior segment of the eye in comparison with dexamethasone products.
The frequency of treatment depends on the severity of the condition. Severe anterior uveitis can be treatedwith subconjunctival corticosteroids given in combination with hourly topical corticosteroids withreevaluation performed again 24 hours after beginning treatment. Moderate to mild uveitis and that foundfollowing surgery of the anterior segment is often treated initially at the QID level with tapering based onclinical response. Anterior uveitis in animals can often be associated with an underlying systemicinfectious or neoplastic condition in animals. Clinicians are advised to evaluate the patient for generalizedinfectious or neoplastic conditions prior to or concurrent with a course of corticosteroid antiinflammatorytherapy, particularly if the condition dictates systemic treatment with these agents in combination withsubconjunctival and topical treatment. Uveitis in the equine species is often treated with either 1%prednisolone acetate ophthalmic suspension or with 0.1% dexamethasone ointment. Many cliniciansprefer to use the ointment because of increased contact time and potency and the logistics of frequenttreatment of this species. 1% prednisolone acetate can be passed through a subpalpebral lavage cathetervery frequently to treat equine patients with anterior uveitis when necessary.
Pred Forte®, Econopred Plus® or generic 1% prednisolone acetate ophthalmic suspension are theprednisolone products most used by veterinary ophthalmologists. There are few indications for
Econopred® or Pred Mild® in veterinary ophthalmology.
Inflammatory condition of the posterior segment require systemic treatment because of poor penetrationof topically applied agents.Dosage Forms/Preparations/FDA Approval Status - Veterinary-Approved Products: None
Econopred® (Alcon); 1% Suspension; Econopred Plus® (Alcon); Pred Forte® (Allerga_n;
Generic; (Rx)
Prednisolone Sodium Phosphate Drops: 0.125% Solution (various manufacturers); 1% Solution(various); (Rx)
Combination of Prednisolone (0.25%) and Atropine (1%) Drops: Mydrapred® (Alcon) in 5 mlbottles; (Rx)
Also available: Fluorometholone or Medrysone drops.
Other routes of administration: Systemically administered corticosteroids (usually orally)may be indicated for non-infectious inflammatory ocular conditions and following intraocularsurgery. Subconjunctival steroids are useful in anterior segment inflammatory disease andfollowing cataract surgery and intraocular glaucoma surgery. Subconjunctival steroids maybe absorbed systemically and should be used with caution in patients with endocrinopathies(e.g., diabetes mellitus) or infectious diseases.
Antibiotics, Single and Combination Agents
Indications/Pharmacology/General Use Considerations - Topical antibiotic agents are commonly usedto treat conjunctivitis and ulcerative keratitis complicated by bacterial infection of the corneal stroma.
These agents are also used to prevent infection following surgery of the eyelids, conjunctiva, cornea, andthe anterior segment. Conjunctivitis in animals is a common clinical entity. Because in most instances thecondition does not threaten vision, it is often treated symptomatically with antibiotic agents or antibioticagents in combination with topical steroids (see antibiotic/corticosteroid combination agents).
Conjunctivitis is an exclusion diagnosis in animals, ruling out other causes for ocular discomfort anddischarge, including anterior uveitis, glaucoma and inflammatory disease of the sclera, episclera andcornea. Triple antibiotic products (neomycin, bacitracin and polymyxin B) are often employed for thispurpose, with or without hydrocortisone, because these drugs are not used systemically and because thecombination of antibiotics is broad spectrum. Triple antibiotic or triple antibiotic HC is often used in dogs4 times daily for 1 to 2 weeks for conjunctivitis. Chronic or recurrent cases of conjunctivitis wouldindicate further diagnostic evaluation to determine an underlying cause. Tetracycline ophthalmic ointmentis often used QID in cats for nonspecific or undiagnosed conjunctivitis. The rationale for this treatment isthe efficacy of tetracycline for Chlamydia spp. and Mycoplasma spp., two infectious agents reported tocause conjunctivitis in the cat. Antibiotic agents with corticosteroids should not be used for the treatmentof conjunctivitis in the cat. The majority of cases are related to primary or recurring infection with felineherpes virus and recent evidence indicates that topical or systemic steroid therapy can potentially prolongthe duration of the viral infection and result in corneal complications in cases which otherwise may haveremained a conjunctival infection. Triple antibiotic with or without hydrocortisone is often used to treatconjunctivitis in the equine species. Sensitivity to triple antibiotic in dogs and cats has been noted and isreportedly the result of neomycin allergy, as is noted in people.
Antibiotic therapy for corneal disease varies from prophylactic therapy to prevent infection to treatmentof established corneal infections. Following an acute superficial injury to the cornea in the dog, cat orhorse, treatment with triple antibiotic ointment or drops 4 times daily is usually sufficient to preventbacterial infection of the corneal stroma. Reevaluation of the patient 24-48 hours after the injury isindicated. Progressive edema, pain, and white opacification of the cornea (cellular infiltrate) wouldsuggest that the antibiotic protocol (agent and frequency) has failed to prevent bacterial infection.
Established bacterial infection of the corneal stroma is managed medically or surgically depending onthe depth of infection. Ulcerative keratitis with bacterial infection causing deterioration of 50-75% of thestromal thickness is usually treated with conjunctival or corneal grafting in addition to antibiotic therapy.
This is done to introduce immune system components and a blood supply to the cornea (conjunctivalgraft) in addition to replacing lost stromal tissue. Conjunctival grafting will usually stabilize stromaldeterioration secondary to bacterial infection but carries the disadvantage of permanent opacification ofthe cornea in the site of previous ulcerative keratitis (unless other surgeries are performed). Aggressivemedical management with topical antibiotic agents is often successful in controlling corneal infectionwhich involves 75% or less of the depth of the cornea. The slit lamp biomicroscope is used byophthalmologists at referral centers and specialty clinics to determine the depth of corneal involvement.
Clinical signs of bacterial infection of the corneal stroma includes increasing pain, progressive cornealopacity, hypopyon, and the development of a progressively expanding indentation or crater in the surfaceof the cornea. Cytology is indicated in the management of such patients. Gram staining is usually notnecessary. Cocci noted with Dif-Quick® or related stains are considered to be gram positive cocci. Thosecocci forming chains are considered to be Streptococcus organisms. Those cocci of variable size andshape and forming grape clusters are considered to be Staphylococcal organisms. Rods are considered tobe gram negative organisms and Pseudomonas spp. is suspected. A degree of suspicion for fungalkeratitis should be maintained while evaluating cytologic material collected from the cornea of the horse.
Fungal hyphae stain dark blue with Dif-Quick® type stains. Culture and sensitivity tests are informativebut the information is available at a time when the efficacy of the antibiotic therapy chosen has alreadybeen established. In 24-48 hours the case will show signs of improvement, indicating efficacy of thetherapeutic protocol or the condition will have advanced and surgery will be under consideration.
Sensitivities are relatively meaningless because aggressive medical treatment can result in corneal drugconcentrations several times the MIC and sometimes beyond that considered toxic on a systemic basis.
The use of eyedrops rather than ointments is recommended for aggressive medical management protocols.
Cytologic evaluation of material from the cornea will dictate antibiotic selection for aggressive medicalmanagement of corneal ulcers. Cocci are often treated with frequent application of triple antibiotic drops.
Gentamicin has limited spectrum for Streptococci spp. and would not be a first choice agent when cocciforming chains are noted on cytologic evaluation of material from an infected corneal ulcer. Gentamicinhas efficacy for some Staphylococcal spp. Chloramphenicol is also an antibiotic available for treatment ofgram positive infections of the cornea. Gram negative infections of the cornea are often treated withgentamicin, tobramycin or the quinolones. Several studies indicate that a bacterial infection of the cornealstroma that responds to tobramycin is usually as responsive to gentamicin applied frequently making thenewer aminoglycoside and quinolone antibiotics rarely necessary. These agents are reserved for veryspecific instances of stromal infection with highly resistant organisms and should not be considered forprophylactic treatment. Applied very frequently, bactericidal concentrations of either triple antibiotic orgentamicin ophthalmic solutions can be achieved in the corneal stroma making these two agents effectivefor the vast majority of corneal infections in companion animals. Relative penetration of antibiotic agentsinto the cornea is irrelevant during the treatment of ulcerative keratitis. All agents are water soluble (eyedrops) and would penetrate the corneal stroma similarly. Penetration of various antibiotic agents into thecornea is a consideration when the corneal epithelium is intact as is often noted with the development ofstromal abscessation in equines.
Aggressive medical management protocols involve hourly or q30 minute application of topicalantibiotics. Sometimes two agents are used with synergistic properties (for example an aminoglycosideand a cephalosporin). One agent is applied on the hour and the other on the half hour. Single agents areusually applied hourly. The case is reevaluated 18-24 hours after initiation of the treatment regimen.
Increased patient comfort, reduced corneal edema and no increase in the depth or width of the cornealulcer are signs of efficacy of the selected treatment plan. In some cases at 24 hours and most cases by 30hours, the peripheral "rim" of the corneal ulcer will fail to take on fluorescein stain, indicating earlyepithelialization of the corneal ulcer. It is the author's (DKO) impression that epithelialization of the ulcerwill not occur until the stromal infection has been arrested. Cytologic evaluation of material collectedfrom the cornea can be repeated to evaluate efficacy of the drug(s) selected. Clinical improvement signalsthe clinician to begin reducing treatment frequency slowly over the next two days, working towards the
QID level. Long term aggressive medical management is not recommended because several agents, especially the aminoglycosides, are epitheliotoxic and prolonged once per hour treatment likely woulddelay healing rather than improve the case.
Aggressive medical management usually requires hospitalization in an intensive care unit for carefultreatment and monitoring of the case. The advantage of aggressive medical management is reducedopacity in the cornea in comparison with conjunctival grafting. This is associated with an improved visualresult, particularly if the injury is central. Medical management is usually less expensive than surgicaltreatment. General anesthesia is not necessary for aggressive medical management. Although aggressivemedical management may result in halting further bacterial deterioration of stromal tissue in very deepcorneal ulcers, reepithelialization of Descemet's membrane or a thin layer of corneal stroma interposedbetween Descemet's membrane and the corneal epithelium leaves the cornea dangerously thin. Minortrauma to the eye could result in rupture of the cornea across this area and loss of the anterior chamber.
Post surgical prophylactic medical treatment usually involves triple antibiotic agents because of theirbroad spectrum and because they are not agents used systemically. Four times daily treatment isrecommended. Ointments are commonly used after surgery of the eyelids, conjunctiva or cornea.
Eyedrops are usually used following surgery of the cornea or anterior segment. Bacterial infection of theanterior chamber alone is uncommon. Bacterial endophthalmitis carries a poor prognosis for saving visionor the globe in animals and is usually managed surgically in people. Gentamicin is sometimes used forprophylactic therapy of the equine species because of a greater number of gram negative organisms in theenvironment of this species, although the aminoglycosides would not be a first choice agent forprophylactic medical treatment of small animals. Tobramycin and the quinolones would not be consideredfor prophylactic treatment following surgery performed under sterile conditions.
Indications/Dosages/Precautions - Topical corticosteroids are used to treat diseases of the eye involvingthe conjunctiva, sclera, cornea, and anterior chamber. Penetration of topically applied corticosteroids intothe eyelids is poor as is penetration to the posterior segment of the eye. Corticosteroid-responsiveconditions affecting these areas are usually managed with systemically administered agents (with orwithout adjunctive topically applied medications).
Conjunctivitis in animals is often treated symptomatically, particularly during the first occurrence of thecondition for any particular patient. Antibiotic agents with hydrocortisone or dexamethasone, or antibioticagents alone initially, are used for conjunctivitis in the dog and the horse. Allergic and eosinophilicconjunctivitis are rare diagnoses in the cat. Topically applied corticosteroids should not be used to treatconjunctivitis in cats. Herpes virus is the most common feline conjunctival pathogen and topically appliedsteroids can induce prolonged disease, steroid dependency and corneal complications including ulcerativekeratitis and/or corneal sequestrum formation.
Inflammatory conditions of the canine sclera and episclera include episcleritis, scleritis, nodulargranulomatous episclerokeratitis, Collie granuloma and others. Potency and penetration of corticosteroidagents is important in the management of these conditions. Dexamethasone sodium phosphate ointment isoften employed and the relatively reduced penetration of the fibrous ocular tunics of this medicationcompared with that of 1% prednisolone acetate ophthalmic suspension is made up for by increasedcontact time of the ointment form of this drug and by the increased potency of dexamethasone (30Xcortisone) relative to prednisolone (4-5X cortisone). Dexamethasone products alone (without antibiotics)are becoming increasingly scarce in the marketplace and because of this, dexamethasone is often used incombination with an antibiotic for availability reasons only. Four times daily treatment is often the initialfrequency with tapering paralleled to clinical response. Topical treatment is often used followingsubconjunctival injection of corticosteroid agents into or adjacent to the lesion (if focal). Systemic steroidtreatment is usually not necessary.
Nonulcerative inflammatory conditions of the cornea of animals include chronic superficial keratitis(pannus) of the German Shepherd and other breeds, eosinophilic keratitis of the cat and certain, oftenpoorly understood, keratopathies of the equine, including Onchocerca related keratitis. German Shepherdpannus may be better managed using cyclosporine ophthalmic solution or ointment with or withoutconcurrent topical steroids initially followed by long term management with cyclosporine ophthalmicalone (see cyclosporine ophthalmic). Eosinophilic keratitis is often treated with subconjunctivalcorticosteroids in addition to topical 0.1% dexamethasone ophthalmic ointment or solution or 1%prednisolone acetate ophthalmic suspension 4 times daily, tapering the dosage frequency based on clinicalresponse. Recent research reveals that eosinophilic keratitis may be an unusual immune response to latentfeline herpes virus in the corneal stroma, calling into question the value of topical steroids in themanagement of a disease with an infectious etiology. Equine keratopathies are treated with 0.1%dexamethasone ointment 4 times daily with tapering of the treatment frequency based on the clinicalresponse.
Corticosteroids are also used to manage anterior uveal inflammatory disease of companion animals. Insmall animals, 1% prednisolone acetate ophthalmic suspension is generally used for this purpose becauseof superior penetration into the anterior segment of the eye in comparison with dexamethasone products.
The frequency of treatment depends on the severity of the condition. Severe anterior uveitis can be treatedwith subconjunctival corticosteroids given in combination with hourly topical corticosteroids withreevaluation performed again 24 hours after beginning treatment. Moderate to mild uveitis and that foundfollowing surgery of the anterior segment is often treated initially at the QID level with tapering based onclinical response. Anterior uveitis in animals can often be associated with an underlying systemicinfectious or neoplastic condition in animals. Clinicians are advised to evaluate the patient for generalizedinfectious or neoplastic conditions prior to or concurrent with a course of corticosteroid antiinflammatorytherapy, particularly if the condition dictates systemic treatment with these agents in combination withsubconjunctival and topical treatment. Uveitis in the equine species is often treated with either 1%prednisolone acetate ophthalmic suspension or with 0.1% dexamethasone ointment. Many cliniciansprefer to use the ointment because of increased contact time and potency and the logistics of frequenttreatment of this species. 1% prednisolone acetate can be passed through a subpalpebral lavage cathetervery frequently to treat equine patients with anterior uveitis when necessary.
Pred Forte®, Econopred Plus® or generic 1% prednisolone acetate ophthalmic suspension are theprednisolone products most used by veterinary ophthalmologists. There are few indications for
Econopred® or Pred Mild® in veterinary ophthalmology.
Inflammatory condition of the posterior segment require systemic treatment because of poor penetrationof topically applied agents.Dosage Forms/Preparations/FDA Approval Status - Veterinary-Approved Products: None
Human-Approved Products:
Prednisolone Acetate Drops: 0.12% Suspension Pred Mild® (Allergan); 0.125% SuspensionEconopred® (Alcon); 1% Suspension; Econopred Plus® (Alcon); Pred Forte® (Allerga_n;
Generic; (Rx)
Prednisolone Sodium Phosphate Drops: 0.125% Solution (various manufacturers); 1% Solution(various); (Rx)
Combination of Prednisolone (0.25%) and Atropine (1%) Drops: Mydrapred® (Alcon) in 5 mlbottles; (Rx)
Also available: Fluorometholone or Medrysone drops.
Other routes of administration: Systemically administered corticosteroids (usually orally)may be indicated for non-infectious inflammatory ocular conditions and following intraocularsurgery. Subconjunctival steroids are useful in anterior segment inflammatory disease andfollowing cataract surgery and intraocular glaucoma surgery. Subconjunctival steroids maybe absorbed systemically and should be used with caution in patients with endocrinopathies(e.g., diabetes mellitus) or infectious diseases.
Antibiotics, Single and Combination Agents
Indications/Pharmacology/General Use Considerations - Topical antibiotic agents are commonly usedto treat conjunctivitis and ulcerative keratitis complicated by bacterial infection of the corneal stroma.
These agents are also used to prevent infection following surgery of the eyelids, conjunctiva, cornea, andthe anterior segment. Conjunctivitis in animals is a common clinical entity. Because in most instances thecondition does not threaten vision, it is often treated symptomatically with antibiotic agents or antibioticagents in combination with topical steroids (see antibiotic/corticosteroid combination agents).
Conjunctivitis is an exclusion diagnosis in animals, ruling out other causes for ocular discomfort anddischarge, including anterior uveitis, glaucoma and inflammatory disease of the sclera, episclera andcornea. Triple antibiotic products (neomycin, bacitracin and polymyxin B) are often employed for thispurpose, with or without hydrocortisone, because these drugs are not used systemically and because thecombination of antibiotics is broad spectrum. Triple antibiotic or triple antibiotic HC is often used in dogs4 times daily for 1 to 2 weeks for conjunctivitis. Chronic or recurrent cases of conjunctivitis wouldindicate further diagnostic evaluation to determine an underlying cause. Tetracycline ophthalmic ointmentis often used QID in cats for nonspecific or undiagnosed conjunctivitis. The rationale for this treatment isthe efficacy of tetracycline for Chlamydia spp. and Mycoplasma spp., two infectious agents reported tocause conjunctivitis in the cat. Antibiotic agents with corticosteroids should not be used for the treatmentof conjunctivitis in the cat. The majority of cases are related to primary or recurring infection with felineherpes virus and recent evidence indicates that topical or systemic steroid therapy can potentially prolongthe duration of the viral infection and result in corneal complications in cases which otherwise may haveremained a conjunctival infection. Triple antibiotic with or without hydrocortisone is often used to treatconjunctivitis in the equine species. Sensitivity to triple antibiotic in dogs and cats has been noted and isreportedly the result of neomycin allergy, as is noted in people.
Antibiotic therapy for corneal disease varies from prophylactic therapy to prevent infection to treatmentof established corneal infections. Following an acute superficial injury to the cornea in the dog, cat orhorse, treatment with triple antibiotic ointment or drops 4 times daily is usually sufficient to preventbacterial infection of the corneal stroma. Reevaluation of the patient 24-48 hours after the injury isindicated. Progressive edema, pain, and white opacification of the cornea (cellular infiltrate) wouldsuggest that the antibiotic protocol (agent and frequency) has failed to prevent bacterial infection.
Established bacterial infection of the corneal stroma is managed medically or surgically depending onthe depth of infection. Ulcerative keratitis with bacterial infection causing deterioration of 50-75% of thestromal thickness is usually treated with conjunctival or corneal grafting in addition to antibiotic therapy.
This is done to introduce immune system components and a blood supply to the cornea (conjunctivalgraft) in addition to replacing lost stromal tissue. Conjunctival grafting will usually stabilize stromaldeterioration secondary to bacterial infection but carries the disadvantage of permanent opacification ofthe cornea in the site of previous ulcerative keratitis (unless other surgeries are performed). Aggressivemedical management with topical antibiotic agents is often successful in controlling corneal infectionwhich involves 75% or less of the depth of the cornea. The slit lamp biomicroscope is used byophthalmologists at referral centers and specialty clinics to determine the depth of corneal involvement.
Clinical signs of bacterial infection of the corneal stroma includes increasing pain, progressive cornealopacity, hypopyon, and the development of a progressively expanding indentation or crater in the surfaceof the cornea. Cytology is indicated in the management of such patients. Gram staining is usually notnecessary. Cocci noted with Dif-Quick® or related stains are considered to be gram positive cocci. Thosecocci forming chains are considered to be Streptococcus organisms. Those cocci of variable size andshape and forming grape clusters are considered to be Staphylococcal organisms. Rods are considered tobe gram negative organisms and Pseudomonas spp. is suspected. A degree of suspicion for fungalkeratitis should be maintained while evaluating cytologic material collected from the cornea of the horse.
Fungal hyphae stain dark blue with Dif-Quick® type stains. Culture and sensitivity tests are informativebut the information is available at a time when the efficacy of the antibiotic therapy chosen has alreadybeen established. In 24-48 hours the case will show signs of improvement, indicating efficacy of thetherapeutic protocol or the condition will have advanced and surgery will be under consideration.
Sensitivities are relatively meaningless because aggressive medical treatment can result in corneal drugconcentrations several times the MIC and sometimes beyond that considered toxic on a systemic basis.
The use of eyedrops rather than ointments is recommended for aggressive medical management protocols.
Cytologic evaluation of material from the cornea will dictate antibiotic selection for aggressive medicalmanagement of corneal ulcers. Cocci are often treated with frequent application of triple antibiotic drops.
Gentamicin has limited spectrum for Streptococci spp. and would not be a first choice agent when cocciforming chains are noted on cytologic evaluation of material from an infected corneal ulcer. Gentamicinhas efficacy for some Staphylococcal spp. Chloramphenicol is also an antibiotic available for treatment ofgram positive infections of the cornea. Gram negative infections of the cornea are often treated withgentamicin, tobramycin or the quinolones. Several studies indicate that a bacterial infection of the cornealstroma that responds to tobramycin is usually as responsive to gentamicin applied frequently making thenewer aminoglycoside and quinolone antibiotics rarely necessary. These agents are reserved for veryspecific instances of stromal infection with highly resistant organisms and should not be considered forprophylactic treatment. Applied very frequently, bactericidal concentrations of either triple antibiotic orgentamicin ophthalmic solutions can be achieved in the corneal stroma making these two agents effectivefor the vast majority of corneal infections in companion animals. Relative penetration of antibiotic agentsinto the cornea is irrelevant during the treatment of ulcerative keratitis. All agents are water soluble (eyedrops) and would penetrate the corneal stroma similarly. Penetration of various antibiotic agents into thecornea is a consideration when the corneal epithelium is intact as is often noted with the development ofstromal abscessation in equines.
Aggressive medical management protocols involve hourly or q30 minute application of topicalantibiotics. Sometimes two agents are used with synergistic properties (for example an aminoglycosideand a cephalosporin). One agent is applied on the hour and the other on the half hour. Single agents areusually applied hourly. The case is reevaluated 18-24 hours after initiation of the treatment regimen.
Increased patient comfort, reduced corneal edema and no increase in the depth or width of the cornealulcer are signs of efficacy of the selected treatment plan. In some cases at 24 hours and most cases by 30hours, the peripheral "rim" of the corneal ulcer will fail to take on fluorescein stain, indicating earlyepithelialization of the corneal ulcer. It is the author's (DKO) impression that epithelialization of the ulcerwill not occur until the stromal infection has been arrested. Cytologic evaluation of material collectedfrom the cornea can be repeated to evaluate efficacy of the drug(s) selected. Clinical improvement signalsthe clinician to begin reducing treatment frequency slowly over the next two days, working towards the
QID level. Long term aggressive medical management is not recommended because several agents, especially the aminoglycosides, are epitheliotoxic and prolonged once per hour treatment likely woulddelay healing rather than improve the case.
Aggressive medical management usually requires hospitalization in an intensive care unit for carefultreatment and monitoring of the case. The advantage of aggressive medical management is reducedopacity in the cornea in comparison with conjunctival grafting. This is associated with an improved visualresult, particularly if the injury is central. Medical management is usually less expensive than surgicaltreatment. General anesthesia is not necessary for aggressive medical management. Although aggressivemedical management may result in halting further bacterial deterioration of stromal tissue in very deepcorneal ulcers, reepithelialization of Descemet's membrane or a thin layer of corneal stroma interposedbetween Descemet's membrane and the corneal epithelium leaves the cornea dangerously thin. Minortrauma to the eye could result in rupture of the cornea across this area and loss of the anterior chamber.
Post surgical prophylactic medical treatment usually involves triple antibiotic agents because of theirbroad spectrum and because they are not agents used systemically. Four times daily treatment isrecommended. Ointments are commonly used after surgery of the eyelids, conjunctiva or cornea.
Eyedrops are usually used following surgery of the cornea or anterior segment. Bacterial infection of theanterior chamber alone is uncommon. Bacterial endophthalmitis carries a poor prognosis for saving visionor the globe in animals and is usually managed surgically in people. Gentamicin is sometimes used forprophylactic therapy of the equine species because of a greater number of gram negative organisms in theenvironment of this species, although the aminoglycosides would not be a first choice agent forprophylactic medical treatment of small animals. Tobramycin and the quinolones would not be consideredfor prophylactic treatment following surgery performed under sterile conditions.