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Volume 55 | Issue 1 Article 10

1993 : Past and Present Management Techniques David M. Tinsley Iowa State University

Daniel M. Betts Iowa State University

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Recommended Citation Tinsley, David M. and Betts, aD niel M. (1993) "Glaucoma: Past and Present Management Techniques," Iowa State University Veterinarian: Vol. 55 : Iss. 1 , Article 10. Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol55/iss1/10

This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Iowa State University Veterinarian by an authorized editor of Iowa State University Digital Repository. For more information, please contact [email protected]. GLAUCOMA: PAST AND PRESENT MANAGEMENTTECHNIQUES

David M. Tinsley, D.V.M.* Daniel M. Betts, D.V.M., MSc., Dip.ACVO.**

Abstract away from the globe. This conventional "corneoscleral" route accounts for 85-900/0 of the This article reviews the clinical signs and total aqueous outflow.2 The remaining 10-15% diagnostic modalities appropriate for glaucoma. exits via the unconventional "uveoscleral" Classification of this disease and currently outflow diffusing posteriorly through the iris, recommended treatment options are discussed. , and choroid into the suprachoroidal 2 space and adjacent sclera. . In order to have an Introduction increased lOP, there must be either an in­ creased production or decreased outflow. Glaucoma is a group of eye diseases Increased production (hyperfiltration) has never characterized by an increase in intraocular been documented, hence, all are pressure which causes pathological changes in based on impaired circulation or outflow. the optic disc and typical defects in the field of vision. 1 Generally accepted normal intraocular Diagnosis-Clinical Signs pressure (lOP) readings in the dog and cat range from 15-30 mmHg. Maintenance of Early recognition of glaucoma is mandatory if normal pressure is through a delicate balance of successful regulation of aqueous production and outflow. The formation with subsequent preservation of vision is to be of aqueous 11umor is dependent on three achieved. Establishing a diagnosis of glaucoma dynamic processes. Active transport is the most is based exclusively on measurement of the important of the three and results in the move­ intraocular pressure. If such diagnostics are to ment of Na+ ions from the blood into the be performed, the clinician must first have a aqueous humor against a concentration gradient reasonable index of suspicion that the disease through the use of energy dependent Na+/K+ is in fact present. As a rule, the presenting ATPase pumps located in the non-pigmented history is unlikely to be of much value. With this epithelial cells overlying the ciliary body pro­ in mind, initial physical examination findings are 2 cesses. . Carbonic anhydrase catalyzes the often the first reliable tool available to the

- reaction: CO2 + H20 <-> H2C03 + HC03 <->H+. clinician in establishing the diagnosis. Unfortu­ Entry of bicarbonate is associated with influx of nately, those clinical signs that are consistently water into the posterior chamber. The remain­ expressed in acute glaucoma mimic those of the der is a cornbination of solute movement down a more commonly presented extraocular red eye concentration gradient (passive diffusion), as disorders. These include lacrimation, well as movement across cell mefl1branes photophobia, blepharospasm and variable secondary to local hydrostatic forces (ultrafiltra­ congestion of the conjunctival/episcleral vessels tion). Resultant aqueous humor collects in the secondary to shunting of aqueous/venous posterior chamber of the globe. It then flows outflow (Fig. 1). Where lOP exceeds 40 - 45 through the pupillary apel1ure, anterior chamber, mmHg, corneal stromal edema develops pectinate ligaments, trabecular meshwork of the secondary to impaired dehydration by the ciliary cleft, scleral venous plexus to be trans­ endothelial based Na+/K+ ATPase pump. ported via the local efferent vascular channels Mydriasis is an important clinical finding which can aid in differentiating glaucoma 'from uveitis. *Dr. Tinsley is a Resident in the Ophthalmology This loss of tone to the constrictor pupillae is a Clinical Scinences Dept. at Iowa State College sequelae to extinguished retinal stimulation and of Veterinary Medicine. direct pressure effects on the iris stroma (Fig. 2). **Dr. Betts is an Ophthalmology Professor in the Blindness results from retinal ischemia as Deparrtmint of Veterinary Clinical Sciences at elevated lOP prevents normal hemodynamic Iowa State University. flow to this tissue. Therapy instituted to

36 Iowa State University Veterinarian normalize lOP may reoxygenate retinal photore­ Table 2 ceptors in time to restore vision. Digital palpa­ Clinical Signs of Chronic Glaucoma tion of the globe may reveal a "hard eye". This 1. Continued engorgement of conjunctival technique is inconsistently reliable in cases of episcleral vasculature moderate pressure elevations. 2. Buphthalmos As the disease progresses, signs that were 3. Blindness initially variable (Table 1) become reliably 4. Corneal edema present. With chronicity, elevated lOP results in 5. Striate keratopathy enlargement of the globe (buphthalmos), 6. Equatorial staphyloma thinning of the equatorial sclera with uveal 7. Mydriasis herniation (equatorial staphyloma) and rupture 8. Lens luxation/subluxation of Descemet's membrane. Ensuing full thick­ 9. Cataracts ness corneal edema is seen clinically as linear 10. Liquefaction of the vitreous (syneresis) white fissure in the stroma (Fig. 3). 11. cupping Malpositioning of the lens is either the cause of 12. Tapetal hyperreflectivity the glaucoma (ie. anterior luxation) or a sequelae to buphthalmos induced zonular Diagnosis - Tonometry rupture (most subluxations). Cataract formation Establishing a definitive diagnosis can only and liquefaction of the vitreous (syneresis) are be through the measurement of the lOP. The fiequently seen associated with altered aqueous most routinely employed method of estimating dynamics. Ophthalmoscopic examination yields lOP in veterinary practice is digital tonometry. two commonly observed abnormalities. Cup­ Although this method elirrlinates the need to ping of the optic nerve head is seen clinically as purchase additional instrumentation, it is entirely truncated retinal vessels at the optic nerve head too insensitive to assess those subtle pressure which is not in the same plane of focus as the alterations occurring in early glaucoma sus­ remainder of the fundus (Fig. 4).Posterior pects. As such, digital tonometry cannot be mechanical displacement of the lamina cribrosa recommended for the recognition or manage­ with subsequent distortion of the laminar pores ment of glaucomatous where retention of prevents the normal axoplasmic and hemody­ vision is the main objective. namic flow necessary for retinal viability. Instrumentation tonometry is generally Accompanying retinal degeneration is seen as divided into two distinct groups, indentation or tapetal hyperreflectivity, retinal vascular applanation tonometry. Both have their attenuation, and hyperpigmentation of the advantages and disadvantages. The Schiotz® tapetal fundus as pigment infiltrates from the indentation tonometer is the most widely adjacent retinal pigment epithelium (Fig. 4). purchased tonometer for veterinary practice. Eventually the diagnosis is obvious, but not until This instrument measures the amount of corneal vision has been irreversibly lost (Table 2). indentation achieved with the addition of a given, yet variable, amount of weight. Although very cost effective and accurate, this instrument Table 1 does posses a relatively large foot plate, thereby Clinical Signs of Acute Glaucoma making it more susceptible to the influences of 1. Lacrimation "scleral rigidity" or concurrent corneal pathology. 2. Photophobia One other drawback, especially when used in 3. Blepharospasm large animal practice, is that it must be used in a 4. Congestion of conjunctival/episcleral vertical orientation. Alternatively, applanation vessels tonometers have the advantages of a relatively 5. Corneal edema small foot plate and can be used in any orienta­ 6. Mydriasis tion. Compared to indentation units, these 7. Blindness instruments determine the amount of pressure 8. "Hard" eyes required to flatten or "applanate" the given area of cornea below their foot plate. Although numerous models are currently marketed, they are considerably more expensive than the Schiotz® tonometer, and usually are available only at referral centers.

Vol 55, No.1 37 Diagnosis - Classification evaluation of the fellow eye helps to establish Once an elevation in lOP has been deter­ whether it is also at risk. Early surgical interven­ mined, classification of the glaucoma is essential tion in the fellow eye appears to significantly if the correct therapeutic approach is to be prolong normal lOP with subsequent retention of undertaken. Numerous classification schemes vision for these patients. In man the vast have been described to date. One of the most majority of primary glaucoma patients are of the widely accepted systems differentiates glauco­ open angle type. Among dogs only the , mas into one of three headings. Primary toy and miniature have been shown to glaucomas are those cases where there is no fall into this category.2 Narrow angle glaucoma antecedent intraocular disease. When glaucoma is the most common form of primary glaucoma is thought to be the result of pre-existing identified in the dog (Table 3). The remainder intraocular disease it is termed secondary have an incompletely developed drainage angle glaucoma. Commonly observed causes of and are classi'fied as goniodsygenesis. Breeds secondary glaucoma include anterior uveitis, typically exhibiting these findings include Basset hyphema, intraocular neoplasia, lens luxation, Hounds, Bouvier des Flandres, Chihuahua, 0 peripheral anterior synechiae, and 360 posterior Giant Schnauzer, American Cocker Spaniel, synechiae \AJith resultant iris bombe. Establish­ C,..rY\",,,,,,rI ,."nrl ~r'\"'\",,"\+h nnn ,,,,iro ~f'\V Torriorc 2 It uClIIIUyCU, o.IIU ulllVVLI I \AI 1'-4 vv II \J • '-''''''' ...... • .. ing the inciting cause for glaucoma maximizes is important to realize that although individuals the chance for successful pressure control as of these breeds often have gonioscopically­ standard medical therapy of primary glaucoma apparent angle abnormalities, they may also is routinely unsuccessful in these individuals. have enough unaffected angle to permit normal Although the management of secondary outflow thereby avoiding clinically evident glaucoma is beyond the scope of this article, elevations in lOP. Basset hounds and American those glaucomas which are secondary to uveitis Cocker Spaniels are the two breeds most likely are best managed by aggressive to develop clinical disease. antiinflammatory therapy, while those resulting from lens luxation must ultimately be corrected with intracapsular lens extraction. In the dog Table 3 and cat, secondary glaucoma is more common Narrow Angle Glaucoma encountered than primary glaucoma. Akita Veterinary ophthalmologists believe primary American cocker spaniel glaucoma in the dog is an inherited disorder.3 At present, the mode of inheritance is unknown. Beagle Primary glaucomas are subdivided into three Chihuahua subsets based on gonioscopic evaluation. Dachshund These include open angle glaucoma, narrow/ closed angle glaucoma and goniodysgenesis. English springer spaniel As most veterinary practitioners are not Maltese equipped with goniolenses or gonioprisms, Miniature and Toy poodle evaluation of the drainage angle is first per­ Norwegian elkhound formed by the veterinary ophthalmologist. A Siberian husky simple method of performing using Smooth and Wire fox terriers a +200 to +300 hand held lens has recently Welsh springer spaniels been described.4 After application of a topical anaesthetic to the cornea, the lids are retracted Treatment and the flat side of the condensing lens is gently pressed against the axial cornea such that the There is little doubt that control of lOP in precorneal tear film wets the lens surface. primary glaucoma patients is one of the most Focusing is achieved by the exanliner moving frustrating aspects of veterinary ophthalmology. closer or further from the patient.4 Although Although there have been a wide variety of differentiating between these three subgroups is techniques proposed by a plethora of authors, unlikely to alter the initial therapeutic approach, the traditional approach has been to control lOP it is still of paramount importance to the patient. through medical management for as long as Since the typical glaucoma referral patient has possible, and to treat surgically only when already lost vision in one eye, gonioscopic medical control was lost and vision was

38 Iowa State University Veterinarian compromised.5 A large part of this rational was glaucomas secondary to intraocular inflamma­ based on the poor long-term success of the tion is unlikely to be effective and cannot be available surgical options at that time. With the recommended. Their main role appears to be in recent advent of significantly improved surgical the short term management of low tension devices, the approach to the glaucomatous glaucomas, as chronic usage often results in individual that still displays the potential for systemic metabolic acidosis. salvageable vision, has changed. A variety of topical direct and indirect acting Our present day protocols for the glaucoma parasympathomimetic drugs also have been suspect is to first determine the potential for advocated in the regulation of elevated lOP. In salvaging vision. For those individuals with a man it has been demonstrated that contraction realistic chance of vision retention, initial of the longitudinal ciliary body muscle results in medical management is indicated. Once increased tension on the scleral spur and pressures have been normalized, surgical subsequent opening of the drainage angle. intervention is generally performed. In those Although a scleral spur has yet to be identified in cases where there is no hope for vision, surgical domestic animals, the use of these drugs have intervention at the surgeons convenience is been extrapolated to these species. In individu­ indicated, with administration of systemic als with a narrow angle glaucoma it is postu­ analgesic medication during the interim. lated that with a pupillary dilation the base of the iris becomes thickened and loose, resulting in ~v1edical Managernent an increased tendency to crowd the already Therapeutics used in glaucoma management compromised drainage angle. Stimulation of the fall into one of 'five classes (Table 4). When constrictor pupillae muscle draws the base of there is a significant elevation in lOP the most the iris axially thereby opening the angle and efficacious class of drugs is the osmotic improving outflow. These smooth muscle diuretics. These drugs function, not through stimulatory effects in combination with occa­ their ability to induce diuresis, but rather through sional contact sensitivity are responsible for the the generation of a hypertonic serum. As serum variable signs of ocular irritation seen in some osmolality increases, fluid is drawn into the patients receiving these medications. vascular compartment from the intracellular and Use of drugs within the following two extracellular fluid spaces. In the presence of an categories are also direct extrapolations from intact blood-eye barrier, fluid is selectively drawn human glaucoma therapy. In general, these from the vitreous and aqueous humor into the products have failed to show consistently periocular vasculature. In eyes with concurrent reproducible clinical success in the manage­ uveitis, the overall efficacy of osmotic diuretics ment of our veterinary glaucoma patients. often is significantly reduced. The clinician must Possible reasons for these disappointing results be cautious when these drugs are used in the may lie in the fact that although the vast majority presence of cardiovascular insufficiency as the of primary glaucoma in the dog are narrow resultant vascular hypertension could further angle glaucomas, in man primary open angle compromise these patients. glaucomas are the routine. As such it may be The second class of drugs is the carbonic unreasonable to expect significant clinical anhydrase inhibitors (CAl). These drugs reduce improvement in our patients while on these the active transport component of aqueous medications. humor production by interfering with the Direct acting sympathomimetic drugs appear carbonic anhydrase enzyme at the level of the to act primarily through their beta effects. nonpigmented ciliary body epithelium. Although Stimulation of beta receptors results in in­ reducing the rate of aqueous formation in creased cAMP activity in the region of the individuals who suffer from a decreased drainage angle resulting in increased outflow coefficient of outflow seems unphysiologic, the facility and decreased lOP. Conversely, net effect is often favourable. It should be noted topically applied beta blockers appear to that the active transport component of aqueous decrease cAMP activity in the region of the humor production often is reduced in the ciliary body processes resulting in decreased presence of significant intraocular inflammation aqueous formation and reduced lOP. Interest­ or elevated lOP. Therefore, using these drugs ingly, in man, combining an agonist (epineph­ as the primary therapeutic regimen in the rine) and an antagonist (timolol/betaxolol) have management of high tension glaucomas or an additive effect to decrease lOP.6 Although

Vol 55, No.1 39 clinical trials in domestic animals suggest that created w~lich extends deep enough to involve such protocols are often unsuccessful in the underlying ciliary body and epithelium. The regulating the problem, research on human goal of this procedure is not to produce massive patients has shown that these results are likely necrosis of tissue, but rather to cause focal areas obtained through an "anatomic separation of of atrophy and fibrosis of the ciliary body and activity"; i.e. epinephrine affecting the outflow covering epithelium with resultant decrease in 11 pathways I timolol and betaxolol influencing the aqueous humor production. ,12 The initial effects 6 ciliary processes • are a related to tissue dehydration. This results in increased electrolyte concentration and cell Table 4 membrane lipoprotein denaturation as extracellu­ lar and intracellular water crystallization occur. 11 Medical Management of Glaucoma A fast freeze is preferred. Slow "freezes result in 1. Osmotic diuretics a progressive depression of the cytoplasmic (i) mannitol (IV) @0.5-1 gml lb. orally freezing point as the extracellular ice crystals pull over 20-30 ITlin. free water from the cells. Thus, intracellular ice (ii) glycerol (oral) @ 0.3-0.5 mil lb. crystallization is less likely to occur and lethal 2. Carbonic anhydrase inhibitors changes in the cell may be delayed.11 This (i) dichiorphenamide (DaJanide+) @ problem can be minimized using a fast freeze 1- 2 mgl lb. PO BID cycle as this results in both intracellular and (ii) methazolamide (Neptazane+) @ extracellular ice crystal formation. With this in 2-4 mgl lb. PO BID mind the trend has been away from nitrous oxide (iii) acetazolamide (Diamox+) @ 5 units and towards liquid nitrogen systems. mgl lb. PO BID Typically a 2.5 mm or 4 mm probe is applied to 3. Miotics the globe 4-6 times approximately 5 mm caudal (i) pilocarpine @ 0.5/1 .012.0 0/0 to the limbus.8,1o,11 As a result of ciliary body topical sol's. temperatures achieved in experimental studies, it (ii) echothiophate (Phospholine has been recommended that the probe remain iodide+) @ 0.06-0.25 % 1 gtt. bid activated until the resultant ice ball extends into (iii) demecarium bromide (Humorsol+) the cornea 1 mm beyond the Iimbus. 11 This @ 0.125/0.25 % 1 gt1. bid appears to provide reliable freezing to the 4. Adrenergic (sympathomimetics) drugs underlying ciliary body. (i) epinephrine - 1 gt1. bid This procedure can be repeated if initial (ii) dipyvalyl epinephrine (Propine+) results are not satisfactory. Chemosis, 1 gt1. bid conjunctivitis, corneal granulation tissue, iris 5. Beta - blockers depigmentation, choroidal effusion with retinal (i) timolol (Timoptic+)- non selective detachment, uveitis, transient elevations in B1 + B2 antagonist; 1 gt1. bid 7 9 10 intraocular pressure - , and phthisis bulbi all (ii) betaxolol (Betoptic+)- selective have been described. As such, most patients B1 antagonist; 1 gt1. bid are treated postoperatively with oral carbonic anhydrase inhibitors and systemic analgesics. It 8 Surgical Management - Visual Eyes is the opinion of certain authors ,9 that the high Veterinary ophthalmologists generally agree prevalence of retinal detachments and postop­ that long term control of glaucoma patients in erative intraocular elevations in lOP should veterinary medicine has been extremely restrict the use of this procedure for non-visual unrewarding. One of the initial surgical attempts mildly buphthalmic globes. Here it routinely was with the application of heat to the ciliary provides relief 'from pain and a cosmetically 8 body by 'first passing an electrode through the acceptable endpoint ,9. At present transscleral overlying sclera. This process of cyclodiathermy cryosurgical destruction of the ciliary body was soon abandoned due the cOlTlplications of remains the most common surgical procedure postoperative inflammation and fistulation.7 used to treat dogs with glaucoma.13 Conversely, Cyclocryosurgery was attelTlpted, first with a in man it has been recommended as a method of 8 10 nitrous oxide - sources and later using liquid treating a variety of causes of glaucoma includ­ 8 nitrogen. ,9,11,12 In this procedure a cryoprobe is ing open and closed angle glaucomas.12 placed on the bulbar conjunctiva approximately More recently, cyclophotocoagulation has 5 mm caudal to the limbus and an ice ball is been employed as an alternative method to

40 Iowa State University Veterinarian reduce aqueous humor production in an effort to surgical site, these techniques are now largely regulate lOP in normotensive? and of historical interest.2,13 glaucomatous individuals.13 In domestic a.nimals One of the new and evolving areas in canine the energy source being used is the neodymium glaucoma research is the use of anterior : yttrium, aluminum, and garnet (Nd :YAG) chamber implants. Currently there are a wide laser. This instrument emits light in the near variety of implant devices being used for infrared spectrum ( wavelength = 1,060 nm) glaucoma management in both man and dog. All which is produced by the photic stimulation of incorporate a hollow silicon tube which 'function the neodymium atoms suspended in a crystal of as a sclerostomy opening to shunt aqueous to yttrium, aluminum, and garnet.? At the present the adjoining polypropylene or silicon foot plate time, the uses of thermal Nd :YAG lasers in (scleral explant) (Fig. 5) Emergent aqueous veterinary ophthalmology include transpupillary collects in the surrounding filtering bleb and is and transscleral cyclophotocoagulation and ultimately taken up by the regional vascular iridotomy.13 Initial results of its use in both channels. 16 Following the development of normotensive and glaucomatous individuals postoperative fibrosis at the 'filtration site, this suggest a prornising future in the regulation of area acts as the main regulator of lOP. Surgica.l lOP in the dog.?·13 Commonly encountered post implantation involves incising a variable length of operative complications include focal conjunctival dorsal bulbar conjunctiva and dissecting hyperemia and edema, aqueous flare with posteriorly to accommodate the scleral explant concurrent iritis, mild diffuse corneal edema and The explant is then secured to the underlying variable ciliary hemorrhage and necrosis.? When sclera and a tunneling dissection between the followed to 24 weeks, occasional cataract conjunctiva and underlying sclera is extended formation was encountered. 13 Of those anteriorly towards the limbus. A few millimeters glaucomatous individuals which were not caudal to the limbus is the site of globe penetra­ controlled by this procedure, 75% had reduced tion. This is often performed using a 20-22 uveal pigmentation. This is not surprising as gauge hypodermic needle after which the silicon thermal energy is preferentially absorbed by tube is trimmed to the appropriate length and pigmented tissues.? Comparison with inserted into the anterior chamber. Finally, the cyclocryosurgery suggests that this procedure is overlying wound is reapposed and the anterior associated with less pain, inflammation, chamber reformed (Fig. 6). There is controversy exudational retinal detachments and a shorter as to whether non-valved systems require period of postoperative intraocular hyperten­ temporary ligation to prevent the immediate sion.?·13 These encouraging findings must be postoperative hypotony seen in man. The exact tempered by the apparent cataractogenic depth in the subconjunctival tissue that the potential along with the inherent cost and limited scleral explant should be in order to optimize the availability of the instrumentation. duration of useful drainage also rema.ins to be determined Although none have proven to be Filtration Procedures superior under all conditions, studies with limited Given that the problem is one of decreased numbers of patients suggest this is a signi'ficantly outflow rather than overproduction, a more improved method for control of canine glauco­ physiological approach would attempt to facilitate mas.5,16 aqueous outflow. Such filtration surgeries can Development of gonioimplants in the dog has best be divided into one of two groups, those only recently been reexplored. First implanted in with implants and those without. A wide variety canine patients in the late 1970's, the original of non-implant procedures have been described Krupin-Denver Valve was tested in both normo­ all of which involve creation of a new conduit for tensive and glaucomatous beagle dogs.1? The aqueous outflow. These include iridencleisis, initial success of these implants proved to be of cyclodialysis, peripheral iridectomy, combined short duration. The primary problem with this iridencleisis-cyclodialysis, corneoscleral trephina­ implant lay in the fact that the posterior end of tion-peripheral iridectomy, cyclodialysis­ the sclerostomy tubing terrninated abruptly in the iridocyclectomy, and posterior sclerectomy­ anterior subconjunctival space without the benefit cyclodialysis-transscleral iridencleisis. 2, 13-15 of an adjoined scleral explant. This resulted in Based on the high degree of expertise required premature scarring and drain occlusion.5 More of the surgeon, along with the tendency for early recently a modi'fication of the Joseph one-piece failure secondary to scarring and 'fibrosis at the drainage implant was used in 15 dogs (21

Vol 55, No.1 41 eyes).18,19 Results obtained over a follow-up eventual size of the globe, based on the size of period of nine months or more suggested the previously selected intraocular prosthesis, it superior long term control over all other currently is not recommended in the presence of corneal used surgical techniques. 18 The principle ulceration or degeneration. Where there is difference between this implant and the previ­ concern of intraocular infection or neoplasia all ously described Krupin-Denver Valve is the affected globes should be enucleated and sent to addition of a large silicon rubber strap-like scleral a veterinary pathologist for histopathologic explant used to distribute the emergent aqueous evaluation. over a much greater surface area. Once the fluid had accumulated in this filtration reservoir it was Summary subsequently absorbed and removed by the surrounding efferent vasculature. As clinical Appropriate management of the glaucoma trials continued, it was determined that the valve suspect requires early recognition of the clinical assembly in this device was unnecessary for the signs and prompt initiation of therapy. Accurate canine as there was no evidence of significant diagnosis can only be established through the postoperative hypotony and anterior chamber use of a mechanical tonometer. Determining the collapse as is routinely observed in man. It was existence of antecedent intraocular disease also the opinion of the author that the vaive may pen-nits selection of the most appropriate interfere with drainage of the copious amounts of therapy. Secondary glaucoma is more common surgically induced exudate often encountered in than primary glaucoma in the dog. Although the the dog, reSUlting in early tube occlusion. 18 To exact mode of inheritance is undetermined, most test this theory many of the implants had their veterinary ophthalmologists believe primary valve assemblies modified to be nonfunctional. glaucomas to be inherited. Treatment of Overall success rates at nine months following secondary glaucoma is directed at the inciting surgery approached 80% with approximately cause. Medical management of primary is only 50% still receiving additional hypotensive recommended for immediate pressure stabiliza­ medication.18 It should be noted that all individu­ tion in eyes where vision is felt to be salvage­ als in this study18 were selected only after able. Long-term management requires surgical medical therapy was found to be inappropriate or intervention. History shows the evolution of ineffective. Furthermore, vision was also numerous medical and surgical options used to maintained in eyes that received surgery prior to regulate lOP. Where such a diversity of tech­ clinically detectable damage to the optic niques exist, likely none excel. Perhaps the nerve.16,18 initially favourable results achieved through the use various gonioimplants will establish this as Surgical Managenlent - Nonvisual Eyes the definitive method of regulating lOP, and more The primary goal of therapy in non-visual importantly preservation of vision, in these eyes is pain relief, while attempting to produce a patients. cosmetically acceptable result for the client. Cyclocryosurgery is exceedingly useful in this References role and is routinely utilized by many veterinary ophthalmologists for this purpose. An alternative 1. Dorland. Medical Dictionary. In: Dorland, ed. method used to permanently reduce aqueous Medical Dictionary. 26th ed. production is that of an intracameral injection of a Philadelphia, PA: W.B. Saunders. 1981. gentamicin/dexamethasone solution. Following administration of the solution, the clinician is 2. Gelatt KN. liThe Canine Glaucomas. 1I In: unable to accurately estimate the final size of the Gelatt, ed. Veterinary Ophthalmology. 2nd ed. treated globe. Furthermore, safe and effective Malvern, PA: Lea & Febiger. 396-428. 1991. introduction of this solution into the globe requires initial aspiration of liquefied vitreous. If 3. Rubin LF. Inherited Eye Diseases in Pure­ not liquefied, the vitreous is difficult or impossible bred Dogs. Baltimore, Maryland: Williams & to aspirate. A third option is the introduction of a Wilkins. 1989. medical grade silicon ball following removal of the entire contents of the globe (evisceration) 4. Bedford PCG. IIA Simple Method of through a linear incision in the dorsal sclera. Gonioscopy for the Dog and Cat. 1I Journal of Although this offers a certain predictability to the Small Animal Practice. 26: 407- 410. 1985.

42 Iowa State University Veterinarian 5. Gelatt KN, Brooks DE. "lssues in Ophthal­ 13. Nasisse MP, Davidson MG, English RV, et mic Therapy: The Development of Anterior al. "Treatment of Glaucoma by Use of Chamber Shunts for the Clinical Management of Transscleral Neodymium:yttrium Aluminum the Canine Glaucomas." Progress in Veterinary Garnet Laser Cyclocoagulation in Dogs." & Comparative Ophthalmology. 2(2): 59-64. Journal ofthe American Veterinary Medical 1991. Association. Aug 1; 197(3): 350-354. 1990.

6. Flach AJ. "Current Concepts of Adrenergic 14. Ashby S, Playter RF, Herron MA. "Pictoral

Pharmacology. II In: Stanford Basic Science Guide for a Surgical Therapy for Glaucoma: Course in Ophthalmology. Stanford University. Sclerectomy, Cyclodialysis and Iridocyclectomy 52-53. 1992. (After Va.inisi)." Canine Practice. 11 (1): 42-43. 1984. 7. Nasisse MP, Davidson MG, Maclachlan NJ, et al. "Neodymium:yttrium, Aluminum, and 15. Pieffer RL, Jr., Gwin RM, Gelatt KN. "Com­ Garnet Laser Energy Delivered Transsclerally to bined Posterior Sclerectomy, Cyclodialysis a.nd the Ciliary Body of Dogs." American Journal of Trans-Sclerallridencleisis in the Management of Veterinary Research. Nov; 49(11): 1972-1978. Primary Glaucoma." Canine Practice. Jun: 54­ 1988 61. 1977.

8. Roberts SM, Severin GA. "Cyclocryotherapy 16. Bedford PCG. "A Clinial Evaluation of a - Part II - Clinical Comparison of Liquid Nitrogen One-Piece Drainage System in the Treatment of and Nitrous Oxide Cryotherapy on Canine Glaucoma." Journal ofSmall Animal Glaucomatous Eyes." Journal ofthe American Practice. 30: 68-75. 1989. Veterinary Medical Association. 20: 828-833. 1984. 17. Gelatt KN, Gum GG. "Evaluation of the Krupin-Denver Valve Implant in Normotensive 9. Vestre WA. "Use of Cyclocryotherapy in and Glaucomatous ." Journal ofthe Management of Glaucoma in Dogs." Modern American Veterinary MedicalAssociation. Veterinary Practice. Feb: 93-97. 1984. Dec 1; 191 (11): 1404-1409. 1987.

10. Brightman AH, 11., Vestre WA, Helper LC, et 18. Bedford PCG. "A Clinical Evaluation of a al. "Cryosurgery for the Treatment of Canine One-Piece Drainage System in the Treatment of Glaucoma." In: ProcAmColIVetOphthal. 157­ Canine Glaucoma." Journal ofSmall Animal 143. 1980. Practice. 30: 68-75. 1989.

11. Roberts SM, Severin GA. "Cyclocryotherapy 19. Bedford PCG. "Use of a One-Piece Drain­

- Part I- Evaluation of a Liquid Nitrogen System. II age System in the Treatment of a Closed Angle Journal ofthe American Animal Hospital Glaucoma in a Dog." Journal ofSmall Animal Association. 20: 823-827. 1984. Practice. 29: 231-237. 1988.

12. Vestre WA, Brightman AH. II, "Ciliary Body Temperatures During Cyclocryotherapy in the Clinically Normal Dog." American Journal of Veterinary Research. Jan; 44(1): 135-143. 1983.

Vol 55, No.1 43 Fig. 1 Clinal signs include lacrimation, photophobia, blepharospasm and variable congestion of the conjunctival/episcleral vessels.

Fig. 2 Corneal stromal edema with resultant Fig. 3 Linear areas of full thickness corneal 3600 vascular invasion, mydriasis, edema superimposed on a diffusely and continued engorgement of edematous stroma, persistence of the conjunctival/episcleral vessels. mydriasis, corneal vascularization and congestion of the associated vessels.

44 Iowa State University Veterinarian Fig. 4 Cupping of the optic nerve head, diffuse retinal degeneration with accompanying tapetal hyperreflectivity, retinal vascular attenuation, and mottled depigmentation of the RPE in the non-tapetal fundus.

Fig. 5 Baerveldt® gonioimplant Fig. 6 Baerveldt® implant immediately prior to implantation. postoperatively.

Vol 55, No.1 45