Glaucoma in Dogs

SMALL ANIMAL | OPHTHALMOLOGY ONLINE EDITION

Glaucoma in dogs – (1) cause, clinical signs and diagnosis Glaucomas refer to a large group of neuro-degenerative diseases caused by persistent and ongoing elevation of intraocular pressure. Eventually this will lead to permanent retinal degeneration and blindness owing to loss of the retinal ganglion cells and optic nerve damage (Pizzirani, 2015). Andra-Elena Enache Dr med vet MVM MRCVS On the other hand, elevated intraocular pressure is termed ocular hypertension and should be distinguished from glaucoma. The final outcome is irreversible blindness After graduating with a Masters Degree from the Faculty of and, in some primary glaucoma cases, bilateral enucleation is required. Veterinary Medicine, Bucharest, Andra spent a short time Although elevated intraocular in general practice before pressure is one of the most relocating to the UK. Here, she consistent risk factors for enjoyed working in general glaucomas, development in practice for four years before dogs (Pizzirani, 2015) genetics, completing an ophthalmology ageing, vascular, immunologic internship at the Animal Health and environmental factors Trust, Newmarket. all contribute to the optic nerve degeneration. Andra began her studies toward a European College According to the European of Veterinary Ophthalmology College of Veterinary Diploma at the Royal Veterinary Ophthalmologists Manual, ‘It College in July 2017. is characterised by an elevation of intraocular pressure (IOP) which, when sustained, Outside of work, she enjoys Figures 1 & 2. Intraocular pressure – can be measured using a tonometer. travelling and spending time results in destruction of with her husband and their cat. intraocular structure and function, resulting in blindness. small, rounded probe on to overextension or flexion of The elevated intraocular the cornea – the higher the the neck. When using the pressure occurs mainly with intraocular pressure, the Tonopen, care should be taken developmental abnormalities quicker the probe returns to to gently flatten the cornea or disease processes affecting the instrument (Figures 1 & 2). without causing an obvious the intraocular circulation indentation – false high IOPs and especially the drainage When measuring the IOP, are easily obtained if the tip of aqueous humour from the one should ensure there is no of the Tonopen is pushed eye through the irido-corneal pressure on or underneath with force against the cornea. angle (ICA). the neck of the patient – Blepharospasm may also for example, tight collars, falsely elevate the IOP owing ‘Diagnosis and classification of harnesses, owners holding to eyelid spasm. glaucoma requires measurement – or on the eye globe itself. of the IOP (tonometry) and When opening the eyelids, the Repeated measurements examination of the iridocorneal fingers should rest on the bony should be taken. If in doubt, angle (gonioscopy). DNA- orbital rims, not on the eye; admit the dog for an IOP tests for primary open angle and it is important to avoid curve (measured every three 1.0 glaucoma (POAG) in specific overstretching the eyelids hours) and monitor in hospital hours* breeds are available.’ as well. (Sanchez et al, 2017). Measuring intraocular The dog should be in a sitting Diagnosis pressure or standing position with It is important to take a *Suggested Personal & Professional This can be performed using the neck straight, and no full history and carry out a Development (PPD) different devices: commonly either by an applanation tonometer (Tonopen) that measures the force to flatten “The final outcome is irreversible blindness a distinct area on the cornea; and, in some primary glaucoma cases, OPHTHALMOLOGY or a rebound tonometer (TonoVet) that expels a bilateral enucleation is required”

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Figures 3-7. Acute onset signs in primary glaucoma cases. thorough general physical Acute onset glaucoma optic nerve head (atrophy), secondary, depending on examination, looking in This is more common in primary attenuation of the retinal their cause. particular for evidence of glaucoma cases (Figures 3-7) as vasculature, cupped optic previous trauma and to rule out evidenced by: nerve head (retinal vessels Congenital glaucoma underlying systemic diseases, severe ocular and head pain stop at the rim of the optic This is rare in the dog. It such as lymphoma. This should lethargy, reduced appetite nerve, no vessels are seen develops within the first few be followed by a full ophthalmic diffuse corneal oedema crossing the optic nerve), months of life (three to six examination: including visual blepharospasm hyperreflectivity of the months) and is a consequence reflexes (‘menace’ response, epiphora tapetum fundus. of extensive goniodysgenesis dazzle and pupillary light marked conjunctival or trabecular meshwork reflexes), pupil size (miotic/ hyperaemia and, sometimes, Chronic glaucoma maldevelopment. Different mydriatic), fluorescein test, mucoid discharge that can be Signs of chronic structural genes have been tonometry (TonoPen/TonoVet), misdiagnosed as conjunctivitis glaucoma include: associated with the trabecular funduscopy and gonioscopy. third eyelid protrusion Haab striae – breaks in meshwork malformation. marked episcleral Descemet membranes Ocular ultrasonography vascular congestion secondary to stretching of Primary and secondary is useful in order to rule mid- to large dilated and the globe glaucomas can be difficult to out intraocular neoplasia, unresponsive pupil buphthalmos – a permanently distinguish clinically. intraocular haemorrhage, deep perilimbal enlarged eye caused vitriitis/vitreous membranes, corneal vascularisation by chronically elevated Primary glaucoma and retinal detachment. mild aqueous flare or intraocular pressure Primary glaucoma is a pigment dispersion in the scleral thinning and bilateral disease that occurs Depending on the stage of the anterior chamber visualisation of the underlying spontaneously with no evidence disease, glaucomas can be changes to appearance of choroid owing to of trauma or other intraocular classified as acute or chronic. the optic nerve – pale or dark globe enlargement disease. There is an increased phthisis bulbi – in advanced incidence of the condition with cases, when the ciliary age and this could be the result of body stops producing changes in the iridocorneal angle “Glaucomas, however, can easily mask aqueous humour. seen with age (Palko et al, 2016). underlying systemic diseases, such as Glaucomas can be classified Primary glaucomas are infectious uveitis and neoplasia” into congenital, primary and classified on the gonioscopic

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appearance as open-angle retriever, Siberian husky, glaucoma – seen particularly cocker spaniel, English in the beagle, petit basset springer spaniel and Welsh griffon vendeen, basset springer spaniel. hound, shar pei, Norwegian elkhound – and closed-angle Primary closed-angle glaucoma which is seen in glaucoma (PCAG) the majority of breeds, for This is the most common example, the cocker spaniel form of primary glaucoma in IRIS and Welsh springer spaniel. dogs. There is a strong breed predisposition – American ICA The ICA can be assessed by cocker spaniel, basset hound, gonioscopy and an abnormal chow chow, Welsh springer ENDOTHELIUM appearance is termed spaniel, miniature and toy goniodysgenesis. This occurs poodles, great Dane – as well KOEPPE LENS owing to a defect in the as a genetic influence. In most development of the angle, breeds, there is a significant Figure 8. In order to perform gonioscopy, a special contact lens which can have a decreased female predisposition and (goniolense, such as the Koeppe lens) is placed on the surface of the width or malformation of the most dogs are middle- to cornea to change the refraction angle of the incoming light. pectinate ligament (Miller and older-aged. Bentley, 2015). A dog can be considered to In order to perform gonioscopy, have PCAG, if it is presented a special contact lens with clinical signs of glaucoma (goniolense, such as the Koeppe (mydriasis, blepharospasm, lens) is placed on the surface elevated IOP), with absence of the cornea to change the of other intraocular diseases refraction angle of the incoming (neoplasia, chronic uveitis light (Figure 8). The ICA with iris bombe, lens can then be visualised using luxation), and abnormal a slit lamp biomicroscope. ICA at gonioscopy of the The pectinate ligament (thin contralateral unaffected eye fibres from the iris base to its (Miller and Bentley, 2015). insertion at the cornea) and the iridocorneal angle width An acute presentation are evaluated by gonioscopy of glaucoma – with no – the latter to determine its other intraocular findings proportion of 360 degrees. A in a dog included on grading scheme of the changes the list of predisposed visualised at gonioscopy is in breeds for PCAG – should place to classify the degree raise the suspicions of of goniodysgenesis – open, primary glaucoma and narrow, closed, closed angle. prophylactic treatment of the contralateral eye should The degree of goniodysgenesis be considered. also changes with age. Evaluation of the ICA in the Early diagnosis and treatment affected glaucomatous eye is essential, because may be difficult because of the normalising the intraocular presence of corneal oedema; pressure reduces the therefore, a gonioscopy of the progression of the disease contralateral unaffected eye is and prolongs the retention recommended. This technique of vision. Therefore, referrals requires practice and training of glaucoma cases should be under specialist supervision. made early, if not straight after, diagnosis. However, despite A list of breeds recognised treating the initial pressure to be predisposed to spike event promptly, the goniodysgenesis may be disease continues to progress. found under the BVA Eye Health Scheme available When presented in the acute online. Pre-eminent among congestive phase, the visual Figures 9-12. Secondary glaucoma occurs when the aqueous humour these are the dandie dinmont reflexes are reduced or absent; outflow is impeded by the presence of other intraocular diseases. terrier, Japanese shiba inu, but they can return if the Leonberger, flat-coated intraocular pressure normalises

“Early diagnosis and treatment is essential, shih tzu and Jack Russell Summary terrier – were found to be at Glaucoma is an irreversible because normalising the intraocular increased risk of glaucoma blinding disease defined by following cataract surgery in a degenerative changes of the pressure reduces the progression of histopathological study (Scott retinal ganglion cells and optic the disease and prolongs the retention et al, 2013). nerve. Elevated intraocular pressure is a consistent risk of vision” Pupil block glaucoma factor in dogs. Early diagnosis This occurs with anterior lens and treatment are essential luxation, anterior vitreous to the prolongation of vision. quickly. The normal canine hyphaema or hypopion in prolapse, mature diabetic Ultimately, all glaucoma cases retina begins to show evidence the anterior chamber, keratic cataracts (intumescent might have the same outcome of effects from an elevated precipitates, iris bombe, lenses) and extensive and require enucleation to IOP at 33mmHg (Gelatt KN anterior or posterior synechiae posterior synechiae. Aqueous restore comfort. et al, 2013). Lowering IOP – which could help in guiding humour circulation from the is critical for maintaining the diagnosis. Pre-iridal posterior to anterior chamber Glaucomas, however, can vision. The optic nerve axons fibrovascular membranes is impeded owing to pupil easily mask underlying are sensitive to pressure (PIFMs) form with chronic block and cannot exit via systemic diseases, such oscillations and their flow uveitis and lead to iris bombe the conventional outflow as infectious uveitis and becomes 100 per cent and obstruction of the (iridocorneal angle). This neoplasia. Therefore, obstructed at an IOP aqueous humour circulation leads to increased pressure submission of the enucleated of 50mmHg (Gelatt KN in the eye and impaired in the posterior chamber, eyes for histopathological et al, 2013). outflow. Always examine the which then displaces the examination is always contralateral ‘unaffected’ eye, iris anteriorly towards the recommended in order to gain Primary open-angle which can reveal subtle signs cornea. The ICA becomes a better understanding of the glaucoma of uveitis, such as flare and narrow and collapses. underlying disease process Primary open-angle glaucoma cells in the anterior chamber. and to rule out intraocular is the least common form of This can be visualised on neoplasia or evidence of glaucoma in dogs and has Cataracts slit lamp examination as the metastatic disease. been linked to a mutation in Cataracts can cause anterior chamber becomes the ADAMTS10 and ADAMTS phacolytic uveitis via the very shallow and the iris The author wishes to express 17 genes in several breeds – ‘leakage’ of proteins in is swollen and anteriorly her thanks to Dr Ursula beagle, Norwegian elkhound, the anterior chamber or displaced (‘iris bombe’). Dietrich, DiplACVO, ECVO, basset hound and petit basset phacoclastic uveitis owing for reviewing this article. griffon vandeen (Komáromy to rupture or tear of the lens Glaucoma secondary to Part 2 will be published in and Petersen-Jones, 2015). capsule (in diabetic cataracts). iridociliary cysts has been the March/April 2019 issue of The iridocorneal angle is Glaucoma occurs either as reported in several breeds – Veterinary Practice Today. normal initially, however it the result of the tumescence golden retriever, great Dane – progressively closes during of the lens – which occludes and although the mechanisms successive months to years the ICA (phacomorphic are not completely owing to the effects of glaucoma); or secondary to understood, it is thought that elevated intraocular pressure. uveitis resulting from extensive glaucoma occurs secondary to posterior synechiae, or anterior displacement of the Secondary glaucoma PIFMs, or secondary to retinal iris and occlusion of the ICA This occurs when the aqueous detachment or inflammation (Pumphrey et al, 2013; Holly et humour outflow is impeded of the vitreous (vitriitis) and/or al, 2015). by the presence of other secondary traction bands. intraocular diseases, such Retinal detachment can lead as uveitis, cataract, post- The incidence of postoperative to glaucoma as a result of the phacoemulsification, iridociliary hypertension after obstruction of the ICA with cysts, lens luxation, neoplasia, phacoemulsification was photoreceptor outer segments retinal detachment and reported to be 18 per cent – released during degeneration haemorrhage (Figures 9-12). in non-Labrador retriever of the retina – and formation dogs and 33 per cent in of PIFMs secondary to retinal Diagnosing glaucoma Labrador retrievers. The latter hypoxia (Matsuo et al, 1986). secondary to chronic are also at increased risk uveitis can be difficult as of postoperative glaucoma Intraocular neoplasia causes inflammation is present in all and blindness – the risk obstruction of the ICA – cases of glaucomas (Weinstein further increasing with anterior uveal melanocytoma et al, 2007). age and whether they had or iris melanoma, for example postoperative hypertension – owing to the space- Signs of active or chronic (Moeller et al, 2011). occupying lesion. When uveitis may already be present Furthermore, other breeds the iris is expanded by the in the glaucomatous or – such as cocker spaniel, tumour, secondary uveitis contralateral eye – with fibrin, Boston terrier, bichon frise, also occurs.

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PPD Questions

1. With respect to primary glaucoma, which of the following sentences is FALSE? A. dogs with primary open-angle glaucoma have a normal iridocorneal angle initially, which becomes abnormal with the progression of the disease B. iridocorneal angle can be evaluated by gonioscopy and this helps identifying dogs that have goniodysgenesis C. dogs with goniodysgenesis have an increased risk of developing primary closed-angle glaucoma D. you can differentiate primary glaucomas from secondary glaucomas based on the lack of inflammation in the former.

2. Regarding gonioscopy, which of the following sentences is TRUE? A. you can evaluate the iridocorneal angle using a direct ophthalmoscope B. gonioscopy of the glaucomatous eye is easy to perform C. special lenses (e.g. Koeppe) are used to aid visualising the iridocorneal angle with a slit lamp biomicroscope D. the iridocorneal angle does not change with age.

3. Regarding secondary glaucoma, which of the following sentences is TRUE? A. lens luxation and tumescent cataracts cause secondary glaucoma owing to pupil block and impeded aqueous humour flow in the anterior chamber B. uveitis causes secondary glaucoma owing to an increased production of aqueous humour C. secondary glaucoma in chronic uveitis occurs through overhydration of the vitreous humour and posterior displacement of the iris

D. retinal detachment causes secondary glaucoma by anterior displacement of the iris and obstruction of the iridocorneal angle.

A 3. C 2. D 1. Answers

References

Gelatt KN et al (2013). Veterinary Ophthalmology. 5th edn. Ed KN Gelatt, Wiley-Blackwell. Pumphrey SA et al (2013). ‘Glaucoma associated with uveal cysts and goniodysgenesis in American Bulldogs: a case series.’, Veterinary Ophthalmology, 16(5): 377-385. doi: 10.1111/ Holly VL et al (2015). ‘Golden retriever cystic uveal disease: a longitudinal study of vop.12000. iridociliary cysts, pigmentary uveitis, and pigmentary/cystic glaucoma over a decade in western Canada.’, Veterinary Ophthalmology, pp. 1-8. doi: 10.1111/vop.12293. Sanchez RF et al (2017). ‘Design of an intraocular pressure curve protocol for use in dogs’, Journal of Small Animal Practice, 58(1): 42-48. doi: 10.1111/jsap.12600. Komáromy AM and Petersen-Jones SM (2015). ‘Genetics of Canine Primary Glaucomas’, Veterinary Clinics of North America – Small Animal Practice, 45(6): 1159-1182. doi: 10.1016/j. Scott EM et al (2013). ‘Major breed distribution of canine patients enucleated or eviscerated cvsm.2015.06.003. due to glaucoma following routine cataract surgery as well as common histopathologic findings within enucleated globes’, Veterinary Ophthalmology, pp. 64-72. doi: 10.1111/ Matsuo N et al (1986). ‘Photoreceptor outer segments in the aqueous humor in vop.12034. rhegmatogenous retinal detachment.’, American Journal of Ophthalmology, 101(6): 673-679. Available at: http://www.ncbi.nlm.nih.gov/pubmed/3717250 (Accessed: 14 October 2018). Weinstein WL et al (2007). ‘Identification of ocular matrix metalloproteinases present within the aqueous humor and iridocorneal drainage angle tissue of normal and Miller PE and Bentley E (2015). ‘Clinical Signs and Diagnosis of the Canine Primary glaucomatous canine eyes’, Veterinary Ophthalmology, 10(s1): 108-116. doi: 10.1111/j.1463- Glaucomas’, Veterinary Clinics of North America – Small Animal Practice. Elsevier Inc, 45(6): 5224.2007.00586.x 1183-1212. doi: 10.1016/j.cvsm.2015.06.006.

Moeller E et al (2011). ‘Postoperative glaucoma in the Labrador Retriever: incidence, risk factors, and visual outcome following routine phacoemulsification.’, Veterinary Ophthalmology, 14(6): 385-394. doi: 10.1111/j.1463-5224.2011.00896.x.

Palko JR et al (2016). ‘Influence of Age on Ocular Biomechanical Properties in a Canine Glaucoma Model with ADAMTS10 Mutation.’, PloS one. Public Library of Science, 11(6), p. e0156466. doi: 10.1371/journal.pone.0156466.

Pizzirani S (2015). ‘Definition, Classification, and Pathophysiology of Canine Glaucoma’, Veterinary Clinics of North America – Small Animal Practice. Elsevier Inc, 45(6): 1127-1157. doi: 10.1016/j.cvsm.2015.06.002.

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