Retinal detachment

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Fundic photograph of the eye of an 8-year-old Llasa Apso with retinal detachment[1]
Pigmented choroidal melanoma adjacent to the optic nerve in a fundus of a 9-year-old Labrador Retriever[2]

Retinal detachment is a relatively common ophthalmic disorder of dogs characterized by separation of the retina from the underlying retinal pigment epithelium and is a leading cause of vision loss in this species.

The retinal pigment epithelium, which is the primary site for various retinal diseases, is sandwiched between the photoreceptors and choriocapillaries. The tight junctions formed between the retinal pigment epithelium cells prevent passive diffusion of molecules and serve as a blood–retina barrier. Unlike most epithelia, which have their apical side face toward the lumen, the apical surfaces of retinal pigment epithelium cells are in close contact with the subretinal space and neural photoreceptors throughout development[3].

Although trauma has been cited as an initiating factor in retinal detachment, retinal detachment in dogs is commonly associated with underlying systemic or local ocular disease. Regardless of cause, pathologic intraocular neovascularization is a key component in separation of the retina from the underlying retinal pigment epithelium[4].

After the retina detaches in dogs, the retinal pigment epithelium changes rapidly, with hypertrophy and hyperplasia, and the epithelial cells may detach from their basement membrane and become migrating cells with macrophage-like properties[5]. When the detachment is chronic, hyphema and uveitis are common sequelae, due to the development of pre-iridal fibrovascular membranes[6].

The degeneration of a detached retina is progressive and begins initially within hours of detachment as a wave of apoptosis spreads across the outer nuclear layer. When photoreceptors are separated from the retinal pigment epithelium, the outer and inner segments of the rods and cones degenerate quite rapidly and the retinal pigment epithelium hypertrophies[7].

After several weeks, the outer and inner segments of the photoreceptors atrophy, and the entire outer retina will eventually degenerate including the outer nuclear and plexiform layers and the inner nuclear layer as well[1].

A number of forms of retinal detachment can occur but the most common in dogs is rhegmatogenous retinal detachment which commonly develops secondary to fibrous vitreous traction bands, as a result of trauma or vitreous inflammation and degeneration[8], frequently resulting in giant retinal tears, commonly seen in Shih Tzu[9][10], Springer Spaniel, Poodle, Bichon Frise, Labrador Retriever.

Other forms of retinal detachment include bullous retinal detachment (separation of the neural retina from the retinal pigment epithelium, due to accumulation of fluid and or cellular debris)[11], tractional retinal detachment and posterior vitreous detachment.

A feature of retinal detachment is persistent retinal vascularisation of the vitreous membrane[12] and elevated levels of vascular endothelial growth factor[13] which exacerbate retinal inflammation.

Causes of retinal detachment include:

- Vitreous degeneration in Shih Tzu, Boston Terrier, Poodle, Brussels Griffon, Chihuahua, Havanese, Italian Greyhound, Lowchen, Papillon, Whippet
- Retinal pigment epithelial dystrophy (retinal dysplasia) in English Cocker Spaniels[14], Springer Spaniel, Labrador Retriever, Miniature Schnauzer[15]
- Uveodermatologic syndrome[16]
- Oculoskeletal dysplasia in Labrador Retrievers and Samoyeds[17]
- Multifocal retinopathy in Great Pyrenees dogs[18]
- Collie eye anomaly in Collie breeds, Australian shepherds[19]
- Persistent hyperplastic primary vitreous[20]
- Toxocara spp[24]
- Anaplasma phagocytophilum infection[25]
- Ehrlichia spp[26]
- Leptospira spp[27]
- Iridociliary cysts (benign)[28]
- Choroidal melanoma[2]
- Retinoblastoma

Retinal detachment in dogs may be partial or focal, and not perceptibly affect vision, or it may be complete and the affected eye is blind. However, in most dogs retinal detachment, unless bilateral, is usually subclinical and manifest with only mild pupillary dilation (anisocoria) to the affected eye. In many cases, the menace responses and the palpebral, oculocephalic, and direct and consensual pupillary light reflexes are present in both eyes. A Schirmer tear test should be performed to exclude keratoconjunctivitis sicca and tonometry (<25 mmHg) to exclude concurrent glaucoma. The pupils are usually dilated with tropicamide for a full fundic examination.

Diagnosis is usually confirmed by ophthalmoscopic examination, and in cases complicated by corneal opacity, ultrasonographic imaging may be required[29].

Medical treatment involves use of topical glucocrticoids to minimize vitreous inflammation and antiglaucoma medications.

Surgical repair of retina detachment requires retinal reattachment via a pars plana vitrectomy, followed by transscleral cryopexy[30] or retinopexy[31]. This is usually reserved to cases where large portions or complete retinal detachment has occurred.

The prognosis for restoring vision is good, provided that the retinal degeneration, which is progressive from the time of detachment until surgical attachment to the retinal pigment epithelium, has not destroyed the entire outer retina[32].

Common complications of surgery include cataract development, silicone prolapse into the anterior chamber, corneal ulceration, retinal degeneration, glaucoma and uveitis.

References

  1. 1.0 1.1 Grahn BH & Sandmeyer LS (2009) Bilateral rhegmatogenous retinal detachments with giant retinal tears. Can Vet J 50(9):989-990
  2. 2.0 2.1 Lim, CC et al (2006) Choroidal melanoma in the right eye with focal retinal detachment. Can Vet J 47(1):85-86
  3. Chuang JZ et al (2010) Chloride intracellular channel 4 is critical for the epithelial morphogenesis of RPE cells and retinal attachment. Mol Biol Cell 21(17):3017-3028
  4. Zarfoss MK et al (2010) Canine pre-iridal fibrovascular membranes: morphologic and immunohistochemical investigations. Vet Ophthalmol 13(1):4-13
  5. Fisher SK & Anderson DH (1998) Cellular responses of the retinal pigment epithelium to retinal detachment and reattachment. In: Marmor MF, Wolfensberger TJ, editors. The Retinal Pigment Epithelium. 2. New York: Oxford Univ Pr. pp:406–419
  6. Hendrix DV et al (1993) Clinical signs, concurrent diseases, and risk factors associated with retinal detachments in dogs. Prog Vet Comp Ophthalmol 3:87–91
  7. Wilcock BP (1993) The eye and ear. In: Jubb KVF, Kennedy PG, Palmer N, editors. Pathology of Domestic Animals. 4. Toronto: Academic Pr. pp:441–529
  8. Vanisi SJ et al (2007) Surgery of the canine posterior segment. In: Gelatt KN, editor. Veterinary Ophthalmology. 4th ed. II. Ames, Iowa: Blackwell Publ. pp:1026–1058
  9. Itoh Y et al (2010) Investigation of fellow eye of unilateral retinal detachment in Shih-Tzu. Vet Ophthalmol 13(5):289-293
  10. Papaioannou NG & Dubielzig RR (2012) Histopathological and Immunohistochemical Features of Vitreoretinopathy in Shih Tzu Dogs. J Comp Pathol Jul 19
  11. Narfstrom K et al (1997) Visual impairment. In: Peiffer RL, Peterson-Jones SM, eds. Small Animal Ophthalmology - A Problem Oriented Approach, 2nd ed. Toronto: WB Saunders. pp:85-165
  12. Labruyere JJ et al (2011) Contrast-enhanced ultrasonography in the differentiation of retinal detachment and vitreous membrane in dogs and cats. J Small Anim Pract 52(10):522-530
  13. Sandberg CA et al (2012) Aqueous humor vascular endothelial growth factor in dogs: association with intraocular disease and the development of pre-iridal fibrovascular membrane. Vet Ophthalmol 15(1):21-30
  14. McLellan GJ & Bedford PG (2012) Oral vitamin E absorption in English Cocker Spaniels with familial vitamin E deficiency and retinal pigment epithelial dystrophy. Vet Ophthalmol 15(2):48-56
  15. Grahn BH et al (2004) Inherited retinal dysplasia and persistent hyperplastic primary vitreous in Miniature Schnauzer dogs. Vet Ophthalmol 7(3):151-158
  16. Blackwood SE et al (2011) Uveodermatologic syndrome in a rat terrier. J Am Anim Hosp Assoc 47(4):56-63
  17. Goldstein O et al (2010) COL9A2 and COL9A3 mutations in canine autosomal recessive oculoskeletal dysplasia. Mamm Genome 21(7-8):398-408
  18. Grahn BH & Sandmeyer LS (2006) Multifocal retinopathy of Great Pyrenees dogs. Can Vet J 47(5):491-492
  19. Lowe JK et al (2003) Linkage mapping of the primary disease locus for collie eye anomaly. Genomics 82(1):86-95
  20. Bayón A et al (2001) Ocular complications of persistent hyperplastic primary vitreous in three dogs. Vet Ophthalmol 4(1):35-40
  21. Leblanc NL et al (2011) Ocular lesions associated with systemic hypertension in dogs: 65 cases (2005-2007). J Am Vet Med Assoc 238(7):915-921
  22. Klein HE et al (2011) Postoperative complications and visual outcomes of phacoemulsification in 103 dogs (179 eyes): 2006-2008. Vet Ophthalmol 14(2):114-120
  23. Sandmeyer LS et al (2007) Diagnostic ophthalmology. Anterior uveitis, cataract, retinal detachment, and an intraocular foreign body. Can Vet J 48(9):975-976
  24. Verallo O et al (2012) Diagnostic aspects and retinal imaging in ocular toxocariasis: a case report from Italy. Case Report Med 2012:984512
  25. Barutzki D et al (2006) Seroprevalence of Anaplasma phagocytophilum infection in dogs in Germany. Berl Munch Tierarztl Wochenschr 119(7-8):342-347
  26. Leiva M et al (2005) Ocular signs of canine monocytic ehrlichiosis: a retrospective study in dogs from Barcelona, Spain. Vet Ophthalmol 8(6):387-393
  27. Townsend WM et al (2006) Leptospirosis and panuveitis in a dog. Vet Ophthalmol 9(3):169-173
  28. Deehr AJ & Dubielzig RR (1998) A histopathological study of iridociliary cysts and glaucoma in Golden Retrievers. Vet Ophthalmol 1(2-3):153-158
  29. Narfstrom K & Peterson-Jones S (2007) Diseases of the canine ocular fundus. In: Gelatt KN, editor. Veterinary Ophthalmology. 4th, ed . Ames, Iowa: Blackwell Publ. pp:944–1025
  30. Braus BK et al (2012) Cataracts are not associated with retinal detachment in the Bichon Frise in the UK--a retrospective study of preoperative findings and outcomes in 40 eyes. Vet Ophthalmol 15(2):98-101
  31. Steele KA et al (2012) Outcome of retinal reattachment surgery in dogs: a retrospective study of 145 cases. Vet Ophthalmol 15(2):35-40
  32. Grahn BH et al (2007) Chronic retinal detachment and giant retinal tears in 34 dogs: Outcome comparison of no treatment, topical medical therapy, and retinal reattachment after vitrectomy. Can Vet J 48:1031–1039