Canis ISSN: 2398-2942

Diabetic retinopathy

Contributor(s): Dennis E Brooks, Rhea Morgan, David L Williams

Introduction

  • Uncommon complication of chronic diabetes mellitus in dogs.
  • Signs: blood vessel tortuosity, alterations in retinal vessel diameter, retinal hemorrhages and microaneurysms.
  • Diagnosis: history, clinical signs, funduscopy, fluorescein angiography, appropriate tests to rule out other causes of retinal hemorrhages and to evaluate adequacy of control of the diabetes.
  • Treatment: non-specific.
  • Prognosis: fair to good.

Pathogenesis

Etiology

  • The exact cause of diabetes-related vascular lesions in the dog is unknown but is probably multifactorial (Landryet al, 2004; Munana, 1995).
  • Increased aldose reductase activity, nonenzymatic glycosylation of proteins, reduced blood flow and local hypoxia, and altered hematologic functions (especially of platelets and red blood cells) may all play a role (Munana, 1995; Ciullaet al, 2003).

Predisposing factors

General
  • Chronic diabetes mellitus.

Pathophysiology

  • Dogs with experimentally-induced diabetes from administration of alloxan or growth hormone, or from galactosemic diets have been studied as models for diabetic retinopathy (Bloodworth & Molitor, 1965; Engelman & Bloodworth, 1965; Engermanet al, 1977; Kadoret al, 1988 & 2002).
  • These studies have revealed a number of events that probably contribute to the development of diabetic retinopathy:
    • Intramural pericytes in retinal capillaries contain high levels of aldose reductase, which becomes activated as metabolism of persistent hyperglycemia shifts to the production of sorbitol. Pericyte function is altered, with decreased autoregulation of blood flow.
    • Ultrastructurally, thickening of blood vessel wall basement membrane occurs, with subsequent weakening and microaneurysm development (Bloodworth & Mollitor, 1965).
    • Blood vessels may rupture, creating hemorrhages that are visible funduscopically.
    • Increased permeability of blood vessels may lead to local exudation.
    • Hematologic abnormalites associated with diabetes, such as increased red blood cell aggregation and decreased deformability, and increased platelet aggregation and adhesion can also affect retinal blood flow and result in retinal ischemia (Ciullaet al,2003).
    • Persistent hypoxia induces compensatory mechanisms that result in changes in vessel diameter and tortuosity.
  • All of the above changes are similar to early, nonproliferative (background) diabetic retinopathy of people (Takahashi & Wyman, 1992).
  • To date, progression to the proliferative form of diabetic retinopathy, which is characterized by neovascularization, has not been documented in dogs.

Timecourse

  • Diabetic retinopathy appears to take several years (after initial diagnosis) to develop.
  • Proposed duration of diabetes ranges from 2.4-5 or more years, but median duration from time of diagnosis to the discovery of retinal lesions has been reported to be as low as 1.4 years (Landryet al, 2004; Engerman & Kern, 1987; Wymanet al, 1988; Barnett, 1981).
  • It may arise even if the diabetes is diagnosed and treated correctly. Although early studies suggested that rapid glycemic control may decrease the chances of the retinopathy, a recent retrospective study found no correlation between the retinopathy and glycemic control scores (Engerman & Kern, 1987; Munana, 1995; Landryet al, 2004).

Diagnosis

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Treatment

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Outcomes

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Landry M P, Herring I P, Panciera D L (2004) Funduscopic findings following cataract extraction by means of phacoemulsification in diabetic dogs: 52 cases (1993-2003). JAVMA 225 (5), 709-716 PubMed.
  • Ciulla T A, Amador A G, Zinman B (2003) Diabetic retinopathy and diabetic macular edema: pathophysiology, screening, and novel therapies. Diabetes Care 26 (9), 2653-2664 PubMed.
  • Kador P F, Takahashi Y, Akagi Y et al (2002) Effect of galactose diet removal on the progression of retinal vessel changes in galactose-fed dogs. Invest Ophthalmol Vis Sci 43 (6), 1915-1921 PubMed.
  • Muñana K R (1995) Long-term complications of diabetes mellitus, part 1: retinopathy, nephropathy, neuropathy. Vet Clin North Am Small Anim Pract 25 (3), 715-730 PubMed.
  • Takahashi Y, Wyman M (1992) Diabetes-like preproliferative retinal changes in galactose-fed dogs. Arch Ophthalmol 110 (9), 1295-1302 PubMed.
  • Mansour S Z, Hatchell D L, Chandler D et al (1990) Reduction of basement membrane thickening in diabetic cat retina by Sulindac. Invest Ophthalmol Vis Sci 31 (3), 457-463 PubMed.
  • Kador P F, Akagi Y, Terubayashi H et al (1988) Prevention of pericyte ghost formation in retinal capillaries of galactose-fed dogs by aldose reductase inhibitors. Arch Ophthalmol 106, 1099-1102 PubMed.
  • Engerman R L, Kern T S (1987) Progression of incipient diabetic retinopathy during good glycemic control. Diabetes 36, 808-812 PubMed.
  • Small K W, Stefansson E, Hatchell D L (1987) Retinal blood flow in normal and diabetic dogs. Invest Ophthalmol Vis Sci 28 (4), 672-675 PubMed.
  • Ono K, Yasuda K, Iwata H et al (1986) Fluorescein angiogram in diabetic dogs. Jpn J Vet Sci 48 (6), 1257-1261 PubMed.
  • Toole D O, Miller G K, Hazel S (1984) Bilateral retinal microangiopathy in a dog with diabetes mellitus and hypoadrenocorticism. Vet Pathol 21 (1), 120-121 PubMed.
  • Ernest J T, Goldstick T K, Engerman R L (1983) Hyperglycemia impairs retinal oxygen autoregulation in normal and diabetic dogs. Invest Ophthalmol Vis Sci 24 (7), 985-989 PubMed.
  • Barnett K C (1981) Diabetic retinopathy in the dog. Br J Ophthalmol 65 (5), 312-314 PubMed.
  • Engerman R L, Bloodworth J M B, Nelson S (1977) Relationship of microvascular diseases in diabetes to metabolic control. Diabetes 26 (8), 760-769 PubMed.
  • Monti F, Bellan B, Perruccio C et al (1976) The clinical picture of diabetic retinopathy in the dog. Folia Vet La 6 (3), 249-274 PubMed.
  • Gepts W, Toussaint D (1967) Spontaneous diabetes in dogs and cats. A pathological study. Diabetologica 3 (2), 249-265 PubMed.
  • Sibay T M, Hausler H R (1967) Eye findings in two spontaneously diabetic related dogs. Am J Ophthalmol 63 (2), 289-294 PubMed.
  • Bloodworth J M B, Molitor D L (1965) Ultrastructural aspects of human and canine diabetic retinopathy. Invest Ophthalmol Vis Sci (6), 1037-1048 PubMed.
  • Engerman R L, Bloodworth J M B (1965) Experimental diabetic retinopathy in dogs. Arch Ophthalmolol 73, 205-210 PubMed.
  • Patz A, Berkow J W, Maumenee A E et al (1965) Studies on diabetic retinopathy. II. Retinopathy and nephropathy in spontaneous canine diabetes. Diabetes 14 (11), 700-708 PubMed.


ADDED