Screening and Diagnosis of Diabetic Retinopathy

Screening for diabetic retinopathy

Diabetic retinopathy (DR) is a progressive microvascular complication that can occur in patients with both type 1 and type 2 diabetes. The therapeutic goals for DR are to prevent or delay its initial development, delay its progression, and prevent vision loss.[1] Therefore, appropriate management includes annual eye exams for early detection and monitoring of DR.[1] The timing of treatments is important; it should be performed when vision is still well preserved and the benefit to the patient warrants the risks of the procedure.[1,2] For example, laser photocoagulation is an effective treatment that does not usually restore vision but can slow DR progression and prevent further vision loss.

Risk factors for development and progression of diabetic retinopathy

Elevated blood pressure, poor metabolic control, longer disease duration, puberty, and pregnancy are associated with greater likelihood or accelerated progression of diabetic retinopathy.[1 Certain ethnic groups (eg, African Americans and Hispanics) have higher rates of retinopathy progression than individuals of northern European descent.[[1] Newly diagnosed patients with the same level of retinopathy progress differently than those with longer duration of disease, who are more likely to progress over the following year.[1]

Screening tests for diabetic retinopathy

If “screening test” is understood to mean a simple, inexpensive procedure that can be done by an individual with minimal training, then there are few true screening tests for diabetic retinopathy. The most commonly recommended screening test for diabetic retinopathy is a limited clinical exam. Some communities have used fundus photography with a nonmydriatic camera in undilated eyes in screening programs for diabetic retinopathy.[1,3] The American Diabetes Association (ADA) and the American Academy of Ophthalmology (AAO) recommend dilated eye examinations as shown in Table 1. Some authorities suggest eye exams for low-risk patients in alternate years, rather than annually.[4] Low-risk patients include those who meet 2 of the following criteria: not on insulin therapy, A1C <7%, or a dilated eye exam in prior year demonstrating lack of retinopathy.[4]

Table 1. Screening schedule for diabetic retinopathy[1,4,5]

Color vision

A tritan-like loss of blue sensitivity correlates with the severity of diabetic retinopathy, particularly macular edema[6,7] Importantly, changes in color vision can be detected prior to visual acuity loss in patients with DR.[7] The correlation between color vision deficits and diabetic retinopathy has been confirmed using a variety of tests, including the Farnsworth-Munsell 100-hue (FM100) test, Farnsworth-Lanthony D-15 test, anomaloscope, and the Mollon-Reffin "Minimalist" test, but sensitivity and specificity limitations have prevented the acceptance of most of these tests for screening purposes.[7] However, recent studies demonstrated that automated tritan contrast threshold (TCT) testing is cost-effective, clinically viable, and compares favorably with British Diabetic Association sensitivity and specificity standards for screening programs[7,8] Although color vision tests are currently not included in clinical guidelines, color vision screening may be recommended in future clinical guidelines.[1,4,5,6,7,8]

Diagnosis of Diabetic Retinopathy

Diabetic retinopathy can cause several types of vitreoretinal pathology, each a consequence of microvascular damage to the retina. The 3 main categories are nonproliferative diabetic retinopathy (NPDR), proliferative diabetic retinopathy (PDR), and diabetic macular edema (DME). DME can coexist with any stage or severity of NPDR or PDR. Diagnostic features associated with each category are shown in Table 2.

Table 2. Signs and symptoms of diabetic retinopathy[9]

*IRMA=intraretinal microvascular abnormalities

Physical findings in diabetic retinopathy

Reduced visual acuity can accompany all forms of diabetic retinopathy but may not be evident until irreversible retinal damage has occurred. Enlarged, tortuous retinal veins are a hallmark of both NPDR and PDR. Vitreoretinal membranes and retinal detachment may be noted in advanced PDR. Neovascularization of the iris and anterior chamber angle structures associated with PDR can contribute to neovascular glaucoma.[5] Iris neovascularization may more easily observed prior to dilating the eye; gonioscopy can detect anterior chamber angle neovascularization.[5]

Staging and grading scales for diabetic retinopathy

Several systems for classifying and staging diabetic retinopathy have been proposed. One such system is the Early Treatment of Diabetic Retinopathy Study Research Group (ETDRS) scale. This system has been used in a number of research studies, but its relatively cumbersome grading scheme makes it impractical for routine clinical use.[10] More recently, the International Clinical Diabetic Retinopathy Disease Severity Scale and the International Clinical Diabetic Macular Edema Disease Severity Scale have been proposed by the AAO and other organizations. These scales are shown in Table 3 and Table 4. Additional scales for DME based on instrumention developed since the ETDRS was conducted have been proposed.[11,12] These scales may aid in selection of the most suitable treatment for subtypes of DME.[11,13,14]

Table 3. International Clinical Diabetic Retinopathy Disease Severity Scale[5]

Table 4. International Clinical Diabetic Macular Edema Disease Severity Scale[5]

Laboratory assessment for diabetic retinopathy

In Table 5, all tests described as components of a comprehensive clinical exam are part of the initial eye examination for diabetic retinopathy. Other tests described below are ancillary to the clinical exam and may enhance patient care.[5] All ophthalmologists and many optometrists can perform a dilated eye exam, but the AAO and ADA recommend prompt evaluation by an ophthalmologist with knowledge and experience in managing and treating diabetic retinopathy for patients with PDR, severe NPDR, or any degree of DME.[1] Some tests may only be available at retina specialty clinics (eg, fundus photography, ultrasound, fluorescein angiography, and optical coherence tomography [OCT]).

Table 5. Tests of visual function in diabetes[15,16,17]

CSME = clinically significant macular edema, IOP = intraocular pressure, PDR = proliferative diabetic retinopathy

Future directions

Digital technology advances have provided new tools for fundus imaging, including digital fundus photography, angiography, ultrasonography, and OCT. Film-based (analog) photography has advantages over digital imaging in terms of equipment cost, image resolution, and stereoscopic viewing.[18] On the other hand, digital photographs are quicker to make and easier to duplicate, transmit, and store. Digital angiography and OCT use is already widespread in retina specialty practices, and current trends point to ever-widening use for other ophthalmic applications.

Faster, higher-resolution ultrasound instruments for anterior segment imaging have been available for a number of years; similar devices for posterior segment imaging are under development, and may permit 3D retinal imaging.[18]

Faster, higher-resolution OCT instruments with 3D imaging capability are also in development.[19] OCT is also being incorporated into a device called an OCT ophthalmoscope that permits layer-by-layer views of the retina superimposed upon a digital representation of the more customary view of the fundus.[18 Prototype OCT ophthalmoscopes are reportedly in beta testing.

Other ocular complications of diabetes

Other ocular complications of diabetes

Diabetic retinopathy represents only 1 category of diabetic eye pathology. Patients with diabetes are also at increased risk for cataract and glaucoma.[2,9] Some of the same factors that increase the risk of developing type 2 diabetes or its complications, such as abdominal obesity, smoking, alcohol use, and positive family history, are also risk factors for developing cataract.[20] Lens extraction with intraocular lens implantation, a common procedure to improve visual acuity in patients with cataract, may be performed on patients with diabetes, but PDR and DME may compromise the visual outcome of such surgery.[21]

Consistently elevated IOP (>21 mm Hg), African descent, age, and family history are among the most prominent risk factors for glaucoma.[15] Because half of patients will not display elevated IOP, IOP measurements alone are not effective for glaucoma screening.[15] A more effective protocol for detecting glaucoma consists of IOP, clinical examination of the optic nerve head, and visual field evaluation.[15]

Referral criteria

The ADA states, “...patients with any level of macular edema, severe NPDR, or any PDR require the prompt care of an ophthalmologist who is knowledgeable and experienced in the management and treatment of diabetic retinopathy…. Early referral to an ophthalmologist is particularly important for patients with type 2 diabetes and severe NPDR, since laser treatment at this stage is associated with a 50% reduction in the risk of severe visual loss and vitrectomy.”[1]

References

1. Fong DS, Aiello L, Gardner TW, et al. Retinopathy in diabetes. Diabetes Care. 2004;27(suppl 1):S84-S87.
2. American Diabetes  Association. Eye complications. Available at: http://www.diabetes.org.utils/printthispage.jsp?PageID=TYPE1DIABETES3_232931. Accessed December 13, 2004.
3. Arun CS, Ngugi N, Lovelock L, Taylor R. Effectiveness of screening in preventing blindness due to diabetic retinopathy. Diabet Med. 2003;20:186-190.
4. Institute for Clinical Systems Improvement. Health care guideline: management of type 2 diabetes mellitus. 8th edition. November 2003. Available from http://www.icsi.org.
5. American Academy of Ophthalmology. Preferred Practice Pattern: Diabetic Retinopathy. San Francisco, Calif. American Academy of Ophthalmology;
6. Fong DS, Barton FB, Bresnick GH for the Early Treatment Diabetic Retinopathy Study Research Group. Impaired color vision associated with diabetic retinopathy: early treatment diabetic retinopathy study report no. 15. Am J Ophthalmol. 1999;128:612-617.
7. Ong GL, Ripley LG, Newson RSB, Casswell AG. Assessment of colour vision as a screening test for sight threatening diabetic retinopathy before loss of vision. Br J Ophthalmol. 2003;87:747-752.
8. Ong GL, Ripley LG, Newson RS, Cooper M, Casswell AG. Screening for sight-threatening diabetic retinopathy: comparison of fundus photography with automated color contrast threshold test. Am J Ophthalmol. 2004;137:445-452.
9. Flynn HW, Smiddy WE, eds. Diabetes and Ocular Disease: Past, Present, and Future Therapies. AAO Monograph No. 14. San Francisco: The Foundation of the American Academy of Ophthalmology; 2000.
10. Early Treatment of Diabetic Retinopathy Study Research Group. Grading diabetic retinopathy from stereoscopic color fundus photographs—an extension of the modified Airlie House classification. ETDRS report number 10. Ophthalmology. 1991;98(5 suppl):786-806.
11. Chan A, Duker JS. A standardized method for reporting changes in macular thickening using optical coherence tomography. Arch Ophthalmol. 2005;123:939-943.
12. Panozzo G, Parolini B, Gusson E, et al. Diabetic macular edema: an OCT-based classification. Semin Ophthalmol. 2004;19:13-20.
13. Gallemore RP, Jumper JM, McCuen BW 2nd, Jaffe GJ, Postel EA, Toth CA. Diagnosis of vitreoretinal adhesions in macular disease with optical coherence tomography. Retina. 2000;20:115-120.
14. Parolini B, Panozzo G, Gusson E, et al. Diode laser, vitrectomy and intravitreal triamcinolone. A comparative study for the treatment of diffuse non tractional diabetic macular edema. Semin Ophthalmol. 2004;19:1-12.
15. American Academy of Ophthalmology. Preferred practice pattern: primary open-angle glaucoma. Limited revision. San Francisco, Calif.: American Academy of Ophthalmology; 2003.
16. Narayanaswamy A, Vijaya L, Shantha B, Baskaran M, Sathidevi AV, Baluswamy S. Anterior chamber angle assessment using gonioscopy and ultrasound biomicroscopy. Jpn J Ophthalmol. 2004;48:44-49.
17. Jaffe GJ, Caprioli J. Optical coherence tomography to detect and manage retinal disease and glaucoma. Am J Ophthalmol. 2004;137:156-169.
18. Yannuzzi LA, Ober MD, Slakter JS, et al. Ophthalmic fundus imaging: today and beyond. Am J Ophthalmol. 2004;137:511-524.
19. Duker J, Fujimoto J, Witkin A, Wojtkowski M. OCT3 and Beyond: New Developments. Managing the open globe calls for creativity and flexibility of surgical approach tailored to the specific case. Rev Ophthalmol. 2005;12. Available at: http://www.revophth.com/index.asp?page=1_719.htm. Accessed April 17, 2006.
20. American Academy of Ophthalmology. Preferred Practice Pattern: Cataract in the Adult Eye. San Francisco, California: American Academy of Ophthalmology; 2001.
21. Chew EY, Benson WE, Remaley NA, et al. Results after lens extraction in patients with diabetic retinopathy. Arch Ophthalmol. 1999;117:1600-1606.