Diabetic retinopathy: methodologies in practice

Screening for diabetic retinopathy using digital colour photography and oral fluorescein angiography

PURPOSE

To evaluate digital colour photography and oral fluorescein angiography (OFA) for diabetic retinopathy screening.

METHODS

Thirty-seven patients were selected from either a diabetic retinopathy screening or a medical retina clinic. Three 45 degrees colour digital images and a single macula 45 degrees OFA image were taken from each eye. Standard seven-field stereo photography with ETDRS grading was used as a gold standard for data comparison. The images were assessed by two graders and the results of each method compared using the McNemar test.

RESULTS

Five eyes had no diabetic retinopathy, 50 had background diabetic retinopathy, 3 had pre-proliferative diabetic retinopathy, 11 had proliferative disease and 3 had quiescent posttreatment disease. Clinically significant macular oedema was present in 25 eyes and absent in 48. For grading diabetic retinopathy digital colour photography produced a sensitivity of 0.87 (specificity 0.83); OFA produced a sensitivity of 0.87 (specificity 0.80) (p = 0.1). For the detection of diabetic maculopathy, the sensitivity of digital colour photography was 0.48 (specificity of 0.95) and for OFA was 0.87 (specificity 0.87) (p < 0.01).

CONCLUSION

This pilot study has shown that both digital colour photography and OFA compare well with conventional methods for diabetic retinopathy screening. The results encourage the further evaluation of OFA in the screening for diabetic maculopathy.

Altered rhodopsin regeneration in diabetic mice caused by acid conditions within the rod photoreceptors

PURPOSE

The experiments were designed to provide details on the characteristics of rhodopsin regeneration in the rod photoreceptors of diabetic mice and to evaluate their mechanistic basis.

METHODS

A genetically-derived diabetic albino mouse was developed. An excised albino mouse eye preparation was used. The preparation allows for direct measurements of rhodopsin concentration and other spectrally distinct intermediates, and maintains the structural integrity of the compartments involved in rhodopsin regeneration. The experiments were conducted at moderate bleaching levels, averaging 13-14%, with mice that exhibited moderate levels of blood glucose concentration.

RESULTS

Rhodopsin regeneration was delayed in both genetically-derived and streptozotocin-injected diabetic mice when compared to non-diabetic mice. During the delay an intermediate of rhodopsin, N-Retinylidene Opsin (NRO440), that precedes the hydrolysis of the bleached chromophore from the opsin and that is associated with acidic conditions was observed. This intermediate was not observed in non-diabetic mice. The delay in rhodopsin regeneration of the diabetic mice was partially eliminated, and the relative concentration of NRO440 was decreased, when the internal pH of the rod photoreceptor was raised by modifying the perfusate composition.

CONCLUSIONS

Following a bleach, both genetic and streptozotocin diabetic mice exhibited abnormalities in rhodopsin regeneration. When studied at moderate bleaching levels with animals that were moderately diabetic, both groups of diabetic mice exhibited a delay in the start of the rhodopsin regeneration. The delay appears to be caused by the formation of an acid intermediate of the bleached rhodopsin resulting from acid conditions within the rod photoreceptors.

Effects of hypoxemia on the electroretinogram in diabetics

PURPOSE

To identify any relationship between retinal dependence on oxygen and the presence or absence of retinopathy in a group of patients with the same duration of diabetes, based on the proposal that diabetic retinopathy results from long-term adaptation to the Crabtree effect, i.e., reduction of oxidative phosphorylation caused by increased intracellular glucose concentrations.

METHODS

Electroretinograms were recorded on 17 patients with insulin-dependent diabetes (of 15 to 17 years duration) and 10 healthy controls. Recordings were made under normal conditions and then after 4 min of hypoxemia (oxygen saturation, 80%). Retinopathy status was assessed from fundus photographs.

RESULTS

Electroretinogram b-wave amplitudes of seven patients without retinopathy were reduced to 69% by the hypoxemia compared to a reduction to 88% for 10 patients with retinopathy (p = 0.039).

CONCLUSIONS

The relative sensitivity to hypoxemia of patients without retinopathy suggests greater dependence on oxidative phosphorylation than in patients with retinopathy. The results appear to be consistent with the Crabtree effect hypothesis. Downregulation of tissue oxygen consumption by the Crabtree effect would lead to a reduction of retinal blood flow by autoregulation and to a reduced concentration of adenosine triphosphate in the retina.

Detection of retinopathy by non-mydriatic fundus photography in diabetics treated with oral hypoglycaemic agents or diet

OBJECTIVE

To determine the prevalence of retinopathy by non-mydriatic fundus photography in diabetics treated with oral hypoglycaemic agents or diet.

DESIGN

Cross-sectional survey of diabetes-induced fundal changes assessed by fundus photography.

SETTING

Area of Health Centre of Oulu. Population 100,000.

SUBJECTS

All 1,228 diabetic patients, aged 30 years or over and treated with oral hypoglycaemic agents or diet at the Health Centre of Oulu.

MAIN OUTCOME MEASURES

Presence and severity of diabetic retinopathy in fundus photographs, need for laser photocoagulation, age, hypertension, body mass index (BMI), duration of diabetes, type of treatment of diabetes.

RESULTS

Retinopathy was observed in 178 (18%) of those 1,015 diabetics examined at the health centre. Retinopathic changes requiring laser treatment were observed in 15 cases, and eight of them had not been diagnosed earlier. Sixty non-attenders photographed at the Central University Hospital were also included, and 12 of them had retinopathy. The presence of retinopathy was associated with long duration of diabetes, poor glycaemic control, and high systolic blood pressure. No association was detected with sex, age at onset of diabetes, BMI, medication for coronary artery disease, or hypertension.

CONCLUSIONS

Non-mydriatic fundus photography detected a high prevalence of retinopathy in diabetic patients. Half of those with preproliferative changes were previously undiagnosed cases, and five were in need of immediate laser treatment. It is concluded that fundus photography is a useful tool for detecting retinopathy in a primary health care setting.