Correlation of Pupil Cycle Time and Postural Hypotension as a Marker for Diabetic Neuropathy

Introduction: Diabetic Neuropathy (DN) can involve autonomic nervous system like cardiovascular system and pupillary reflex. Cardiovascular DN can be measured by estimating the change in Blood Pressure (BP) based on position. Ocular DN can be evaluated by using Pupil Cycle Time (PCT), which is an early diagnostic tool to estimate ocular DN. It is a simple way to measure autonomic reflex activity and is a specific test to study parasympathetic function.

Aim: To assess the correlation of effects of postural hypotension and PCT on persistent diabetes.

Materials and Methods: The prospective cross-sectional study was conducted in Ophthalmology Out Patient Department (OPD) at KS Hegde Medical Academy, Mangalore, Karnataka, India, from January 1st 2019 to December 31st 2019. The study included 60 male patients between the age group of 40-60 years which were divided into two groups of 30 diabetics (Random Blood Sugar (RBS) >200 mg/dL, Fasting Blood Sugar (FBS) >126 mg/dL and Glycated Haemoglobin (HbA1c) >6.5%) and 30 non diabetics. The blood pressure of all the patients were recorded using a sphygmomanometer in sitting and standing positions. PCT was measured in both eyes using Haggstreit-type of slit lamp after the subject was seated in a dimly lit room after dark adaptation for 15 minutes.

Results: The mean age of patients in the diabetic group was 54±3.2 years and the non diabetic group was 52±2.7 years. The mean HbA1c of diabetics was 6.9±0.8%. The mean BP among diabetics in standing position was 133.86±29.34 mmHg systolic and 87.4±16.72 mmHg diastolic whereas in sitting position, it was 141.66±28.17 mmHg systolic and 85.26±13.39 mmHg diastolic. The mean BP among non diabetics in standing position was 129.46±24.84 mmHg systolic and 83.46±13.52 mmHg diastolic whereas in sitting position, it was 132.06±26.48 mmHg systolic and 81.26±11.45 mmHg diastolic. The mean PCT-I and PCT-II in diabetics was 1000.52±187.73 and 1006.09±199.45, respectively. The systolic and diastolic BP, both during sitting and standing postures, in diabetic patients were high. The mean PCT-I and PCT-II in non diabetics was 853.23±181.54 and 880.17±192.72, respectively. The PCT-I and PCT-II were found to be significantly high in diabetic patients as compared to controls. The PCT-I and PCT-II negatively correlated with both diastolic and systolic blood pressure in sitting and standing postures.

Conclusion: Prolongation of PCT in diabetics correlates significantly with evidence of autonomic neuropathy obtained from testing of postural BP variations. Patients whose cardiovascular reflexes are very abnormal tend to have pupils which cycle slowly.