Abstract
Purpose:
The detection of metabolic changes in the retina is the goal of fluorescence lifetime ophthalmoscopy (FLIO). Changes in the blood sugar level (BSL) may cause short-term alterations in the cellular metabolism and thus affect FLIO measurements. We performed an observational clinical study in young healthy volunteers to learn about the changes in the fluorescence lifetimes during an oral glucose tolerance test.
Methods:
In 10 healthy volunteers (28.9±3.9 years) time-resolved retina auto-fluorescence was measured (scanning laser ophthalmoscope: 30° of fundus, 34µm resolution; excitation: diode laser with pico-second pulses, 473nm, 80MHz repetition rate; detection: spectral channels 500-560nm (ch1) and 560-720nm (ch2), time-correlated single photon counting method). All subjects had a crystalline lens. The pupil was not dilated. The BSL was measured based on blood samples taken from the finger using an Accu-Chek® Aviva self-monitoring device. Volunteers were instructed to fast for 10-16 hours prior to the study. A baseline measurement of BSL and FLIO was taken before the volunteers were drinking 300ml solution, which contained 75g of glucose (Accu-Chek® Dextrose O.G.T.). Every 15 minutes BSL and FLIO were measured. A modified 3-exponential approach was applied to determine the fluorescence lifetimes. The ETDRS grid was applied to the FLIO measurements, its inner ring was used to compare the fluorescence lifetime before and after glucose intake.
Results:
Results are mean ± standard deviation over all volunteers in ch1. The baseline BSL was 5.3±0.4 mmol/l (SI unit), τ1: 57±5ps, τ2: 307±49ps, τ3: 1086±120ps and the τmean: 148±13ps. The highest BSL of 8.4±1.1 mmol/l was observed 30min after glucose intake. The corresponding fluorescence parameters are: τ1: 51±5ps, τ2: 282±41ps, τ3: 1043±103ps and τmean: 140±13ps. The measurements after 90 minutes resulted in: BSL: 6.3±1.4 mmol/l and τ1: 48±5ps, τ2: 278±40ps, τ3: 1104±106ps and the τmean: 139±13ps. Results of ch2 are show even smaller deviations in the fluorescence lifetimes.
Conclusions:
The fluorescence lifetime changes during the oral glucose tolerance test are within the standard deviation. Thus, FLIO measurement in young healthy volunteers are mostly independent of short-term changes in the blood sugar level. Volunteers don’t have to fast to obtain reliable fluorescence lifetimes from the retina.