Automatic Retinal Oximetry

PURPOSE

To measure hemoglobin oxygen saturation (SO(2)) in retinal vessels and to test the reproducibility and sensitivity of an automatic spectrophotometric oximeter.

METHODS

Specialized software automatically identifies the retinal blood vessels on fundus images, which are obtained with four different wavelengths of light. The software calculates optical density ratios (ODRs) for each vessel. The reproducibility was evaluated by analyzing five repeated measurements of the same vessels. A linear relationship between SO(2) and ODR was assumed and a linear model derived. After calibration, reproducibility and sensitivity were calculated in terms of SO(2). Systemic hyperoxia (n = 16) was induced in healthy volunteers by changing the O(2) concentration in inhaled air from 21% to 100%.

RESULTS

The automatic software enhanced reproducibility, and the mean SD for repeated measurements was 3.7% for arterioles and 5.3% venules, in terms of percentage of SO(2) (five repeats, 10 individuals). The model derived for calibration was SO(2) = 125 - 142 . ODR. The arterial SO(2) measured 96% +/- 9% (mean +/- SD) during normoxia and 101% +/- 8% during hyperoxia (n = 16). The difference between normoxia and hyperoxia was significant (P = 0.0027, paired t-test). Corresponding numbers for venules were 55% +/- 14% and 78% +/- 15% (P < 0.0001). SO(2) is displayed as a pseudocolor map drawn on fundus images.

CONCLUSIONS

The retinal oximeter is reliable, easy to use, and sensitive to changes in SO(2) when concentration of O(2) in inhaled air is changed.

Screening compliance and visual outcome in diabetes

PURPOSE

To study the relationship between screening compliance and visual outcome in a screening programme for diabetic eye disease.

METHODS

A retrospective case control study. The screening compliance of all the diabetes patients (n = 22) listed at the Icelandic National Registry for the Blind (visual acuity <0.3) was compared to a matched group of 44 non-blind diabetes patients (visual acuity > or =0.3) who participated in the same screening programme for diabetic retinopathy. Glycaemic control (HbA1c), office blood pressure and cholesterol levels were assessed.

RESULTS

The study group had a significantly lower level of compliance with the screening programme (27% +/- 38% [mean +/- SD] versus 77% +/- 26% [mean +/- SD]; p < 0.0001). Macular oedema or proliferative diabetic retinopathy was found in 60% (13/22) of the study group when entering the screening programme, compared to 7% (3/44) in the control group. Blood pressure (except diastolic BP among type 1 diabetes mellitus), blood glucose and cholesterol levels were identical. The prevalence of blindness and low vision amongst diabetes patients in Iceland is about 0.5%.

CONCLUSIONS

There was a significant relationship between screening compliance and visual outcome in diabetes patients in our screening programme.

[Chemical injuries of the eye - management of alkali burns.]

Chemical injuries are among the most severe injuries to the eye. Young men are most often affected. Work related injuries are more common than other types of injuries. Immediate treatment is paramount in preventing blindness. In the case of an alkali injury, an opaque cornea and a white edematous conjunctiva indicate a serious injury. In contrast, a clear cornea and a mildly to moderately irritated conjunctiva indicate a better prognosis. Copious irrigation is always the first treatment for all chemical injuries to the eye. Irrigation should be initiated as soon as possible and is to be continued until the tearfluid has regained a normal pH. Antibiotic ointment, lubrication and cycloplegic drops (e.g. Cyclogyl(R)) form the basis of treatment.