[Age-related contractility of retinal arterioles during pure oxygen breathing]

Dorzolamide Influences the Autoregulation of Major Retinal Vessels Caused by Artificial Intraocular Pressure Elevation in Patients with POAG: A Clinical Study

PURPOSE

The study investigated whether dorzolamide influences the autoregulatory behavior of major retinal arterioles in glaucoma patients via a moderate perfusion pressure reduction.

METHODS

The study included one eye each of 12 untreated patients with a primary open-angle glaucoma (POAG) (age 60.8 +/- 8.3, IOP 22.3 +/- 6.5 mmHg). Changes in the diameter of a retinal artery segment before (120 s), during (100 s), and after (380 s) artificial IOP elevation to 38 mmHg for 100 s were recorded continuously by means of a Retinal Vessel Analyzer. The measurement was repeated after 4-week treatment with dorzolamide eye drops t.i.d.

RESULTS

Ocular perfusion pressure (mmHg) was reduced by the intraocular pressure (IOP) elevation from 58 (+/- 10) to 41 (+/- 11) in the pretreatment examination and from 60 (+/- 8) to 40 (+/- 8) posttreatment (differences between the examinations n.s.). Before IOP elevation, the arterial diameter was found to be +1.7 +/- 3.5% greater in the posttreated eyes than in the pretreated eyes (p < 0.02). During IOP elevation, the arterial diameter decreased by -1.8% +/- 3.8 in the pretreated eyes, whereas dilatation by +1.4% +/- 2.5 was observed in the posttreated eyes (p = 0.02). At the end of the observation period following IOP elevation, the vessel diameter in the pretreated eyes had increased by +1.8% +/- 4.2, whereas in the posttreated eyes it had decreased by -1.7% +/- 3.0. On average, dorzolamide reduced IOP by -5.6 mmHg (p = 0.001).

CONCLUSIONS

The arterial diameter dilatation during IOP elevation in dorzolamide-treated eyes could be an accelerated counter-regulation on the induced elevated IOP and could constitute an additional therapeutic effect.

[The myogenic response of retinal arterioles in diabetic retinopathy]

OBJECTIVES

The retinal vessel analyzer (RVA) offers the unique opportunity for noninvasive online measurements of the "Bayliss effect." In the presented study this myogenic response is used to test vessel contractility of retinal arterioles in different stages of diabetic retinopathy (DR).

METHODS

Forty patients with diabetes were exposed to a standardized rise in blood pressure. The myogenic response of a retinal arteriole was measured by continuous use of the RVA during this time. The subjects were divided into four groups (each n=10) according to different stages of DR. Group I: no DR, group II: mild/moderate DR, group III: moderate/severe nonproliferative DR with laser treatment, and group IV: proliferative DR with laser treatment.

RESULTS

A similar blood pressure rise was achieved in all subjects. In response to this BP rise, group I demonstrated a vasoconstriction of -7.6% (+/-4.1). In group II -0.85% (+/-4.3) and in group III a mild vasodilation of +0.44% (+/-5.9) was found. Group IV presented a vasodilatation of +3.2% (+/-5.9).

CONCLUSION

According to the progression of the morphological changes in diabetic retinopathy a functional deficit in the autoregulation of retinal arterioles can be measured with the RVA.