Effect of Glucose on Ocular Blood Flow

Inclusion Criteria: * No history of the following problems: ocular or systemic disease; chronic or current systemic or topical medication; or of drug or alcohol abuse * normal blood pressure (100-140 / 60-90 mmhg) * best corrected visual acuity above 20/25 in both eyes * no pathological findings upon a slit-lamp examination and indirect fundoscopy * ametropia within -3 to +3 diopters of spherical equivalent * less than 1 diopter astigmatism * IOP \< 20 mmHg in both eyes * Subjects will be classified as vasospastic if they relate a clear history of frequent cold hands (answering yes to the questions: "do you have always cold hands, even during summer time?" and "do other people tell you that you have cold hands?") and as normals if they deny such a history * Vasospastic propensity will also be assessed by capillaroscopy Exclusion Criteria: * Subjects describing "sometimes cold hands" * if the test substance cannot be ingested * not obtainable ocular blood flow measurements * abnormally high levels of glucose at any point in time