CA1 and proliferative diabetic retinopathy: Abnormal levels or activities of these enzymes have been associated with many disorders such as obesity, gastric ulcers, glaucoma, acid‐base imbalances, cancer and epilepsy.14 Carbonic anhydrase I (CA I) is a zinc metalloenzyme belonging to the α CA family.12 It is involved in pH homeostasis, respiration, erythroid differentiation and some pathological processes such as anaemia, chronical acidosis, proliferative diabetic retinopathy and diabetic macular and vasogenic oedemas.14, 15 Variations in the expression of CA I have recently been associated with some malignancies.