tldr Glucose, when broken down in in presence of oxygen, produces energy (ATP) ~15x more efficiently. But, the inner retina of bird eyes don't have blood vessels so are not served oxygen. And, retinas are comprised of the body's most energy intensive neural tissue. So how are bird retinas producing so much energy without oxygen? By the less efficient and oxygen-free anaerobic glycolysis. Without oxygen, the retina needs a lot more glucose to meet its energy requirements. The function of the pecten oculi is to deliver this glut of glucose and to remove the byproducts of anaerobic glycolysis (lactate).
tldr Glucose, when broken down in in presence of oxygen, produces energy (ATP) ~15x more efficiently. But, the inner retina of bird eyes don't have blood vessels so are not served oxygen. And, retinas are comprised of the body's most energy intensive neural tissue. So how are bird retinas producing so much energy without oxygen? By the less efficient and oxygen-free anaerobic glycolysis. Without oxygen, the retina needs a lot more glucose to meet its energy requirements. The function of the pecten oculi is to deliver this glut of glucose and to remove the byproducts of anaerobic glycolysis (lactate).