Electron histochemical study of alkaline phosphatase activity in the pecten oculi of the chick

Doppler ultrasonography of the pectinis oculi artery in harpy eagles (Harpia harpyja)

Twenty harpy eagles (Harpia harpyja) without systemic or ocular diseases were examined to measure blood velocity parameters of the pectinis oculi artery using Doppler ultrasonography. Pectinate artery resistive index (RI) and pulsatility index (PI) were investigated using ocular Doppler ultrasonography. The mean RI and PI values across all eyes were 0.44±0.10 and 0.62±0.20 respectively. Low RI and PI values found in the harpy eagle´s pectinis oculi artery compared with the American pekin ducks one and other tissue suggest indeed a high metabolic activity in pecten oculi and corroborates the hypothesis of a nutritional function and/or intraocular pressure regulation.

Hemodynamics of the pectinis oculi artery in American pekin ducks (Anas platyrhynchos domestica)

OBJECTIVE

To measure blood velocity parameters of the main detectable branch of the pectinis oculi artery and compare with values found in other arteries in other species to form a hypothesis of the function of the pecten oculi in birds.

METHODS

Eleven American pekin ducks (Anas platyrhynchos domestica) without ocular diseases were examined with ocular Doppler ultrasonography. The pectinate artery resistive index (RI) and pulsatility index (PI) were calculated.

RESULTS

The mean of RI and PI values resulted, respectively, in: left eye (0.43 ± 0.07; 0.58 ± 0.13), right eye (0.37 ± 0.09; 0.47 ± 0.14), and both eyes (0.40 ± 0.08; 0.53 ± 0.14).

DISCUSSION

The low RI and PI values found in the main branch of the pectinis oculi artery compared with other arteries in other tissues suggest a high metabolic activity in the pecten oculi, and it could indicate a nutritional function and/or intraocular pressure regulation.

Saccadic oscillations facilitate ocular perfusion from the avian pecten

THE evolution of the eye is constrained by two conflicting requirements--good vascular perfusion of the retina, and an optical path through the retina that is unobstructed by blood vessels. Birds are interesting in that they have higher metabolic rates and thicker retinas than mammals, but have no retinal blood vessels. Nutrients and oxygen must thus reach the neurons of the inner retina either from the choroid through 300 micron of metabolically very active retina, or from the pecten, a pleated vascular structure protruding from the head of the optic nerve into the vitreous chamber, and more than a centimetre away from some retinal neurons. Despite the diffusional distance involved, several lines of evidence indicate that the pecten is the primary source of nutrients for the inner retina: the presence of an oxygen gradient from pecten to retina, the large surface area produced by macroscopic folds and by microscopic infoldings of the luminal and external surfaces of the capillary endothelium, extrusion of circulating fluorescein, high content of carbonic anhydrase and alkaline phosphatase, and retinal impairments after pecten ablation. Another peculiarity of birds, their saccadic oscillations, occur with a large cyclotor-sional component during every saccadic eye movement. In different species, saccades, which occur at intervals of 0.5-40 s, have up to 13 oscillations with frequencies of 15-30 Hz and ampliá-tudes of about 10 degrees. Therefore, as much as 12% of some birds' total viewing time may be subject to the image instability caused by the oscillations. Using fluorescein angiography, we show here that during every saccade, the pecten acts as an agitator which propels perfusate towards the central retina much more effectively than is observed during intersaccadic intervals.