Editing Saccade (section)

==Comparative physiology==
Saccades are a widespread phenomenon across animals with image-forming visual systems. They have been observed in animals across three [[phylum|phyla]], including animals that do not have a [[Fovea centralis|fovea]] (most vertebrates do) and animals that cannot move their eyes independently of their head (such as insects).<ref name="pmid10555268">{{cite journal |year=1999 |last1=Land |first1=MF |title=Motion and vision: Why animals move their eyes |volume=185 |issue=4 |pages=341–52 |journal=Journal of Comparative Physiology A |doi=10.1007/s003590050393 |pmid=10555268|s2cid=18278126 }}</ref> Therefore, while saccades serve in humans and other primates to increase the effective visual resolution of a scene, there must be additional reasons for the behavior. The most frequently suggested of these reasons is to avoid blurring of the image, which would occur if the response time of a [[photoreceptor cell]] is longer than the time a given portion of the image is stimulating that photoreceptor as the image drifts across the eye.

In birds, saccadic eye movements serve a further function.  The [[Bird vision#Anatomy of the eye|avian retina]] is highly developed. It is thicker than the [[mammalian eye|mammalian retina]], has a higher metabolic activity, and has less [[blood vessel|vasculature]] obstruction, for greater visual acuity.<ref>{{cite journal |last1=Pettigrew |first1=John D. |last2=Wallman |first2=Josh |last3=Wildsoet |first3=Christine F. |title=Saccadic oscillations facilitate ocular perfusion from the avian pecten |journal=Nature |date=January 1990 |volume=343 |issue=6256 |pages=362–363 |doi=10.1038/343362a0|pmid=14756148 |bibcode=1990Natur.343..362P |s2cid=4278614 }}</ref> Because of this, the retinal cells must obtain nutrients via diffusion through the [[choroid]] and from the [[vitreous humor]].<ref>{{cite journal |last1=Potier |first1=Simon |last2=Mitkus |first2=Mindaugas |last3=Lisney |first3=Thomas J. |last4=Isard |first4=Pierre-François |last5=Dulaurent |first5=Thomas |last6=Mentek |first6=Marielle |last7=Cornette |first7=Raphaël |last8=Schikorski |first8=David |last9=Kelber |first9=Almut |title=Inter-individual differences in foveal shape in a scavenging raptor, the black kite Milvus migrans |journal=Scientific Reports |date=December 2020 |volume=10 |issue=1 |pages=6133 |doi=10.1038/s41598-020-63039-y|pmid=32273526 |pmc=7145841 |bibcode=2020NatSR..10.6133P }}</ref> The [[pecten oculi|pecten]] is a specialised structure in the avian retina. It is a highly vascular structure that projects into the vitreous humor. Experiments show that, during saccadic eye oscillations (which occupy up to 12% of avian viewing time), the [[pecten oculi]] acts as an agitator, propelling perfusate (natural lubricants) toward the retina. Thus, in birds, saccadic eye movements appear to be important in retinal nutrition and [[cellular respiration]].<ref>{{cite journal |pmid=14756148 |year=1990 |last1=Pettigrew |first1=JD |last2=Wallman |first2=J |last3=Wildsoet |first3=CF |title=Saccadic oscillations facilitate ocular perfusion from the avian pecten |volume=343 |issue=6256 |pages=362–3 |doi=10.1038/343362a0 |journal=Nature|bibcode=1990Natur.343..362P |s2cid=4278614 }}</ref>