ANP 1106 Lecture 23: ANP1106 – Vision Paths
29 Apr 2018
School
Department
Course
Professor
ANP1106 – Vision Paths
Vision: Light Path
- Light passes through cornea, anterior chamber, pupil, posterior chamber,
lens, posterior segment of retina, ganglion cells, bipolar cells, photoreceptors
- White part of eye and inner eyelids contain a membrane called conjunctiva
- Eye is formed of 3 layers:
o 1) Fibrous – contains cornea (transparent, no blood vessels, no
rejection in transplantation) and sclera (white part of eyeball, anchors
ocular muscle, joins dura mater to form optic nerve)
o 2) Vascular (uvea) – contains iris (dilates/constricts pupil which lets
light pass into eye), ciliary body (changes shape of lens attached via
suspensory ligaments), choroid, ora serrate (junction between ciliary
and choroid)
o 3) Sensory (retina) – contains pigmented (covers choroid, ciliary and
posterior iris, absorbs light to avoid reflecting inner eyeball) and
neural layers (covers choroid, yellow spot called macula lutea
contains fovea centralis, blind spot has no photoreceptors because it’s
the site of passage for axons/blood vessels
- 2 types of photoreceptors
o 1) Cones – sensitive to color, found in fovea centralis
o 2) Rods – insensitive to color but sensitive to weak light, found in
periphery
- Lens divides eyeball into:
o 1) Posterior segment – contains vitreous humor
o 2) Anterior segment – contains aqueous humor, divided by iris into
anterior chamber and posterior chamber
▪ Aqueous humor formed by filtration through capillaries
▪ Aqueous humor evacuation done by scleral venous sinus (canal
of Schlemm)
▪ *Blockage of this causes intraocular pressure and glaucoma
- Contraction of circular muscles (parasympathetic) produces pupillary
constriction and contraction of radial muscles (sympathetic) produces
pupillary dilation
Vision Pupillary Light Reflex
- Pupillary reflex is fast contraction of circular smooth muscles of iris in
response to excess light
- Pathway: light transduced by retina, activates retinal ganglion cells, pretectal
nucleus neurons, Edinger-Westphal nucleus neurons, project via 3rd cranial
nerve, to ciliary ganglion neurons, innervate constrictor muscle of iris
- Refraction – caused because the speed of light slows in a medium of higher
density, transition between air and cornea causes 80% of refraction and
other 20% is due to lens
o Lens of eye focuses light and inverts the image on retina
o Light is absorbed by pigmented layer of retina
find more resources at oneclass.com
find more resources at oneclass.com
