Chapter 15 (eyes and vision) Flashcards
HEY! LOOK AT THE EYE!
(oooh im so glad i looked at that eye…)
what are major features of a vertebrate’s eye?
anterior chamber (filled with aqueous humour), iris, lens, posterior chamber (filled with vitreous humour) lined with the retina.
what does the spherical lens connect to?
cornea.
the cornea is a transparent section of WHAT of the eyeball?
Scleroid coat
how is the lens suspended?
suspensory ligament
what is between the retina and the sclera (scleroid coat)?
highly vascularized choroid layer. (BLACK) (absorbs stray light)
CHOROID BODY
IS A RETE MIRABILE. prominent in the choroid layer of many teleosts (and bowfin). structure and function similar to that of the gas gland.
WHAT IS THE FUNCTION OF THE CHOROID BODY?
serving to provide a high partial pressure of oxygen to the retina.
what do you call a shark eyelid?
nictitating membrane
shark eyeballs? slide four. maybe check it with Jer.
ok
what is dependant upon for calm water to be able to reflect up to 80% of the light striking it
dependant upon the angle of incidence.
what is SNELL’S WINDOW?
a circle subtended by a 97.2% cone above each eye. (refraction or bending of light rays entering water)
at what angle do rays become reflected as they hit the water’s surface?
<40degrees
what does refraction and image formation depend almost entirely on?
on the lens
how does a fish’s eye move between near and far sightedness in comparison with a tetrapod?
tetrapod: lens changes shape
fish: slight anterior and posterior movement of the lens that change the distance between the lens and retina.
are lampreys near sighted or far sighted?
near-sighted (myopic)
the closer the lens moves toward the retina the:
narrower the field of view but the better the distance vision.
what muscle fibres in elasmobranchs, that are located in the anterior part of the choroid layer that pull the lens outward, away from the retina and closer to the cornea?
protractor muscles
elasmobranchs are known as being near or far sighted?
farsighted (hyperopic)
Tapetum lucidum
amplifies light
why is the benefit of a spherical lens in an elleipsoid retina?
the effect acheived is that relatively distant objects lateral to the fish are in focus but close objects are not. anteriorly objects in the binocular field are in better focus than more distant objects
IN REGARDS TO EYESIGHT, TELEOSTS ARE THOUGHT AS BEING:
1) HYPEROPIC (FAR SIGHTED LATERALLY)
2) MYOPIC (NEAR SIGHTED ANTERIORLY)
how does light regulation occur and its adaption to light/dark?
- swim to or away from the source of illumination
- pigment in the cornea or lens that filters
- most elasmobranchs and some teleosts have contractile irises
- some fish have pupillary operculum that expands/cuts off light
- nictitating membranes
- movements of pigments and visual cells
how does the eye adapt under bright illumination?
movement of melanin toward the visual cells, movement of rods into pigmented area where they are sheilded from light
in dim light, what moves?
cones opposite to rods,
how long does it take for light adaptation to occur?
30 minutes for light, hour for dark
what are responsible for absorbing light?
visual pigments, or retinenes
general rules for relating visual pigments to visual tasks
1- deep sea species have rod pigments that absorb maximally at a relatively short wavelength (470-490nm)
- marine fishes living at intermediate depths~460-540
- benthic fw fish: 530-620
- fw fish in shallows: 430
- anadromous salmon shift their wavelengths
