distance vision is blurred when light rays focus behind the retina
How to correct hyperopia
correction with a plus lens allows light to once again focus on the retina
What is myopia?
distant vision is blurred when light rays from distant objects come to focus in front of the retina
How to correct myopia
correction with a minus lens allows light to once again focus on the retina
What are the three tunics?
eye divided into 3 layers/ coats
sensory tunic (retina)
Fibrous tunic has __ different regions. What are they?
forms posterior portion and majority (85%) of fibrous tunic
anterior part covered by simple squamous epithelium: conjunctiva
very high in collagen (dense connective regular tissue that is linear to give a crystalline and clear tendency
anterior portion of fibrous tunic (approx. 15%)
regular arrangement of collagen fibers make it crystal clear
many pain fibers and fibers associated with reflex blinking and lacrimal secretion
no vessels, derives nutrients from aqueous humor
What are the parts of the vascular tunic?
highly vascular, dark brown (contains much melanin) pigmented
continuous anteriorly with ciliary body and iris
has tapedum: in nocturnal animals only [must be able to see at night]= reflective surface
- reason: minimum amount of light will reflect around the eye to allow it to see
humans have no tapedum; they have a choroid
contains bundles of smooth muscles (ciliary muscles)
suspensory ligaments: connect ciliary body to lens
tension on ligaments causes lens to flatten
When ligaments relax, lens get thicker due to internal elasticity
Ciliary process: highly vascularized portion of ciliary body that produces aqueous humor; has blood vessels
makes fluid in front of lens; aqueous humor
visible colored part of the eye (gives the color) pigmented (melanin)
located between lens and cornea
forms central opening, the pupil, through which light enters eye
acts as reflexively activated diaphragm
in bright light, smooth muscles of iris contract causing pupil to constrict, and vice versa
constriction/ dilation also controlled by sympathetic (dilation) and parasympathetic (constriction) fibers
canal of schlem
Explain the tapedum.
similar to the choroid of nocturnal animals only; must be able to see at night; acts as reflective surface
in humans, we have the choroid
the reason a minimum amount of light will reflect around the eye to allow it to see
What are pupils?
What is red eye?
black holes since the light that goes in can't come back out.
light reflecting off of the capillaries; there is so much light that the choroid can't absorb
How many layers of the retina are there? What are the most important three?
ganglioin cell layer (has ganglion cells)
bipolar cell layer (bipolar, horizontal, and amacrine cells)
rods and cones cell layer (photoreceptors)
What is the third tunic? What does it contain?
sensory tunic (retina)
Neural (nervous) layer
direct mediator of vision
outpocketing of the brain
Has five cell types: photoreceptors, bipolar cells, ganglion cells, horizontal cells, amacrine cells
Optic disc (optic nerve head)
small circular area in medial retina where the optic nerve exits the eye
no photoreceptor cell present in this part of the retina (no rods or cones)
functionally, it is the "blind spot"
focal point for light on the retina. Center of the visual field
point of greatest visual acuity (sharpest vision)
light passes directly to photoreceptors since all other cells displaced, i.e., bipolar and ganglion cells off to side
site of greatest cone concentration (nothing but cones)
Refraction by the Cornea
parallel light rayes from object greater than 20 ft.
Accommodation by the Lens
accommodation= lens changes shape for near vision
divergent light rays
ciliary muscles (from the ciliary body)contract to relieve tension on lens (lens get fatter, thickening by its own elasticity)
incraesed curvature increases refractive power
What does the cornea function for?
objects greater thantwenty feet away
What does the lens function for?
objects nearer than twenty feet
Normal vs. Abnormal:
eyeball too short; light focuses behind retina
hardening of lens that accompanies aging; lens unable to flatten sufficiently during relaxation adn unable to fatten sufficiently during accommodation; due to cross-linking of collagen fibers; loses elasticity
irregularities in the curvature of the cornea or lens that produce different amounts of refraction
Snellen eye chart
20/20 vision: numer of feet required by a gien individual to discriminate characters on a specific line in the eye chart over the number of feet average perage person requires to view the same line
light absorbing molecule; synthesized from vitamin A (retinol)
cis (bent), but becomes trans when the light hits it
opsin (protein that starts the response) and retinal; red pigment called "visual purple" important for vision in dim light
also called visual purple
deactivation of rhodopsin by bright light; separation into opsin and retinal
(rods are more sensitive to light than cones)
Rods are for __. Rods are not really used in daylight because what?
When there is not enough light for cones and rods are inactive, what?
light is so intense
the rods kick in; night vision
Rods and Cones
photoreceptors of the vertebrate eye
more sensitive to light than cones, but don't distinguish color
responsible for daytime color vision; visual acuity, best visual discrimination for visual acuity
The __ has nothing but __ because of the __.
fovia (pit/ indentation)
__ subclasses of cones, each with its own type of __ associated with __ to form visual pigments:
red, green, blue
What is the mechanism?
light causes shape change in retinal
triggers chain of metabolic events that decrease signal to cells with which photoreceptor cells synapse
it is a decrease in the chemical signal that serves as the message
rods and cones synapse with bipolar neurons, which synapse with ganglion cells
eye cup of planarians
compound eye of invertebrates
Explain the eye cup of planarians.
simple light receptor that responds to light intensity and direction without forming an image
planaria are negative photropic to avoid predation
Compound eye of invertebrates
e.g.: insects, crustaceans, and some polychaete
Thousands of light detectors called ommatidia, each with its own cornea and lens
results in mosaic image
The lens is a __ into what?
space in front: anterior segment
space behind: posterior segment
subdivision of the anterior segment in front of the iris and behind the cornea