Vision (2) Flashcards
What is the focal distance?
distance from the refractive surface to the point where parallel light rays converge
A measure of the refractive power of a transparent surface is what?
diopter; reciprocal of the focal distance in meters
The cornea and sclera present what functionally?
tough physical barrier to trauma and infection, protects internal structures of the eye.
The refractive power of the cornea depends on what?
slowing of light at the air-cornea interface; most of the refractive power, 42 diopters
Aqueous humor fills what? Produced by what?
anterior chamber;ciliary processes of the ciliary
body
What function does aqueous humor serve?
Provides nutrients for avascular tissues ant. segment (lens, cornea), Removes waste, Maintains intraocular pressure, Contains very little protein, no blood, allowing light to pass w/o scattering
What is the function of the retina?
Regulates amount of light falls on retina; iris dilator muscle contracts->pupil dilates (mydriasis) iris sphincter muscle contracts, pupil constricts (miosis).
Sympathetic innervation to iris utilizes what NT? Sympatholytic substances do what? Sympathomimetic substances?
NE; constrict pupil - Hexamethonium; dilate pupil- cocaine
Parasympathetic innervation to iris utilizes what NT? Parasympatholytic substances? Parasympathomimetic substances?
ACh, dilate pupil- Atropine, constrict pupil- Pilocarpine
The size of the pupil determines what? Small opening? Large Opening?
cone angle of a bundle of rays that come to a focus in image plane; highly collimated parallel rays, sharp focus at the focal plane; uncollimated rays, sharp focus only for rays with certain focal length.
What is the F-number?
focal length / aperture diameter; ratio of the focal
length of the eye (from cornea to retina) and physical
aperture (pupil opening); Each smaller F-number doubles area of opening & amount of light entering; Wide apertures=small depths of field
When we accommodate we constrict our pupils, what happens to the F-number?
gets larger, aperture gets smaller and depth of field gets larger
What is the function of the lens? When does it change?
focus light on the retina; shape of the lens can change in order to enable accommodation.
What does a Convex (converging) lens do?
bring light rays together at a focal plane a focal distance away from the lens.
What does a concave (diverging) lens do?
spread light rays apart so that the focal plane is a virtual plane in front of the lens.
What is the function of the ciliary processes?
Produce aqueous humor, Site of attachment of lens zonules
What is the function of the ciliary muscle?
Involved in accommodation, Site of drainage of some aqueous humor
The lens is involved in the accommodation when?
formation of point images closer than about 9 meters.
rays from objects at this distance or closer diverge, greater refractive power is required to bring them into focus on the retina.
What are the Steps in accommodation?
ciliary muscles contract, Suspensory ligaments attached to lens relax, lens becomes more spherical due to
inherent elasticity, curvature of lens surface increases, refractive power increases.
Other changes occurring during accommodation include what?
eyes converge, pupils constrict, F-number gets larger, the depth of field gets larger
What is myopia? Type of corrective lens?
nearsighted; diverging or concave
What is hyperopia? Type of corrective lens?
farsighted; converging or convex
What is astigmatism? Corrective lens needed?
irregularities in the curvature of the cornea or lens is corrected by cylindrical lenses
What is presbyopia? Corrective lens?
hardening of the lens is corrected by bifocals or trifocals.
What is the theory of opponent colors?
six primary colors, coupled in three pairs: red-green, yellow-blue and white-black. Any receptor that was turned off by one of these colors, was excited by its coupled color
What are the different trichromats?
Normal- Can distinguish about 150 hues; Protanomalous-Reduced red sensitivity, Can distinguish only 5 to 25 hues; Deuteranomalous- Reduced green sensitivity; distinguish only 5 to 25 hues
What are the different dichromats?
Protanopes=No red sensitivity (red looks black to them)
Deuteranopes= No green sensitivity
Tritanopes= Rare individual who are insensitive to short wavelengths
of light.
What is a Monochromat?
totally colorblind, world is shades of gray
How is color vision tested?
ishihara plates
What are the eye field genes? What do they do?
Rx, Pax6, Six3, and Lhx2 delineation of an eye field in the
developing neural plate
Where is the optic groove formed? When? What does it become? How does it remain connected to the brain?
either side midline at boundary of telencephalon and diencephalons; 3 weeks; evaginate from diencephalon form bilateral optic vesicles (3-4 weeks). continuous with third ventricle through the optic stalk
What are the six neuronal and one glial cell types in the retina? Match them with their developmental stage.
early stage of histogenesis (embryonic): retinal ganglion cells(RGCs), cone photoreceptors, 3 horizontal cells and amacrine cells; late stage of histogenesis (perinatal)
rod photoreceptors, bipolar cells and Muller glial cells
the outer nuclear layer contains what?
cell bodies of rod and cone photoreceptors
the inner nuclear layer contains what?
bipolar cells, horizontal cells, amacrine cells, and Muller glia.
The RGC layer consists of what?
RGCs and displaced amacrine cells
The outer and the inner plexiform layers represent what?
the fiber layers where synapses are located
What is the outermost cell and the innermost cell of the retina?
Photoreceptors- outermost (face the outer layer of the optic cup, the RPE); RGCs - innermost (toward the lens)
Light travels through what to reach photoreceptors?
RGC, plexiform, and nuclear layers
What are the characteristics of a rod/cone cells?
outer segment contains stack of membranous discs. which contain visual signal transduction machinery, renewed by diurnal shedding of discs- phagocytosed by
RPE.; inner segment contains nucleus and proteinsynth machinery. outer and inner connected by cilia
The light absorbing visual pigment in rods is what?
rhodopsin (contains non light absorbing opsin and light absorbing retinal)
Opsin is a transmembrane protein consisting of what?
348 amino acids; 11-cis retinal, obtained from the dietary vitamin A (11-trans retinol), attached covalently to residue 296 (lysine)
What are the functional characteristics of rods?
high sensitivity, rods are densely packed with photo
pigments; few photons can evoke maximum response in a rod, (dim light), adapt slowly to changing light levels.
What are the three different kinds of cones?
blue-Short-wave,S cone; least numerous, most sensitive), green-middle-wave, M cone, and red-long wave or L cone; most numerous but least sensitive cones
What are the characteristics of cones?
lower sensitivity, less photo pigments than rods; hundreds of photons are needed to evoke maximum response, adapted for day phototopic vision. Cones adapt faster than rods to changing light levels; reading, face recognition
What are bipolar cells?
second order neurons in retina carry information vertically from photoreceptors to RGCs
What are the properties of ON bipolar cells?
Depolarizing; depolarize in response to direct
illumination, due to presence of GPCR (=depolarized in light ON condition)