Term
| How is the refractive index of a substance calculated? |
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Definition
| The velocity of light in air divided by the velocity of light in a substance |
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Term
| When light strikes a substance with a different refractive index than the wave front (perpendicular), what does the degree of bending depend on? |
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Definition
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Term
| What do convex lens with correct curvature cause parallel light rays to bend onto? |
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Definition
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Term
| What does a concave lens cause parallel light rays to do? |
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Definition
| diverge away from a certain point |
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Term
| What is different about cylindrical lenses? |
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Definition
| light is refracted towards or away from a line, rather than a point |
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Term
| Cylindrical lenses combined at what angles have the same focusing effect as one spherical lens? |
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Definition
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Term
| What condition is treated with cylindrical lenses? |
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Definition
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Term
| At what distance does an object have to be for light rays to be essentially parallel? |
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Definition
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Term
| What does light from a nearby source do? |
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Definition
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Term
What happens as a light source is brought closer to the eye?
How does the eye accomodate for this? |
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Definition
the focal point moves farther away
the lens becomes more convex (muscles relax) |
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Term
| In what unit is the refractive power of a lens is usually described? |
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Definition
diopter
reciprocal of refractive index |
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Term
| What information must be given to describe cylindrical lens, along with diopter strength? |
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Definition
*axis
if focal line is horizontal, lens has an axis of 0 degrees
if focal line is vertical, lens has an axis of 90 degrees |
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Term
| What are the four refractive interfaces of the eye? |
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Definition
between air and anterior surface of cornea
between posterior surface of cornea and aqueous humor
between aqueous humor and anterior surface of lens
between posterior surface of lens and vitreous humor |
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Term
| Where does most of the refractive power of the eye come from? |
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Definition
| anterior surface of cornea |
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Term
| How much of the refractive index of the eye comes from the lens? |
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Definition
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Term
| what is the total refractive power of the eye? |
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Definition
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Term
| How far away is the center point of the lens from the retina? |
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Definition
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Term
| What is the total refractive power of the eye? |
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Definition
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Term
| What is the major function of the lens? |
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Definition
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Term
What is the refractive power of the lens?
How strong can it be at its highest point of accomodation in children? |
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Definition
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Term
| About how many suspensory ligaments hold the lens in place? |
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Definition
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Term
| What is the lens like at normal resting conditions? |
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Definition
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Term
| What muscle attaches to the suspensory ligaments? |
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Definition
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Term
| What happen when meridional fibers are tensed? |
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Definition
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Term
| What happens when circular fibers are contracted? |
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Definition
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Term
| Which muscles in the lens system are controlled by the parasympathetic nervous system? |
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Definition
| ciliary muscles; they contract to relax lens, adapt for near vision (rest) |
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Term
| How does parasympathetic firing adapt to view nearby objects? |
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Definition
if distant object approaches eye, parasympathetic input to ciliary muscle increases
conversely, if nearby object moves away from eye, parasympathetic input to ciliary muscle decreases
accomodation is both voluntary and reflexive |
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Term
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Definition
| diminished accomodation with age |
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Term
| What has reflexive control over pupil diameter? |
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Definition
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Term
| What is pupil dilation called? Pupil constriction? |
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Definition
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Term
| What is depth of focus or depth of field? |
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Definition
| range of distances over which objects remain in focus |
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Term
| What type of pupil diameter results in a large depth of focus? |
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Definition
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Term
| When eyes fixate on nearby object, a reflex with what three reflexes is evoked? |
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Definition
convergence
accomodation
miosis |
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Term
What is an Argyll Robertson pupil?
What condition is this strongly associated with? |
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Definition
bilateral small pupils that constrict when patient focuses on near object, but do not constrict when exposed to bright light
*neurosyphilis |
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Term
| What causes degradation of emmetropic (perfect) vision? |
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Definition
| Mismatch between eyeball length and strength lens system |
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Term
| What causes hypertropia (farsightedness)? |
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Definition
| either an eyeball that is too short, or a lens system which is too weak |
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Term
| What causes myopia (nearsightedness)? |
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Definition
| either an eyeball that is too long, or a lens system which is too strong |
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Term
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Definition
light from one plane (e.g., vertical) is focused at a different distance than light from a second plane (e.g., horizontal)
uneven curvature of cornea in one of its planes is a common cause |
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Term
| Can accomodation compensate for astigmatism? Why or why not? |
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Definition
| lens accommodation cannot compensate for astigmatism since lens changes equally in all planes |
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Term
| What kind of lens is prescribed for hyperopic eyes? |
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Definition
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Term
| What type of lens is prescriber for myopic eyes? |
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Definition
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Term
| How can an eye with hyperopic or myopia plus astigmatism be corrected? |
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Definition
| eye with astigmatism and hyperopia or myopia requires lens with both spherical and cylindrical components |
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Term
| Which of the humors of the eye is free-flowing? |
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Definition
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Term
| What causes exchange between aqueous and vitreous humor? |
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Definition
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Term
| What determines ocular pressure? |
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Definition
| Balance between formation and reabsorption determines intraocular pressure |
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Term
| What forms aqueous humor? |
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Definition
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Term
| What are the mechanisms for aqueous humor secretion similar to? |
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Definition
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Term
| What is the path of aqueous humor flow? |
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Definition
between suspensory ligaments
through pupil into anterior chamber
into angle between cornea and iris
through trabecular meshwork
out of eye through canal of Schlemm
into venous circulation |
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Term
| What is glaucoma? What is it associated with? |
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Definition
| *damage to the optic nerve) associated with elevated intraocular pressure (risk factor) |
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Term
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Definition
medication to improve outflow, decrease formation of aqueous humor
surgery to improve outflow |
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Term
| Is damage to the optic nerve always associated with intraocular pressure? |
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Definition
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Term
| What is the role of the optical system of the eye? |
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Definition
| to focus light energy so that it effectively stimulates retinal photoreceptors |
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Term
| What happens if you combine a concave and convex lens of the same strength? |
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Definition
| they cancel out - system strength is 0 diopters |
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Term
| The optical system forms an image on the retina in what orientation compared to the external world? |
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Definition
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Term
| What two separate sets of muscle fibers is the ciliary muscle composed of? |
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Definition
| meridional fibers and circular fibers |
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Term
| How does the parasympathetic nervous system control the ciliary muscle? |
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Definition
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Term
| How long does reflexive accomodation of the eye take? |
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Definition
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Term
| How does the power of accomodation of the eye change as you age? |
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Definition
| The power of accommodation in a young child is about 14 diopters. This decreases to approximately 2 diopters by 45-50 years of age, and to essentially 0 diopters by 70 years. |
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Term
| How does the sympathetic nervous system affect the iris? |
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Definition
| Pupil dilation - mydriasis |
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Term
| By how much can the diameter of the pupil vary? |
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Definition
| The diameter of the pupil can vary between 1.5 and 8 mm, adjusting the quantity of light entering the eye 30-fold |
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Term
| What is an example of a condition that would be better treated by contact lenses than glasses? |
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Definition
| in keratoconus, a progressive thinning and bulging of the cornea distorts vision, due to altered refraction across the cornea. An appropriately shaped contact lenses may be sufficient to correct vision. |
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Term
| How are cataracts treated? |
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Definition
| removal of a lens that has been clouded over, which has to be replaced by an artificial lens or treated with a convex lens in front of the eye |
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Term
| On what part of the eye is visual acuity best? |
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Definition
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Term
| What is the closest that two points of light can be together and the eye still differentiate between them? |
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Definition
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Term
| What is normal intraocular pressure? What is it mainly cause by? |
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Definition
| 15±2 mm Hg. This pressure is mainly determined by the resistance to outflow through the canal of Schlemm |
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Term
| Intraocular pressure above what level is dangerous if sustained for long periods? |
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Definition
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Term
| What are the pharmalogical treatments for glaucoma? How do they work? |
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Definition
| Pharmacological treatments may decrease the rate of formation of intraocular fluid (including beta- blockers -- β-adrenergic receptor antagonists, and carbonic anhydrase inhibitors) or increase the rate of fluid outflow from the eye (including prostaglandin analogs, and parasympathomimetics). |
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