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59 Cards in this Set
- Front
- Back
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What is the definition of a diopter? What is one diopter equal to?
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The unit of measurement for the divergence/convergence of light rays
One diopter = a lens converges parallel rays coming in at a focus of 1 m from the lens |
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What is the relationship between the power of the lens (diopters) and focal length?
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The inverse
Power = 1/focal length |
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If vision is ideal, where is light focused?
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On the retina
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Where does the focusing power of the eye come from? How much comes from each component?
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Intraocular lens: +16 diopters
Cornea: +45 diopters 61 total. |
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What part of the visual system has variable focusing power? How does this happen?
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Lens
Contraction/relaxing of the ciliary muscles |
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What is the definition of accommodation?
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A change in the shape of the lens to increase lens power
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If an object is brought closer, what kind of change needs to happen to the lens?
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The lens needs to become thicker-->contraction of the ciliary muscles
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What kinds of signals are sent to the brain during accommodation?
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1. Image hits retina
2. CNII brings image to the brain 3. Brain sends signal via CNIII to ciliary muscles 4. Contracting/relaxing, depending on what needs to be done |
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How does accommodation occur?
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1. Ciliary body muscle contracts (CNIII)
2. Zonules that insert into the lens loosen 3. Lens becomes more spherical |
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Accommodation is required for what type of vision?
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Close-up vision
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What is the definition of refraction?
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The deviation of light rays in passing through media of differing densities and surface curvatures
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How do you go about correcting refractive disorders?
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Glasses
Contact lenses Surgery |
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What are the different kinds of refractive disorders?
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Emmetropia
Myopia Hyperopia Astimatism Presbyopia |
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What is the definition of emmetropia?
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The eye with the lens at rest converges the parallel rays of light to focus on the retina
This is good, clear vision |
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What is the definition of myopia?
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Nearsightedness: you can't see what's far away
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In myopia, what is the problem with focusing power?
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You've got too much of it
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In myopia, where is the light focused?
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In front of the retina
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What are causes of myopia?
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Eye is too long
Cornea is too steep |
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What's the prevalence of myopia? Who really gets this?
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25% of adults
Asians have it the worst |
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What are some causes of myopia?
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Congenital
Developmental Medications DM Trauma Age-related |
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What congenital conditions are associated with myopia?
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Chr 18p
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What developmental conditions are associated with myopia?
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Reading
Night lights Increased ocular pressure |
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What medications are associated with myopia?
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Sulfa drugs
Diuretics Neostigmine Pilocarpine |
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Does accommodation hep myopia?
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NO!
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How does one see something clearer in myopia?
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Bring something closer to the eye
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What kind of glasses do you give for myopia?
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MINUS glasses
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What is the definition of hyperopia?
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Farsightedness: you can' see things that are near
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What are causes of hyperopia?
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Eye is short
Cornea is flat |
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What problems with focusing power do you have in hyperopia?
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Not enough of it
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Where is the light focused in hyperopia?
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Behind the retina
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What is he effect of age on hyperopia?
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Increasing difficulty with it.
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What are some causes of hyperopia?
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Congenita
Developmental Trauma Orbital tumor Anticholinergics |
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Will accommodation help hyperopia?
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YES!
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How do you manage hyperopia?
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You give PLUS glasses
Contacts Refractive surgery |
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What is the definition of an astigmatism?
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An uneven corneal surface (football instead of a basketball)
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What kinds of vision problems are had with an astigmatism?
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Blurry near and far vision
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What are the different types of astigmatism? Which is more common?
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Corneal - more common
Lenticular |
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How do you correct for astigmatism?
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You give glasses that have multiple different prescriptions within the same lens
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What is the definition of presbyopia?
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Loss of accommodation with age
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When does presbyopia begin to set in?
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At around age 40.
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What is the cause of presbyopia?
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Buildup of insoluble protein within the lens that cause you to be unable to acommodate
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If someone has presbyopia, what do they do?
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They hold the newspaper farther out.
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What is the management of presbyopia?
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Reading glasses
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What is the effect of presbyopia on hyperopia?
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Even greater need for accommodation!
Give people bifocals |
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What is the effect of presbyopia on myopia?
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It kind of negates it.
Decreased focusing power from presbyopia negates the excessive focusing power ofmyopia |
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What is the goal of refractive surgery in:
Myopia? Hyperopia? Astigmatism? |
Myopia: flatten cornia-->reduce power
Hyperopia: steepen cornea-->increase power Astigmatism: reshape uneven curves of the cornea |
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What is radial keratotomy? What kinds of conditions can this cure?
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Incisional surgery
Corrects: -Myopia -Astigmatism |
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What is LASIK? What does it correct?
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Laser-assisted in situ keratomileusis
Corrects: -Myopia -Hyperopia -Astigmatism |
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What is LASEK? What does it correct?
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Laser subepithelial keratomileusis
Corrects: -Myopia -Astigmatism |
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Wht is PRK? What does it treat?
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Photorefractive keratectomy
Treats the corneal surface |
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What is ICRS? What does it correct? What is an advantage?
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Intracorneal stromal ring (flattens cornea)
Corrects: Mild nearsightedness It's reversible |
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What is CK? What does it correct?
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Conductive keratoplasty (incisions on lateral conrea, causes steepening)
Corrects: Farsightedness |
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What is a phakic intraocular lens? What can it correct?
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Puts a lens inside the eye, either in the posterior or anterior chamber
It can correct stuff up to -20.0D |
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What are some complications that you can get after refractive surgery?
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Under/overcorrection
Glare/halo Dry eyes Lamellar keratitis Scarring |
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What kinds of vision abnormalities can contacts correct?
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All of them!!!
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What is a requirement for contacts to work?
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An adequate tear film
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What would cause someone to not be able to use contacts?
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Astigmatism
Tear film problems Sensitive cornea Age - can't handle them |
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What are some danger signs from contact lens use?
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Spectacle blur edema: you have blurred vision for a couple of hours after using the contacts because of ischemia to the eye
Corneal scarring/warping Corneal vascularization Papillary conjunctivitis Infection |
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What is the use of corneal refractive therapy?
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Wearing gas-permeable contacts that serve to flatten the cornea all night long
They correct myopia by flattening the lens Used in Taiwan, where myopia is endemic |
