NB8-3 - Visual System & Retina and DLAs Flashcards
What is focal length (distance) and refractive power? What is the refractive power of the cornea?
Focal Length - distance from refractive surface to the point where parallel rays converge
Refractive Power (optical power) - The degree to which a lens converges/diverges light. It is equal to the reciprocal of the focal length.
Refractive power of the cornea is ~42 diopters
By how many diopters can the lens accomodate?
up to about 15 diopters
Why is it you can see objects in greater detail when they are closer? Why are objects in the center of your visual field seen in much greater detail than the in the periphery?
An object emits the same number of light rays no matter how far it is from your eyes. However, when you are farther away more of those light rays get focused on the retina. Because of this, there are more light rays to resolve than there are photoreceptors which results in visual spatial resolution decreases.
The fovea has the highest density of photoreceptors and has only cones (no rods, blood vessels, bipolar, or ganglion cells) this allows for minimal light scattering and the highest spatial resolution in the central visual field.
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A
What are the technical terms for the normal-sighted, near-sighted, and far-sighted conditions. What causes these conditions? How are they corrected?
- The normal sighted, aka emmetropic, eye can focus parallel rays onto the retina with accomodation
- The near-sighted, myopic, eye is too long and the lens cannot accommodate enough resulting in an image focused in front of the retina and blurry vision. This is corrected with concave lenses.
- The far-sighted, hyperopic, eye is too short and the lens cannot accommodate enough resulting in an image focused behind the retina and blurry vision. This is corrected with convex lenses
Why type of cone focus on which type of color?
L (long λ) cones focus on Red
M (medium λ) cones focus on Green
S (short λ) cones focus on Blue
LMS RGB
What is the technical term for color blindness? List the most common types of color blindness.
Most color blindness is only partial and is known as dyschromatopsia (abnormal color vision). Total color blindness (rare) is known as achromatopsia. The most common type of color bindness is Red-green color blindness because there are two different disorders that cause it:
Protanopia - insensitive to red light (also difficult to distinguish blue and green)
Deuteranopia - insensitive to green light
What is the term for having an absent or defective type of cone?
Dichromats are completely missing a type of cone
Anomalous trichromats have a defective type of cone
How can you tell from a fundoscopic image whether you’re looking at the right or left eye?
The optic disk is always located medially
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What abnormality is present here? What usually causes this? What are the common symptoms of this? How is it typically treated?
This is papilledema which is swelling of the optic disk usually caused by increased intracranial pressure which presents with short disturbances in vision, headache, and vomiting. It is treated, in the short term, by relieving ICP via a LP until the cause fo the increased ICP is found.
B
What are the common symptoms of retinal detachment?
Early symptoms include sudden appearance of floaters and flashes, and reduced vision. Can lead to retinal tears and vision loss in the area of detachment.
Describe what diabetic retinopathy is and how it progresses.
Chronically high blood sugar from diabetes is associated with damage to small retinal blood vessels. It is the leading cause of vision impairment and blindness among working-age adults
- Early Stage - microaneurisms and fluid leakage
- Later Stage - proliferation of new vessels and scar tissue
Once the macula is inovled vision loss progresses quickly
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What is the defect?
Diabetic retinopathy
What are the defects?
Left is dry AMD
Right is wet AMD
