Flashcards in Chapter 49 Deck (28):
What is a converging lens?
also known as Convex Lens, will focus the light together, to a single point, known as the focal point. This is from the angle of the light hitting the lens, as a perpendicular angle to the lens will cause light to move in a straight line through the lens, an angled lens will cause the light to refract accordingly. A typical example would be a magnifying glass, something small at the focal point becomes big when you look through the convex lens of a magnifying glass.
What is a diverging lens?
Also known as Concave Lens, it will focus the light away from each other, causing light to refract away. The focal length would actually be on the opposite side as the above converging lens. Basically just the opposite of the convex lens.
What is the focal length?
is described as the length at which parallel rays converge at the focal point, or all of the light converges to a one localized spot. If the rays are already diverging from a source, then the focal length increases as the light must bend more than if it had just come straight at the lens.
What is The equation for focal length?
1/f = 1/a + 1/b, f is focal length for Parallel rays, a is the distance from a light source, and b is the distance of focus.
What is a diopter?
the measure of refractive power, so basically the greater the angle that the light rays bend after passing through the lens, the greater number of diopters it has
What is the diopter eqn?
It can be expressed in 1 meter / focal length = number of diopters. 1 diopter will mean that the focal length is 1 meter, and 2 diopters means the focal length is .5 meters. 10 diopters focal length is 1 meter / 10 diopters = focal length = .1 meter or 10 centimeters. Note also that there can be negative diopters, from concave lens, so if a concave lens diverges light as much as a convex lens converges the light, then they would just cancel each other out (equal power of refraction and diffraction) and it would appear as though nothing happened (0 refractive power).
What is accommodation?
the eye changing optical power or changing the shape of the lens (making it fatter or pulling it to make a thinner lens) to accommodate for near objects or far objects, and is controlled by the ciliary muscle
What is the physiological mechanism to accommodation?
the contraction of the ciliary smooth muscle actually allows the ligaments that attach to the lens to relax, and allows the lens to become more spherical, increasing its refractive power
What is Presbyopia?
when the lens becomes totally non-accommodating, so the lens have become inelastic and unable to change shape due to old age and the lens proteins denaturing over time. The eyes are always at the same focal length and the person will need bifocals.
What is the fxn of the iris?
function is to increase the amount of light that enters the eye during darkness, and to decrease the light that enters during daylight
Why does squinting cause better vision?
By decreasing the aperture by making your pupil smaller, you can focus better on a single point even if you move around. The small aperture only allows the rays closest to the center of lens to pass through, whereas the bottom ones, the rays are going all over the place.
What is emmeatropia?
normal vision, distant objects are in sharp focus when the ciliary muscle is relaxed.
What is hyperopia?
Farsightedness, or not enough refractive power in the eye, or possibly a short eyeball
Where is the focal point in hyperopia?
The focal point is somewhere behind the eyeball
What might cause hyperopia?
The ciliary muscle may not have enough power to bring the focal point forward to the actual retina
How can you fix hyperopia?
Hyperopia can be corrected with convex lens by converging the rays a bit before hitting the lens.
What is myopia?
Nearsightedness, or too much refractive power in the eye, or possibly a long eyeball
Where is the focal point in myopia?
The focal point is in front of the retina
How can you fix myopia?
Myopia can be corrected with concave lens by diverging the rays a bit before hitting the lens.
What is Astigmatism?
is when the lens is a weird shape so that images have different focal lengths – think of an egg shaped lens, the top part will have a different focal length than the bottom part, distorting the resulting image. Accommodation will have no effect on a lens with astigmatism
How can u treat astigmatism?
Astigmatism can be corrected by two cylindrical lens that are next to each other, and the two different lens would be found by just trying on different lens of varying strengths until one would work, then you would move onto the next problematic area. You would also need to find the axis of where the lens would need to be placed (find the location of the problem, then find the strength needed to correct it). This would be done via a chart with angular orientating parallel black bars
What are cataracts?
common eye abnormality in old people, and is a cloudy or opaque section of the lens. This can be from protein denaturation, and these proteins can coagulate together. The light cannot get through, and may require surgical removal of that part of the lens.
How can u treat cataracts?
You can either give them a powerful convex lens, or you can put in a plastic lens in place of the missing piece
What does 20/50 mean?
20/50 means that at the standard 20 feet length, a person can only see letters that a normal person would see at 50 feet. First number is standard, second number is what the person sees at that standard length, and becomes a ratio of normal versus that persons visual acuity.
What are the three mechanisms of depth perception?
1. Sizes of the image of known objects on the retina (If I look at a 6’ tall person, I know how far away he is based on his known height)
2. Phenomenon of moving parallax (the sun never moves because it is so far away, but waving my hand across my face will move very quickly across my field of vision due to it being very close)
3. Stereopsis – think stereo as in surround sound, so basically your two eyes give you stereo vision, so if you close one eye and a close object changes location as compared to your other eye, that gives you an idea of how far away that object is. Again closing one eye and looking at a skyscraper and switching eyes will tell you that since the skyscraper is not going anywhere means that it is really far away.
Where is intraocular fluid recycled?
Canal of Schlemm in the anterior chamber
What is glaucoma?
one of the most common causes of blindness, it is when intraocular pressure becomes too high, (60 mm Hg) and as low as 25-30 can cause loss of vision. As pressure rises, it can damage the optic nerve and compress it. Increase resistance from the trabeculae blockage can lead to glaucoma