3.1.1 Vision and Physiological Optics Flashcards
What is accomidation and how can it change with age?
Lens changes curvature to adapt to changes
Ciliary muscle contract - leading to increased curvature of the lens
Accomidation will decrease with age. Causes presbyopia
What is the difference between concave and convex lens in regards to focal points?
Convex lens focuses light at a point behind the lens (away from light source)
Concave lense focuses light at a point in front of the lens
What is a hyperopic eye?
This is considered farsighted.
Parallel rays are focused in an area posterior to the retina
What are the covered parts?
Left - angle of incidence
Right - Angle of refraction
What is the numerator and demoinator in the snellen acuity notation?
Example - You sat 20 feet in front of a chart
The gaps and strokes of the smallest letters you could read would subtend 1 min arc at 360ft
(Essentially someone with normal acuity could read letters correctly at 360 ft.
What is the index of refraction?
n=C/V
Meaning that this is how a new medium will change the speed of light
What is the power of the cornea and lens?
Cornea (42D)
Lens (20D)
What is the difference between convex and concave lenses?
What are the characteristics of an emmetropic eye?
The cornea and lens work to focus light on the retina in a correct fashion
How does focal length compare to lense curvature in a convex lens?
Larger radius (think the earth) has flatter lens
Flatter lens will bend the light less, so it has to travel further before meeting
What is the definition of legal blindness?
20/200 or visual field of less than 20 degrees
What would you use to correct myopia?
Bi concave lens would create diverging rays
Explain the differences in the 2 mediums in figures A, B and C?
If index of refraction (n2) is larger, then light bends towards the normal
In Example A, n2 >n1, like light going from air through glass
In Example B, n2>>n1, so more refraction, greater angle of refraction
In Example C, n1=n2 (eg: light going from 2 pieces of glass held against each other)
What is the physiological limit of visual acuity?
It is limited by the space between rods and cones from each other in the retina
How does the power of a strong lens compare to a weak lens?
Power is the inverse of focal length in meters.
Meaning a stronger lense will have a focal length with a smaller value.
What is astigmatism?
Vertical axis curvture and horizontal axis curvature on the cornea are different
What are the characteristics of a myopic eye?
Parallel rays are focused anterior to retina
Would could you use to correct hyperopia?
Convex lense would cause the focal length to become shorter
