What is a possible consequence of tear film breakup for vision?
contrast sensitivity is reduced when a person voluntarily stops blinking
Which component predicts refractive error?
Vitreous Chamber Depth (VCD)
Can you name a possible benefit of the Stiles-Crawford effect?
Reduces glare from intraocular light scatter
Describe an optical role for the sclera of the eye?
Provides support for retina. It keeps the VCD stable and therefore keeps refractive error stable
List each of the optical components of the eye along with its main optical function
see Steph Wong guide
Give an example of how the wide variability in corneal radius of curvature between individuals is of relevance to optometric practvice
contact lens fitting
Give an example of an optical property of the pupil that affects vision in daily life
retinal illuminance
Why is it advantageous to have accommodation in daily life?
maintain sharp images of near objects
The cornea contributes___ and the crystalline lens___
Cornea: 2/3
Lens: 1/3
DRAW a schematic eye showing the radii of curvature and thicknesses of the optical components of the eye, and their approximate refractive indexes
Draw
What is the meaning of the entrance pupil? How is it different from the aperture stop of the eye?
EP: image of the AS through all preceding lenses; Clinical pupil (what observer sees; image of pupil)
AS: Opening that determines the cone angle of a bundle of rays; Iris = AS in the eye; actual pupil is AS
Understand Helmholz model of accommodation
Contraction of ciliary body = relaxes tennis on zonular fibers = allows lens to become more curved
During positive accommodation, the equatorial diameter of the lens decreases, anterior surface becomes more curved
DRAW two cross-sections of a human eye: one w/ relaxed accommodation and one w/ increased accommodation.
Show the difference in lens, thickness, diameter, and radii of curvature in slight exaggeration
DRAW
Describe in simple language the sequence of events when an eye accommodates for a near object
The muscles around the eye contracts and release the tension on the lens which makes it become short and thick (more curved)
Describe w/ a PICTURE the difference between lens equatorial diameter and thickness
DRAW
Equatorial diameter: diameter of lens at equator (left to right of lens)
Lens thickness: fore-aft (from front to back of lens)
What is cataract?
Loss of transparency of crystalline lens
How might presbyopia influence your daily activities as you grow older?
As your accommodative maximum decreases, you lose the ability to focus on and read near objects
Which photoreceptors operatin in scotopic (darker) and photopic (brighter) lighting conditions?
Scotopic: Rods
Photopic: Cones
How do cone and rod densities vary across the retina?
Cone density is maximal at of fovea
Rod density is maximal at about 20 degrees eccentricity.
No rods in central 1 degree of retina
Why might it be difficult or impossible to see very small, dim objects when fixating them directly at night?
Fixating on something will place the image on the fovea where few rods exist. Rods are necessary to see in darker conditions.
What is the blind spot? Why do you have one?
It corresponds to the optic nerve head, which has no photoreceptors there
Ingrid is studying the visual abilities of a rare mouse. She has several retina specimens. She can calculate the average spacing of the photoreceptors by microscope. How could she predict the potential visual acuity of these mice? Include a diagram.
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How could you define the Stiles-Crawford effect in simple language?
Light entering through the center of the pull is more effectively absorbed the light not at the center. This helps reduce glare.
Which part of the eye causes the Stiles-Crawford effect?
Photoreceptors