application to the human eye 2.3

Question 1

What is an optical axis?

Answer 1

-hypothetical line which passes through the centres of curvature of all surfaces of the system

Question 2

What is the most sensitive part of vision?

Answer 2

fovea centralis
-best acuity , highest density of photorecpeptors
however doesn’t lie on the optical axis

Question 3

What is a visual axis?

Answer 3

-When you look at an object (fixate) the light falls on your fovea centralis to use your best acuity.

Question 4

What is the optical axis in the eye?

Answer 4

-no clear optical axis in the eye -its approximate optical axis instead

Question 5

Why is there an angle between visual axis and optical axis?

Answer 5

because of the relative location of fovea compared to where optical axis crosses the retina.

Question 6

What is the angle between the visual axis and optical axis?

Answer 6

angle a (alpha)
-It is 5 degrees nasal and 2 degrees upward on average for both eyes

Question 7

What is the cornea approximating by?

Answer 7

• one single surface by combining anterior and posterior surface of cornea and treat as one- homogenous
• • in the human eye it is not homogenous, as the refractive index is changing about

Question 8

What is good first level of approximating lens with a homogenous?

Answer 8

-as a good first level of approximation you can use a single refractive index for the crystalline lens in our eyes

Question 9

What is the difference between number plate and Snellen chart?

Answer 9

• Letter spacing closer than on Snellen chart- crowding effect
• contrast may be less- black on yellow
• number plates include wider range of opotypes with differing legibilities
• font no on 5x4 grid- stroke width and gaps not same
• not carried out under standardized lighting and test conditions.