Chapter 9  (Refraction by the eye)
1. In the schematic eye of Gullstrand:
a. the human model eye is based on the principal of thick lenses

b. the eye is about 24.0 mm in axial length

c. the nodal points lie on either side of the posterior surface of the lens

d. the nodal points coincide with the principal points

e. the cornea contributes 2/3 to the power of the eye

2. In the reduced eye of Listing:
a. the refractive power is stronger than that of the schematic eye of Gullstrand

b. the whole eye is regarded as a single refractive surface

c. the second focal point lies on the retina

d. the nodal point lies at the posterior surface of the lens

e. the principal plane lies at the anterior surface of the lens


3. The back vertex power:
a. is the reciprocal of the back vertex distance

b. of a convex meniscus lens can be calculated from its second focal length

c. of a convex meniscus lens is stronger than its front vertex power

d. gives the equivalent power of a lens

e. is used to grade spectacle lenses


4. The following definitions are true for accommodation:
a. the far point of distinct vision of an emmetropic eye is at infinity 

b. the near point of distinct vision refers to clear near vision when maximum 
    accommodation is used.

c. range of accommodation is the difference in dioptric power between the 
    eye at rest and the fully accommodated eye

d. dynamic refraction refers to the dioptric power of the accommodated eye

e. static refraction refers to the dioptric power of a resting eye


5. Regarding accommodative convergence / accommodation ratio:
a. the eye could not accommodate in the absence of convergence

b. the normal range of accommodative convergence/ accommodation ratio
    is 3:1 to 5:1

c. the interpupillary distance needs to be known if the ratio is to be 
    calculated using the gradient method

d. the value obtained using the heterophoria method tends to be lower than
    that calculated using the gradient method

e. esotropia that occurs as a result of too high an AC/A ratio tends to have
    a larger angle of deviation for near than for distance.


a6. The catoptric images :
a. are formed at the refracting interfaces of the eye

b. can be used to measure the ocular accommodation

c. are all virtual images

d. are all erect images

e. are made up of 2 images produced by the cornea and 2 images 
    by the crystalline lens

7. The first image of the captoptric image can be used for:
a. measuring ocular deviation in strabismic patient

b. keratometry

c. measuring accommodation

d. measuring corneal thickness

e. measuring anterior chamber depth

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