Board Certified Ophthalmologist Optics and Refraction Principles 5

Question 1

What refractive index does a standard keratometer assume to convert corneal radius of curvature into dioptric power?

Accepted Answer

1.3375

Answer

The keratometric index of 1.3375 is a fictitious value chosen to account for the negative power of the posterior cornea.

Question 2

What wavelength does the argon fluoride excimer laser used in refractive surgery emit?

Accepted Answer

193 nm

Answer

The ArF excimer laser emits ultraviolet light at 193 nm, which ablates corneal tissue by photodecomposition.

Question 3

What optical thickness does a single-layer anti-reflective coating need for destructive interference of reflected light?

Accepted Answer

One-quarter wavelength

Answer

A quarter-wave coating makes the two reflected waves differ by half a wavelength in path, so they cancel.

Question 4

What is the approximate optimal pinhole diameter for clinical testing of potential visual acuity?

Accepted Answer

1.2 mm

Answer

A pinhole of about 1.2 mm balances reduced blur circle size against increasing diffraction at smaller apertures.

Question 5

Without correction, at what distance can an otherwise normal -3.00 D myope read clearly with accommodation fully relaxed?

Accepted Answer

33 cm

Answer

The far point of a myope is 1 divided by the refractive error, so 1 / 3 = 0.33 m.

Board Certified Ophthalmologist Practice Test