The eye can be regarded as a single refracting surface. The radius of this surface is equal to that of cornea (7.8 mm). This surface separates two media of refractive indices 1 and 1.34. Calculate the distance from the refracting surface at which a parallel beam of light will come to focus.

Using the lens maker's formula for a single refracting surface:

(n₂/v) - (n₁/u) = (n₂ - n₁)/R

where:

• n₁ is the refractive index of the first medium (1)
• n₂ is the refractive index of the second medium (1.34)
• u is the object distance (∞ for a parallel beam of light)
• v is the image distance (what we need to calculate)
• R is the radius of curvature of the surface (7.8 mm)

Substituting the values:

(1.34/v) - (1/∞) = (1.34 - 1)/7.8

(1.34/v) = 0.34/7.8

v = (1.34 × 7.8) / 0.34

v ≈ 30.7 mm

Converting to cm:

v ≈ 3.07 cm

The closest option is 3.1 cm.