Q 01/05

Roughly how wide is a typical adult human eyeball from front to back?

A) 24 mm

B) 28 mm

C) 32 mm

D) 36 mm

Answer · why

A) 24 mm

It holds about 6.5 millilitres and grows from 16 to 17 mm at birth to full size by around age 12.

Q 02/05

Which part of the eye provides most of its focusing power?

A) The cornea

B) The lens

C) The retina

D) The pupil

Answer · why

A) The cornea

The clear dome is about 11.5 mm across and half a millimetre thick at the centre; the lens does the fine-tuning.

Q 03/05

The pupil of a human eye can range in diameter from about 2 mm to more than what?

A) 3 mm

B) 5 mm

C) 6 mm

D) 8 mm

Answer · why

D) 8 mm

The iris does the adjusting, controlling how much light gets in.

Q 04/05

How many muscles move each human eye?

A) Two

B) Four

C) Six

D) Eight

Answer · why

C) Six

Four straight recti muscles and two obliques let the eye look in every direction and roll slightly.

Q 05/05

Which photoreceptor cells in the retina work in dim light and see only in shades of grey?

A) Cones

B) Rods

C) Ganglion cells

D) Bipolar cells

Answer · why

B) Rods

The retina holds around 7 million cones and somewhere between 75 and 150 million rods.