Contact Lenses

Question 1

What determines the refracting power of a contact lens

Answer 1

anterior and posterior curvatures, thickness and refractive index

Question 2

What is the posterior central curvature (PCC)

Answer 2

The posterior surface of the optical zone is defined by its posterior central curvature (PCC), also known as the base curve

Question 3

What determines contact lens fit

Answer 3

The base curve and the diameter of the contact lens determine how tightly the lens fits the cornea and how easily it moves with each blink.

Question 4

What is the tear lens

Answer 4

The tear film between the posterior surface of a contact lens and the anterior surface of the cornea is known as the tear lens
If it has uniform thickness it has plano power

Question 5

What factors increase the negative power of the contact lens

Answer 5

the lens moulds to the surface curvature of the cornea, the evaporation of water increases the refractive index and an increase in temperature increases the curvature
The dry atmosphere of an aircraft cabin may cause blurred vision during and after a flight because of the increased evaporation of water from soft contact lenses.

Question 6

What is corneal warpage

Answer 6

is the change in corneal curvature induced by wearing a contact lens which is not associated with corneal oedema. It regresses after the lens is removed over hours or days

Question 7

What is corneal warpage

Answer 7

is the change in corneal curvature induced by wearing a contact lens which is not associated with corneal oedema. It regresses after the lens is removed over hours or days