defintions

Question 1

define emmetropia (2)

Answer 1

• a state of vision where refractive system of eye and axial length is in proper correlation
• parallel pencil of light rays from distant object focuses exactly on macula/fovea

Question 2

differentiate the 4 types of ametropia (1,1,2,2)

Answer 2

1. myopia
   - focal (near) point in front of retina
2. hyperopia
   - focal (near) point behind retina (virtual)
3. presbyopia
   - stiffening of lens decreasing accomodative amplitude of eye
   - images are formed behind the retina
4. astigmatism
   - irregular shape causing different powers at different principal meridians -> creating elongated image of a dot point source
   - corneal (most common) or lenticular

Question 3

define accomodation (1+2)

Answer 3

• refractive power of eye increases to provide clear vision from distance to near
• ciliary muscle relaxes -> lens at minimum strength for distant vision
• ciliary muscle contracts -> lens surface becomes more round to maximum strength for near vision

Question 4

define vertex distance (2)

Answer 4

• positive distance from back vertex of lens to the eye

- typically 10-14mm