occular correction (near)

Question 1

describe accommodation amplitude

identify factors that affect (4)

Answer 1

max amount of accom eye is capable of

• age
• capacity of ciliary body
• general health of patient
• vascular and granular defects

Question 2

when are patients labelled presbyopic? (1)

when is Add required for correction (1)

Answer 2

• presbyopia is labelled when the subjective amplitude of accommodation falls below 3.00D
• requires Add when below 4 dioptres

Question 3

how is near reading add prescribed (2)

-L-(amps/2)

Answer 3

• subject can view near target by exercising half their Amp, with the other half being provided by the Add
• patient comfortable when exercising less than or equal to Amps/2 when reading

Question 4

outline 3 methods to determine correct near Add (2+1+2)

Answer 4

1. range of clear vision
   - the distance between the closest and furthest that the subject can see clearly
   - working distance should ideally be at dioptric centre (ie. midpoint of the range)
2. trial lens
   - fine tuning of Add by adding low power spherical lenses while subject looks at test card at working distance
3. bichromatic test
   - performed at working distance
   - Add adjusted to obtain slight red preference or equality

Question 5

outline depth of field (1+3)

Answer 5

• the range of clear vision when accommodation is constant
• > increase range of clear vision
• depends on pupil size
  if pupil size decreases -> depth of field increases (as blur circle size is directly proportional to pupil size)
• for a fully accomodated eye, depth of field is like an increase in Amp (accom)
• for relaxed eye, depth of field is like negative accom (see beyond far point)

Question 6

outline depth of focus (1+2)

Answer 6

• the corresponding range in the intraocular image space
• blur size circle too small to affect depth of focus
• outside the depth of focus, blur is noticable

Question 7

identify the condition anisometropia and its correction (1+2)

Answer 7

a condition in which the eyes have unequal refractive power

corrected by either:

1. iseikonic lenses (up to 3.00D diff between the eyes)
2. contact lens (removes effect of vertex distance and spec thickness imbalance)