11. Presbyopia

Question 1

what happens to the amplitude of accomodation as we age

Answer 1

steadily declines

Question 2

why does accomodation decline as we age

Answer 2

1. sclerosis of the fibres of the cystalline lens
2. changes to the capulse which reduce the spontaneous steepining of its srugfaces
3. ciliary muscle becomes less efficient with advancing age (after 40years)

Question 3

how much accommodation is the infant eye capable of

Answer 3

14D

Question 4

how much accommodation AT 45 YEARS

Answer 4

4d

Question 5

how much accommodation at 60 yeas

Answer 5

1D

Question 6

how much accomdation is required at reading distance (25cm)

Answer 6

emmetropic eye 4D

Question 7

how much accomadative reserve is required for comfortable near vision

Answer 7

1/3

Question 8

when would you start getting discomfot

Answer 8

Decayed to 6D
usually between 40 to 45 years of age

Question 9

why can’t presbyopia be defined in amplitude of accommodative reserve

Answer 9

onset of symptoms varies for patients

Question 10

how to work out presbyopic correction

Answer 10

Need to know:
1. remaining amplitude at near point
2. desired working distance

Question 11

Presbyopic correction example:
emmetropic patient with remaining accomodation of 3D at 25cm

Answer 11

3D at 25cm
comfort = use 2D out of 3D (1/3 remaining)
to see well at 25cm need 4D
Thf presbyopic correction would require 2D

Question 12

presbyopia in hypermetropia

Answer 12

Occurs earlier in uncorrected hypermetropia than emmtropia

as hypermetropia must accommodate more to achieve near vision

Question 13

presbyopic correction
hypermetropia with 3D

Answer 13

Hypermetrope needs to exert 3D of accommodation to see clearly at infinity
therefore to see clearly at 25cm 7D of acommodation is needed
3D + 4D

Question 14

Myopia and presbyopia

Answer 14

presbyopia in uncorrected myopia is delayed

Question 15

presbyopia and working distance

Answer 15

correction must be adjusted for working distance

Question 16

how to check for over-correction

Answer 16

ensure patient can read N5 at reading
and N8 at arms lenght

Question 17

what are bifocal lenses

Answer 17

sinlge pair of spectacles provudes separate distance and near prescriptions for each eye

Question 18

Split franklin bifocals

Answer 18

• flat bottom of two lenses that abutt together

Question 19

Cemented wafer bifocals lens

Answer 19

• have near portion constrecuted by attaching a supplementary lens to the surface of a distance lens of the same refractive infex
• UV cured epoxy is used

Question 20

Fused bifocals

Answer 20

• near portion is made by heat-fusing a button of flint glass to a corresponding depression in a crown glass main lens which has a lower refractive index
• different types of flint glass allow variation in the refrective index and power of the segment

Question 21

segment shapes for right eye fused bifocal lenses

Answer 21

Question 22

solid bifocals

Answer 22

• single piece construction
• near is produced by a different curvature of either the front or back surfacep

Question 23

plastic bifocals are always

Answer 23

solid / exectutive bifocals

Question 24

DVP and NVP

Answer 24

Distance visual point
Near visual point

Question 25

DVP and NVP are assumed to be

Answer 25

the visual axis is directed while the spectacles are in use

Question 26

NVP is relation to DVP

Answer 26

2mm nasal to and 8mm below the DVP