unit 6

Question 1

3 principle measures for near VA

Answer 1

-unaided near va (near vision)
-habitual near va (w own gls)
-optimal near va (w/ best refractive correction)

Question 2

to focus on a near object the eye needs to do what ?

Answer 2

increase it dioptric power so it will be positive accomodation

Question 3

when an eye changes focus from near to distance the eye needs to what?

Answer 3

decrease its dioptic power so it is negative accomodation

Question 4

what is the purpose of accomodation

Answer 4

neutralize negative vergence from a near object

Question 5

3 main components of the eye involved in the process of accomodation?

Answer 5

-ciliary muscle
-zonules
-crystaline lens

Question 6

what happens to the eye structures when unaccomodated?

Answer 6

-when looking in distance, the ciliary muscle is relaxed
-the crystaline lens is pulled and stretched into a thinner and flatter form by the zonules

Question 7

what happens to the structures of the eye when accomodating?

Answer 7

• the ciliary muscles contract causing it to move forward
  -this in turn relaxed the tension on the zonules, resulting in an increase in curvature of the crystaline lens

Answer 8

-tonic
-convergence
-proximal
-refelex
-voluntary

Question 9

tonic accomodation

Question 10

convergence accomodation

Answer 10

amount of accommodation stimulated by convergence
- in young pxs the accommodative response follows convergence of the eye

Question 11

what is the reaction time for convergence?

Answer 11

0.2 seconds
-2x faster than reaction time for accomodation

Question 12

proximal accomodation

Answer 12

amount of accomodation induced by the individuals awareness of the proximity (nearness) of an object

Question 13

reflex accomodation

Answer 13

the normal involuntary response to blur in order to maintain a clear retinal image

Question 14

voluntary accomodation

Answer 14

-does not depend on the presence of a stimulus
-ability to relax accommodation from some near focus position is easily learned

Question 15

amplitude of accomodation

Answer 15

Total amount by which an eye can change in power
-eyes max power minus the eyes min power

Question 16

Blur technique

Answer 16

-requires the use of the RAG near point rule
-centimetre scale
-diopter scale
-age scale

Question 17

push up to blur method

Answer 17

-distance correction in place
-RAF rule is placed in a slightly depressed positin to mimic the action of the eyes when reading
-Monocular amps are measured first
-Binocular amplitude is usuaully greater than monocular bc convergence drives accomodation
-USE N5 letter as target
-individual moves the near card along the sliding scale from the end of the rule until the print just blurs
-the amplitude of accomodation is read off at this point

Question 18

push down to clear method

Answer 18

-individual starts with the print at the end of the scale closest to the face
-move the print away until its just legible
-the amplitude of accomodation is read off at this point
-if both techniques are used, the recorded amplitude of accomodation should be ;
the average of the readings obtained with both methods

Question 19

What is presbyopia

Answer 19

the amplitude of accommodation decreases gradually with advancing age

Question 20

when is presbyopia said to be present

Answer 20

When the A of A dropped to around 3.00D
-causes px to require reading gls

Question 21

what happens to the lens and ciliary muscle with presbyopia?

Answer 21

-the lens capsule gradually loses elasticity
-the lens nucleus begins to stiffen (from about 30 years old)
-thickening of the ciliary muscle and growth of the lens reduce tension in zonules

Question 22

at what age does presbyopia usually occur/

Answer 22

around 45 years old

Question 23

clinical evidence suggests that px are able to maintain comfortable near vision if they exert…?

Answer 23

no more than two thirds of their amplitude of accomodation

Question 24

-symptoms of presbyopia

Answer 24

-near blur
-distance blur after prolonged close work
-eyestrain or headaches
-headache around the temple and forehead
-reading difficulty in poor lighting

Question 25

presbyopia / ADDformula

Answer 25

ADD= / L / - 2/3 Amp
/L/ = 1/l (working distance in meters)
/L/ = vergence of the incident light arriving at the spec lens

Question 26

‘normal’ patients may be divided into 3 groups for presbyopia

Answer 26

1. pre- presbyopes
2. early presbyopes
3. late presbyopes

Question 27

early presbyopes

Answer 27

-around age 40 but some younger px who have abnormal accomodation
-near addition required depends on wokring distance and the accomodation still available
-amplitude of accomodation may still be usefully measured

Question 28

late presbyopes

Answer 28

-have no remaining accomdation of their own
-reading addition is largrely determined by the working distance

Question 29

would you measure amplitude of accomodation of pxs over 55?

Answer 29

No it is unproductive so it is rarely attempted

Question 30

prescribing of a reading addition consists of two phases

Answer 30

1. An addition is estimated by considering the age, accomodation and any existing correction that the px may have
2. Refine subjectively, taking into account the occupational and lifestyle needs of the px

Question 31

if the working add is much less than 40cm what would you do to the tentative add?

Answer 31

increase the add

Question 32

what would you do to the add for computer work at 50-60cm

Answer 32

decrease the tentative add by about 0.50

Question 33

negative relative accomodation

Answer 33

the max ability to relax accomodation while maintaining clear, single binocular vision

Question 34

positive relative accomodation

Answer 34

the max ability to stimulate accomodation while maintaing clear, single binocular vision

Question 35

balancing NRA/PRA

Answer 35

-Adjust phoropter to near PD and attach the near point card
-make sure the optimal distance correction is in place and OU can view the near card
(bring vergence levers in)
-direct pxs attention to letters one or two lines larger than best va
-Ask the px if they are clear
-If they are not, add +0.25 at a time until px reports the letters are clear
-this becomes the initial tentative near add

Question 36

NRA balancing

Answer 36

-Add plus lenses binoculary, +0.25 at a time, untilt he px reports the first substained blur
-the total amount of plus added is the NRA
-return the lenses in the phoropter to the initial tentative near add found earlier

Question 37

PRA balanacing

Answer 37

-add minus lenses binocularly, -0.25 at a time until px reports the first sustained blur
-The total amount of minus added is the PRA

Question 38

Near duochrome / bichrome method

Answer 38

-Start with estimated add in place
-testing monofulcarly, plus lenses are added until the red chart at near is clearer for each eye
-reduce the plus lenses binocularly until the green chart is clearer and the plus lens remaining is the prebyoic add
-NOT COMMONLY USED

Question 39

The higher the add what happens

Answer 39

-smaller the depth of focus
-the progression characteristics and the near field of view may be affected in PAL

Question 40

Refining the near add

Answer 40

-aim is to arrive at an add that allows clear and comfortable vision at all distances at which px habitually works
-should be preformed after the distance rx has been determined

Question 41

what is the range of clear vision

Answer 41

the distance between the artifical far point and the artificcal near point

Question 42

artifical far point

Answer 42

-the point conjugate with the centre of the macula at the corrected and unaccomodated eye

Question 43

artifical near point

Answer 43

the point conjugate with the centre of the macula at the corrected but fully accomodated eye

Question 44

in some cases it is impossible to cover all a pxs requriments with one near add - true or false

Answer 44

TRUE - additional pairs of specs may be required to cover part of the range
-progressives or occuptational progressives may be required

Question 45

Most common errors in reading adds

Answer 45

-Estimating the tentative add based on pxs age, not WD
-Not determining the pxs near vision needs
-estimating distances instead of measuring w a tape measure
-over plussing
-under plussing - px w a nuclear cataract may require the distance rx to be reduced to reflect the myopic shift