Prescribing for different refractive states (distance vision)

Question 1

list 4 things that will be done before addressing an rx as a final subjective i.e. referred to as the refractive end point

Answer 1

• Monocular refraction
• Binocular balancing
• Binocular addition
• Fixation disparity

Question 2

what is the risk of a final subjective rx

Answer 2

Patient will be intolerant to their new glasses

Question 3

what is the range of average spectacle dissatisfaction rate for UK optometry practices

Answer 3

• is in the range of 1% - 2%

assuming 2% this would mean about 400,000 patients intolerant to their glasses each year

Question 4

list 6 things that decision making when prescribing is based on

Answer 4

• Prescriber’s experience – PERSONAL
  Prescribers are more likely to alter their final subjective findings
  as they become more experienced (Howell-Duffy et al 2011)
• Patient’s age
• Assessment of patient’s ability to adapt to change
• The prescription currently worn
• Binocular status
• The patient’s needs/requirements/occupation etc.

Question 5

what are the 2 most important factors of decision making when prescribing

Answer 5

• Assessment of patient’s ability to adapt to change

- The prescription currently worn

Question 6

how is the patient’s age a factor of decision making when prescribing

Answer 6

older patients are less likely to adapt to change in their rx

Question 7

what must you always do before prescribing a new rx to a patient and why

Answer 7

Demonstrate to the patient the difference in acuity between previous and new prescriptions (Rx), and hence show the patient the improvement in VA with the new Rx

Because:
Some feel that Best Practice for changing a Rx is a two-line improvement in VA

Question 8

what do some practitioners feel is best practice for changing a Rx

Answer 8

a two-line improvement in VA

Question 9

list the 4 prescribing recommendations and who this was recommended by

Answer 9

Elliott, 2008

• Don’t change a Rx if the patient is happy with current glasses
  “If it ain’t broke don’t fix it”
  Approximately 50% of UK optometrists in a survey would not alter a patient’s Rx if the patient had no symptoms and there was negligible improvement in VA (Howell-Duffy et al, 2010)
• Consider a partial increase in plus power when significantly increasing a hyperopic prescription
• Consider a partial change when significantly altering cyl. power and/or axis
• Make any large changes (1.00DS+) in prescription in stages, particularly in elderly patients

Question 10

what shouldn’t you do for hypermetropic non-presbyopic Patients who are asymptomatic and how does this apply to younger patients

Answer 10

• do not prescribe glasses for distance use
• young patients usually have a large amplitude of accommodation
  If it ain’t broke don’t fix it

Question 11

when may a distance correction be appropriate for near for a hypermetropic non-presbyopic Patient

Answer 11

use as these patients approach presbyopia

Question 12

when may prescribing for Distance Vision may not be necessary for a hypermetropic presbyopia px

Answer 12

• is asymptomatic

- meets the legal driving standard

Question 13

for this Hypermetropic presbyopia px:

Unaided Vision R 6/12 L 6/12 Binoc 6/9
Wears Near Vision specs only
Final subjective: R +1.50DS 6/5 L +1.50DS 6/5
Add +2.00D R + L = N5

• what is the outcome of their legal driving requirements
• list 2 things you can do/explain to this patient
• what is it good practice to do when it comes to the decision making process and who is this stated by

Answer 13

• Patient should still meet legal driving requirements
• Demonstrate the improvement in VA for DV
• Explain distance vision blur through NV Rx and discuss possibility of bifocals and PPLs
• In general it is good practice to involve the patient in the decision making process
  GOC Code of Conduct: Point 7: “Respect the rights of patients to be fully involved in the decisions about their care.”

Question 14

for this Hypermetropic presbyopia px:

Unaided Vision R 6/18 L 6/18 Binoc 6/18
Wears NV specs only

Rx: R +2.00DS 6/5 L +2.00DS 6/5
Add +2.00D R + L = N5

• what is the outcome of their legal driving requirements and why
• what must you explain to this patient

Answer 14

• This patient would not meet the legal driving standard without DV Rx (needs at least 6/12 VA binocularly and must pass the “Number Plate Test”)
• Advise the patient of the legal requirements for driving

Question 15

list 3 things you must do if a patient who does not meet the legal requirements for driving does not accept your advice of not to drive unless they wear their rx

and what the patient’s responsibility is to do about this

Answer 15

• Explain that the patient’s insurance may be affected if they do not wear their glasses
• Annotate record card with advice given to the patient
• If the patient refuses DV Rx or refuses to wear the Rx for driving, note this on the record card and consult AOP
• It is the patient’s responsibility to inform the DVLA if they are below the required visual standards for driving

Question 16

what about a lens can be important for a myopic px and what is used to measure this, also explain why this is important

Answer 16

• lens form can be important
• use of lens measure

Because:

• Base curve changes can affect spatial perception
• Myopes are often quite particular when it comes to their spectacles

Question 17

for this myopic px:

Patient aged 48, asymptomatic with current glasses.
Current Rx R –1.50 = 6/6 L –1.50 = 6/6
Reads N5
Final subjective R –2.00 = 6/5 L –2.00 = 6/5 Reads N5

Prescription issued = R + L –2.00

Patient returns “unable to read properly with new glasses”

what can the problem be
how can you avoid this sort of difficulty and give 4 possible options for this patient

Answer 17

• Problem is the extra 0.50D accommodation required for reading
  Distance Rx = -2.00
  Wearing = -1.50 (-2.00 + 0.50 = -1.50)
• Discuss, before prescribing, possible solutions to the patient’s visual problems, explaining dis/advantages

4 possible options for this px:

• Use new Rx for critical DV and old glasses for general use
• Bifocals
• PPLs
• Continue with old glasses

Question 18

what is very important to consider when it comes to altering a patient’s distance rx, for all types of patients: myopes, hyperopes, non-presbyopes and presbyopes

Answer 18

Never alter an Rx for DV without considering the consequences for NV

Question 19

for which 2 reasons will a practitioner regard a 0.25D cyl when prescribing (as it is usually disregarded)

Answer 19

• the cylinder is already worn in the current Rx

- the patient notices a subjective improvement in VA with the 0.25 cylinder

Question 20

why can low/moderate cylinders prescribed for the first time be another non-tolerance area, what symptom may this type of patient complain of what can the practitioner do before prescribing this change in cyl

Answer 20

• Correction will give a clear retinal image, but the brain is unaccustomed to interpreting this sharp image
• Patient may complain of distortion e.g. straight edges appear curved etc
• Patient must be counselled at the time of refraction (not after when px comes to collect rx)

Question 21

for this high cylinders prescribed for the first time px:

Patient aged 20. No previous correction
Wishes to learn to drive
Unaided  R 6/24   L 6/24
Final subj: 
R +2.00/ -4.00 x 180  =  6/18   L +2.00/ -4.00 x 180  =  6/18

list the 2 possible options for this px
what must be warned to this px

Answer 21

• Give full Rx, VA may improve. Incentive is certainly there!
• Give partial correction with follow-up
  (e.g. R&L +1.00/-2.00 x 180)
  NB. Should give Mean Sphere Equivalent, but many optoms did not when surveyed (Howell-Duffy et al 2010)
• No correction (definitely the best option if patient had been elderly rather than a 20 year old)

Patient must be warned that they may never achieve the driving standard

Question 22

how can VA improve in adult amblyopic eyes

Answer 22

• Recent studies show remarkable plasticity in adult visual cortex
• Some amblyopes show spontaneous improvement after losing the fellow eye
  Mallah at al (2000) reported amazing plasticity in amblyopes with AMD in their fellow eye

Question 23

for this px who has had a change in their cylinder axis:

Current Rx R +1.00/ -0.75 x 30 - 6/5
Final subjective R +1.25/ -0.75 x 40 - 6/5

what will you prescribe
explain why
what should you always record with any modified rx

Answer 23

• Prescribe R +1.25/ -0.75 x 30
• There should be a noticeable improvement in VA
  to justify the change in cylinder axis
• Always record VA achieved with any modified Rx

Question 24

what should you be careful of in young patients particularly when prescribing for DV and explain how this can easily happen

Answer 24

• be careful not to over plus for distance vision (non-tolerance area)
• it is easy to over-plus patients for infinity by 0.25D
  Testing distance is usually 6m, so correct Rx for 6m leaves patient over-plused by 0.16D for 
  Patient may not appreciate the blur introduced as you first overplus

Question 25

for which type of patient may over-plusing for DV may not cause problems and give 2 reasons why

Answer 25

• In the elderly

Because:

• Different visual activities (which are usually at a closer distance e.g. reading)
• Tend to get more hyperopic anyway

Question 26

what 2 things can you consider doing to avoid overplusing younger patients

Answer 26

• prescribing for infinity +0.25 less binocularly than “maximum plus consistent with best VA”,
  or
• leave patient binocularly just green on duochrome

Question 27

what must you be careful of not to do in older patients when prescribing for DV and explain how this can easily happen and why

Answer 27

• easy to over-minus elderly patients with lens opacities if you use the duochrome test

Because:
Green wavelengths are scattered more than red by the cataract so there is a tendency for black circles to be clearer on the red

Question 28

what 2 things can you consider doing to avoid over minusing older patients

Answer 28

• prescribing for infinity “maximum plus consistent with best VA”,
  or
• avoiding the duo chrome (or put them on red)
  “leaving patient clearer on the green prior to crossed cyl”
  young patients can accommodate to put circle of least confusion back on the retina, but elderly patients cannot