Prescribing for different refractive states (distance vision) Flashcards Preview

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

- Monocular refraction
- Binocular balancing
- Binocular addition
- Fixation disparity


what is the risk of a final subjective rx

Patient will be intolerant to their new glasses


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

- is in the range of 1% - 2%
assuming 2% this would mean about 400,000 patients intolerant to their glasses each year


list 6 things that decision making when prescribing is based on

- 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.


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

- Assessment of patient’s ability to adapt to change

- The prescription currently worn


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

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


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

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

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


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

a two-line improvement in VA


list the 4 prescribing recommendations and who this was recommended by

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


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

- 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


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

use as these patients approach presbyopia


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

- is asymptomatic
- meets the legal driving standard


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

- 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.”


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

- 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


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

- 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


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

- lens form can be important
- use of lens measure

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


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

- 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


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

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


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

- the cylinder is already worn in the current Rx

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


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

- 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)


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

- 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


how can VA improve in adult amblyopic eyes

- 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


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

- 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


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

- 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


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

- In the elderly

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


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

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


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

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

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


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

- prescribing for infinity “maximum plus consistent with best VA”,
- 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