Prescribing for different refractive states (near vision) Flashcards
which 3 refractive groups of patients will you consider prescribing for near vision
- Non-presbyopic Hyperopes
- Presbyopes in general
- Myopic presbyopes
for this non-presbyopic hyperope:
35 year old
Symptoms: Headaches towards the end of the day associated with near vision. No problems with distance vision.
Vision: 6/5 R & L No previous Rx
Final subj: +1.50DS R + L = 6/5
Amplitude of accommodation (AOA) = 5D R + L (measured with px wearing the +1.50DS final subjective)
will you prescribe for this px? How and why
- Prescribe the DV Rx of +1.50 R + L, but prescribe it for NV
Because:
It is the answer to the patient’s symptoms
Without the distance Rx this patient is using +1.50D accommodation for D/V.
AOA = 5D, which leaves 5D – 1.5D = 3.5D accommodation available for NV
It is when their accommodation is reduced to approximately 3.50D that patients often first need help for near vision tasks
So this patient presents with typical symptoms of presbyopia
When wearing the glasses, this restores the available accommodation to 5D and the patient’s symptoms should disappear
list 3 main aims when prescribing for presbyopia in general
- Give comfortable N5 at preferred working distance (PWD)
Crucial to establish PWD - Give a useful range of clear vision
Good guide is if you can move in x cm from PWD and move out 2x cm from PWD then patient is likely to be comfortable - Not too much change from current prescription for near vision
what does it mean for the patient when your reducing the positive power or increasing the negative power for near and when is the ONLY time you will do this for a near
- the patient has to exert more accommodation
- if the patient complains that they have to hold the material too close
how much should a positive power for near vision be increased for:
Emmetrope. Complaining of difficulties reading
small print with current glasses.
Current Rx for near vision R + L +2.00
Refraction DV = Plano R and L = 6/5 R+L
explain why
- +2.50 R + L
Because just increasing it to +2.25D won’t make enough difference and +2.50D is enough for the patient to make a difference and not too much to cause intolerance problems
give 2 reasons as to why if the positive power is increased too much, the patient may not tolerate the new Rx
- The established relationship between accommodation and convergence is upset
- The range of distinct vision may be reduced to an unacceptable extent
Most “intolerances” in practice are related to increasing the positive power for near by too much
what happens to the near vision range for a emmetropic patient:
Old Rx:
Plano with Add +2.00 R + L
Patient is looking through +2.00DS when reading
New Rx:
Plano with Add +3.00 R + L
Patient is looking through +3.00DS when reading
explain the outcome and why
what can you do to avoid over plussing the patient
- The range for near vision is reduced
Px will be happy with the +2.00DS add as their range = 50cm, so will be relatively blurred 50cm away from the eyes
Px will be unhappy with the +3.00DS ass as their range = 33cm, so will be relatively blurred 33cm away from the eyes (which is too small of a range)
- Must ask patient questions about their working distance to avoid over plussing the px
for this myopic presbyope:
Patient aged 50. Asymptomatic. Takes glasses off to read. Wants bifocals or PPLs for convenience.
Wearing –2.50DS R + L = 6/5
Final subj: -2.50DS R & L Add +1.00 = N5
Patient returns complaining that glasses are not good enough for reading (as it was better when they took their glasses off to read)
explain why this patient cannot tolerate their new rx
give 3 options for this patient
Reason:
- When patient removed old glasses:
She was looking through Plano, or
through an effective Add of +2.50D
- With the perfectly correct Rx of -2.50 and a +1.00D Add
She is looking through -1.50D for near work
Compared with her previous situation (taking glasses off), the prescriber has reduced the positive power for N/V by 1.50D
Options:
- Continue with single vision DV Rx and remove for near work
- Prescribe an Add less than but close to that which patient is accustomed, e.g. Add +2.00D
Too high for patient’s age, but closer to usual situation
Patient may benefit from greater range of clear vision and from holding material a bit further away
Show the px the difference from having a +2.00D and a +2.50D - Prescribe a +2.50D Add to leave the patient in exactly the same visual situation as before for near vision
what must you always do before prescribing/changing rx for near vision
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
list 4 main symptoms of a px with a nuclear sclerosis cataract
- Patient complains of gradual painless progressive loss of vision
- Visual acuity may remain reasonable for years (as can correct with specs)
- VA tends to be worse in bright light as pupil shuts down and cataract is central
- “Second sight”
explain what causes this “second sight” in patients with a nuclear sclerosis cataract, what the outcome is and how its managed
- Increase of refractive index produces an increase in myopia (second sight)
- Increase in myopia may be quite rapid in advanced cases, could be 1D in three months
- VA may remain reasonable for years
- Management of second sight in optometric practice – need for regular eye exams etc
- Distance vision affected more than near
other than due to reduced range of near vision, name one other time when you will consider reducing the positive power for near
for a patient with a nuclear sclerosis cataract
for this patient:
65 year old, with healthy eyes apart from nuclear sclerosis cataract in both eyes.
No binocular vision problems
Symptoms:
Distance vision blur with latest glasses (bifocals), steadily getting worse.
Prefers reading with an old pair of bifocals because he is now having to hold reading material too close with latest glasses
Wearing (latest Rx): DV R + L Plano = 6/12 R + L NV R + L Add +2.50 = N5 at 25cm Old Rx preferred for reading: DV R + L +0.75DS = 6/24 R + L NV R + L Add +0.75 = N5 at 40cm Final subj: DV R + L -1.00DS = 6/6 R + L NV R + L Add +2.50 = N5 at 40cm
Old Rx (preferred) and Final subj Rx both = looking through a +1.50D add for reading
give 4 possible prescribing options for this px, naming the best and most expensive option out of the 4
- New DV Rx only
- To continue to use old bifocals for reading
- New DV and NV Rx as bifocal
- New DV and NV Rx
Do not prescribe and refer for cataract surgery
Best option:
New DV Rx only
Most expensive option:
New DV and NV Rx as bifocal - as rx will continue to change
when do most optoms in the UK prescribe a first add of +0.75D
if symptoms are present
when do most optoms in the UK prescribe a first add of +1.50D
if no symptoms are present
