24,27 Presbyopic Correction

Question 1

Symptoms of presbyopia? (apart from near blur)

Answer 1

• Frontal headaches
• “Trombone” as arms too short
• More light needed when reading
• Momentary blur when changing from distance to near.

Question 2

Reason for needing more light when reading if presbyopic?

Answer 2

• Dilate pupil in dim light which decreases depth of field.
• May be tired after end of day.

Question 3

Overall procedure of finding near add required?

Answer 3

• Establish WD of task.
• Determine the add
• measure range of clear vision w/ add
• Refine power if needed.

Question 4

Describe binocular cross cylinder
What about monocular?

Answer 4

Measures accuracy of accommodation. Have patient look at near target cross. Place JCC so –ve axis is at 90 degrees. Most presbyopics will have a lag of accommodation meaning the horizontal line at the front is focused (since vertical focal point in object space is closer to patient would would require lead of accommodation). Add +ve until both horizontal and vertical lines are equally clear (make sure to find reversal first). At this point, patient can comfortably accommodate to near target.
Add +ve if horizontal line clearer.

Monocular = Same procedure but monocularly. Same results will likely apply and if not, try binocular balancing again.

Question 5

Describe plus build up

Answer 5

Ask patient to read smallest line at WD. Add plus DS until there’s no improvement in VA.

Question 6

Descrine Nott retinoscopy

Answer 6

No extra lenses needed. When a with movement is seen (lag), retinoscope moves backwards to increase WD and vice versa. Find neutral reflex.
Example: Target at 40cm, neutralised at 50cm. Since 50cm means they are accommodating 2D when they should be accommodating 2.5D, we add +0.50DS.

Question 7

Describe MEM retinoscopy

Answer 7

With normal room illumination, attach MEM card onto your retinoscope or have patient at set distance from MEM card as they hold it. Add plus lenses to neutralise reflex.
Lenses are flashed in and out, not held in place to avoid changing accommodative state.

Question 8

Describe near duochrome in measuring near add.

Answer 8

40cm w/ dueochrome unit. If green clearer, add more +ve, and if red clearer, add move –ve.

Problems:
- Patients find it more difficult than other tests to give reliable answers.
- Red green targets need to be matched in brightness

Question 9

What’s effective add? How to calculate?

Answer 9

It’s how much actual add they are experiencing (after their full distance prescription is corrected). This can be different from the add they are prescribed because sometimes, the distance portion of the glasses aren’t correcting them fully so the near add ends up making up a small part of the distance portion.

Near rx = Distance Rx + near add

Question 10

1) What’s NRA/PRA or BPA/BMA? Measurements are for what purpose?
2) If add = +1.50DS, NRA = 1.50DS, and PRA = 1.00DS, what to do?

Answer 10

1) How much extra plus or minus they can tolerate.
BPA = Binocular plus acceptance
BMA = Binocular minus acceptance
NRA = negative relative accommodation
PRA = postive relative accommodation

NRA/BPA is how much extra plus they can tolerate (how much extra accommodation they can relax)
PRA/BMA is how much extra –ve they can tolerate (How much accommodation they can still give out)
You measure this and ideally want this to be balanced i.e. the same absolute value.
2) Change add to +1.75DS so that NRA = +1.25DS and PRA = -1.25DS.

Question 11

Why avoid overplussing in near adds?

Answer 11

Range of vision decreases w/o acuity improvement for near task