Multifocal Ophthalmic Lenses 1

Presbyopia

Accommodation reduced to where near work is difficult

AA less than 5D (assuming 40cm working dist)

Presbyopia signs and symptoms

• Uncomfortable with near work

• Blurry near vision

• Headache/eyestrain and holding near work far away

• Needs more work for reading

Onset of presbyopia

Around 42 years old

Hyperope > Emmetrope > Myope

How to calculate near power

Distance Rx + ADD

Near power for high myopes

Will be minus → Pushes out FP

First ADD powers

Usually +1.25 because pt will push off higher power until needed

Anti-fatigue lens

Marketed as single vision but has ADD in a blended segment

Changing ADD power as pt grows older

Increase +.25D every 2-3 years, max out at +2.25 or +2.50 (typical working dist)

When would you use higher ADD powers?

Low vision pts

Factors that influence ADD power

• Age

• Occupation/visual demands

• Arm length

• Pupil size

Why does pupil size influence ADD power

Pupil is an aperture

Smaller → Larger DOF so pt doesn’t experience blur

Determining tentative ADD

• Age table

• BCC

• Plus build up

• AA (allow pt 5 use 50% of AA at near)

Why would you not give everyone +2.50 as their ADD?

Convergence and proximal targets drive people to accommodate

• Hard adaptation for PALs

• Image jump (prismatic effect)

• BV/accommodation reasons

• Limited range of comfortable clear vision

Maximum range of clear vision

Distance between where pt can see with relaxed and fully engaged accommodation

Range of clear comfortable vision

Uses ½ AA → Maximum Comfortable Accommodation (MCA)

More accurate to true functional vision

Calculating FP through near Rx

1/ADD

Calculating NP through near Rx

1/ADD + AA

Calculating near comfort point through near Rx

1/ ADD + MCA

Calculating FP through distance Rx

At infinity

Calculating NP through distance Rx

1/AA

Calculating near comfort point through distance Rx

1/MCA

Clear comfortable vision will _____ with doable vision

Overlap

What happens when you overcorrect someone’s ADD?

Gap in clear comfortable vision → Pt can still accommodate through it

will not be comfortable and pt will have intermediate vision complaints

What happens when AA is between 1.00-1.50D?

Intermediate distance gap in clear vision even with appropriate ADD power

Prescribe a progressive or trifocal

Trifocal

Typically specify 50% of ADD in intermediate