Refraction Methods

Auxiliary cyl power lenses

Used to extend the range in the phoropter

Placed into eyehole with arrows parallel to axis arrow → Decrease cyl power to 4.00DC

Endpoint with auxiliary cyl power lens

Cyl power in the window plus -2.00DC

Directing testing of cylinder

Rotate axis until pt reports best clarity (approach from both sides to bracket)

Refine power by adjusting -.25DC steps

Line astigmatism tests

Subjective test that estimates the axis

Lines parallel to axis of astigmatism will be out of focus

Have pt judge clearest line and set axis 90 away, do not adjust for SE

Line astig test WTR

Horizontal blur from stronger vertical meridian

Axis 180

Line astig test ATR

Vertical blur from stronger horizontal meridian

Axis 090

Adjusting axis in line astig test

Add plus to blur all lines → Slowly decrease and have pt define clearest line

If all lines become clear at the same time during line astig test…

Pt is sph

If one line becomes clear first during line astig test…

Axis = Smaller number x 30

Adjusting power in line astig test

Have pt watch most blurred line and add cyl power until it matches the clearest line

Which meridian do you want to keep on the retina during the clock dial test?

The most plus meridian

Manual keratometry

Objective measurement of anterior curvatures of the cornea

Measures reflected images, curvatures represented in diopters

Maximum and minimum powers are compared to estimate corneal astig

Uses of keratometry

• Predict corneal astigmatism and refractive astigmatism

• Fit CL

• Assess corneal health/structure (keratoconus, dry eye, surface irregularities

How to calculate astigmatism in keratometry

Difference between meridians, weaker meridian is cyl axis

Lenticular astig is estimated to be _____ for vast majority of eyes

-0.50 × 090

Determining refractive astig with keratometry

Sum keratometry astig with lenticular

May need to convert lenticular to plus cyl to match axis (doesn’t have to be perfect)

Vectographic balance

Alternative to prism dissociated balance

Includes a fusion lock so pt is not dissociated (strab pts cannot do this because they are never fused)

Helpful for large phorias and variable accommodation

Vectographic balance procedure

Add +.50DS to relax accommodation and use polaroid filter → Eyes will see different aspects of the target

Have pt compare right and left images → Add +.25DS to side that appear clearer until equalized

Do not change sph power of one eye to keep balance

Dissociated R/G bichrome balance

Alternative to prism dissociated balance when there is unequal acuity between eyes, controls accommodation

R/G filter creates a chromatic interval, green focuses in front

Trying to find sph lens that centers interval between 2 foci

Dissociated R/G bichrome procedure

Add plus to relax accommodation → Red will be clearer

Use prism to dissociate pt → Ask to compare top red/green letters and change .25DS to OD to equalize and repeat for bottom change and OS

Endpoint is documented manifest

Monocular bichrome R/G balance

Alternative to prism dissociated when pt suppresses and does not see double

Same procedure as dissociated bichrome

Endpoint is documented manifest

Refraction with cycloplegic drops

• Damp: Tropicamide

• Wet: Cyclopentolate

Big pupils may prevent 20/20, same steps as manifest but no binocular balance

When would you use cycloplegics during refraction?

• Children

• Latent hyperopes

• Amblyopes

• Accommodative spasm, psuedomyopia

• Esotropia, high esophoria

• Prior to refractive Sx

Binocular refraction

OU open during entire refraction, mimics real world

When would you perform binocular refraction?

• Cyclophoria pts: Pts who have a 10+ degree shift in axis under binocular vs monocular conditions

• Nystagmus

• Accommodation fluctuations

Binocular refraction techniques

• Humphriss technique

• Polarization

• Septum

Humpriss technique

Uses +1.00 or +1.50DS to blur but not enough to suppress

Still need a binocular balance method, preferably one that maintains fusion

Helpful for latent nystagmus; Cyclophoria or nystagmus → Monocular VAs with fogging

Polarization/Vectographic technique

Need charts that consist of letters with polarization that will only appear to one eye at a time

Borish near card

Vectographic card for near testing

Good for latent nystagmus or cyclophoria

Septum method (Turville Infinity Balance)

Septum with mirrors on either side place to block each eye from viewing the other’s chart

Refraction is performed using standard method but without occlusion