OP1201 – Basic Clinical Techniques

Binocular balance and final prescriptionDr Kirsten Hamilton-Maxwell

The refraction routine so far…Our refraction routine has included

Initial sphere powerCylinder axis and power

In today’s lecture, we will look atFinal sphere powerMaking the vision equal in both eyes (binocular

balance)The final binocular distance prescription

BE

Today’stopic

Final sphereImagine that you have just completed x-cyl for

the REPrior to performing x-cyl, we intentionally left the

patient with green-clearest on duochrome, or equalThey are probably still accommodating!

Final sphere aims to relax accommodation, so need to check the sphere power again after x-cylMonocular test

ProcedureFor all patients, the procedure is the same

Go back to the plus/minus test and “push the plus”Direct subject to smallest Snellen line achievable and

ask “Is it clearer with or without?” while presenting/removing +0.25DS

Make sure lens is clean!

ProcedureInterpretation

If clearer or no difference with +0.25DS, incorporate and repeat

If/when clearer without: do not incorporate this final blurring +0.25DS because it means you have reached the end

Record final lens power and VASphere(DS)/Cyl(DC)xAxis and VA

PrecautionsRemember that a change in VA must correspond to

the change in lens power, relative to the current correction0.25DS per line of vision0.50DC per line of vision

Be wary of >+0.50D change and any minus lens changeDuochrome for final sphere as it tends to over-minus

Can still use as a confirmation lens

Why is too much minus a problem?Your patient will be required to accommodate to see

clearly, even in the distanceHeadaches, tired eyes, discomfortPotential to induce myopia (?)

We have dealt with how to avoid this already

Why is more plus a problem?The cyl findings are probably incorrect

Circle of least confusion needs to be on, or slightly behind, the retina

So if more minus needed in the final stages, your patient was over-plussed on cross-cyl

Your patient may be a latent hypermetropeConsider a cycloplegic refraction

From your patient’s point of view, blur!A major cause of needing to remake spectacles

Avoiding over-plussingGenerally applies to elderly patients, but

possible in all patientsSmall pupils

±0.25DS sphere will make minimal difference to blur circle: consider ±0.50DS pendulum

+1.00DS test will not blur back as far as 6/18, so encourages you to add more plus

Media opacification or other pathology causing poor VACreates problems detecting 0.25DS change

Binocular balancingWe have only considered one eye at a time BUT

most of your patients will use both of their eyesClear and comfortable vision is the ultimate goal!

So that both eyes can work together, binocular balancing is a technique used to equaliseVisionAccommodative demand

Occlusion can stimulate accommodationRefracting under monocular conditions may not get

out all the plus!So binocular balance also serves to check sphere

under binocular conditions

ProcedureAlways done after the monocular refraction for each

eye has been completedi.e. initial sphere, x-cyl., then final sphere

Many different techniques are available, but fogging techniques are easiest in practice

Humphriss fogging methodOne eye fogged (blurred), other eye clear+0.75DS blur will reduce VA in fogged eye to about

6/12Shifts attention to the unfogged eye

Allows assessment of the spherical refractive error in the unfogged eyeWhile maintaining peripheral fusion (ie. binocularity)

which helps control accommodation

Procedure: Right eyeCheck RE first!After the monocular refraction, blur left eye by

+0.75DSRE is still occluded because you have just finished

monocular refraction of the LEVA should drop to about 6/12 because looking through

the fogging lensThen remove occluder from RE

VA should improve, indicating that the RE is being used

If it does not, stop here!Push the plus in right eye as described earlier

Procedure: Left eyeNow check the LE!Add +0.75 DS in front of right eye and ensure

VA is worse (is there sufficient fog?)Remove +0.75DS from left eye and ensure VA

improves (check attention has shifted)Push the plus in left eye and adjust accordinglyEssentially, you are repeating what you did

earlier to determine the monocular final sphere, but you are pushing the plus with the other eye fogged rather than occluded

Recording resultsRecord the lens power added to the monocular

subjective findingsEg. Binocular balance RE +0.25DS and LE +0.50DS

Include binocular acuity

Unequal binocular balanceBe wary of unequal findings

This almost never happens if monocular refraction went well – at most, there is 0.25DS difference

So use this as a double check of your monocular findings!

Limitations of Humphriss techniqueWill not work if unfogged eye VA is worse than 6/12

Cannot shift attention to the unfogged eye. Abandon.

May not work if there is unequal acuity (particularly if VA in the unfogged eye approaches 6/12) Increase fogging power or abandon?

Will not work if fogged eye VA is worse than 6/12; Lose binocularity and simulates monocular refraction. Reduce

fogging power.

May not work if one eye is heavily dominantMust check that VA worsens/improves as stated above If this does not occur, then abandon

Other methodsYou will look at this in more detail in your semester 2

coursework, plus year 2The Humphriss method is preferred because it forms part

of the binocular refraction technique that you will learn next year

Occlusion methodsTurville infinity balancePolarisation

Dissociation methods (both eyes open but not truly binocular)Comparison of fogged imagesComparison of duochrome

Successive comparison

What not to do…When not to use binocular balancing

A patient with strabismusAmblyopia or other cause for significant visual reductionUneven acuities of more than one Snellen lineOnly makes sense if patient is using both eyes (has binocularity)!

When to be wary of binocular balancingPatients with compromised binocularity e.g. evidence of a poorly

compensated phoria – this will make sense next semesterAnisometropia (uneven prescriptions), especially on fogging

techniquePerform on patients with no accommodation (???)

For you, still do it as it is a double check of your monocular findings

Doesn’t work well in patients with small pupils due to the increased depth of focus

Final steps of refractionIf all has gone to plan, the vision is now equal in

both eyes and excess accommodation has been neutralised

The final step of refraction is to push the plus binocularlyie. +0.25DS over each eye simultaneously

This is the final double check for over-minussing!In my experience, the final Rx will usually be

+0.25DS more in each eye than the monocular subjective findings

Final steps of refractionAlso need to check for too much plus!So far, we have tried to avoid minus spheres after x-

cylThis is because we are trying to push the plus/relax

accommodation, but can result in over-plussingTo check, offer binocular -0.25DS’sIf patient says letters are definitely clearer (i.e. a

demonstrable improvement in VA) and NOT smaller and darker, then incorporateOften worth double checking thisPatients will often “prefer” a slightly over-minussed

refraction in the consulting room, so check for clarity

Recording results

The extra factor: Vertex distanceThis is the distance between the cornea and the

back of the spectacle lensIt needs to be recorded for all prescriptions that are

more than ±4.00DSThe effective power of a lens changes with distance

from the eyeEstimate by using the scale on the side of your trial

frameYou will be shown other methods in Dispensing

There is no box for this so you will need to remember to measure and record it, when appropriate

In summaryOur refraction routine now consists of

RetinoscopyRefinement of sphere prior to x-cylJackson x-cylRefinement of monocular sphere, record monocular

VABinocular balanceRecord final distance refraction, record binocular VA

You’ve now got an entire refraction routine!

Elliott, Section 4.16