1. Subjective refraction
OP1201 – Basic Clinical Techniques
Binocular balance and final prescription
Dr Kirsten Hamilton-Maxwell

2. The refraction routine so far…
Our refraction routine has included
Initial sphere power
Cylinder axis and power
In today’s lecture, we will look at
Final sphere power
Making the vision equal in both eyes (binocular balance)
The final binocular distance prescription

3. Subjective refraction
Check sphere
Check cyl
(Axis and power)
Recheck sphere LE
Subjective refraction
Today’s
topic BE
Binocular balance
Final prescription (Rx)

4. Final (monocular) sphere

5. Final sphere Imagine that you have just completed x-cyl for the RE
Prior to performing x-cyl, we intentionally left the patient with green-clearest on duochrome, or equal
They are probably still accommodating!
Final sphere aims to relax accommodation, so need to check the sphere power again after x-cyl
Monocular test

6. Procedure For 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!

7. Procedure Interpretation Record final lens power and VA
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 VA
Sphere(DS)/Cyl(DC)xAxis and VA

8. Precautions
Remember that a change in VA must correspond to the change in lens power, relative to the current correction
0.25DS per line of vision
0.50DC per line of vision
Be wary of
>+0.50D change and any minus lens change
Duochrome for final sphere as it tends to over-minus
Can still use as a confirmation lens

9. Why is too much minus a problem?
Your patient will be required to accommodate to see clearly, even in the distance
Headaches, tired eyes, discomfort
Potential to induce myopia (?)
We have dealt with how to avoid this already

10. 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 hypermetrope
Consider a cycloplegic refraction
From your patient’s point of view, blur!
A major cause of needing to remake spectacles

11. Avoiding over-plussing
Generally applies to elderly patients, but possible in all patients
Small 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 VA
Creates problems detecting 0.25DS change

12. Binocular balancing

13. Binocular balancing
We have only considered one eye at a time BUT most of your patients will use both of their eyes
Clear and comfortable vision is the ultimate goal!
So that both eyes can work together, binocular balancing is a technique used to equalise
Vision
Accommodative demand
Occlusion can stimulate accommodation
Refracting under monocular conditions may not get out all the plus!
So binocular balance also serves to check sphere under binocular conditions

14. Procedure
Always done after the monocular refraction for each eye has been completed
i.e. initial sphere, x-cyl., then final sphere
Many different techniques are available, but fogging techniques are easiest in practice

15. Humphriss fogging method
One eye fogged (blurred), other eye clear
+0.75DS blur will reduce VA in fogged eye to about 6/12
Shifts attention to the unfogged eye
Allows assessment of the spherical refractive error in the unfogged eye
While maintaining peripheral fusion (ie. binocularity) which helps control accommodation

16. Procedure: Right eye Check RE first!
After the monocular refraction, blur left eye by +0.75DS
RE is still occluded because you have just finished monocular refraction of the LE
VA should drop to about 6/12 because looking through the fogging lens
Then 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

17. Procedure: Left eye Now check the LE!
Add 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 accordingly
Essentially, 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

18. Recording results
Record the lens power added to the monocular subjective findings
Eg. Binocular balance RE +0.25DS and LE +0.50DS
Include binocular acuity

19. Unequal binocular balance
Be 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!

20. Limitations of Humphriss technique
Will 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 dominant
Must check that VA worsens/improves as stated above
If this does not occur, then abandon

21. Other methods
You will look at this in more detail in your semester 2 coursework, plus year 2
The Humphriss method is preferred because it forms part of the binocular refraction technique that you will learn next year
Occlusion methods
Turville infinity balance
Polarisation
Dissociation methods (both eyes open but not truly binocular)
Comparison of fogged images
Comparison of duochrome
Successive comparison

22. What not to do… When not to use binocular balancing
A patient with strabismus
Amblyopia or other cause for significant visual reduction
Uneven acuities of more than one Snellen line
Only makes sense if patient is using both eyes (has binocularity)!
When to be wary of binocular balancing
Patients with compromised binocularity e.g. evidence of a poorly compensated phoria – this will make sense next semester
Anisometropia (uneven prescriptions), especially on fogging technique
Perform 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

23. Final prescription

24. Final steps of refraction
If 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 binocularly
ie DS 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

25. Final steps of refraction
Also need to check for too much plus!
So far, we have tried to avoid minus spheres after x-cyl
This is because we are trying to push the plus/relax accommodation, but can result in over-plussing
To check, offer binocular -0.25DS’s
If patient says letters are definitely clearer (i.e. a demonstrable improvement in VA) and NOT smaller and darker, then incorporate
Often worth double checking this
Patients will often “prefer” a slightly over-minussed refraction in the consulting room, so check for clarity

26. Recording results

27. The extra factor: Vertex distance
This is the distance between the cornea and the back of the spectacle lens
It needs to be recorded for all prescriptions that are more than ±4.00DS
The effective power of a lens changes with distance from the eye
Estimate by using the scale on the side of your trial frame
You 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

28. In summary Our refraction routine now consists of
Retinoscopy
Refinement of sphere prior to x-cyl
Jackson x-cyl
Refinement of monocular sphere, record monocular VA
Binocular balance
Record final distance refraction, record binocular VA
You’ve now got an entire refraction routine!

29. Further reading
Elliott, Section 4.16