Subjective refraction
OP1201 – Basic Clinical Techniques
Binocular balance and final prescription
Dr Kirsten Hamilton-Maxwell
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
Subjective refraction
RE
LE
Check sphere
Check sphere
Check cyl
(Axis and power)
Check cyl
(Axis and power)
Recheck sphere
Recheck sphere
BE
Binocular balance
Final prescription (Rx)
Today’s
topic
Final (monocular) sphere
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
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!
Procedure
 Interpretation
 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
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
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
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
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
Binocular balancing
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
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
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
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
Procedure: Left eye
 Now 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 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
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
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!
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
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
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
Final prescription
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. +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 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
Recording results
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
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!
Further reading
Elliott, Section 4.16