Subjective refraction OP 1201 Basic Clinical Techniques Binocular

$Subjective refraction OP 1201 – Basic Clinical Techniques Binocular balance and final prescription Dr$

Subjective refraction OP 1201 – Basic Clinical Techniques Binocular balance and final prescription Dr Kirsten Hamilton-Maxwell

$The refraction routine so far… Our refraction routine has included Initial sphere power Cylinder$

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

$Subjective refraction RE LE Check sphere Check cyl (Axis and power) Recheck sphere BE$

Subjective refraction RE LE Check sphere Check cyl (Axis and power) 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. 25 DS Make sure lens is clean!

Procedure Interpretation If clearer or no difference with +0. 25 DS, incorporate and repeat If/when clearer without: do not incorporate this final blurring +0. 25 DS because it means you have reached the end Record final lens power and VA Sphere(DS)/Cyl(DC)x. Axis and VA

Precautions Remember that a change in VA must correspond to the change in lens power, relative to the current correction 0. 25 DS per line of vision 0. 50 DC per line of vision Be wary of >+0. 50 D 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. 25 DS sphere will make minimal difference to blur circle: consider ± 0. 50 DS pendulum +1. 00 DS 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. 25 DS 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

$Procedure Always done after the monocular refraction for each eye has been completed i.$

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. 75 DS 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

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

Procedure: Right eye Check RE first! After the monocular refraction, blur left eye by +0. 75 DS 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. 75 DS 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. 25 DS and LE +0. 50 DS 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. 25 DS 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

$Final steps of refraction If all has gone to plan, the vision is now$

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. 25 DS over each eye simultaneously This is the final double check for over-minussing! In my experience, the final Rx will usually be +0. 25 DS more in each eye than the monocular subjective findings

$Final steps of refraction Also need to check for too much plus! So far,$

Final steps of refraction Also need to check for too much plus! So far, we have tried to avoid minus spheres after xcyl This is because we are trying to push the plus/relax accommodation, but can result in over-plussing To check, offer binocular -0. 25 DS’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. 00 DS 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

$In summary Our refraction routine now consists of Retinoscopy Refinement of sphere prior to$

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!