The College of Optometrists

Whilst getting through a few tests today and doing mainly binocular refractions I was wondering if the frequently used +1.00 blur test really has a use is such a situation. If the idea behind binocular refractions/balancing is to equal the accomodative effort between the eyes and correct any latent hyperopia that may be present on occlusion of the fellow eye then what's the use in checking a monocular acuity afterwards? Surely to accurately do a +1.00 blur test the other eye should be occluded, or blurred well beyond 6/12 which will effectively give monocular status, and as a result any latent hyperopia that may occur during monocular viewing will be present again and the patient will be over plussed, compromising the results. Does anyone else have any thoughts on this? And if doing a monocular refraction followed by balancing with Humphriss is it worth doing a quick +1.00 test before balancing rather than after? And having said all this given that the +1.00 test is dependent on a number of factors anyway such as pupil size is it really as useful a test as we are lead to believe?

And thoughts on this are appreciated.

On a further note I refracted a young-ish chap today, small myopic Rx using binocular refraction, unaided 6/7.5 corrected 6/4. When doing a cover test after the refraction he noted that his left eye was slightly more blurred, on occlusion his VA was 6/6, but with a +0.75 in front of the RE is vision in his left was 6/5+. I explained that his prescription is designed to give him clear vision with both eyes open, he seemed to understand and went on his merry way. Does anyone see many people coming back complaining that one eye seems blurred when the other eye is covered after eyes have been balanced binocularly? Just a thought, I sometimes wonder if binocular balancing is as important as the textbooks say.

I quite agree with yr reasoning. The plus one lens blur does vary with pupil size - and it is not the Holy Grail. I think it has value for kids - I normally end using + 1.00 in each eye to ensure that it does blur back ( and so, not an undercorrection). I think the other eye being occluded gives the best result - but I don't often use a +1.00 on adults. I push them to a 6/4.5 or smaller if I can then use a +0.25 blur lens withthe other eye occluded - they will soon tell you what happens ! When you gain experience - you won't use the +1.00 lens thaty much - with humphries technique the other eye is blurred by +0.75 ( a quick flick of the occluder will proove to you that it is) - then away you go.

Your youngish chap_ well - some people can tell a slight blur and it can worry them. Typically they are youngish and newish to spec wearing. As an aside, it always surprises me that - yes he will spot a tiny blur with spex (and fly back to complain !) - but with contact lenses - they never complain. I mean - you try doing monovision with specs - and see the px reaction!

Many people notice a degradation with one eye occluded - perhaps it is due to the pupil dilating slightly. So you blur instead - and 'cos there is no pupil dilation - no degradation. It is important to realise that acuity can be sharp or hazy. The difference is due to the depth of focus of the eye. You want a sharp 6/6 - not a hazy 6/6. Try forgetting about the evils of leaving them slightly accomodating - and try to simply get it sharp for them. Try also to alter the Rx to give them what they want. Always measure DV with their reading spex on. Don't be dogmatic about what they have to have. Your youngish man may have had a small Astig correction slightly out (for example) - this is often corrected by simply trying a -0.25 cyl at 45,90,135 and 180 and seeing which is best. I don't want to bang-on - but do try to pull all yr techniques appart - and develop them into your very own (that will deal with all these issues) : good luck - Steven

Thanks for the reply.

With regards to the guy that I mentioned, let's say for arguments sake that I didn't miss a cyl and his refraction was correct. If you do a monocular refraction and find a Rx of -1.00, with +0.25 causing blur and -0.25 giving no increase in clarity, duochrome equal all spot on etc and then proceed to the phenomenon of 'binocular balancing'... OK you put a +0.75 in front of the other eye to blur it and low and behold you can add +0.25 to the Rx causing no further blurring, giving a final Rx of -0.75. Now where does this +0.25 come from? Textbooks will say it is caused by residual accomodation that can exist during monocular conditions. Well if this is so that accomodation will return should the patient close or occlude one eye, and the vision will not seem as sharp.

Although we may be happy that we have given him a 'comfortable' prescription he will notice that his vision isn't quite right if he occludes an eye and is likely to return. Now just how bad would it be for the patient if we had left him unbalanced, and simply refracted monocularly and sent him away with the end result? Given that a refraction is a subjective process that can vary day-to-day and with different practitioners is pushing that extra bit of plus binocularly really that essential? How many patients are really likely to notice if their 'accomodative effort' is slightly imbalanced? And lets be honest we see plenty of patients come in for a routine assessment, perfectly happy with their specs and then find a significant difference between the eyes after a refraction.

Small note to my assessor: Binocular balancing is essential, it is terrible practice for a patient to leave after a sight test with an unbalanced prescription, It is a vital part of the refraction routine and should be carried out on all appropriate patients. :o)

I really like yr reasoning :-) I suppose you could also do something similar by doing monoc accom. test. THere is an interesting book in the library which discusses all these issues - I will get the title for you. My own copy is on loan itself. I give you another thought - So you do all the tests and arrive accurately at the final Rx - then bin balancing with minimum blur on the non-test eye and 6/5 and try +-0.25 on the tets eye. Small discrepancy!! These things can also occur in different head postures. Try it and see - px tilts head to right R=L but tilts the other way now L is blury. This can also occur on nodding and wagging. It makes me think perhaps the best lens is the minimum power as this would affect the eye the least. I sussed out a whole way of testing vision by wagging and nodding. ( And it never fails - but I rarely use it now) - good luck and thanks for th comments - palf