Binocular Balancing 1 and 2 - Week 2 Flashcards
When do you perform Binocular Balancing?
[from sharpen your subjective refraction technique pdf I found online]
Once the monocular subjective refraction has been completed for each eye
(start by fogging the eye)
True or false: Binocular Balancing is only done when the visual acuity is different between the 2 eyes
[from sharpen your subjective refraction technique pdf I found online]
False.
Binocular balancing is mainly done when the V.A is RELATIVELY EQUAL between the 2 eyes
(If unequal use Duochrome target)
State the purpose of Binocular Balancing
To balance or equalise the ‘accommodation’ of the 2 eyes
What happens if accommodation is not balanced?
This will lead to symptoms and uncomfortable vision
What is the theoretical basis of binocular balancing techniques? What does this mean?
ocular accommodation is a consensual reflex
- this means that any active accommodation occurring in one eye will induce the same amount of accommodation in the other eye
After JCC, how do you assess monocular end point?
By adding +/-0.25DS and getting them to read the letter chart
– note: add +ve first, keep going if ‘clearer’
(then you do blur check etc)
What principle should you adhere to when assessing monocular end point?
Maximum plus power (or least minus) consistent with best vision – i.e. be more +ve/less -ve
When assessing monocular end point, what if V.A is worse than 6/9 still?
Try using pinhole (PH) If PH improves V.A: - could be uncorrected refractive error (most likely) - could be a paracentral media opacity (e.g. cortical cataract) If PH does NOT improve V.A: - refraction correct - could be Amblyopia - could be Pathology
What’s the abbreviation for when pinhole gives you no improvement?
NIPH
why do some patients seem uncertain as to what lens gives the clearest vision?
The depth of focus can add uncertainty to a finite end point
- hence if px undecided, follow the maxim of maximum +ve power
Depth of focus also varies with pupil size
- is larger for smaller pupils
(revision) in relation to the retina, during chromatic aberration, where are shorter and longer wavelength brought into focus for an emmetropic eye when accommodation is relaxed?
Shorter wavelengths (blue) brought into focus in front of retina Longer wavelengths (red) behind retina
How can we use the nature of chromatic aberration to help determine monocular end point of refraction?
Duochrome
- if green clearer, add +ve (0.25)
- if red clearer, add =ve
In what cases may duochrome incorrectly suggest a change of more than 0.50DS from previously determined refraction?
- elderly
- hyperopes and pseudomyopes
In what cases is Binocular Balancing not productive?
When the patient does not have any functional binocular vision - could be due to: strabismus, amblyopia, pathology
When there is no active accommodation (elderly >60yr)
(in each case, attempt to get same response from both eyes - use techniques as for monocular endpoint refinement)
List the 5 basic techniques of binocular balancing.
in order of increasing sensitivity from 1 to 5
- Successive alternate occlusion
- Vertical prism dissociation
- Blurring or fogging techniques
- Septum techniques
- Polaroid techniques
Way to remember:
** Success in vertical blurring of the septum involves polaroids
Which of the following are NOT binocular techniques: A) Successive alternate occlusion B) Vertical prism dissociation C) Blurring or fogging techniques D) Septum techniques E) Polaroid techniques
A and B.
Successive alternate occlusion and Vertical prism dissociation
Explain Successive alternate occlusion
Px reads smallest line they can with both eyes. PD occluder is alternated from one eye to the other, and px is asked to compare.
- if both views are equally clear, good
- if not, add +0.25DS to the eye with clearer vision
On what type of patients do you perform successive alternate occlusion?
Px with poor binocularity
is vertical prism dissociation a binocular technique? why/why not?
No. Because you totally suspend fusion and therefore do not stimulate binocular vision
Explain Vertical prism dissociation
Add 2-3diopters BU in one eye, and BD in other eye, then ask them to compare a line of letters (6/9 line) on the letter chart (ask if top or bottom perceived line is clearer).
- if both lines the same, good
- if not, add +0.25DS to the eye with clearer vision
True or False: Vertical prism dissociation can be performed using duochrome as the target
True
How much should you fog the eye when doing Humphriss Fogging Technique? Why?
Fog the open eye by at least 2 lines, to be certain this eye is not being used for critical vision (generally we fog 2-3 lines)
When fogging the eye, should you tell the patient?
No
What are the advantages of the Humphriss fogging technique?
- it fully relaxes accommodation, therefore there is little need to do binocular addition afterwards
- Is quick and simple for both px and practitioner
- is relatively accurate
What is the Humphriss Immediate Contrast (HIC) technique, and how does it differ from the normal humphriss fogging?
Is almost identical except that +0.25DS (1sec) and -0.25DS (0.5sec) are immediately presented one after the other
- and the px is asked if lens 1 or 2 is more ‘comfortable’
- note: only add -0.25 if px immediately reports that this lens is better
What does the fog do in Humprhis fogging?
The fog is used to suspend foveal vision in one eye but allows paracentral and peripheral vision to act as a binocular lock
What are the 6 major tests in practice that employ either the septum or a polaroid technique?
Turville - septum Freeman - septum Wilmut - polaroid Cowan/Mallet - polaroid Grolman - polaroid vectograph
note: the names on the left are the inventors
How do polaroid techniques work?
Use polaroid filters before both eyes (oriented at 90deg) with 2 similar test charts (also polarised at 90deg) to be seen by each eye separately
- direct px to 6/9 line, ask px which side is clearer
- if equally clear, good
- if not, add +0.25DS to the eye with clearer vision
How does septum differ from polaroid technique?
It’s basically the same except for septum, the view is split into 2 by something physically in your field of view (rather than through polarised light filtering)
After binocular balancing, is px accommodation fully relaxed? What should you perform at the end of your routine?
Not necessarily, therefore you should always attempt binocular addition at the end of your routine.
Explain the technique of Binocular Addition
Ask px to view smallest line and place +0.25DS in front of both eyes simultaneously
ask px are the letters “clearer, just the same, or actually worse”
If better or same, continue adding +0.25DS
i.e. it’s basically just BVS but you are doing it on both eyes at once, and you’re only adding 0.25
What are Binocular Refraction techniques? Do you need to binocular balance after this?
It’s when you refract under binocular conditions throughout your subjective refraction routine.
Negates need for binocular balancing at end
What type of patients is binocular refraction useful for?
younger patients and latent hyperopes
When fogging in binocular refraction, do you occlude the other eye?
No, you fog other eye by +0.75DS/+1.00DS rather than occluding, then you perform normal monocular refraction routine on other eye
True or False: When doing ‘binocular’ refraction techniques, you must first do retinoscopy?
True
List errors in Rx (4)
- incorrect prescribing
- failure to adjust prescription
- ocular pathology
- communication
