8.1.1. Assesses binocular status using objective and subjective means.

Question 1

What is a heterophoria?

Answer 1

A phoria is a misalignment of the eyes that only appears when binocular viewing is broken and the two eyes are no longer looking at the same object.

Question 2

How is a tropia described?

Answer 2

a) Direction of movement
b) Incomitancy - i.e. does the size increase in a certain direction of gaze?
c) Congenital or acquired
d) Neurogenic or mechanical
e) Relationship with accommodation, especially important in congenital deviations.
f) Presenting symptoms with heterotropia

Question 3

Decompensating Phoria (LO-FAT)

Answer 3

• Location - Is the eyestrain BEs? Is diplopia when BEs are open?
• Onset - When did you start to notice it? Has it been worsening? Onset may be gradual & has become worse recently due it being decompensating beforehand, suggesting that it has recently broken down
• Frequency - When is it worse? During any time of the day/particular task? Intermittent or constant? If close up task, then gives idea that near cover test will show phoria or tropia worse than distance. If worse during end of day then most likely fatigue related, again linking to decompensating
• Associated symptoms - Diplopia? Eyestrain? Headaches? Photophobia? Blurred vision?
• Treatment - Anything done to alleviate it? E.g. closing one eye? Taking regular breaks?

Question 4

Convergence Insufficiency

Answer 4

Convergence insufficiency (CI) is the inability to maintain adequate eye convergence for comfortable binocular vision at near distances, crucial for reading. Convergence involves extraocular muscles aligning the eyes’ visual axes on close objects for bifoveal fixation. CI can occur alone or with convergence weakness (exophoria or exotropia) and other neurological or motor issues.

Question 5

Measuring convergence insufficiency

Answer 5

• Measuring near point of convergence
• Measuring jump convergence
  *

Question 6

Treatment of convergence insufficiency

Answer 6

Pencil push up exercises
Dot card
Orthoptic exercises with stereograms

Question 7

Diplopia Questions:

Answer 7

• Is it in both eyes or just one?
• When did it start?
• When do you get the double vision? Is it associated with anything specific? e.g. reading. (tells you if distance or near). Noticed at any particular time of day?
• How long does it last?
• How severe is it?
• Is the double vision horizontal or vertical?
• Are there any other symptoms associated with the double vision? e.g. headaches
• Does anything make the double vision go away?

Question 8

REMEMBER with fusion…

Answer 8

• your brain is trained to go through 3 steps to obtain binocular vision. These are 1. Simultaneous perception (seeing 2 images), 2. Fusion (of the 2 images), 3. Stereopsis (depth perception from the single image formed)
  
  • If ANY of these steps are interupted, true binocular vision is prevented.

Question 9

How does cover test work

Answer 9

The brain relies on sensory fusion for BSV. Sensory, meaning brain. The cover test occludes one eye, causing the simultaneous perception to be stopped (i.e. only 1 image seen), which means no fusional reflex can come in to fuse 2 images as it needs 2 images to begin with to do so! Essentially, the patient is completely dissociated i.e. monocular (to state the obvious). This means the eye under the cover can sit back & relax as it does not need to do any work, as it is not being utilised, neither for monocular nor binocular vision. However, once the cover is off, it gets back into position and stops being in its natural position as it needs to get back to work e.g. an XOP would be out under the cover. Things are a bit different with a tropia.

Question 10

How to do cover test:

Answer 10

• Target required - Patient fixates on a letter one line above the VA of the worst eye.
  Use a spotlight if VA worse than 6/18 in one eye.
• Working distance - either distance or near (distance where patient reads most comfortably)
• With & Without Spectacle correction for distance & near

Question 11

Difference between cover and uncover test:

Answer 11

• Cover & Uncover —> do this once for each eye for 3-4 seconds (literally count in your head!). You can distinguish between tropia & phoria. Allows binocular fusion when eyes uncovered
• Alternating Cover —> Prevents binocular fusion as eyes are only briefly uncovered.
  Cannot distinguish between a tropia and phoria.
  Reveals the total tropia and phoria - usually when the px is tired or stressed.
  Reveals intermittent tropias (phorias that break down into a tropia)
• Rule of thumb for estimation of size of squint: Movement small, but seen on careful cover test = 5-10Δ. Easy to see on cover test, but cosmetically acceptable = 10-20Δ. Large movement on cover test, cosmetically obvious = 20-30Δ.

Question 12

Instructions

Answer 12

‘this test allows me to determine how well your eye muscles are
working together’ …. ‘all I want you to do is look at this target - if it appears to move, please follow it with your eyes’.

Question 13

Prism cover test

Answer 13

this is again, objective and can gather the size of the deviation

Question 14

Motility with cover test

Answer 14

Assessment of the smooth pursuit system
If the deviation remains the same in all directions of gaze the deviation is said to be comitant i.e. nil muscle weakness.
If the deviation changes in any position of gaze the deviation is said to be incomitant and there is likely to be an associated muscle problem.

Question 15

How to tell if deviation is incomitant?

Answer 15

• Subjective responses: widest seperation of images in a particular direction/line of gaze of palsied muscle
• Underacting eye - furthest image seen, disappears on cover
• Corneal reflexs - some asymmetry in a particular gaze direction - palsied muscle
• Alternating cover test - largest deviation in a line of gaze of palsied muscle

Question 16

Ocular motility: Target, working distance, specs? Technique to perform, instructions.

Answer 16

• Target required - pen torch to note corneal reflexes as you do the test
• Working distance - 55-60cm best to prevent accommodation being induced. Can lead to pseudotropias!
• Spectacle correction - none
• Technique to perform - head kept still, track out the eyes until they stop moving & just where the reflex goes away. Always ask if the patient reports double vision, whether it is horizontal or vertical
• Instructions - “I am going to check how well the muscles of your eyes are working. Follow this light with your eyes, keeping your head nice & still and tell me if you get any pain or double vision.” You may need to double check if the patient gets double vision in certain positions by asking them

Question 17

Hirschberg

Answer 17

Useful for estimating size of tropia especially in infants

Question 18

Bruckner

Answer 18

View from direct ophthalmoscope (need to get both eyes into view) and assess corneal, pupil & fundus reflexes. Difference in brightness of fundus reflexes suggests anisometropia. If elliptical then suggests significant astigmatism. Difference in size of fundus reflex can suggest different sized pupils so pupil abnormality. Asymmetry of corneal reflexes suggest strabismus

Question 19

Stereopsis

Answer 19

Remember the 3 stages of binocularity. This is the last step! However, if patient is struggling even to do step number 2 i.e. fuse the images together & maintain it, then getting accurate stereopsis will not be as easy. This may be the case in a near decompensating phoria or convergence insufficiency

• Target required - depends on test used
• Working distance - 40cm
• Spectacle correction - near correction preferrable
• Technique to perform - depends on test. Titmus is quite basic for adults to understand
• Instructions - “I’ll just be checking how good your depth perception is and this will give me an idea of how well your eyes are working together.” Titmus - “On number 1, there are 4 circles. Tell me which one is coming out towards you or is sticking out compared to the rest, top, bottom, left or right?”

Question 20

Fusional reserves

Answer 20

The maximum amount the eyes can converge or diverge

The fusional reserve that opposes the heterophoria is measured first (convergent, using base-out prisms, for exophoria), to blur point (if present), break point, and then the prism is reduced until the recovery of single vision.

Question 21

Fixation disparity - explain

Answer 21

When viewing an object binocularly the visual axes are directed at the object of regard so that an image falls on each fovea. However, it is possible to fixate an object without the visual axes intersecting precisely on the object and still have binocular single vision, providing the misalignment is within Panum’s areas. Panum’s areas are small and horizontally oval. A fixation disparity is present when one or both of the visual axes are not directed precisely on the fixation object (From Elliot)

Fixation disparity is a normal binocular vision physiological variant

The level of prism needed to correct the fixation disparity is called the aligning prism or associated phoria

Patient only partially dissociated so less invasive than cover test

• Target required - OXO
• Working distance - depends on if doing near or distance
• Spectacle correction - required depending on working distance

Question 22

Fixation disparity - technique

Answer 22

• Position OXO chart horizontally with room lights on. Ask if patient sees the X and two red strips aligned above and below.
• Explain that adding the filter will change the chart color; top strip is seen by the left eye, bottom by the right.
• Confirm patient sees both strips. If only one is visible, check for deep central suppression.
• Ask if strips align with the middle X—if so, no fixation disparity. Repeat vertically.
• Neutralize any disparity using the lowest prism or positive lenses for esophoria. For unilateral disparity, add prism to the slipping eye; for bilateral, choose either.
• Use the prism matching disparity or adjust between Base IN/OUT based on patient feedback.
• At near, use grey polaroid and ensure patient reads small text on Mallett for accurate accommodation before OXO.
• Recording:
• If 2 strips aren’t visible, record the suppressed eye and whether suppression is constant or intermittent.
• No disparity: “Mallett: No FD D&N.”
• Disparity: record lowest prism/lens used (e.g., “Near 1 prism dioptre BI LE” for unilateral disparity).
• For symptomatic patients, leave the prism for a few minutes; if slip reappears, prism may be less useful, common in abnormal binocularity cases.
• The test alone is limited for decompensating phoria but useful with other symptoms or when testing spherical manipulation or effects of exercises.
• Isolated eso/exo disparity may indicate decompensated phoria.
• Prism adaptation suggests strong fusional reserves; lack of adaptation suggests decompensation. In cases with diplopia, don’t focus heavily on prism adaptation.

Question 23

NPC

Answer 23

• Near triad of responses take place: 1. Convergence 2. Accommodation 3. Pupil constriction
• NPC values —> <10cm is normal, 12-15cm is suspect, >15cm is abnormal
• Inability to obtain or maintain sufficient convergence for comfortable binocular vision for near targets
• Generally without Rx on. Avoid detailed target as they will then confuse blur with diplopia.
• ‘This test determines how well your eyes can turn in to follow a close object.’ Ask px if it’s double or just blurred!
• Bring a target from 50cm or a point where there is no diplopia towards patient’s nose at a speed 1–2cm per second. Ask the patient to report diplopia, watching for any eye turn (break point) or both eyes turning out. When diplopia reached, ask px to hold target at that distance so that you can take a measurement
• Subjective NPC means based on px response. Objective means you see the eyes & eyebrows start to struggle e.g. one eye goes out suddenly
• Worth repeating test twice for reliability
• Jump Convergence - Hold two objects, one at 15cm and one at 50cm. Watch for fixation alternating between the two targets. Repeat 3–4 times. Movements should be smooth. The nearer target can also be brought closer to the nose and the closest distance recorded.

Question 24

Maddox Rod

Answer 24

Used to test type and size of heterophoria at distance and very rarely at near

Red or clear lens composed of a series of parallel, plano-convex cylinders used. Spotlight shown & line will be seen 90 degrees to orientation of lines. Sensory fusion prevented by allowing one eye to see spotlight & other, the lines. The cover test relies on occlusion but this test relies on distortion of the image

Normally for checking the phoria after getting the spectacle correction

• Target required - spotlight
• Working distance - 6m
• Spectacle correction - with or without, depends on which deviation you are measuring
• Technique - Place prism infront of RE, ensuring completely horizontal. Room lights dimmed! If they can’t see the line, cover each eye in turn to make it more noticeable; sometimes a green filter can be put in front of the spotlight eye to increase contrast. If only line or spot seen still then change rod to LE. If still not working, then suppression may be present.
  
  • If line seen to left of spotlight (crossed images), then exophoria (rod infront of RE)
  • If line seen to right of spotlight (uncrossed images), then esophoria (rod infront of RE)
  • Deviation measured by adding prism infront of either eye until aligned.
  • Repeat procedure with prism put vertically.
  • If line seen above spotlight, then right hypophoria (only if rod infront of RE)
    
    • Due to retinal correspondance & projection, if the line is higher than the spot, it indicates the right eye is lower
  • If line seen below spotlight, then left hypophoria (only if rod infront of RE)
  • Rule of thumb - prism base is orientated in direction of the line
• Instructions - “I am going to see how well the muscles of your eyes are working together (with the current Rx).” “Can you see a red vertical line?, Good, where is it in relation to the spot, going straight through it or off to the side?”
• So Mallett unit looks at Associated phoria whilst Maddox rod looks at Dissociated phoria

Question 25

Maddox Wing

Answer 25

Unlike the Maddox rod, the eyes are dissociated using a septum that provides distinct, separate images for the eyes; one eye sees a vertical & horizontal tangent scale while the other sees an arrow.

RE sees the arrows, left sees the scales. Cover each eye in turn if px struggles to see both together otherwise suppression present

Ask if arrow to right or left of 0 on the scale. Tells you of if phoria present.

Ask which number the white arrow points to - gives size. Even numbers are exophoria and odd are esophoria

If arrow keeps moving to higher number, wait until it stops then record. If varies between max & min value then record midpoint

Do the same with the red scale & arrow for vertical deviation

Question 26

Management of Hetrophoria (6 lines of action): (from specsavers essentials)

Answer 26

1. Removing the cause of decompensation e.g. illness
2. Refractive management - We need a balance between the two eyes and a clear image in case of refractive management. The goal is to reduce modification over time, reviewing 3-4months (if needed)
3. Giving eye exercises - look into convergence & divergence excersises. In the BV lectures!
4. Prescribing prism (not the best to use for CI as convergence not used when prism in place!)
5. Referral to another practitioner.
6. Monitoring if nothing to manage.

Question 27

And…what in the world is the AC/A ratio?

Answer 27

This is the amount of accommodative convergence induced per dioptre of accommodation exerted. Normal range is 3-5. A constant value staying stable until presbyopia where there’s an increase in the response AC/A ratio but the actual AC/A is relatively stable. Anyhow, it’s not very relevant for presbyopes.

Question 28

Esophoria: Symptoms

Answer 28

• Divergence weakness, distance difficult, worse end of day
• Divergence excess: Frontal headaches, ocular fatigue, distance focus reduced after prolonged work

Question 29

Esophoria: Refractive correction

Answer 29

• Esophoria and hyperphoria: Max plus = relax accom, therefore compensates for esophoria
• Esophoria @ Near and hyperopia: multifocals or bifocals - extra plus blur distance
• Esophoria and myopia: Less minus possible, since too might minus = drive accom, hence esophoria

Question 30

Esophoria: Eye exercises

Answer 30

• If Rx correct, review in 1month, if symptoms remain consider exercises
• Works best in young px 12-35yrs
• If exercises given, review every 3-4months
• Develelops divergent reserves/and or relative accom
• Establish distance rx:
• Ask px to view small letters on card @40cm from eye
• Add lenses -0.25Ds steps (drives accom) until blurry
• Trains divergence system without needing to converge

Question 31

Esophoria: Prism used

Answer 31

Base OUT

Question 32

Exophoria: Symptoms

Answer 32

• Less marked than esophoria
• Frontal headaches after prolonged use of eyes
• Ocular fatigue
• Sometimes intermittend diplopia
• Symptoms more related to near work

Question 33

Exophoria:Refractive correction

Answer 33

• Exophoria and myopia: Min plus, as want more minus so they can accom over to correct exophoria
• Hyperopia+exophoria: Partial correction, since full correction relax accom making exophoria worse
  Or….
• Full correction c prisms and exercises
• Partial correction c prisms and exercises
• Full correction with negative add

Question 34

Exophoria: Eye exercises

Answer 34

• develop convergent fusional reserves
• Develop correct appreciation of diplopia
• Treat supression that has been demonstrated
• Negative relative accom

Question 35

Exophoria: Prism used

Answer 35

BASE IN