8.1.3. Investigates and manages adult patients presenting with heterophoria.

Question 1

A phoria is a

Answer 1

tendency for your eyes to drift but you can keep it in check via fusion

What are Fusional Reserves?? a measure of how much vergence a person has in reserve that can be used to overcome aheterophoria

Question 2

Causes of decompensating Phoria

Answer 2

• Optical:
  
  • Refractive error uncorrected —> little or excess accommodation induces it, & fusional reserves stop being able to manage it
  • Ill fitting glasses
  • Aniseikonia —> barrier to fusion hence reserves cannot manage it
• Medical:
  
  • Illness/GH - fatigue etc reduces reserves
  • Head trauma - fusion centre in brain affected
  • Medication e.g. tricylic antidepressants affect accommodation
• Other:
  
  • Change in visual demands —> induces accommodation or reduces it & affects ability to manage muscles with fusional reserves

Question 3

History questions:

Answer 3

• Diplopia gradual onset
• Headaches
• Covering one eye
• Towards end of the day
• Px reports eyes tending to drift - suggesting intermittent tropia stage
• If decompensated then may have head tilt or face turn so adapting or more longstanding

Question 4

Steps to treat Decompensating Phoria

Answer 4

1. Refractive error - overcorrect hyperopia or undercorrect myopia (not easy as affects VA) for esophoria, undercorrect hyperopia or overcorrect myopia for exophoria
2. Excersises - stereograms - good for small phorias where small improvement needed in FRs
3. Prisms - ONLY GIVEN IF SYMPTOMS NO MATTER HOW LARGE!! Fresnel is the best option to allow px to “live” with the prism to adapt to what’s correct! It will keep fluctuating & will cost the practice. You might be able to get away with small angle phorias but large angle definitely require a fresnel.
4. Botulinum toxin
5. Surgery

Question 5

How do you manage a decompensating phoria if turning into a constant tropia?

Answer 5

• It would be best to trial the prismatic need with Fresnel prisms before incorporating if possible.
• Often the maximum amount of incorporated prism is not sufficient to relieve diplopia. The patient will not be happy paying for incorporated prisms that are not helpful. It’s also costly for your practice if this keeps happening

Question 6

Why is giving prism not as good as refractive error or excersise?

Answer 6

• You want the px to learn to control the deviation themselves.
• With Rx, you give the eyes a chance to work & accommodate to overcome the deviation. With excersises, again, it’s more work for the eyes. However, prism does the work for the px so they struggle to learn to overcome the deviation themselves.

Question 7

When is botulinum toxin given?

Answer 7

• If small angle phoria that can’t be corrected by surgery due to it being too small but also because prism isn’t working. It’s an inbetween.
• The aim is to overcorrect then let the eyes realign. Whilst this happens, the px should start developing more control over deviation as toxin wears off, which is a good thing!
• Surgeries:
  
  • Convergence weakness —> MR Resection done (when a portion of the muscle is cut away and the new shortened muscle is reattached to the same insertion point)
  • Divergence excess —> LR Recession done (weakening of LR)

Question 8

What happens when phoria decompensates?

Answer 8

• Retinal correspondence is lost as the eye turn chooses different point on fovea to focus on. So there is simultaneous perception but the ability to fuse the images is stumped hence double vision (if adult, children can suppress if visually immature). This means for an adult, using spherical manipulation won’t work as although accommodation of the lens is still there, the eyes cannot converge to fuse the images. This will also mean eye excerises are null. Therefore, prism is a good solution but fresnel is best! If recently decompensated, then even a max amount of prism incorporated may not be good enough as variable so fresnel prism worth using
• If the level of prism required is small - may not need a fresnel
• Look out for any signs of intermittent control!

Question 9

Can surgery work if they have decompensated?

Answer 9

• It can, if there is potential for BSV pre-operatively determined by correcting the tropia with prism and checking if they regain any stereopsis.
  
  • If this is the case, then surgery will be done to decrease the angle of the tropia and a residual or consecutive tropia left. This is to reduce the size of phoria as much as possible in order to allow for fusion
  • Diplopia can be managed with prism and regular orthoptic excersises given to work on those fusional reserves e.g. positive FRs for residual XT.
  • Care taken not to over-correct deviation as turning an esophoria into an exophoria will be difficult as px will not have had experience dealing with a different type, no matter if small
• If no potential for BSV, then surgery only cosmetic, and px will need prism to manage their tropia or the toxin on a regular 4-6 month basis.

Question 10

 Sheards

Answer 10

if more than half the fusional reserves need to be used to control the phoria, the visual system will be under stress & the phoria decompensates

Question 11

Esophoria types of

Answer 11

• Convergence Excess (Deviation Greatest at Near)
  
  • Symptoms:
    
    • Frontal headaches, ocular fatigue, reduced distance focus after prolonged near work.
  • More common than divergence weakness.
• Divergence Weakness (Deviation Greatest at Distance)
  
  • Symptoms:
    
    • Worsens at the end of the day, distance viewing difficulties.
  • Common causes:
    
    • High myopia (large eye → relaxed state leads to divergence).
    • Possible 6th nerve involvement.
  • Management options:
    
    • Prism correction or surgery (only options).
• Non-Specific Cases
• Causes of Decompensated Deviation
  
  • Narrow pupillary distance (PD).
  • High hyperopia.
  • High AC/A ratio (6:1, normal = 4:1).
  • Close working distance (WD).
  • Weak divergent fusional reserves (FRs).
• Management Strategies
  
  • Improve divergent fusional reserves:
    
    • Plus flippers or base-in (BI) prism flippers (negative reserves harder to strengthen).
  • Fully correct refractive error (maximum + prescription).
  • Use bifocals for near tasks (for convergence excess with tropia).
  • Increase working distance (larger WD).
  • Base-out prism for symptomatic cases.
  • Use stereograms (for phoria cases).
  • Exercises are challenging to implement effectively.

Question 12

Exophoria types:

Answer 12

• Deviations
  
  • Convergence Weakness: Deviation greatest at near.
  • Divergence Excess: Deviation greatest at distance.
  • Non-Specific Cases: Variable presentations.
• Symptoms
  
  • Less severe than SOP (Superior Oblique Palsy).
  • Frontal headaches after prolonged eye use.
  • Ocular fatigue.
  • Intermittent diplopia.
  • Symptoms more pronounced with near work.
• Causes
  
  • Wide pupillary distance (PD).
  • Myopia or presbyopia.
  • Age-related factors.
  • Weak convergent fusional reserves.
• Management
  
  • Strengthen convergent fusional reserves.
  • Over-minus lenses.
  • Pen-to-nose exercises.
  • Base-in prism for symptomatic relief.
• Other Deviations
  
  • Hyperphoria/Hypophoria: Recovered as R/L or L/R depending on which eye is higher.
  • Cyclophoria: Includes excyclophoria and incyclophoria.

Question 13

Fixation disparity

Answer 13

• Definition
  
  • Fixation disparity: A slight misalignment of the visual axis under binocular viewing conditions.
• Characteristics
  
  • Smaller and typically occurs in the same direction as the underlying phoria.
  • Indicates struggling vergence mechanisms and potential phoria decompensation.
• Testing
  
  • Partial Dissociation:
    
    • Involves dichoptic stimuli with binocular blocks (e.g., black lines).
  • Measures the relieving prism needed to eliminate the fixation disparity (clinically more relevant than absolute phoria size).
• Management
  
  • Prescribe the minimum prism required to maintain stable binocularity.
• Key Concept
  
  • Fixation disparity involves stereoscopic fusion, where two eyes perceive slightly different images.

Question 14

Fusional reserves

Answer 14

• Prism Fusion Amplitude
  
  • Maximum prism strength that can be fused by the visual system.
• Fusional Reserve Testing
  
  • Exophoria:
    
    • Convergence required to overcome it = positive fusional reserves (measured with BO prism).
  • Esophoria:
    
    • Divergence required to overcome it = negative fusional reserves (measured with BI prism).
• Principle
  
  • Opposite to prism prescribing (i.e., base direction).
  • Same as prism exercises (e.g., BO for convergence, BI for divergence).
• Testing Order
  
  • Measure fusional reserves opposing the phoria first:
    
    • Exophoria: Measure positive fusional reserves (BO prism).
    • Esophoria: Measure negative fusional reserves (BI prism).

Question 15

Normal levels of fusional reserves

Answer 15

• Distance Fusional Reserves
  
  • Positive (Base Out): 15Δ.
  • Negative (Base In): 5Δ / 7Δ.
• Near Fusional Reserves
  
  • Positive (Base Out): 35Δ / 40Δ (higher convergence ability at near).
  • Negative (Base In): 15Δ.
• Vertical Fusional Reserves
  
  • Base Up (BU) / Base Down (BD): 3Δ.

Question 16

Management options

Refractive

Answer 16

 In many cases, decompensated phorias become compensated when refractive correction is given
 Due to:
o Accommodation-convergence relationship - uncorrected spherical error may result in abnormal degree of accomm – this results in stress on convergence
o Blurring - blurred vison makes BV more difficult
o Anisometropia -produces interocular differences blurring – again makes BV more difficult

Esophoria

 Needs hypermetropic correction
 Max plus relaxes accommodation therefore compensates for esophoria due to convergence-accommodation relationship (relaxing accomm = relaxed convergence = reduces SOP)
 SOP at near only may need bifs/varis with extra plus at near only so DVA remains clear
 If SOP & myopia – correct for clear vision but be careful not to over correct (least minus possible)

Exophoria

 Needs myopic correction / over minused (need “negative add”)
 Manipulate AC/A ratio – over minus = more accommodation = more convergence = reduces XOP
 Myopic overcorrection can be considered if px’s amplitude of accomm is adequate
 Minimum overcorrection required to compensate should be given
 Overcorrection is gradually reduced over a period of moths so that the px’s fusional reserves increasingly compensate for more of the deviation

Bifocals
o Convergence excess SOT = additional plus @ near
o Convergence insufficiency = additional minus @ near
o Divergence excess XOP = minus @ distance

Question 17

Management options

Prism

Answer 17

 Used to obtain/maintain BSV
 Temporary measure to maintain BSV while awaiting surgery, or longer term if no other option
 Only prescribe to symptomatic patient; smallest amount that relieves diplopia
 BASE IN = EXO
 BASE OUT = ESO
 Fresnel’s available up to 40^; will reduce VA slightly, temporary, stuck onto back of lens
 Incorporated - lower amount of prism, longer term for stable angles

Question 18

Orthoptic exercises

Answer 18

Exercises may be given to:
 Decompensating phoria – to compensate the latent strabismus (stereograms)
 Improve control of an intermittent strabismus
 Convergence insufficiency (dot card; pens to nose)

 Refractive correction trialled 1st before exercises are issued
 Should be done little & often – 5x morning 3-4 mins, 5x night 3-4 minutes
 XOP responds best
 Only useful in deviations <15^

 Dot card: patient looks at furthest dot, should obtain crossed physiological dip of the line and closer dots. Patient fixates on each dot getting closer to nose and fuse images (train tracks fused into single line. Patient repeats this until can no longer fuse, relax back to furthest dot & repeat

 Dot card can also be used for jump convergence

 Card with letters rather than dots – accommodative insufficiency

 Pen to nose: hold pen at arm’s length, move it towards to nose until diplopia (cannot fuse), move pen back until single – repeat
o Useful in convergence issues / XOP

 Stereogram (3 cats)
o Demonstrate physiological dip with 2 pens
o Make the 3rd cat through physiological diplopia
o Distance stereogram (SOP) - card held @30cm – px fixates on distance target just over the top of the card
o Near stereogram (XOP) – card @ 40cm problems at near: look at near object in front of stereogram, appreciated 3rd image
o Flat fusion = eyes ability to produce a composite picture from two images which you are looking at

 Prism bar to exercise fusional reserves
o Positive / convergent fusional reserves – base out prism for XOP
o Negative / divergent fusional reserves – base in prism for SOP

Question 19

Referral may be considered if:

Answer 19

 There is a factor contributing to decompensation that requires attention by another practitioner e.g., deteriorating health
 Cause of anomaly is suspected to be pathological / related to recent head injury
 The anomaly has not responded to refractive correction, exercises or prisms