Help me in revising the question regarding 15 degree exophoria for long case in MS Ophthal practical exam
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Long case revision: 15° Exophoria
One-line diagnosis
A 15° exophoria is a latent outward deviation controlled by fusional convergence under binocular viewing. It becomes manifest only after dissociation, such as on alternate cover test.
Do not call it convergence insufficiency from the angle alone. You must establish whether the deviation is greater at near, associated with remote near point of convergence (NPC), reduced positive fusional vergence, and near-work symptoms.
In clinical practice, deviation is preferably documented in prism dioptres (PD) at distance and near. If measured on synoptophore, retain the reading in degrees. A 15° angle corresponds roughly to 27 PD geometrically, but do not casually interchange the two measurement systems in your presentation.
How to present the case
Case summary format
“Mr/Ms ___, aged ___ years, presented with ___ [asthenopia/headache/blurred vision/diplopia on reading, or cosmetic concern]. Visual acuity is ___ in each eye, refraction is ___, and anterior and posterior segments are normal. Ocular movements are full with no overaction or underaction. Cover testing shows no manifest deviation under binocular conditions; after dissociation, there is an exophoric movement, measuring 15° on ___ [synoptophore/Maddox wing], at ___ [distance/near]. Binocular single vision/stereopsis is ___, and fusional convergence reserve is ___. The final diagnosis is ___.”
Examination sequence for MS practical
1. History
Presenting symptoms
Ask specifically:
- Headache, eyestrain, tired eyes
- Blurring while reading or using screens
- Intermittent horizontal diplopia, usually worse on prolonged near work
- Difficulty sustaining reading, skipping lines, loss of concentration
- Symptoms worse late in the day, during illness, fatigue, or stress
- Any outward deviation noticed by patient or relatives
Essential history
- Age at onset and duration
- Sudden or gradual onset
- Trauma, fever, neurological illness, concussion
- Previous glasses, prism, patching, orthoptic exercises, or squint surgery
- Family history of squint or refractive error
- Occupation and near-visual demand
- Developmental history in children
- Diabetes, thyroid disease, myasthenia symptoms, neurologic symptoms if onset is acute or diplopia is new
2. General ocular examination
- Visual acuity - unaided, with glasses, pinhole, near vision.
- Refraction - dry and cycloplegic where indicated.
- Pupils and eyelids - exclude ptosis, anisocoria.
- Hirschberg and Krimsky - typically orthotropic appearance in pure phoria.
- Ocular movements - assess all cardinal positions:
- Look for limitation, overaction, A/V pattern, dissociated vertical deviation.
- If incomitant or associated with limitation, do not label it a simple exophoria without further evaluation.
- Anterior segment and fundus - include optic disc and macula. Assess for torsion if indicated.
3. Squint and binocular vision work-up
A. Cover tests: the most important bedside finding
Cover-uncover test
- In a well-controlled exophoria, there is no movement of the uncovered eye, because there is no manifest tropia.
- If the uncovered eye refixates, a manifest exotropia is present, at least intermittently.
Alternate cover test
- Break fusion with repeated alternate cover.
- In exophoria, the covered eye drifts outward.
- On uncovering, it makes an inward refixation movement, that is, adduction, to regain fixation.
Viva statement:
“On alternate cover testing, the eye shows an inward corrective movement on uncovering, confirming an exophoria.”
“On alternate cover testing, the eye shows an inward corrective movement on uncovering, confirming an exophoria.”
Kanski describes exophoria as a heterophoria that may produce symptoms when fusional amplitudes are inadequate, particularly during stress or poor health. Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed., p. 751.
B. Measure the deviation
Measure at:
- Distance: 6 m
- Near: 33 cm
Use:
- Prism bar cover test, preferably
- Maddox rod with prism bar for distance
- Maddox wing for near
- Synoptophore for objective and subjective angle, sensory status, and fusional amplitudes
Record like this:
- “Exophoria: 15° at near, ___ PD at distance and ___ PD at near.”
- Or, if only a synoptophore reading is available: “15° exophoria on synoptophore.”
C. Determine pattern
| Pattern | Finding | Significance |
|---|---|---|
| Basic exophoria | Similar at distance and near | Usually compensated if asymptomatic |
| Convergence-weakness exophoria | Greater at near | Consider convergence insufficiency |
| Divergence-excess type | Greater at distance | Evaluate control and distinguish intermittent exotropia |
| Decompensating exophoria | Symptoms, poor fusional reserve, may become intermittent XT | Needs active treatment |
D. Binocular single vision and sensory status
Perform:
- Worth four-dot test at distance and near
- Bagolini striated glasses
- Stereopsis: Titmus/Randot/TNO
- Synoptophore: simultaneous perception, fusion, stereopsis
In uncomplicated exophoria, expect:
- Binocular single vision present
- Good stereopsis
- No suppression under usual viewing conditions
E. Near point of convergence
Measure NPC using an accommodative target.
- Record break point and recovery point.
- A remote NPC supports convergence insufficiency, particularly when near exophoria and reduced positive fusional vergence coexist.
F. Fusional reserves
Assess on synoptophore or with prism bar:
- Positive fusional vergence (PFV) equals convergence reserve and is the relevant reserve for exophoria.
- Negative fusional vergence (NFV) equals divergence reserve.
In symptomatic exophoria, the key abnormality is often inadequate PFV to compensate for the exophoric deviation.
How to distinguish exophoria from intermittent exotropia
| Feature | Exophoria | Intermittent exotropia |
|---|---|---|
| Deviation under ordinary binocular viewing | Latent, absent | May be manifest intermittently |
| Cover-uncover test | No refixation movement of uncovered eye | Refixation movement when cover is removed |
| Alternate cover test | Reveals outward drift after dissociation | Often reveals larger exotropia |
| Control | Fusion maintains alignment | Control variable, may deteriorate with fatigue |
| Symptoms | Asthenopia/near symptoms may occur | Outward deviation may be noticed, suppression/diplopia possible |
| Management | Usually conservative | Observation, non-surgical measures or surgery depending on control and severity |
Important examiner point: A large “phoria” that breaks easily, recovers slowly, or appears spontaneously may actually represent poorly controlled intermittent exotropia, not simple exophoria.
Diagnosis to give based on findings
If distance and near angles are similar and patient has no symptoms
“Compensated basic exophoria of 15° with satisfactory binocular single vision.”
If near angle is larger with near symptoms, remote NPC, and low PFV
“Symptomatic convergence-weakness exophoria, consistent with convergence insufficiency.”
Typical convergence insufficiency is associated with near-work symptoms, exophoria greater at near than distance, remote NPC, and poor near fusional convergence amplitudes. Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed., p. 751.
If manifest outward deviation appears after fatigue or cover testing and recovery is slow
“Intermittent exotropia with poor/fair control,” rather than simply exophoria.
Management
1. Reassurance and observation
Appropriate for:
- Asymptomatic patient
- Good control
- Normal or adequate fusional reserves
- Good stereopsis
- No progression to tropia
Small exophorias are common and often need no treatment.
2. Correct refractive error
- Give full appropriate correction, especially significant refractive error.
- Ensure accommodation is not contributing to symptoms.
- In myopia, appropriate correction may improve visual clarity and fusion.
Kanski recommends correcting any significant refractive error in heterophoria. Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed., p. 751.
3. Orthoptic treatment
Main treatment for symptomatic convergence-weakness exophoria or convergence insufficiency:
- Pencil push-ups, if used as a simple home exercise
- Home convergence exercises
- Office-based vergence/accommodative therapy where available
- Synoptophore exercises, jump convergence, and fusional reserve training
Aim:
- Bring NPC closer
- Increase positive fusional vergence
- Relieve asthenopia and near diplopia
Orthoptic treatment is particularly useful in convergence-weakness exophoria. Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed., p. 751.
4. Prism
- Consider base-in prism for persistent symptomatic cases, especially near tasks, when exercises fail or are unsuitable.
- A temporary Fresnel prism may be trialed first.
- Prescribe the minimum prism that relieves symptoms.
Kanski notes that Fresnel prism can be used for symptom relief and later incorporated into spectacles, generally up to 10-12Δ total, split between the eyes. Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed., p. 751.
5. Surgery
Rare for pure exophoria. Consider only if:
- Large, decompensated deviation
- It has evolved into clinically significant intermittent or constant exotropia
- Symptoms/cosmesis persist despite appropriate conservative treatment
Common viva questions with short answers
What is heterophoria?
A latent ocular deviation kept controlled by fusional mechanisms and revealed only when fusion is interrupted.
What is exophoria?
A latent tendency of one eye to deviate outward, controlled under binocular viewing by fusional convergence.
What movement confirms exophoria on alternate cover test?
The uncovered eye makes an inward refixation movement, that is, adduction.
Which fusional reserve compensates exophoria?
Positive fusional vergence, or convergence reserve.
What causes symptoms in a phoria?
Symptoms arise when the phoria is large relative to available fusional reserve, or when fusional capacity is reduced by fatigue, illness, stress, uncorrected refractive error, or prolonged near work.
What is Sheard's criterion?
For a comfortable phoria, the compensating fusional reserve should be at least twice the magnitude of the phoria. For exophoria, use the positive fusional vergence reserve. It is a clinical guide, not an absolute rule.
When do you diagnose convergence insufficiency?
When there are near-work symptoms plus exophoria greater at near than at distance, remote NPC, and reduced PFV.
Does every 15° exophoria need surgery?
No. Treatment depends on symptoms, control, binocular function, refractive error, and fusional reserve, not the angle alone.
A polished final presentation
“On evaluation, the patient has a 15° exophoria, demonstrated after dissociation on alternate cover testing, with inward refixation movement on uncovering. There is no manifest deviation in primary position under binocular viewing. I would quantify the deviation separately for distance and near in prism dioptres, assess sensory fusion and stereopsis, measure NPC and positive fusional vergence, and perform cycloplegic refraction. If the near deviation is greater with a remote NPC and poor convergence reserve, I would diagnose convergence-weakness exophoria/convergence insufficiency. Management includes correction of refractive error, orthoptic convergence exercises, and base-in Fresnel or spectacle prism for persistent symptoms. Surgery is rarely indicated for isolated exophoria.”
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