The examiner's approach to a strabismus patient can take two entirely different paths leading to the same conclusion or diagnosis:

The Inductive Response: Definition - Inductive relates to an initial experience - "It came in a flash."
The Deductive Response: Definition - Deductive traces the course - Sherlock Holmes did this.

For Example:

A six month old child is brought in by his mother because the eyes have been crossed since birth. The diagnosis of congenital esotropia is made immediately. This is the inductive process.

The work up then proceeds to 1) Quantify the strabismus - how many prism diopters?, 2) Identify any unusual characteristics such as nystagmus, torticollis, "A" or "V", oblique dysfunction, etc., 3) Differential diagnosis; rule out Duane, VI N palsy, refractive ET (cycloplegic refraction), sensory ET (retina, media exam), pseudo ET, etc.

In almost every case the initial diagnosis will stand - but, of course, it is still necessary to do a complete evaluation. With congenital ET it is difficult to carry out anything other than the inductive process.

A more complicated example:

A five year old boy presents with a chin up, face right, head posture - the inductive process takes the examiner immediately to a diagnosis of left Brown syndrome. This is immediately confirmed by straightening the head and asking the patient to look up and to the right - note the inability to elevate the left eye in adduction.

The diagnosis could be confirmed by demonstrating restricted passive ductions for elevation in adduction in the left eye. This may not be possible in the clinic. The mechanical part can be usually inferred during the clinical examination.

Differential diagnosis: Left inferior oblique palsy, blowout FX OS, double elevator palsy, etc.

The workup then proceeds: 1) versions and ductions, 2) stereo acuity, 3) differential intraocular pressure (higher OS looking up confirms mechanical restriction, 4) PCT primary deviation (OD Fix) secondary deviation (OS Fix), 5) palpate trochlea, 6) orbit CT may be done, 7) forced ductions may be tested in a cooperative patient, but are rarely done or needed before going to the OR.

A Common Example:

A thirty-five year old woman presents with a left head tilt, slight chin depression and eyes looking up and to the right - on closer inspection the right face looks fuller.

Inductive diagnosis: congenital right superior oblique palsy

Differential diagnosis: Almost nothing! Long shot, Duane, blow out fracture, etc. But watch out for masked bilateral superior oblique palsy.

Quantifying workup proceeds: 1) Prism and Cover Test in the 9 Diagnostic Positions, 2) Stereo Acuity, 3) Bielschowsky Head Tilt Test, 4) Versions and Ductions, 5) Double Maddox Rod Test for Torsion, 6) Fundus Exam for Torsion.

In any case, if the original inductive diagnosis is incorrect, the workup follows the deductive process toward diagnosing another, possibly less common cause for vertical strabismus. For example, diagnosis of inferior oblique palsy always takes extra "sleuthing".

Next Example:

A five year old boy is brought in with a history, according to his mother, of having a lazy eye.*

Inductive diagnosis: Intermittent Exotropia - Ask mom, "Does he close one eye when in bright sunlight" - If "yes", this helps confirm diagnosis, and makes you look smart in the parent's eyes.

Quantifying workup follows: 1) Stereo Acuity, 2) Cover test - may require prolonged cover testing - and a distant target - even out of the window, 3) Refraction. After this, be sure to ask how often eye goes "out"? Under what circumstances? How brisk the recovery? Parents can be sent home with a "report card". Be sure parents see both the deviation and recovery.

* Always believe mom - a similar history can be obtained with onset of refractive ET except parents usually are more accurate in noting that eyes are crossed.

Do you get the idea? There is a gradual process whereby the measurement part of the workup becomes more quantification and confirmation and less diagnostic. That does not mean that the measurement part of the workup is unnecessary or superfluous. Watch out for the patient with a rare condition such as ocular myasthenia or incomplete third nerve palsy.

Finally, try this:

A 71 year old woman presents with a complaint of double vision after having her second cataract removed. She is wearing a patch over this eye.
Inductive diagnosis: Vertical Strabismus. (Diplopia after cataract surgery.)
What will you see behind the occluder lens? Right Hypotropia.
How did it happen? Local anesthetic in RIR.
What will you do about it? Recess RIR.

OS Fix OD Fix