The experienced strabismologist uses the inductive process for diagnosis of strabismus as described in the previous Strabismus Minute (Vol. 1, No. 1). But, this ability is based on a sound understanding of the basics. No athlete, performer, or strabismologist, for that matter, can perform difficult feats with dazzling skill without a solid grounding in the fundamentals of their discipline. For the strabismologist basics include anatomy, physiology, and examination techniques as will be discussed here.

Step 1 - The Form: You should develop or adopt a useful form. This facilitates collection of data in an orderly way, ensures completeness, and allows quick accurate perusal of old charts and of those completed by other office personnel.

Step 2 -

Step 3 - Vision: Distance - Near - with - without Rx - Pin Hole - minus lenses if you suspect myopia in a new patient. Pick the tests that will give you most information, use appropriate symbols.

The BVAT will save you lots of time and effort but any calibrated vision testing apparatus is okay. Computer vision testing equipment is expensive, but extremely useful. Don't forget to check near point of accomodation especially in youngsters with reading/learning disability, or near complaints.

Step 4 - Sensory: Stereoacuity - Titmus - (easier but monocular cues), Randot (more difficult - no monocular cues - for the purist)

Worth four-lights - peripheral fusion (near-far)

Other tests such as Lang, Bagolini,

two pencil test, etc.

Step 5 - Amplitude of Motor Fusion: Haploscope

You probably will not do this test unless an orthoptist is available - this device also tests sensory fusion

Fusional amplitudes - free space

Motor fusional amplitudes can be measured with a rotary prism (best) smooth Near point of convergence - use accommodative target starting at arms length and moving the target closer

Or a Prism Bar - Acceptable but images jump!

Step 6 - Fixation: Does the patient alternate? Prefer OD or OS? - How much preference? Or are the eyes aligned and patient fuses? - Is nystagmus present? If so, is it pendular? jerk? latent? manifest? Is there a null point? Is there head nodding?

Step 7 - Versions in Diagnostic Positions: Also called "Screen Comitance". This measures relative motility. Is there "over" or underaction of yoked muscles? i.e., RIO-LSR, RLR-LMR, etc. or OAIO OU, etc.

Patient RSR RLR RIR Examiner

RID RMR RSO

LIO LMR LSO

LSR LLR LIR

Recorded as Overaction RIO Can grade 1+ to 4+

Recorded as Underaction LIR Can grade -1 to -4

Evaluation of ductions (single eye movement) is accomplished by simply covering one eye and asking the patient to follow a target right-left, up-down, etc. Special testing may be done when movement is limited and includes saccadic velocity and passive duction testing.

Limited Adduction OS

Saccadic Velocity
Left Gaze	If OS saccade to right Rapid but limited = MR is intact, restriction LR (or elsewhere)	OS floats = LMR paresis		Forced Deductions After topical anesthesia full adduction = No restriction or can't forcibly complete adduction = restriction

Generated Force Restrain the OS in abduction, then ask patient to look slowly to the right - Feel pull = Generated force in muscle Feel no or little pull = paretic MR muscle

Testing of Force Ductions and Force Generation

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Requires Patient Cooperation