1. Eye Muscle Actions & Testing (The "H" Test)

Clinical Pearl: To isolate a muscle, you must first align the eye axis with the muscle pull.

Muscle	Primary Action	How to Test (Isolate)	Innervation
Superior Rectus	Elevation	Look Out, then Up	CN III
Inferior Rectus	Depression	Look Out, then Down	CN III
Lateral Rectus	Abduction (Out)	Look Out	CN VI
Medial Rectus	Adduction (In)	Look In	CN III
Superior Oblique	Depression + Intorsion	Look In, then Down (Reading/Stairs)	CN IV
Inferior Oblique	Elevation + Extorsion	Look In, then Up	CN III

2. Cranial Nerve Palsies

Nerve	Signs	Why?
CN III (Motor)	Down & Out Eye, Ptosis.	Unopposed LR (Out) and SO (Down). Levator failure = Ptosis.
CN III (Pupil Rule)	Surgical (Aneurysm): Dilated Pupil. Medical (Diabetes): Sparing Pupil.	Parasympathetic fibers are on the outside (compressed by blood). Motor fibers are deep (ischemia affects them first).
CN IV (Trochlear)	Diplopia looking down (stairs). Head tilt AWAY.	Eye is Extorted (due to loss of SO Intorsion). Patient tilts head opposite way to align images.
CN VI (Abducens)	Medial deviation.	Unopposed Medial Rectus.

3. Pupillary Reflexes

Pathology	Details
Marcus Gunn (RAPD)	Optic Nerve Lesion. Swing flashlight to bad eye -> Both Dilate (Brain thinks it's dark).
Argyll Robertson	Neurosyphilis. Accommodates (Near response) but NO light reaction. Pretectal lesion.
Horner's Syndrome	Ptosis, Miosis, Anhidrosis. Sympathetic Chain lesion (Pancoast tumor, Carotid dissection).
Adie's Tonic Pupil	Dilated pupil, slow reaction. Ciliary Ganglion lesion.

4. Visual Fields

• Meyer's Loop (Temporal): "Pie in the Sky" (Superior Quad).
• Dorsal Radiation (Parietal): "Pie on the Floor" (Inferior Quad).
• PCA Stroke: Macular Sparing (Dual blood supply MCA/PCA).