A 4-year-old boy presents with inward deviation of the right eye noted by his mother for the past 6 months. On examination, the angle of deviation increases when the child looks to the left and decreases when looking to the right. All of the following statements regarding this condition are correct EXCEPT:

Explanation

## Analysis of Incomitant (Paralytic) Strabismus **Key Point:** This clinical presentation describes RIGHT LATERAL RECTUS PALSY (incomitant/paralytic strabismus). The key distinguishing feature is that the angle of deviation VARIES with direction of gaze — it increases when looking away from the paralyzed muscle and decreases when looking toward it. ### Clinical Presentation Breakdown - **Right eye esotropia (inward deviation)** → Right lateral rectus is weak/paralyzed - **Angle increases on left gaze** → Looking away from the paralyzed muscle increases the deviation - **Angle decreases on right gaze** → Looking toward the paralyzed muscle (attempting to compensate) decreases the deviation ### Incomitant vs Comitant: Key Differences | Feature | Incomitant (Paralytic) | Comitant (Non-paralytic) | |---------|------------------------|-------------------------| | Angle of deviation | **VARIES** with gaze direction | Constant in all directions | | Primary vs Secondary | Secondary > Primary | Primary ≥ Secondary | | Muscle status | Paralyzed/weak | Structurally normal | | Diplopia | Present (unless suppression) | Absent (suppression common) | | Head posture | Abnormal (to minimize diplopia) | May be abnormal | | Prism cover test | Varies with direction | Constant | **High-Yield:** **"INCOMITANT = INCONSTANT"** — the angle is inconstant (variable) in different directions of gaze. **Mnemonic:** **"SECONDARY > PRIMARY in Paralytic"** — Remember this reversal: in paralytic strabismus, the secondary deviation (of the normal eye) exceeds the primary deviation (of the paralyzed eye). ### Why Option 3 Is Incorrect The prism cover test will show a **VARIABLE** (not constant) deviation depending on the direction of gaze. This variability is the hallmark of incomitant strabismus and is used to differentiate it from comitant strabismus. ### Why the Other Options Are Correct 1. **Right lateral rectus is weak/paralyzed:** Correct — esotropia of the right eye indicates failure of abduction, pointing to lateral rectus weakness. 2. **Secondary deviation > Primary deviation:** Correct — in paralytic strabismus, this is always true. The normal eye must deviate more to maintain binocular alignment. 3. **Child will experience diplopia:** Correct — if suppression has not developed (common in acute-onset paralysis), the child will experience binocular diplopia. [cite:Parson's Diseases of the Eye 21e Ch 11]