A 40-year-old diabetic patient presented with the squint. On examination, the secondary deviation was found to be more than the primary deviation. Forced duction test is negative. Which of the following types of squint is most likely to be present in this patient?

Explanation

## Correct Answer: D. Paralytic squint In a paralytic squint, the secondary deviation exceeds the primary deviation—this is the cardinal discriminating sign. The pathophysiology: when the affected eye fixates, the normal eye must abduct maximally to maintain fixation, creating a larger secondary deviation. Conversely, when the normal eye fixates, the paralyzed eye cannot adduct fully, creating a smaller primary deviation. The negative forced duction test confirms this is not a mechanical restriction (e.g., fibrosis, entrapment). In a 40-year-old diabetic, the most common cause is cranial nerve palsy—CN III (oculomotor), CN IV (trochlear), or CN VI (abducens)—due to microvascular ischaemia from hyperglycaemia and chronic hyperglycaemia-induced endothelial dysfunction. CN VI palsy is most frequent in diabetes, presenting with horizontal diplopia and inability to abduct the affected eye. The negative forced duction test rules out restrictive causes (thyroid eye disease, orbital fibrosis, mechanical entrapment), which would show positive forced duction. This clinical triad—secondary > primary deviation, negative forced duction, and diabetic neuropathy—is pathognomonic for paralytic squint. ## Why the other options are wrong **A. Pseudosquint** — Pseudosquint (false squint) is an optical illusion due to anatomical variants like wide intercanthal distance or epicanthic folds—there is no actual ocular misalignment. The patient would have normal ocular motility, normal cover test findings, and no secondary deviation. This does not fit the clinical presentation of measurable deviation and diplopia in a diabetic patient. **B. Restrictive squint** — Restrictive squint occurs when mechanical factors (thyroid eye disease, orbital fibrosis, entrapment) limit extraocular muscle movement. The forced duction test would be **positive** (resistance to passive movement), but this patient's test is negative. Restrictive causes are rare in isolated diabetes without orbital pathology and would not explain the secondary > primary deviation pattern. **C. Comitant squint** — In comitant (non-paralytic) squint, the primary and secondary deviations are **equal or nearly equal** because both eyes have full, symmetrical ocular motility. The deviation is constant in all gazes. This patient's secondary deviation exceeding primary deviation and the clinical context of diabetes with nerve involvement directly contradicts comitant squint pathophysiology. ## High-Yield Facts - **Secondary > Primary deviation** is the hallmark of paralytic squint; in comitant squint, they are equal. - **Negative forced duction test** rules out mechanical restriction; positive test indicates restrictive squint (thyroid, fibrosis). - **CN VI palsy** is the most common diabetic cranial neuropathy causing paralytic squint; presents with horizontal diplopia and inability to abduct. - **Microvascular ischaemia** from chronic hyperglycaemia is the mechanism of diabetic cranial nerve palsies in India; typically self-limiting over 3–6 months. - **Diplopia** (binocular) is present in paralytic squint but absent in comitant squint, which presents with monocular visual confusion or suppression. ## Mnemonics **SECONDARY > PRIMARY = PARALYTIC** When secondary deviation exceeds primary deviation, think **paralytic squint**. The paralyzed eye cannot move fully, so the normal eye must overcompensate when it fixates (larger secondary). Use this as your first discriminator in any squint question. **FFD (Forced duction Findings Discriminate)** **Positive FFD** → Restrictive (mechanical block). **Negative FFD** → Paralytic (nerve/muscle weakness). This single test separates mechanical from neurogenic causes in squint. ## NBE Trap NBE pairs diabetic patients with squint to lure students into choosing comitant squint (the most common type overall), but the key discriminator—secondary > primary deviation—is pathognomonic for paralytic squint. Students who memorize "diabetes → comitant" without checking deviation ratios will miss this. ## Clinical Pearl In Indian diabetic clinics, CN VI palsy from microvascular ischaemia is the leading cause of acute-onset paralytic squint in middle-aged patients. The key bedside finding—inability to abduct the affected eye with secondary > primary deviation—should prompt urgent glycaemic control and reassurance that most diabetic cranial palsies resolve spontaneously within 3–6 months without specific neuro-ophthalmology intervention. _Reference: Bailey & Love Ch. 32 (Strabismus); Parson's Diseases of the Eye (Ch. 9, Ocular Motility Disorders)_