How can I differentiate between neurological and ocular causes of diplopia in a primary care setting?

To differentiate between neurological and ocular causes of diplopia in a primary care setting, start with a detailed history and focused clinical examination. Key historical features include whether the diplopia is monocular or binocular; monocular diplopia typically suggests an ocular cause such as refractive errors or lens abnormalities, whereas binocular diplopia usually indicates a neurological or muscular cause affecting eye alignment ¹ (Glisson, 2019).

Next, assess the pattern of diplopia: Neurological causes often present with diplopia that worsens in specific gaze directions due to cranial nerve palsies or neuromuscular junction disorders, while ocular causes like cataracts or corneal irregularities cause constant diplopia regardless of gaze ¹ (Glisson, 2019).

Perform cover-uncover and alternate cover tests: These help detect ocular misalignment (strabismus) indicative of neurological or muscular dysfunction ¹. If diplopia resolves when one eye is covered, it confirms binocular diplopia, supporting a neurological or muscular cause (Glisson, 2019).

Examine for associated neurological signs: Presence of ptosis, pupil abnormalities, limb weakness, or sensory changes suggests a neurological cause requiring urgent referral ¹ (Glisson, 2019).

Evaluate ocular structures: Inspect for corneal clarity, lens opacities, and perform visual acuity testing to identify ocular causes such as cataracts or corneal irregularities (Glisson, 2019).

In summary, monocular diplopia and ocular abnormalities point to ocular causes, while binocular diplopia with gaze-dependent changes and neurological signs indicate neurological causes. Prompt referral is warranted if neurological signs or sudden onset diplopia occur ¹ (Glisson, 2019).