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X-linked corneal endothelial dystrophy (XECD) is an extremely rare posterior corneal dystrophy reported only in a single Austrian family. It shows X-linked dominant inheritance, with males presenting congenital ground-glass corneal opacities and nystagmus, while females remain asymptomatic with only moon-crater-like endothelial changes.

Xanthelasma (xanthelasma palpebrarum) is a yellowish, flat elevation commonly occurring on the inner canthus of the upper eyelid, formed by the accumulation of foam cells containing lipids. Approximately 50% of cases are associated with dyslipidemia, and it can serve as an indicator of cardiovascular risk.

The Xen gel stent (XEN45) is a minimally invasive glaucoma surgery (MIGS) device that drains aqueous humor from the anterior chamber to the subconjunctival space. It is a 6 mm tube made of porcine gelatin and received FDA approval in 2016.