A 68-year-old man presents with chronic tearing and redness of the left eye. On examination, the structure marked **A** in the diagram is noted to be everted away from the globe. The patient reports that tears constantly overflow onto his cheek, and the lower eyelid margin no longer contacts the eye surface. Which of the following is the PRIMARY mechanism responsible for this eyelid malposition in this patient?

Explanation

## Why "Age-related horizontal laxity of medial and lateral canthal tendons with loss of lid tone" is right The clinical presentation of a 68-year-old with the lower lid everted away from the globe (marked **A**) is classic for **involutional (senile) ectropion**, which is the most common type of ectropion. According to Khurana Ophthalmology 7e, involutional ectropion results from age-related horizontal lid laxity caused by stretching of the medial and lateral canthal tendons. This allows the eyelid margin to turn outward, exposing the palpebral conjunctiva and displacing the inferior punctum away from the tear lake, resulting in epiphora (tearing overflow). The absence of acute trauma, burn history, or facial nerve palsy signs makes this the most likely etiology. ## Why each distractor is wrong - **Vertical skin shortage from previous thermal burn or chemical injury**: This describes cicatricial ectropion, which results from vertical skin shortage pulling the lid downward and outward. While this can cause ectropion, there is no history of burn, trauma, or chronic dermatitis in this patient, and cicatricial ectropion is less common than involutional ectropion in elderly patients. - **Facial nerve (CN VII) paralysis with loss of orbicularis oculi muscle tone**: This describes paralytic ectropion, which occurs when CN VII palsy causes paralysis of the orbicularis oculi muscle, resulting in loss of lid tone and closure ability. The clinical presentation does not mention facial asymmetry, inability to close the eye, or absent Bell phenomenon, which would be expected with CN VII involvement. - **Mechanical weight from a lower eyelid mass causing gravitational eversion**: This describes mechanical ectropion, caused by a tumor or mass weighing down the eyelid. There is no mention of a visible mass or lesion on the lower eyelid, making this the least likely diagnosis. **High-Yield:** Involutional (senile) ectropion = most common type; caused by age-related horizontal canthal tendon laxity → epiphora + exposure keratitis; managed with lubricants (mild) or lateral tarsal strip surgery (definitive). [cite: AK Khurana Ophthalmology 7e Ch 14]