The majority of arachnoid cysts are congenital intracranial lesions that develop in the early embryonic stages as a result of a slight irregularity in the cerebrospinal fluid's (CSF) passage through the embryonic mesenchyme. Most of the time, these cysts are asymptomatic all throughout life. Diplopia caused by an arachnoid cyst is extremely rare. We present a rare event of isolated fourth nerve palsy in a 56-year-old woman brought on by an intracranial arachnoid cyst. Her only presenting symptom was vertical diplopia for one week. She denied any history of trauma. Ocular motility revealed limitation of abduction in her right eye. We proceeded with neuroimaging and the magnetic resonance imaging (MRI) confirmed the presence of a well-circumscribed left retro-cerebellar lesion which follows the CSF signal intensity in all sequences causing compression onto the posterior aspect of the left cerebellum, keeping with the diagnosis of an arachnoid cyst. This uncommon pathology tends to be difficult to diagnose and treat.

This article describes the case of a 21-year-old female habitual contact lens wearer who complained of left eye pain, redness, and decreased vision for one week. When a ring-shaped corneal infiltration indicative of an Acanthamoeba infection was discovered, standard anti-amoebic topical therapy with polyhexamethylene biguanide and chlorhexidine was commenced. However, her keratitis worsened. At the same time, corneal scraping revealed no pathogens. An anterior chamber examination revealed a loss of corneal sensation, and a positive herpes simplex virus (HSV) immunoglobulin G serology test indicated HSV keratitis. She was eventually treated with oral anti-viral medication and recovered completely. Her case was unusual, as she had a history of contact lens use, painful corneal ulceration, and the development of Acanthamoeba keratitis-like corneal ring infiltration. This case also reinforces the various manifestations of HSV keratitis, which lead to delayed diagnosis and treatment.