Multiple Sclerosis: This condition can cause episodes of fever and vision disturbances, including blurring of vision, due to its effects on the central nervous system. The on and off nature of the symptoms aligns with the relapsing-remitting pattern often seen in multiple sclerosis.

Migraines: Migraines can cause visual disturbances, including blurring of vision, and are sometimes preceded by or associated with fever-like symptoms. The episodic nature of migraines fits the on and off pattern described.
Sinusitis: Sinus infections can cause fever and, if the sinuses around the eyes are affected, can lead to blurring of vision due to swelling or pressure on the eyes.
Optic Neuritis: This condition, often associated with multiple sclerosis but can occur independently, causes inflammation of the optic nerve leading to vision loss or blurring, and can be accompanied by fever in some cases.

Giant Cell Arteritis: Although less common, this condition is critical to diagnose because it can lead to permanent vision loss if not treated promptly. It typically presents with fever, headache, and visual disturbances in older adults.
Endophthalmitis: A severe infection within the eye that can cause fever, severe eye pain, and vision loss. It's a medical emergency requiring immediate attention.
Cavernous Sinus Thrombosis: A rare but potentially life-threatening condition that can cause fever, vision changes, and other neurological symptoms due to a blood clot in the cavernous sinus.

Neurosyphilis: A complication of untreated syphilis that can cause a wide range of neurological symptoms, including vision problems and fever.
Vogt-Koyanagi-Harada Disease: A rare autoimmune condition that can cause inflammation in various parts of the body, including the eyes, leading to vision disturbances and fever.
Sarcoidosis: An autoimmune disease that can affect multiple parts of the body, including the eyes, causing vision problems and systemic symptoms like fever.