Pseudomyopia is sudden nearsightedness or nearsightedness that rapidly gets worse because of an underlying cause, such as uncontrolled diabetes. Symptoms of pseudomyopia may be the same as those of nearsightedness, but pseudomyopia usually clears up when the underlying cause is treated.

A number of diseases and drugs can increase the power of the lens so that light rays come to a focus in front of the retina. Overuse of the eyes for close work in poor or glaring light can also cause pseudomyopia.

Diseases that may cause pseudomyopia include:

• Uncontrolled diabetes. Pseudomyopia is often the first sign of type 2, or adult-onset, diabetes. Diabetes in adults may cause unstable vision or an increase in nearsightedness.
• Myasthenia gravis (a disease leading to progressive muscle weakness, including the muscles of the eye).
• Nervous system disorders.

Medicines that can cause pseudomyopia include:

• Hydralazine hydrochloride.
• Phenothiazines. These are antipsychotics, tranquilizers, and drugs to reduce nausea.