From MedlinePlus Genetics
Researchers have described two forms of vitelliform macular dystrophy with similar features. The early-onset form (known as Best disease) usually appears in childhood; the age at which symptoms begin and the severity of vision loss vary widely. The adult-onset form begins later, usually in mid-adulthood, and tends to cause vision loss that worsens slowly over time. The two forms of vitelliform macular dystrophy each have characteristic changes in the macula that can be detected during an eye examination.

Vitelliform macular dystrophy causes a fatty yellow pigment (called lipofuscin) to build up in cells underlying the macula. Over time, large amounts of this substance can damage cells that are critical for clear central vision. As a result, people with this disorder often lose their central vision, and their eyesight may become blurry or distorted. Vitelliform macular dystrophy typically does not affect side (peripheral) vision or the ability to see at night.

Vitelliform macular dystrophy is a genetic eye disorder that can cause worsening (progressive) vision loss. This disorder affects the retina, the specialized light-sensitive tissue that lines the back of the eye. Specifically, vitelliform macular dystrophy disrupts cells in a small area near the center of the retina called the macula. The macula is responsible for sharp central vision, which is needed for detailed tasks such as reading, driving, and recognizing faces.  https://medlineplus.gov/genetics/condition/vitelliform-macular-dystrophy