Alopecia is known as an autoimmune disorder where hair follicles are attacked by body's own immune system which further causes hair loss in various patches. Usually it is characterized as a skin disease rather than a hair disorder.
Retinitis Pigmentosa is a disorder of retinal degeneration It is basically an eye disorder and and affects the cell-rich retina of the eye. It causes destruction of photoreceptor cells and sometimes death of rods and cons causing poor vision and sometimes complete loss.
Achalasia is an esophageal motility disorder which is common on the smooth layer of the esophagus and lower esophageal sphincter. It causes incomplete relaxation of the lower esophageal sphincter and increase in LES tone. It causes a lot of difficulty moving food down the esophagus therefore causing indigestion and loss of appetite.