The study, which will be published in the Journal of Nervous and Mental Disease, found that there were significant changes in visual acuity, in the shape and curvature of the eye and in refraction from personality to personality in the real patients, but hardly any among the others tested.

The opthalmic exam also found some clinical differences apart from the standard tests. One woman had three personalities, aged 5, 17 and 35. When the five-year-old was examined, she had a condition, common in childhood, known as ''lazy eye,'' in which one eye turns in toward the nose. The condition was not present in the 17-year-old or the 35-year-old.

Similar differences were found in other patients. ''One patient had had his left eye injured in a fight, so that it turned out,'' said Dr. Miller. ''But the condition only appeared in one of his personalities. It disappeared in the others, nor was there any evidence of muscle imbalance.''

The study corroborates an observation of vision differences that had often been made by those treating multiple-personality cases. ''Many patients have told me they have a drawer full of eyeglasses at home, and they never are quite sure which to bring when they go out,'' Dr. Braun said. How Mind Regulates Biology

The medical phenomena being discovered in multiple personalities stretch the imagination, but researchers believe that they represent only the extreme end of a normal continuum. The effects found in these patients, they say, are graphic examples of the power of states of mind to regulate the body's biology. By studying them, researchers hope to find clues to links between mind and body that can help people with other psychiatric problems, as well as point the way to powers of healing that may one day be of use in treating normal medical patients.

The lesson for psychophysiology from multiple personalities is that a given personality has as its biological underpinning a specific pattern of mental and biological states, according to Dr. Frank Putnam, a psychiatrist at the Laboratory of Developmental Psychology at the National Institute of Health. In a sense, Dr. Putnam said, there is a ''biological self'' that corresponds to the psychological self; as the psychological one shifts, so does the biological.

''We have a work self and a play self, for instance, but we are the same person,'' said Dr. Putnam. ''But each of those selves has its own repertoire of emotional states, memories and, to some extent, an underlying biological pattern. Those minor differences are seen in their extremes in the patients with multiple personality.''