Cal. Bus. & Prof. Code § 2544
(a) Notwithstanding any other provision of law, an assistant in any setting where optometry or ophthalmology is practiced who is acting under the direct responsibility and supervision of an optometrist or a physician and surgeon may fit prescription lenses. Under the direct responsibility and supervision of an optometrist or ophthalmologist, an assistant in any setting where optometry or ophthalmology is practiced may also do the following:
(9) Perform preliminary subjective refraction procedures in connection with finalizing subjective refraction procedures performed by an ophthalmologist or optometrist, subject to the following conditions:
(B) Any preliminary subjective refraction procedures shall be performed as follows: