Is lay opinion testimony admissible in medical malpractice cases?

"Lay opinion testimony is admissible where no particular scientific knowledge is required, or as 'a matter of practical necessity when the matters... observed are too complex or too subtle to enable [the witness] accurately to convey them to court or jury in any other manner.' " (People v. Williams (1988) 44 Cal.3d 883, 915.) In this regard, Evidence Code section 800 provides as follows: "If a witness is not testifying as an expert, his testimony in the form of an opinion is limited to such an opinion as is permitted by law, including but not limited to an opinion that is: [] (a) Rationally based on the perception of the witness; and [] (b) Helpful to a clear understanding of his testimony."