This section is an exception to the rule as regard the exclusion of opinion evidence. If a witness is permitted to express his opinion, it would amount to delegation of judicial function. A witness has to state fact which he has seen, heard, or perceived and not the conclusion which he has formed on observing or perceiving them (s. 60 IEA). The opinions of experts are relevant upon a point of (a) foreign law, (b) science, (c) art, (d) identity of handwriting and (e) finger impressions. The expert opinion is only the opinion of evidence and is not helpful to the court in interpretation of the law.
It is general rule that the opinion of witness possessing peculiar skill is admissible, whenever the subject-matter of inquiry is such that inexperienced persons are likely to prove cable of forming a correct judgment upon it without such assistance. In other word, this is so when it so far partakes of the character of a science or art as to require a course of previous habit or study to obtain a complete knowledge of its nature. The need to hear the expert opinion is the first and foremost requirement.
Howsoever the opinion of the expert is important to the court to draw the conclusion but in no circumstances the opinion of expert may have any binding effect on the court. The Court does not become functus officio because of an expert opinion. It is not the province of an expert to act as a judge or jury. (refer Ramesh Chandra Agarwal v. Regency Hospital Ltd. AIR 2010 SC 806: (2009) 9 SCC 709 ) the ultimate opinion has to be formulated by the court. Expert opinion is merely an aid to the Court to arrive at a conclusion. Such an opinion is not binding. It is optional for the Court to accept or to reject it. However, interpretation by a technical body in regard to purely technical matter deserves acceptance and will not be interfered with, unless it is arbitrary or unreasonable. (refer Grid Corpn. Of Orissa Ltd. Eartern Metals & Ferro Alloys, (2011) 11 SCC 334 ). Therefore, the opinion of third person under s. 45 of Indian Evidence Act is not binding on the Court.