You are exactly right in your thinking. Different drops are used to dilate eyes. Tropicamide (mydriacyl) is the most common drop and it comes in two strengths, % and %. The % will not last quite as long but it is not a large difference. Tropicamide will dilate the eyes and interfere with near focusing. Phenylephrine is often added as a second drop with mydriacyl to enhance the dilation. Phenylephrine enlarges and hastens the dilation but has no effect on focusing and usually does not prolong the dilation. Paremyd is another drop containing % hydroxyamphetamine and % tropicamide. It does not dilate the eyes as well but tends to last a shorter time period and not interfere with near focusing as much. Longer lasting drops include cyclopentolate and homatropine. They have a longer mode of action and exert significantly more interference with close vision. They are usually used for children.