The procedure is performed in an operating room , usually under local anesthetic. However, some ophthalmologists give patients only a topical anesthetic. A trabeculectomy involves removing a tiny piece of the eye-ball, During a trabeculectomy, the patient's eye is held open with a speculum. The outer layer, or conjunctiva, and the white of the eye, or sclera, are cut open (A). A superficial scleral flap is created and a plug of sclera and underlying trabecular network is removed (B). This allows the fluid in the eye to circulate, relieving pressure. The scleral flap is closed and sutured (C). The conjunctiva is closed (D). ( Illustration by GGS Inc. ) where the cornea connects to the sclera, to create a flap that allows fluid to escape the anterior chamber without deflating the eye. The area is called the trabeculum. After the procedure, fluid can flow out onto the eye's surface, where it is absorbed by the conjunctiva, the transparent membrane that lines the sclera and the eyelids.
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.