The pupil of the human eye is able to constrict to less than a millimeter and is capable of dilating to about 9 mm. This must entail marked structural changes of the iris stroma, vessels, muscles, nerves, melanocytes, and epithelial cells. However, in order to investigate such changes and to examine the eye histologically, extreme miosis or full mydriasis has to be maintained after enucleation. This fails with the usual procedures. Enucleation itself lessens the degree of miosis or mydriasis, and this is further reduced when the eye is in the fixation fluid. Fuchs1 and Grunert2 enucleated the human eye after atropine or eserine and commented on the loss of miosis and particularly of mydriasis. Their histological descriptions contain little detail, since Fuchs was mainly concerned with the macroscopical changes in the iris, and Grunert with the anatomy of the dilator muscle.
In order to prevent pupillary changes
van ALPHEN GWHM. The Structural Changes in Miosis and Mydriasis of the Monkey Eye. Arch Ophthalmol. 1963;69(6):802-814. doi:10.1001/archopht.1963.00960040808023