The use of molded contact glasses has largely superseded the use of ground contact glasses because the final results are better with the former method. The taking of a true impression, or negative, of the anterior ocular calotte is a fundamental procedure in this method. It is an important procedure because, a perfect negative having been obtained, the manufacture of the molded contact glass is a relatively easy matter.
Factors which interfere with the taking of a true negative of the cornea and sclera are (a) unsuitability of the plastic material, (b) movements of the eye while the impression is being taken, (c) pliability of the tissues of the eye and the formation of folds in the conjunctiva, (d) changes in the shape of the negative before the positive cast is made and changes in its shape while the negative is being dislodged from the eye and (e) episcleral and
Boshoff PH. USE OF ZELEX IN MAKING IMPRESSIONS OF THE EYE FOR MOLDED CONTACT GLASSES. Arch Ophthalmol. 1943;29(2):282–284. doi:10.1001/archopht.1943.00880140128009
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