Measurement of corneal DNA content

deviations). This may be attributed to the accuracy to which corneal thickness can be read with the specular microscope. All three methods appeared to be equally precise from session to session (as indicated by the intercession standard deviations). On the other hand, the Mishima-Hedby attachment demonstrated a decreasing trend from session to session (as indicated by the analysis of variance result), which suggests that this method may not be appropriate for longitudinal studies. Finally, no conclusion can be drawn about the validity (i.e., truth of the measurement) of these methods. Well-controlled clinical trials involving longterm longitudinal studies of the effects of various eye diseases, drugs, and surgical procedures on the eye are becoming increasingly important. During the developmental stages of a proposal to study the effects of intraocular lenses on the corneal endothelium by specular microscopy and corneal thickness measurements, we devised the current study to determine which method would be appropriate for a long-term prospective analysis. Although measurement of corneal thickness by the Haag-Streit pachometer with or without the Mishima-Hedby modification has become a standard practice, it requires a fully trained ophthalmologist. For purposes of long-term longitudinal studies involving large numbers of patients, this is relatively impractical, especially if an alternative requiring only paramedical personnel is available. Specular microscopy would seem to offer such an alternative, in that a highly trained technician can take photographs, count cells, and at the same sitting, measure corneal thickness. In a practitioner's office practice, however, routine use of a pachometer would seem a more practical and certainly less expensive technique. In addition, the ophthalmologist has ready access to the slit lamp-mounted pachometer following routine biomicroscopy without switching the patient to another area for specular microscopy. The use of the specular microscope for measurement of corneal thickness would seem to be reserved for instances where endothelial cell counts were also being performed or in cases of large, clinical studies where a highly skilled assistant could routinely perform both tests (corneal thickness and cell counts). In summary, it would appeal* that specular microscopy offers a very real and valuable alternative to the measurement of corneal thickness. The measurements are precise and reproducible, and the technique offers the great advantage of having skilled technical personnel available for repeated studies, not only of cell morphology and cell density measurements but also, at the same time, of the measurement of corneal thickness.