Corneal eccentricity as a tool for the diagnosis of keratoconus.

Ninety-nine eyes with keratoconus of 64 patients were examined using the sagittal radii method to determine the corneal flattening and compared with 100 eyes of 50 healthy controls. To express the degree of this flattening, four numerical eccentricity (E) values for each eye were calculated. The highest E value of the four was chosen as a parameter for diagnosis of the disease. In keratoconus patients in whom the highest E values of keratoconus eyes were > or = 0.8, the specificity of the test was 98% and the sensitivity was 97%. This abnormal eccentricity was observed in keratoconus eyes with a visual acuity of 1.0, whereas slit-lamp examination showed no abnormalities. This study demonstrates that eccentricity can be helpful to diagnose keratoconus at an early stage.

Four years experience with a mercury shielded irregular field system (MSIFS).

A mercury shielded irregular field system (MSIFS) has been in use in our department since January 1979. The system is described and illustrated. Experience in treating 225 patients demonstrated that the system is accurate and reproducible. The system offers a choice of shielding efficiency in a transmission range from 100 to 3.5% for 18 MV photons. Routine measurements of mercury vapor concentration in the treatment room showed values below 0.02 mg Hg/m3 air. (The maximum acceptable concentration in The Netherlands is 0.05 mg Hg/m3 air.) It is concluded that the system is cost-effective, easy to use, and flexible and safe.