Immersion in Optical

Question

We received information at the Academy meeting that when performing immersion A-scan to still place the measurement in the ‘Optical’ field for the Holladay calculation. Only use the Ultrasound field for contact A-scan. Is this correct information?

Answer

Yes … immersion Ascan and Optical biometry give the same mean for large groups. However, the Optical Keratometers give 0.3 D flatter K readings than the manual keratometer requiring an 0.3 D higher Aconstant. As long as you use the Optical Keratometer (not manual), then the immersion AL should be the same.