When verifying glasses with a lensometer, which lens should be measured first?

When verifying glasses with a lensometer, measuring the lens with the strongest power at 90 degrees first is crucial due to its impact on the overall optical performance. The strongest lens typically determines the primary sphere of vision and is essential for ensuring that the corrective effect is accurate.

By measuring this lens first, you establish a strong reference point, allowing you to ensure that subsequent readings for other lenses are directly correlated to this dominant lens. This approach also emphasizes the importance of properly orienting the lens in the lensometer to capture the effect of any cylinder power that may be associated with it.

This method leads to improved accuracy in the results, as it simplifies the process by allowing for the detection of any discrepancies in lens power right from the start. In comparison, measuring the weakest power, least curvature, or highest index of refraction first may lead to complications or inaccuracies in correlating the measurements across the lenses. Therefore, focusing on the strongest power at the correct orientation enhances verification efficiency and reliability in optical examinations.