Watch On-Demand Study Sessions

Total Lens Power

This video shows how, mathematically, the three curves of a lens work together to create the total power of the lens. It explains that the back curve of a modern ophthalmic lens is always minus. When the minus curve is then combined with a front curve, the optical cross method shows that the total power of the lens curves results in the two true powers.

Uploaded on: 2 days ago

Prism Direction and Prentice’s Rule

Highlighted with diagrams and step-by-step mathematical determination, this video answers many questions about what unwanted prism is and how to find the power of the prism.

Uploaded on: 2 days ago

The Optical Cross

An optical cross can be used to map out how the front curve diopter combined with the ocular curve diopter results in the two true powers. This video shows how using an optical cross, the optician can easily find the “missing” curve diopter of a lens when the other two curves are known. It can also be used to determine the ocular curve(s) when the base curve is known or determined.

Uploaded on: 2 days ago

Diopter to Radius

The diopter of a lens and its radius have a scientific consistency, and this video shows the relationship of the two lens factors. It diagrams easy ways to see that when one factor increases, the other decreases, and why this is important.

Uploaded on: 2 days ago