Hi, i think you can measure de intraocular pressure with and without contact lens using the Goldmann tonometer, and use de Young Modulus to calculate the elasticiti.

Hi. I am measuring the IOP over 4 different disposable contact lenses with varying modulus with the rebound tonometer as well as the ORA. So far the results are interesting with the IOP on average being lower measured over the lenses of varying powers except with the higher modulus Pure Vision lenses. I have the CH and CRF data but thought it would make sense to calculate the combination modulus in the final analysis. I will have a look at Liu and Roberts paper and see if I can use the data I have to work it out. CH should give a good idea. Thanks for your help.

Hi Dirk

Threre are always shear Movements between cornea and contact lens. Therefore i domt think that the assumption of a combination is appropriate in this case. if you apply stress to the cornea, corneal modulus is valid, the same is valid in the case of the lens. In the case of bending both together, I would calculate both bending forces separately and add them.

Best regards Hartmut Kanngiesser

Thanks Hartmut

Makes sense, I will give this a go. I wonder if the CH and CRF can be used to estimate the modulus? According to the Reichert (2013), CH represents ocular resistance due to the combined effects of CCT, ocular rigidity, and the corneas viscoelastic properties. CRF is dominated by the elastic properties of the cornea and appears to be an indicator of the overall resistance of the cornea. The problem is that CH and CRF are specific responses to the ORA measurement process and can therefore not be considered corneal properties. It would be interesting to compare these values with a calculated value.

Hi Dirk,

The reliability of calculated values is always questionable because of the nonlinearity and anisotropy of corneas behavior. Cornea may not be calculated as a bulk material. To my knowledge the interaction between the layers of the corneal structure has not been calculated satisfactory in general but only for specific stress cases so far. Thats why you find many contradictory values in the literature.

Best Hartmut