Spectacle lens power over what diopter strength requires compensation for vertex distance?

In ophthalmic optics, vertex distance refers to the distance from the back surface of the lens to the front surface of the eye. As the power of the lens increases, the effect of the vertex distance on the effective power of the lens becomes more pronounced. When the spectacle lens power exceeds a certain threshold, changes in vertex distance can significantly affect the perceived strength of the lens.

The general guideline is that if the spectacle lens power is greater than approximately 7.00 diopters, adjustments need to be made for the vertex distance to ensure accurate prescription performance. This is because as the power increases, any change in the vertex distance can lead to a substantial difference in how the lens performs optically, potentially causing either undercorrection or overcorrection of the refractive error.

Thus, spectacle lenses with a power of 7.00 diopters or higher warrant careful consideration of vertex distance to guarantee that the patient receives the intended visual correction.