The different company produces the flexometer supposition's cornea refraction index is different, the range of variation is 332~3372, the most companies use 33 In the cornea refractometer's system, has cornea's radius of curvature besides the sign, but also the sign has the corresponding cornea refraction  cheapest oakley sunglasses strength, these cornea refraction strength's number of degree is calculates according to the supposition cornea refraction index, cannot the direct measurement. The cornea refraction strength and the cornea refraction index, and cornea's radius of curvature and so on relations, the available following formula indicated: D= (N-N')/R .

And: D represents take diopter (D) as unit's cornea refraction strength; N on behalf of cornea's refraction index (multipurpose supposition value); N'daibiao air refraction index; R represents take the rice as unit's cornea front surface average curvature radius. The cornea curvature creates the artificial lens number of degree counting error's 3 primary causes is:?Uses the supposition the cheap oakley sunglasses sale cornea refraction index.?Because cataract patient has poor eyesight, is unable to regard the survey error which firmly and so on reasons create.?After surgery's cornea curvature is different before the surgery the cornea curvature. Beforehand angle secure reason big margin, after the technique, the cornea is flat, the average error reduces O.50D, but with modern micro technology, after the technique, the cornea tendency changes raised, says accurately, is the vertical meridian radius of curvature changes is small.

If before the technique, patient's cornea is the horizontal meridian radius of curvature is smaller than the vertical meridian (counter-gauge astigmatism), then after the technique, the cornea becomes the trend spherical surface, before the radius of curvature reading is smaller than a technique. Moreover, when survey cheap oakley sunglasses for sale the patient does not cooperate, the eyeball has the external force to oppress (for example eyelid), surveys outside region deviation optical center 3mm, the epithelia corneal incomplete as well as the cornea counts axial inconsistent and so on may affect its accuracy obviously with the axis oculi.