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[The characteristics of the optically calculated axial length and the predicted refraction when using the
1Department of Ophthalmology, Iwate Prefectural Kitakami Hospital, 3-15-36 Kunenbashi, Kitakami 024-0063, Japan.
Purpose:
To understand the effect of the error in corneal refractive power on the optically calculated axial length (AXO) and the postoperative predicted refraction (Q'gl) calculated from the aphakic refraction (Qaph).
Method:
We used the Gullstrand's schematic eye, in which the intraocular lens (+20 D) was inserted at a depth of 5 mm, and calculated Qaph and postoperative refraction (Qgl) geometrically when the corneal radius of the anterior surface (Rfc) changed from 7 mm to 9 mm. AXO was calculated using the calculation formula from a previous report, and then Q'gl was calculated from the AXO and the true axial length (AXT) using the theoretical calculation formula (regarding the fictitious corneal refractive index as 1.3315).
Results:
When the measured corneal radius of the anterior surface (K) was equal to Rfc, the error of the AXO was largest (AXO/AXT = 101.512) when K was 9 mm. The error in power prediction (Qgl-Q'gl) of the AXT was 7.7 times larger than that of AXO.
Conclusion:
If K is exact, AXO is useful to predict the intraocular lens depth because the error of AXO is small. The error in power prediction of AXO is smaller than that of AXT.