[The characteristics of the optically calculated axial length and the predicted refraction when using the intraoperative refraction].
OBJECTIVE
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).


METHODS
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.


CONCLUSIONS
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.
Iwami
S
S
Department of Ophthalmology, Iwate Prefectural Kitakami Hospital, 3-15-36 Kunenbashi, Kitakami 024-0063, Japan.
Senoh
K
K
D003315:Cornea / Q000033:anatomy & histology*; D006801:Humans; D007910:Lenses, Intraocular; D008433:Mathematics; D008962:Models, Theoretical; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000175:diagnosis