Abstract
Purpose: :
Although a few recent studies have used objective image analysis to determine toric intraocular lens (IOL) rotation and centration, the repeatability of the technique has not been assessed.
Methods: :
Forty patients implanted with the Akreos AO Aspheric IOL with orientation marks in one eye were dilated and the intraocular lens imaged at 10x magnification in retroilluminantion using a CSO SL-990 digital slit-lamp biomicroscope. Images of resolution 1392x1040 were analysed using purpose designed Labview software. The axis of rotation of the IOL was determined by drawing a line to join the IOL orientation marks and normalise for any rotation of the eye in front of the slit-lamp between visits by comparing the axis of a line joining two consistent conjunctival vessels or iris features. The centre of ovals overlaid to circumscribe the IOL optic edge and the limbus were compared to determine the IOL centration. Two images of each eye were captured and analysed immediately after surgery to assess intra-session repeatability of the technique and two patients images were analysed 10 times to assess the repeatability of the analysis. Images were also captured two days after surgery to assess the initial rotational stability of the Akreos AO Aspheric IOL with orientation marks.
Results: :
The standard deviation of intra-session rotation of the IOL was ±0.79º and centration was ±0.10mm horizontally and ±0.10mm vertically. The standard deviation of repeated analysis of the same image IOL rotation was ±0.70º and centration was ±0.20mm horizontally and ±0.31mm vertically. Stability of the Akreos AO Aspheric IOL with orientation marks over the first two days after surgery was 4.2±5.4º (70% within 5º, 89% within 10º) for absolute rotation and 0.24±0.20mm (89% within 0.5mm, 100% within 1.0mm) for horizontal and 0.21±0.14mm (94% within 0.5mm, 100% within 1.0mm) for vertical absolute centration. Eye rotation (absolute) with the head stabilised on a chin and forehead rest between the visits was 3.1±2.8º (84% within 5º, 97% within 10º)
Conclusions: :
Objective analysis allows sensitive assessment of toric IOL stability. Eye rotation between images can lead to significant errors if this is not compensated for. The Akreos AO Aspheric IOL with orientation marks is relatively stable in the eye over the initial period following implantation.
Keywords: intraocular lens • astigmatism