Abstract
Purpose :
In addition to providing visual correction of aphakia, toric intraocular lenses (TIOL) correct pre-existing corneal astigmatism, increasing the spectacle independence for distance vision. For performing preclinical image quality measurements (IQMs) on TIOLs, the ISO 11979-2: 2014 standard indicates two alternative methods: measuring on both low and high power meridians or using a null lens for cylinder compensation. The purpose of the study is to provide a comparative analysis of the IQMs performed on TIOLs with and without toric null lenses (TNLs).
Methods :
TNLs with cylinder powers ranging from 1.00 to 8.00 D (10 individual powers) were fabricated from transparent thermoplastic polymer. On an optical bench, the TNLs were mounted in front of an ISO11979-2 eye model fitted with a pupil, a model 2 cornea and a TIOL immersed in a water cell. Both horizontal and vertical slits as well as USAF targets were imaged by means of a CCD camera. For each meridian, through focus and through frequency modulation transfer function (MTF) curves were subsequently acquired. Across the cylinder power range, Tecnis Toric 1-piece IOLs with 20.0 D spherical equivalent (SE) power were measured with and without null lens utilizing a 5 mm pupil, water and green light (550 nm) conditions.
Results :
Measurement results indicate that TNLs effectively compensate TIOLs’ astigmatism leading to IQM results comparable to the case without null lenses. As an example, for repeated measurements, for a TIOL with 20.0D SE power and 4.00D cylinder power, at 50 c/mm and averaged across meridians, the MTF difference between the without and with TNL is 0.03 with a SD of 0.02 for both test cases. On average, across all toric powers, at 50 c/mm, the best focus MTF differences between with and without TNL measurement cases is less than 4%. For two orthogonal meridians, the through focus MTF measurements evidenced best foci position relative defocus values inferior to 0.15D in the IOL plane, indicating the compensation by the TNL of the TIOL’s cylinder. For the test cases using a TNL, the best focus USAF target images qualitatively demonstrated a good overall image quality.
Conclusions :
The current study demonstrated the feasibility of utilizing TNLs to compensate TIOL cylindrical power and measure its IQ. Once TIOL’s astigmatism is canceled, the measurements are less sensitive to system alignment, enabling IQMs for a rotationally symmetric IOL.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.