Measurement and Prediction of Tilt and Decentration of the Clareon Intraocular Lens and Evaluation of It's Effect of Visual Acuity

During cataract surgery an artificial intraocular lens is implanted in the eye to replace the lens and to correct the refraction for distance vision. Misalignment of intraocular lenses can cause severe loss of visual quality. Different types of misalignments are known. Tilt, one type of intraocular lens misalignment is thought to play a negative role for the optical performance in eyes with intraocular lens designs, especially, if they have aspheric, toric, or multifocal optics. For example, in the case of aspheric intraocular lenses, it appears that even slight amount of tilt may result not only in the loss of the effect of reducing spherical aberrations but in more severe cases even a worsening of the optical quality compared to spherical intraocular lenses. In the case of toric intraocular lenses, tilt introduces higher order aberrations potentially mimicking astigmatism. In the case of multifocal intraocular lenses, tilt increases higher order aberrations, which leads to decreased visual quality.

Various methods to measure intraocular lens misalignments have been described. Studies assessing the intraocular lens position have used subjective grading methods at the slit lamp examination or a Scheimpflug camera to assess intraocular lens decentration and tilt. The subjective grading at the slitlamp may display considerable variability between examiners. This method is more qualitative than quantitative and does not allow fine resolution when reporting intraocular lens tilt. The fact that the patient has no standardized target to focus on makes the method even less reliable. Scanning methods such as Scheimpflug photos require a very well dilated pupil exceeding 6mm to assess the intraocular lens position. Additionally, it can be difficult to identify the anatomical structures of the eye that need to be used as points of reference. Scheimpflug camera images have been used for assessing intraocular lens tilt previously, but erroneous results, often due to corneal magnification, have diminished their widespread use. Another possibility to assess tilt is the use of Purkinje reflexes. The light reflections of Purkinje images at ocular surfaces to evaluate ocular alignment have recently been utilized. Since light is reflected at all interfaces of media with a difference in refractive index, these reflections, called Purkinje images, can be used to assess tilt and decentration of intraocular lenses. Two different clinically applicable Purkinjemeter system provide the measurement of intraocular decentration and tilt. The main problem with Purkinje meters is accessibility, as there are only a few prototypes available worldwide.

The most recently developed method for tilt quantification is the use of optical coherence tomography. This method has several advantages compared to the previous methods: optical coherence tomography based devices are available in most clinics, the resolution of modern optical coherence tomography devices is high, and the measurements are reproducible.