A comparison of small aperture implants providing increased depth of focus in pseudophakic eyes

Presbyopia is characterized by a decreasing ability of accommodation - the eye's ability to alter the focus between far and near distance objects. After cataract surgery, accommodation is completely lost. Several years ago, small aperture (pinhole) implants have been presented in order to increase the depth of focus providing functional vision at far and near distance without the need for spectacles. We simulated the theoretical depth of focus with three different pseudophakic eye models in order to investigate the potential benefit arising from the implantation of small aperture optical (SAO) implants. The purpose was to compare the achievable defocus range of a SAO intraocular lens with a SAO corneal inlay.

We created three pseudophakic eye models with an aberration correcting intraocular lens (IOL): one with a corneal SAO implant (M1), a second one with a SAO intraocular lens (M2) and a third one with a conventional intraocular lens of the same optical design but without SAO (M0). Defocus curves were created by varying the focal length of a thin lens in front of the eye - which mimics the clinical assessment of defocus curves.

With a Strehl ratio threshold of 0.05, the reference design M0 provided a maximum defocus range of approximately 1.7D (with a 2.0mm pupil) whereas both pinhole implants (M1 and M2) showed a defocus range up to 3.0 and 3.3D, respectively. With large natural pupil diameter, where light passes outside the SAO aperture, the defocus range drops to 0.8D/0.7D for M1 and M2 compared to 0.7D with M0.

The SAO intraocular lens showed a similar defocus range as the SAO corneal inlay. Both concepts have the potential of increasing depth of focus compared to a conventional intraocular lens. In case of large physiological pupil diameters these advantages of SAO implants may be lost.