Development of a novel multifocal lens using a polarization directed flat lens: possible candidate for a multifocal intraocular lens

Abstract

Background: A polarization-directed flat (PDF) lens acts as a converging lens with a focal length (f) > 0 and a diverging lens with f < 0, depending on the polarization state of the incidental light. To produce a multifocal lens with two focal lengths, a PDF and a converging lens having shorter focal length were combined. In this study, we tested a bifocal PDF to determine its potential as a new multifocal intraocular lens (IOL).

Methods: Constructed a multifocal lens with a PDF lens (f = +/- 100 mm) and a converging lens (f = + 25 mm). In an optical bench test, we measured the defocus curve to test the multifocal function. The multifocal function and optical quality of the lens in various situations were tested. An Early Treatment Diabetic Retinopathy Study (ETDRS) chart as a near target and a building as a distant target were photographed using a digital single-lens reflex (DSLR) camera. Both lenses (multifocal and monofocal) were tested under the same conditions.

Results: For the 0 D and - 20 D focal points, the multifocal lens showed sharp images in the optical bench test. In the DSLR test using the multifocal lens, the building appeared slightly blurry compared with the results using the monofocal lens. With the multifocal lens, the ETDRS chart's images became blurry as the ETDRS chart's distance decreased, but became very clear again at a certain position.

Conclusions: We confirmed the multifocal function of the multifocal lens using a PDF lens. This lens can be used as a multifocal IOL in the future.

Keywords: Multifocal lens; Polarization-directed flat: intraocular lens.

Fig. 1

Polarization-directed flat (PDF) lens. When the incidental light is right-handed circular polarization (RHCP), the focal length of the PDF lens is positive. On the other hand, left-handed circular polarization (LHCP) generates a negative focal length. That is, the PDF lens acts as a converging lens with focal length (f) > 0 and a diverging lens with f < 0, depending on the polarization state of the incidental light

Fig. 2

The principle of the new multifocal lens. By combining a polarization-directed flat (PDF) lens and a converging lens with a shorter focal length, a multifocal lens with 2 focal lengths can be constructed

Fig. 3

The polarization-directed flat lens used in this study. A focal length +/− 100 mm, diameter 25 mm, and thickness 0.45 mm; B Concentric rings could be seen under a stereomicroscope (X20)

Fig. 4

Optical bench test setting. A white light-emitting diode (LED; 3-3/4 in. LED Square Plate for Microscopes, AmScope), USAF 1951 resolution target (2“ x 2” Negative 1951 USAF Hi-Resolution Target, Edmund Optics), Badal lens (achromatic lens, focal length + 25 mm; Thorlabs Inc.), 4 mm-diameter pupil, PDF lens (focal length +/− 100 mm), achromatic lens (focal length + 25 mm), and charge-coupled device (CCD) camera (acA1600-20uc, Basler, Ahrensburg, Germany) were arranged linearly

Fig. 5

USAF 1951 resolution target. As a reference template image for obtaining the cross-correlation coefficient, a middle rectangular area was selected and analyzed from a clear USAF resolution image (from group 2 to 7 elements)

Fig. 6

Digital single-lens reflex (DSLR) camera test setting. To test the multifocal lens, a 4-mm pupil, focal length +/− 500 mm (+/− 2 D) PDF lens (provided by Professor Seok Ho Song), achromatic lens (focal length 100 mm), and a DSLR camera were used

Fig. 7

Polarization-directed flat (PDF) lens used for digital single-lens reflex (DSLR) camera test. This PDF lens has a focal length of +/− 500 mm (+/− 2 D) depending on the polarization state of the incidental light and allows some of the light to pass through without refraction. Combining this PDF lens with an achromatic lens (focal length 100 mm, + 10 D) results in a trifocal lens (+ 8, 10, 12 D)

Fig. 8

Optical bench test (monofocal lens). This figure shows USAF resolution of target images taken with a monofocal lens. With the monofocal lens, the image was sharpest (in focus) when the distance between the USAF target and Badal lens was 25 mm (0 D), but the images quickly became blurry when it was out of focus

Fig. 9

Optical bench test (multifocal lens). With the multifocal lens, when the distance between the USAF resolution target and Badal lens was 25 mm (0 D), the USAF resolution target image was clear. As the distance decreased, the image became blurry, but the image became clear again when the distance between the USAF resolution target and Badal lens was 12.5 mm (− 20 D)

Fig. 10

Cross-correlation coefficient of monofocal and multifocal lens. The cross-correlation coefficient curve of monofocal lens showed a very high and narrow peak centered at 0 D. The cross-correlation coefficient curve of multifocal lens showed the profile of a bifocal lens showing two peaks, at 0 D (cross-correlation coefficient: 0.878) and − 20 D (cross-correlation coefficient: 0.863)

Fig. 11

The images at near and distant focus taken with blue (top), green (middle), and red (bottom) filters. In quantitative analyses, the cross-correlation coefficient was 0.907 at distant focus and 0.914 at near focus with a blue filter. The cross-correlation coefficient was 0.872 at distant focus and 0.910 at near focus with a green filter. The cross-correlation coefficient was 0.888 at distant focus and 0.906 at near focus with a red filter

Fig. 12

Digital single-lens reflex (DSLR) camera test (Far distance, day). This figure shows a far-distant building photograph taken with a monofocal lens (A) and a multifocal lens (B). With the monofocal lens, the building appeared very clear. With the multifocal lens, the building appeared slightly blurry compared with the results from the monofocal lens. This was especially true around bright objects. Chromatic aberration was observed around the bright objects

Fig. 13

Digital single-lens reflex (DSLR) camera test (Near distance). With the monofocal lens, as the distance from the Early Treatment Diabetic Retinopathy Study (ETDRS) chart decreases, the images become increasingly blurry. With a multifocal lens, as the distance from the ETDRS chart decreases, they become very clear at a certain position. At this position, the distance between the pupil and ETDRS chart was approximately 500 mm. As the distance becomes smaller, it becomes blurry again. A Monofocal lens (the distance between the achromatic converging lens surface and the DSLR camera sensor: 660 mm); B Monofocal lens (distance: 500 mm); C Multifocal lens (distance: 660 mm); D Multifocal lens (distance: 500 mm)

Fig. 14

Digital single-lens reflex (DSLR) camera test (Far and near distance). With the monofocal lens, the building appeared very clear (A) but the letters in the ETDRS chart were very blurry at a distance of approximately 500 mm (B). With the multifocal lens, the building appeared slightly blurry (C) compared with the image from the monofocal lens, but the letters in the ETDRS chart appeared very clear (D) at a distance of approximately 500 mm