J. Biophotonics 10, 1110–1114 (2017) / DOI 10.1002/jbio.201600320 1 2 3 4 5 LETTER 6 7 Diffractive corneal inlay for presbyopia 8 9 Walter D. Furlan,* ,1 Salvador Garcı´a-Delpech,2 Patricia Udaondo,2 Laura Remo´n,3 10 Vicente Ferrando,4 and Juan A. Monsoriu4 11 12 1 13 Departmento de Óptica y Optometría y Ciencias de la Visión, Universitat de València, 46100, Spain 2 14 Ophthalmology Department, Hospital Universitario La Fe, Valencia, 46026, Spain 3 15 Departamento de Física Aplicada, Universidad de Zaragoza, España 4 16 Centro de Tecnologías Físicas, Universitat Politècnica de València, Valencia, 46022, Spain 17 Received 18 December 2016, revised 13 April 2017, accepted 27 April 2017 18 19 Keywords: Presbyopia, refractive surgery, cornea, diffractive lenses 20 21 22 23 A conceptually new type of corneal inlays for a custom- roundings of the far and near foci, are also shown. 24 ized treatment of presbyopia is presented. The dif- Picture: Simulation of the appearance of the Diffractive 25 fractive inlay consists on a small aperture disc having an corneal inlay on a real eye. 26 array of micro-holes distributed inside the open zones of 27 a Fresnel zone plate. In this way, the central hole of the 28 disc lets pass the zero order diffraction and produces an 29 extension of the depth of far focus of the eye, while the 30 diffracted light through the holes in the periphery pro- 31 duce the near focus. Additionally, the micro-holes in the 32 inlay surface fulfill the essential requirement of allowing 33 the flow of nutrients through it to the cells of the cor- 34 neal stroma. Theoretical and optical-bench ex- 35 perimental results for the polychromatic axial Point 36 Spread Function (PSF) were obtained, showing an im- 37 proved performance compared to the small aperture 38 corneal inlay currently in the market (Kamra). Images 39 of a test object, obtained at several vergences in the sur- 40 41 42 43 1. Introduction the refractive index, or its curvature [2]. On the oth- 44 er hand, the small aperture corneal inlay, commer- 45 The treatment of presbyopia has been historically cially known as KamraTM (AcuFocus, Irvine, CA, 46 addressed from different perspectives: from spec- USA), is based on the pinhole effect, thanks to 47 tacles and contact lenses [1], to surgical approaches which it is possible to increase the depth of focus 48 [2]. The most recent alternative is the use of intra- (DOF) of the eye, providing good vision at inter- 49 corneal implants, also known as corneal inlays. Ac- mediate and short distances. The Kamra inlay is an 50 cording to their physical properties, this type of im- opaque (black) thin ring of polyvinylidene fluoride 51 plants can be divided in two main groups. On the (PVDF) with 3.8 mm diameter and a central aper- 52 one hand, refractive inlays are intended to locally ture of 1.6 mm [2,3]. It has 8,400 micro-holes 53 modify the power of the cornea by changing either, (of 5–11 mm diameter) randomly distributed in its 54 55 56 * Corresponding author: e-mail: [email protected] © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim J. Biophotonics 10 (2017) 1111 1 surface for facilitating the flow of nutrients to the 2 cells of the corneal stroma. With these dimensions, 3 the Kamra let pass through the central hole only 4 about 20 % of the light that reaches it, and around 5 5 % is diffracted through the permeable material. 6 Therefore, it is implanted only in one eye (mono- 7 vision). In spite of the good clinical outcomes, the 8 small aperture inlay has some shortcomings. A sig- 9 nificant reduction in the contrast sensitivity of the 10 surgical eye has been reported [3]; which is caused 11 by the combination of the small aperture (pinhole 12 effect) and the diffracted light by the micro-holes in 13 the opaque ring. Additionally, under low illumina- 14 tion, the use of a small aperture inlay could make 15 reading difficult, and also can cause problems in 16 stereoscopic acuity due to the differences between 17 the luminance of retinal images [4,5]. 18 In this letter we present a conceptually new ampli- 19 tude corneal inlay, with improved light throughput. 20 This Diffractive Corneal Inlay (DCI), in addition to 21 produce an extension of the depth for the far focus of 22 the eye, it creates a near focus taking advantage to the 23 light diffracted by the nutrient micro-holes in its sur- 24 face. Numerical simulations of the axial PSF are pre- 25 sented for different pupil diameters. The improved fo- 26 cusing and imaging performance of the DCI is Figure 1 a) Diffractive Corneal Inlay (DCI) (see the main 27 demonstrated with experiments performed under pol- text for details of design parameters); b) Small aperture 28 ychromatic illumination in an optical bench. inlay with the dimensions of the Kamra. Dashed red lines 29 in a) and b) represent the 3 and 5 mm diameter pupil. c) Monochromatic theoretical axial PSFs for 45 nm (blue 30 line), 550 nm (green line) and 650 nm (red line) computed 31 2. Diffractive inlay design for a 3 mm pupil diameter (c) and 5 pupil diameter (e). d) 32 and f) Idem c) and d) but computed for the small aperture 33 The main idea behind the design of the DCI is to inlay. 34 exploit the intrinsic diffraction produced by the nu- 35 trient-permeable micro holes, redistributing them in 36 annular zones that coincide with those of an ampli- 37 tude Fresnel zone plate (see Figure 1a), to create a by the light diffracted by the micro-holes in the an- 38 diffractive lens. A similar concept, called photon nuli (first diffraction order). Hence, the effects of 39 sieve, was proposed formerly by Kipp et al. [6] for the high diffraction orders on the far and near im- 40 focusing X-rays. ages are minimized, because of the destructive inter- 41 A photon sieve is in fact a variation on the Fres- ferences produced by the spatial distribution of the 42 nel zone plate, which instead of alternate trans- micro-holes [6,9]. Moreover, the spatial distribution 43 parent and opaque rings of equal area, is an opaque and diameter of micro-holes in each zone can also 44 disc with non-overlapping pinholes distributed in the be modified to obtain an optimized relative intensity 45 corresponding transparent Fresnel zones. It was re- between the near and far foci, and/or to correct high 46 ported that photon sieves can achieve a sharper fo- order ocular aberrations. A typical example of a 47 cus by suppressing the secondary maxima and high- DCI is shown in Figure 1a. The construction param- 48 er-order diffraction effects as compared to a Fresnel eters are listed in Table 1, in comparison with the 49 zone plate [6–9]. Accordingly, the diffractive corneal only small aperture inlay available on the market: 50 inlay (DCI) here proposed, is a single micro- the Kamra, shown Figure 1b. 51 structured device (with any substrate) that combines As can be noted, in this particular example the 52 the concepts of small aperture inlay and photon distribution of the micro-holes in Figure 1a alter- 53 sieve. Therefore, a DCI has two main foci: one, the nates an azimuthal sequence of two and three holes 54 far distance focus, which is formed mainly by the per zone. 55 light that passes through the central hole; and the To evaluate the focusing properties of the DCI 56 other one, the near distance focus, that is generated we have computed the axial irradiance provided by www.biophotonics-journal.org © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1112 W. D. Furlan et al.: Diffractive corneal inlay 1 Table 1 DCI and Kamara corneal inlays construction parameters. 2 3 Design wave- Addition Central External di- Total number of Maximum hole di- Minimum 4 length (Ad) hole ameter holes ameter hole di- 5 diameter ameter 6 DCI 550 nm 1.50 D 2.00 mm 4.15 mm 2,290 30.5 mm 18.8 mm 7 8 KAMRA 550 nm NA 1.60 mm 3.80 mm 8,400 11 mm5mm 9 10 11 both devices under plane wave coherent illumina- 12 tion. By using the Fresnel approximation, we nu- 13 merically computed monochromatic irradiances for 14 different wavelengths [10] and two pupil diameters: 15 3.00 mm and 5.00 mm. These pupils diameters were 16 selected because they are representative for people 17 from 40 to 60 years old, in bright and dim environ- 18 ments respectively [11] and also because they were 19 adopted in other studies dealing with Kamra [12]. 20 The results are shown in Figures 1c–1f. As expected, 21 the diffracted intensities are wavelength-dependent 22 with maximum irradiances for the design wave- 23 length. As can be noted in Figures 1e and 1f, the 24 5.00 mm pupil allows the light to pass outside the in- Figure 2 Scheme of the experimental setup employed to 25 lays increasing the values of the axial intensity, and obtain the polychromatic axial PSF.A 30 mm pin-hole 26 creating an interference pattern along the optical (PH) acts as a point object. LP 458 are linear polarizers to 27 axis. Note that, for each pupil diameter, the same allow the system to work in amplitude-only mode. L1 and 28 normalization was adopted to represent the results L2 are achromatic lenses of 200 mm focal length.