Method for manufacturing aphakic intraocular lens
A method of manufacturing an aphakic intraocular lens that is capable of ensuring every multi-focusing effect more securely, while reducing the impact of aperture changes and lens eccentricity. At least two reliefs whose first order diffracted lights give respective focal distances different from one another are set to overlap with each other in at least a part of an area in a radial direction of the lens, and with respect to every grating pitches of one relief having a maximum grating pitch among the reliefs set up in overlap, grating pitches of another relief are overlapped periodically in order to obtain a relief pattern, so that the resulting relief pattern is formed on a lens surface.
1. An aphakic intraocular lens adapted to be set in place in a lens capsule, and provided with a diffraction grating having a relief pattern extending concentrically on a lens surface, comprising:
a synchronous structure where various types of reliefs including at least two reliefs whose first order diffracted lights give respective focal distances different from one another are set to overlap with each other in at least a part of an area in a radial direction of the lens, and with respect to every grating pitches of one relief having a maximum grating pitch among the reliefs set up in overlap, grating pitches of another relief being overlapped periodically.
2. The aphakic intraocular lens according to claim 1 , wherein a focal distance different from that of any first order diffracted light generated by the various types of reliefs is set for a 0th order light by a refractive surface of the lens.
3. The aphakic intraocular lens according to claim 2 , wherein the lens surface formed with the relief pattern is the refractive surface.
4. The aphakic intraocular lens according to claim 1 , wherein each relief depth of the relief having the maximum grating pitch, which is obtained by overlapping the various types of reliefs, is made constant in a zone direction.
5. The aphakic intraocular lens according to claim 4 , wherein in each zone in the relief having the maximum grating pitch, another type of relief with at least two relief depths is formed in the area in the radial direction of the lens where the various types of reliefs set up in overlap, and dimensions of the at least two relief depths relative to a virtual base curve surface vary gradually in the zone direction.
6. The aphakic intraocular lens according to claim 4 , wherein in each zone in the relief having the maximum grating pitch, another type of relief with at least two relief depths is formed in the area in the radial direction of the lens where the various types of reliefs set up in overlap, and dimensions of the at least two relief depths relative to a virtual base curve surface are set constant in the zone direction.
7. The aphakic intraocular lens according to claim 1 , wherein each of the various types of reliefs has a ridge line extending circumferentially with a cross-section formed with an acute vertex angle and a valley line extending circumferentially with a cross-section formed with an acute included angle.
8. The aphakic intraocular lens according to claim 1 , wherein a 0th order light by a refractive surface of the lens is set to a focus for far vision, the first order diffracted light by one type of the relief is set to a focus for near vision, and the first order diffracted light by another type of the relief is set to a focus for intermediate vision.
9. The aphakic intraocular lens according to claim 1 , wherein a 0th order light by a refractive surface of the lens is set to a focus for near vision, the first order diffracted light by one type of the relief is set to a focus for far vision, and the first order diffracted light by another type of the relief is set to a focus for intermediate vision.
10. The aphakic intraocular lens according to claim 1 , wherein the various types of reliefs are arranged to satisfy a following equation:
A =(2( m−NM )+ a )/ N
where A is a zone constant of the one relief, ‘a’ is a zone constant of the other relief, M is a zone number of the one relief, m is a zone number of the other relief, and N is a ratio of a focal distance of the one relief relative to that of the other relief, which is expressed as:
(focal distance of the one relief)/(focal distance of the other relief).
11. The aphakic intraocular lens according to claim 1 , wherein the various types of reliefs are arranged to satisfy a following equation:
D ≦λ/( N lens −N med )
where D is a dimension of a relief depth, λ is a design wavelength, N lens is a refractive index of an optical material, and N med is a refractive index of a surrounding medium.