YY 0290.2-2021 PDF in English
YY 0290.2-2021 (YY0290.2-2021) PDF English
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Ophthalmic optics -- Intraocular lenses -- Part 2: Optical properties and test methods
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Standards related to: YY 0290.2-2021
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YY 0290.2-2021: PDF in English YY 0290.2-2021
YY
PHARMACEUTICAL INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 11.040
C 40
Replacing YY 0290.2-2009
Ophthalmic optics - Intraocular lenses - Part 2: Optical
properties and test methods
(ISO 11979-2:2014, MOD)
ISSUED ON: MARCH 09, 2021
IMPLEMENTED ON: APRIL 01, 2023
Issued by: National Medical Products Administration
Table of Contents
Foreword ... 3
Introduction ... 6
1 Scope ... 7
2 Normative references ... 7
3 Terms and definitions ... 7
4 Requirements ... 8
Appendix A (Normative) Measurement of optical power ... 14
Appendix B (Normative) Measurement of resolution ... 24
Appendix C (Normative) Measurement of MTF ... 27
Appendix D (Informative) Precision of optical power measurements ... 34
Appendix E (Informative) Precision of image quality measurement ... 35
Appendix F (Informative) Verification of ray tracing calculations ... 36
References ... 37
Ophthalmic optics - Intraocular lenses - Part 2: Optical
properties and test methods
1 Scope
This Part specifies the main optical performance requirements and test methods of
intraocular lenses (IOLs).
This Part applies to spherical, aspheric, monofocal, toric, multifocal and/or
accommodating intraocular lenses, which are implanted in the anterior segment of the
human eye. The generic character "intraocular lens (IOLs)" used in this Part also
includes phakic intraocular lens (PIOL).
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
GB/T 4315.1 Optical transfer function - Part 1: Terminology and symbol (GB/T
4315.1-2009, ISO 9334:2007, MOD)
GB/T 4315.2 Optical transfer function - Part 2: Directives of measurement (GB/T
4315.2-2009, ISO 9335:1995, MOD)
GB/T 9045-2006 Photography - Photographic materials - Determination of ISO
resolving power (ISO 6328:2000, IDT)
YY 0290.1 Ophthalmic implants - Intraocular lenses - Part 1: Terminology (YY
0290.1-2008, ISO 11979-1:2006, MOD)
YY 0290.3 Ophthalmic implants - Intraocular lenses - Part 3: Mechanical properties
and test methods (YY 0290.3-2018, ISO 11979-3:2012, MOD)
YY 0290.4 Ophthalmic implants - Intraocular lenses - Part 4: Labeling and
information (YY 0290.4-2008, ISO 11979-4:2000, IDT)
3 Terms and definitions
The terms and definitions, which are defined in YY 0290.1 and GB/T 4315.1, apply to
4.3.1 Overview
Image quality depends on the match between the optical design of the IOL and the
optical performance evaluation conditions. Image quality can be expressed by
resolution or modulation transfer function (MTF) value, under specified spatial
frequency conditions. Perform the resolution test, according to the method specified in
Appendix B. Perform the modulation transfer function (MTF) test, according to the
method specified in Appendix C.
The modulation transfer function (MTF), which is determined by the method described
in Appendix C, is related to the matching -- between the optical design and the model
eye suitable for optical performance evaluation. For the method described in Appendix
C, example model eye parameters have been given. The manufacturer may also propose
an equivalent method or model eye suitable for the intended use and design optical
properties. In such cases, the model eye and method shall be adequately described,
along with justification for its applicability. Unless otherwise specified, image quality
requirements apply to all available optical powers.
If, due to theoretical limitations, negative and low power intraocular lenses, which has
the simulated eye described in Appendix C, do not apply to the requirements specified
in 4.3.2 ~ 4.3.6, the manufacturer shall verify the applicable spatial frequency and
requirements.
If the image quality of a specially designed intraocular lens for a special purpose is not
applicable to the requirements specified in 4.3.2 ~ 4.3.6, the manufacturer shall set and
verify the applicable spatial frequency and requirements.
Note 1: The optical resolution is expressed in terms of spatial frequency. The unit is usually line
logarithm/mm (lp/mm) or cycle/mm (c/mm or mm-1). In ophthalmology literature, the
commonly used unit is cycle/degree (c/degree). For the eyes, the image square node distance is
considered to be 17 mm; the conversion formula between the two is as follows:
c/degree = 0.297 × c/mm
Note 2: The test aperture, which is provided in 4.3 and Appendix A, Appendix B, Appendix C,
indicates the central area of the test intraocular lens exposure, which is different from the
aperture stop of the test system.
4.3.2 Monofocal intraocular lenses
4.3.2.1 Overview
The image quality of monofocal intraocular lenses shall meet any of the requirements
specified in 4.3.2.2, 4.3.2.3 or 4.3.2.4.
4.3.2.2 Resolution
If tested according to the method in Appendix B, the resolution of the intraocular lens
shall not be less than 60% of the diffraction-limited cut-off spatial frequency, under the
3 mm aperture. In addition, the image shall be free of detectable aberrations other than
spherical aberration.
4.3.2.3 MTF measurement using model eye 1
If tested according to the method of model eye system 1 (C.3.1) in Appendix C, the
modulation transfer function (MTF) value of the intraocular lens, in the model eye
system, shall meet one of the following two conditions, at a spatial frequency of 100
mm-1:
a) Greater than or equal to 0.43;
b) Greater than or equal to 70% of the calculated maximum attainable value, which
is given by the design and analysis of the intraocular lens in the model eye system;
however in any case, it shall not be less than 0.28.
Note: For PMMA intraocular lenses within the range of 10D ~ 30D, the evaluation criteria given
in 4.3.2.2 and 4.3.2.3a) have good consistency.
4.3.2.4 MTF measurement using model eye 2
If tested according to the method of model eye system 2 (C.3.2) in Appendix C, the
modulation transfer function (MTF) value of the intraocular lens, in the model eye
system, shall meet the requirement that the intraocular lens, under the aperture of
greater than or equal to 3 mm, at the spatial frequency of 100 mm-1, reaches 70% of the
calculated maximum achievable value given in the design and analysis of model eye
system; however, in any case, it shall not be less than 0.28.
4.3.3 Toric intraocular lens (TIOL)
4.3.3.1 Overview
The image quality of the toric intraocular lens shall meet the requirements, which are
specified in 4.3.3.2 or 4.3.3.3.
4.3.3.2 Resolution
When using the compensating lens method in Appendix B, the resolution requirements
specified in 4.3.2.2 shall apply to the combined system of toric intraocular lens and
compensating lens.
4.3.3.3 MTF
The MTF requirements, which are specified in 4.3.2.3 or 4.3.2.4, shall apply to the
meridian of highest and lowest optical power.
Use a spectrophotometer, to measure and record the spectral transmittance of the
intraocular lens in the test solution, in the range of 300 nm ~ 1100 nm with an aperture
of 3 mm. If it is measured in air, it can be corrected, according to the principle of
specular reflection. The transmittance accuracy shall be better than ±2%; the resolution
shall not be less than 5 nm. The sample shall be an actual IOL or an alternative plate of
IOL optical material, the thickness of which shall be equal to the central thickness of a
20D IOL; meanwhile, it shall be subjected to the same manufacturing process as the
finished IOL, including sterilization.
Note 1: The aqueous humor can be replaced by saline solution, which contains 0.9% NaCl
during the test.
Note 2: If the spectral transmittance of the intraocular lens material changes with the
temperature in the solution, the spectral transmittance shall be measured, at a simulated
intraocular temperature.
Note 3: If the thickness of the test solution, in the measurement optical path, is changed due to
the insertion of the intraocular lens or the plate into the test solution during the test, then the
influence of the change in the spectral transmittance on the test results shall be analyzed and
corrected, if necessary. A feasible correction method is to measure the transmittance, within the
spectrum of the replaced equivalent thickness of the test liquid, as a correction factor.
4.4.2 Spectral transmittance record
The manufacturer shall give a record of the spectral transmittance of the intraocular
lens or equivalent with a focal power of 20D, within the wavelength range of 300 nm ~
1100 nm (for example: recorded in the instruction manual or on the packaging).
Under the same test conditions, the measured value in the spectral range of 380 nm ~
1100 nm shall be consistent with the record, which is given by the manufacturer. The
spectral transmittance shall drop by 5%, in the range above the wavelength
corresponding to the inflection point; the spectral transmittance deviation shall not be
greater than ±5%.
4.4.3 Cut-off wavelength
Spectral transmittance records shall show that the IOL is filtered out in the ultraviolet
(UV) portion of the spectrum. For an intraocular lens, which has a focal power of 20D
or equivalent, when the wavelength corresponding to the spectral transmittance of 10%
is used as the UV cut-off wavelength, the wavelength shall not be less than 360 nm.
Appendix A
(Normative)
Measurement of optical power
A.1 Overview
This Appendix gives a variety of methods for the determination of optical power. These
methods are applicable to spherical and aspheric monofocal, toric or multifocal IOLs.
The power values of all intraocular lenses are defined in the intraocular state (refer to
YY 0290.1). The peak wavelength of the light source is 546 nm ± 10 nm; the full width
at half maximum is 20 nm or less. For the measurement methods A.3 and A.4, the
diameter of the aperture stop is 3.0 mm ± 0.1 mm.
Note 1: For the detailed description of the measurement and calculation of optical power, please
refer to relevant optical books.
Note 2: It may be necessary to modify the measurement device (such as an additional convex
lens, select a microscope objective with an appropriate numerical aperture, etc.), to measure the
focal length of negative power and low power intraocular lenses.
A.2 Calculation of optical power by measuring dimensions
A.2.1 Steps
The radius of curvature, which has a diameter of about 3 mm, can be measured by a
dedicated spherometer, interferometer or optical coherence tomography (OCT). Lens
thickness can be measured by a micrometer or similar device. The calculation of optical
power adopts formula (A.1):
Simulate the state conditions in the eye, where:
F - Intraocular lens power, in diopters (D);
Ff - The optical power of the front surface of the intraocular lens, in diopters (D);
Fb - The optical power of the posterior surface of the intraocular lens, in diopters
(D);
tc - The central thickness of intraocular lens, in meters (m);
nIOL - The refractive index of the intraocular lens optical material in the intraocular
Due to the complexity of the optical design of multifocal IOLs and astigmatic IOLs,
this method is limited to monofocal IOLs.
A.3 Calculation of optical power by measuring back focal length or effective focal
length
A.3.1 Principle
The method described in A.3 assumes that measurements are made in air. However,
with appropriate adjustments, this method is also suitable for measurements in
simulated intraocular conditions.
Back vertex focal length (BFL) refers to the distance -- from the posterior vertex of the
intraocular lens to the on-axis focal point. This method has previously been used for
measurements on monofocal crystals in air.
Effective focal length (EFL) refers to the distance -- from the second principal plane of
the intraocular lens to the on-axis focal point. The effective focal length (EFL) is
measured, through the nodal slide rail.
Both methods are suitable for intraocular lens, multifocal intraocular lens, toric
intraocular lens measurements, when the following adjustments are made.
Note 1: The focus position depends on the spatial frequency used for focusing. If there is
spherical aberration, the measured lens focus position does not match the paraxial focus
position. Measuring focus is often referred to as "best focus".
Note 2: BFL, EFL and correction are all vectors. The positive direction is the direction, in which
the optical axis faces the image.
A.3.2 Equipment
The optical bench, as shown in Figure A.1, has the following characteristics:
a) The collimating achromatic lens with basically no aberration is used in
conjunction with the light source; the focal length of the collimating lens should
be more than 10 times the focal length of the intraocular lens to be tested;
b) On the focal plane of the collimating lens, diffuse light from the light source
illuminates a spatial frequency reticle, such as the U.S. Air Force 1951 resolution
version (see Figure B.1);
c) The maximum distance -- from the aperture stop (3.0 mm ± 0.1 mm) to the front
of the tested intraocular lens -- is 3 mm;
d) The surrounding medium is air;
e) The numerical aperture of the microscope objective lens shall be larger than the
spatial frequency.
Calculation of the effective focal length EFL, f of the intraocular lens can be carried
out, by formula (A.11):
Add spherical aberration correction value (see A.5) to f, to obtain the paraxial focal
length, fair. Further calculate the optical power in air and solution, according to the
formula (A.8), formula (A.9), formula (A.10).
A.4.4 Applicability
The method described above is applicable to rotationally symmetric spherical or
aspheric IOLs.
A.4.5 Precision
For monofocal intraocular lenses, the repeatability and reproducibility are the precision
characteristics of optical power, which should be 0.5% and 1%, respectively.
A.5 Determination of optical power and axial error of toric intraocular lens
A.5.1 Overview
The method, which is described in A.2 and A.3, can be modified to measure the optical
power on the main meridian of the highest and lowest optical power, AND to allow the
measurement axis to be aligned with the axis mark of the lowest optical power meridian.
A.5.2 Without compensating lens
For toric IOLs, the optical powers of the two principal meridians are determined as
follows:
a) According to A.2: Calculate the optical power by measuring the dimensions
(including the radius of curvature) of the two principal meridians.
b) According to A.3: Calculate the optical power, by measuring the back vertex focal
length of the two principal meridians. The measured principal meridian is aligned
with the applicable target, by obtaining a sharp and clear image.
c) According to A.4: Calculate the optical power, by measuring the magnification of
the two principal meridians. The measured principal meridian is aligned with the
applicable target, by obtaining a sharp and clear image.
The calculation method of spherical equivalent focal power (SE) is as follows:
SE = (Power of high power meridian + power of low power meridian)/2
Cylinder lens power (CYL) is calculated as follows:
CYL = Power of high power meridian - power of low power meridian
Note: This method is suitable for cylindrical lens focal power below 5D.
A.5.3 Using compensating lenses
The optical bench described in A.3.2 can be modified, to add a positive cylindrical lens
(compensation lens), which is installed behind or in front of the toric intraocular lens to
be tested, for determining the equivalent spherical lens power (SE) and cylindrical lens
power (CYL).
Compensating lenses are capable of compensating for the cylindrical lens of a toric
intraocular lens (TIOL). The cylindrical axis of the compensating lens shall be aligned
with the principal meridian of the toric intraocular lens (TIOL) meridian of highest
power. The focal power and position of the compensating lens are selected, to ensure
that the optical combination of the compensation lens and the intraocular lens can obtain
a clear image of the two-dimensional target. Use the method described in A.3 or A.4, to
measure the uncorrected power of the main meridian of the highest power; then measure
the position of the compensating lens. According to the focal power of the
compensating lens and the position of the main plane of the meridian relative to the
lowest focal power of the toric intraocular lens, the cylinder power of the intraocular
lens can be calculated, by using a combination formula.
A.5.4 Determination of axis position error
A.5.4.1 Without compensating lens
Use A.5.2b) or A.5.2c) method, to determine the axial error. When a best-focus image
is obtained, calculate the angle -- between the target principal direction and the axial
marker. This angle is the axis position error.
A.5.4.2 Using compensating lenses
Use the method in A.5.3, to determine the axis position error. When the best focused
image is obtained, calculate the angle -- between the cylindrical axis of the
compensation lens or its orthogonal meridian and the axial mark of the toric IOL, the
smaller of which is the axial error.
Note: Orthogonality errors -- between the lowest and highest focus meridians -- are evident in
image quality measurements.
A.6 Power determination for multifocal intraocular lenses (MIOL)
Two methods of determining optical power apply to multifocal intraocular lenses (A.3
and A.4). The measurement of optical power shall be carried out under the aperture of
Appendix B
(Normative)
Measurement of resolution
B.1 Overview
This Appendix presents principles, devices, and methods applicable to the measurement
of intraocular lens resolution.
B.2 Principle
The resolution limit of an intraocular lens, expressed as a percentage compared to the
diffraction-limited cutoff spatial frequency of an ideal lens with the same focal length,
has equivalent aperture stop, wavelength, media environment. The aperture is 3.0 mm,
the surrounding medium is air, the peak wavelength of the light source is 546 nm (±10
nm); its full width at half maximum is 20 nm or less.
B.3 Equipment
Optical bench as shown in Figure A.1.
Note: The image quality measurement of negative power and low power intraocular lenses may
require a modified workbench (such as additional convex lens, microscope objective lens with
appropriate numerical aperture, etc.) for quantification.
B.4 Steps
Place the intraocular lens in the optical bench; position its center on the optical axis as
much as possible.
Focus the image on the resolution plate, by moving the objective lens of the microscope,
to obtain an image that is as comprehensive and balanced as possible with thick and
thin line patterns (see Figure B.1).
Determine the thinnest pattern (group, unit), in which horizontal and vertical lines can
be resolved at the same time. In addition, all thick lines shall be resolved. See 5.3.5.1
of GB/T 9045-2006, for judgment criteria of resolution.
B.5 Calculation
B.5.1 For the spatial frequency ν, expressed in the reciprocal of millimeter (mm-1), the
finest discernible pattern is calculated from formula (B.1):
Appendix C
(Normative)
Measurement of MTF
C.1 Overview
This Appendix presents the principles, equipment, methods, which are applicable to the
measurement of the modulation transfer function of rotationally symmetric monofocal
intraocular lenses. For other types of IOLs, the required modifications are given at the
end of this Appendix.
C.2 Principle
The intraocular lens is placed in the model eye; the modulation transfer function (MTF)
is measured using monochromatic light. The peak wavelength of the light source is 546
nm (±10 nm); its full width at half maximum is 20 nm or less.
The model eye, which is described in this Appendix, is a tool for establishing quality
criteria for intraocular lenses. It is used to formulate the limits in 4.3, not as a reference
for actual human eye performance.
C.3 Equipment
C.3.1 Model eye 1
Model eye 1 has the following properties:
a) The simulated cornea is a lens, which has minimal aberrations, as described in
Table C.1;
b) The front surface of the intraocular lens is placed on a plane, which is 26 mm ~
28 mm in front of the focal point of the simulated cornea; the refractive index of
the imaging medium is 1.336;
c) The converging beam from the simulated cornea is irradiated on the central
circular area of the intraocular lens; the applicable test diameter tolerance is ±0.1
mm;
d) The intraocular lens is placed in a liquid medium -- between two planar windows;
e) The difference -- between the refractive index of the intraocular lens and the liquid
medium and the condition in the eye -- shall be within 0.005;
f) The image plane falls in the air, which is outside the last window of the model eye.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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