Annex A
(normative)
Optical Characterization
A.1
General
The manufacturer shall characterize the optical design of the EDF IOL and a monofocal
IOL of the same distance power, against which the optical performance of the EDF IOL is to be
compared, as described below.
This characterization includes measurements of the optical performance of the EDF IOL that will
assist in predicting performance of an individual with the EDF IOL implanted in their eye on
visual acuity testing as specified in 10.2.
In particular, this characterization will assess the optical resolution of the EDF IOL and the
comparison monofocal IOL when used to view distant objects. It will assess the optical
resolution of the EDF IOL and the comparison monofocal IOL when viewing objects at
increasing near distances.
A.2
Optical characterization
A.2.1
Theoretical evaluation
The manufacturer shall perform a theoretical evaluation (e.g., ray trace evaluation) of the optical
design demonstrating the additional depth of focus of the EDF IOL compared to a monofocal IOL in
an eye model with a physiologically appropriate cornea and white light at 3, and 4.5 mm apertures. An
eye model cornea considered to be appropriate is described in Annex C.
The theoretical evaluation shall include calculation of the modulation transfer function of the eye
under entering vergence conditions, the conditions of lens tilt and de-centration specified in
A.2.2.1. Using the calculated modulation transfer function data, the expected performance of
the implanted lens during visual acuity testing shall be assessed with the method of A.7.
A.2.2
Optical testing
The following testing shall be performed on the EDF IOL and on the comparison monofocal IOL:
A.2.2.1
Modulation transfer function (MTF) testing
For this MTF testing, use 10 representative samples each of low, medium and high power for throughfrequency-response MTF testing, and 10 representative samples of medium power for through-focusresponse MTF testing.
Modulation transfer function testing shall be performed with the lens placed in a model eye, as
specified in Annex C or equivalent. The modulation transfer function shall be measured using
the method specified in Annex C or equivalent.
The modulation transfer function shall be measured at a fixed plane within the model eye, this
position determined and set as specified in A.3.
The modulation transfer function shall be measured for each of the following vergences of light
entering the model eye from the target.
- Range 0 D to -2.5 D
- Increment or vergence step 0.25 D
The subtended angle of the target features shall be the same for each step within the vergence
range. Annex C gives an optical method to fulfill these vergence and target requirements.
The modulation transfer function shall be measured over the entering vergence dioptric range
specified above with a model eye having a pupil aperture of 3 mm and again with a model eye
having a pupil aperture of 4.5 mm.
The modulation transfer function shall be measured for the case of entering target vergence of 0
D with the lens centered in 4 mm diameter pupil aperture, de-centered 1 mm and centered but
titled 5 degrees with respect to the pupil plane.
The modulation transfer function measurements shall be done using white light as specified in
A.4.
A.2.2.2 Simulated depth of focus performance
The simulated depth of focus performance of the EDF IOLs and the control monofocal IOL shall be
determined in the following way.
1) With the IOL placed in the model test eye specified in Annex C or equivalent and with the
vergence of the light entering the model eye from the test target equal to 0D adjust the image
plane for best focus as specified in A.3. The test target shall be a 0.2 logMAR optotype.
2) Change the vergence of light entering the test eye in - 0.25 D steps while keeping the subtended
size of test target constant until the image of the test target formed by the model can no longer be
resolved.
3) The total negative vergence change to the end point of 2) is the simulated depth of focus
comparison value that is used to compare the depth of focus value of the EDF IOL to the control
monofocal IOL.
Annex C gives an optical method that will fulfill the vergence and target requirements of A.2.2.2
A.2.2.3 Spurious imaging testing
The lens shall be tested while in the model eye for the creation of spurious images, such as halos,
various types of glare or secondary images, by examining the image of a ‘point source’ of light
for concentrations of light other than the expected primary image. The lens shall be centered in
the pupil aperture of the model eye, whose diameter is 4.5 mm, during testing. The vergence of
light entering the eye from the point source of light shall be 0 D. Polychromatic, i.e. white light
shall be used for the test.
The image capture system shall be able to examine the image formed by the lens within the
model eye over a visual angle of 5 degrees. The image capture system can be moved laterally, if
needed, to cover this range.
The image capture system shall be able to record image intensities over a range of so that
spurious images that can be seen by a human observer at night but not under daylight conditions
can be identified. Can be done, for instance, by using a neutral density filter to reduce the light
from the target in conjunction with increasing the imaging camera gain.
Spurious images observed to form shall be recorded by noting their relative visual angular
position with respect to the primary image and their intensity relative to that of the primary
image.
The point source target shall subtend an angle of no more than 0.35 arc minutes.
A.3
Determination of distance image plane within the model eye
The distance image plane is defined as the plane within the model eye where the best image of
the target forms when the vergence of light from the target, as it enters the model eye is 0 D.
However, in the case of EDF-IOLs, where a very good image of a 0 D target forms over an axial
range within the model eye, a method is needed to fix a single axial position for the image
capture plane. Note that a microscope system for image transfer will have a very short depth of
focus so object plane of the camera system is well defined.
The distance image plane will therefore be experimentally found by first insuring that the target
vergence is 0 D as it enters the model eye. While using a point target and while observing the
image formed by the camera system, the distance between the camera system and the model eye
is varied while noting the peak intensity of the captured image. The model eye is moved until
the intensity is observed to take a maximum value. Then the camera system is moved away from
the model eye until the peak intensity falls to 80% of the maximum peak intensity previous
found. This procedure is equivalent to the procedure used in subjective eye refraction of
increasing plus spherical power until blur is positively detected. This is done to insure that
there is not an axial position giving good image resolution beyond the selected distance axial
position. Finally the model eye is moved toward camera system until the peak intensity returns
to 95 % of the maximum peak intensity found.
A.4
White light
For the purposes of this Annex white light is defined a polychromatic radiation covering at least
the range of visible light, i.e. 380 nm to 700 nm, that has a spectral signature similar that used for
illumination of visual acuity targets. An acceptable source of such radiation is a thermal source
such as a quartz halogen lamp with a color temperature of at least 2800 K.
A.5
Image resolution analysis using modulation transfer function measurement data
The expected visual acuity for a given testing condition is found by using the measured
modulation transfer function in the following way.
Each modulation transfer function value whose spatial frequency is between 10 and 50 cycles per
millimeter is first divided by its spatial frequency to form an array of weighted modulation
transfer function values. The sum of the values in this array is found and multiplied by the
spatial frequency increment squared of the measured data. This value is the weighted
modulation transfer volume and it is well correlated to performance during visual acuity testing
when the test IOL is implanted in a human eye and testing is done with an acuity target a
distance such that the vergence of light entering the eye is the same as was the case for the model
eye when the modulation transfer function was measured.
The expected visual acuity value,
given in logMAR units, is given by Eq. A.2. (to be added)