Name: scanning light scattering profiler (slps) based methodology to quantitatively evaluate forward and backward light scattering from intraocular lenses
Uploaded: 2017-06-06T15:30:00
Description: Watch this Scientific Journal Video about Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses at JoVE.com

The authors would like to thank the companies for the access of their monofocal and multifocal IOLs. This work was supported by Oak Ridge Institute for Science and Education (ORISE) and the Medical Device Fellowship Program (MDFP) and their contributions are appreciated. In addition, the authors would like to thank Samuel Song for his contributions in the laboratory.

1. SLSP Measurement Platform Preparation
NOTE: All alignment steps require precision and patience to ensure accurate quantitation when measuring light scatter. An overview of the SLSP setup in provided within Figure 1. Here, an illustration (Figure 1a) shows the basic concept of the SLSP setup. In addition, Figures 1b and 1c help define the various angles referenced within the discussion. Specifically, the following three angles...

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M., Felipe, A., Navea, A., Carmen Garcia-Domene, M., Pons, A., Mataix, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+scattering+in+intraocular+lenses+by+spectrophotometric+measurements.">Determination of scattering in intraocular lenses by spectrophotometric measurements.</a> J. Biomed. Opt. 19 (12), (2014).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ophthalmic+implants+-+Intraocular+lenses+Part+2:+Optical+properties+and+test+methods.">Ophthalmic implants - Intraocular lenses Part 2: Optical properties and test methods.</a> The International Organization for Standardization (ISO). ISO 11979 (2), (2014).</li></ol>

The results from the SLSP platform experiments have found that using simple goniophotometry principles can lead to a powerful tool for evaluating the properties of light scatter associated with unique IOL designs and materials. Specifically, the SLSP platform has observed a direct correlation between the amount of detectable scattered light and the beam diameter of the light source. In addition, the multiple scattered peaks found in multifocal IOLs were easily observed with the SLSP. Furthermore, as the source of light a...

The scanning light scattering profiler (SLSP) approach was first introduced to address the need to quantitatively evaluate light scattering characteristics of intraocular lenses (IOLs) in a non-clinical setting1. Developing a test methodology to evaluate the light scattering tendencies of IOL designs and materials is of significant interest in order to help identify potential unwanted light scattering problems. Light scatter is commonly reported by patients and observed as glare, glistening, optical imperfections, and other forms of dysphotopsia2, sometimes leading to a patient requesting the IOL explantation. In addition to dysphotopsia, scattered light reduces the amount of ballistic light, resulting in lower overall image quality3. Developing a device that can non-clinically evaluate the IOL potential to scatter the incoming light (and later correlated with clinically reported outcomes) can be useful.
Evaluating optical properties of IOLs (the lens used to replace the human crystalline lens after cataract surgery) is of particular interest as it is the most commonly implanted medical device in the world (almost 20 million per year)4 and the United States (over 3 million per year)5. As a result, even a small percentage of patients reporting dysphotopsia may have a large impact. In addition, rapidly improving technologies (e.g. new IOL designs, materials, and optical capabilities) have the potential to increase concerns related to light scattering. For example, multifocal IOLs have been designed to improve near and far visual acuity by designing lenses that utilize refraction and diffraction optical principles. Although highly successful, these lenses have also been found to increase the amount of reported halos and glare, largely associated with scattering of light6.
A few non-clinical laboratory studies attempt to predict dysphotopsia from scattered light as it passes through IOLs7. For example, research has identified that IOL haptics (the arms of the IOL used to set it in place) and the edge of the IOLs are prone to induce a large amount of the observed glare scattered light8. One method, a ballistic-photon removing integrating-sphere method (BRIM), was introduced to quantitatively measure the amount of total non-ballistic light after passing through an IOL9. However, this highly sensitive technique is designed to measure the total intensity of scattered light and is unable to identify directionality of the scattered light. Computer simulation software can be used with model eyes to help predict intensity and directionality of light scatter from various IOL designs and materials. For example, the propensity for the IOL edge to induce the light scattering was simulated to identify designs that would limit the amount of scattered light10. Furthermore, computer simulations that incorporated the Mie scattering theory verified that increased light scatter can reduce the modulation transfer function (MTF) of the IOL (a direct correlation to image quality)3. Although helpful, real bench tests would be necessary to verify these predictive simulations.
To verify predictive simulations a bench test is necessary that is capable of detecting and quantitatively evaluating two distinct forms of scattered light, forward scattered and backward scattered light. Although not a source of dysphotopsia, backward scattered light (light scattering away from the eye) is a cause for reduced image quality, as less light passes through the IOL to ultimately reach the retina. Forward scattered light (light scattering towards the retina) is a concern for ophthalmologists as it may result in complaints of dysphotopsia (e.g. glare, halo, and glistening). One common example is patients reporting additional unwanted glare from passing oncoming cars during night driving; this issue is particularly common with multifocal IOLs11. However, current practice to identify potential forward scattered light is for ophthalmologists to shine light onto the patient&#39;s eye and qualitatively observe how much light is reflected back (backward scattered light) and assuming that the backward scattered light will be approximately the same as the forward scattered light (which is not always the case)12.
Here, we describe a simple test methodology using goniophotometry principles to quantitatively measure the magnitude and direction of scattered light at it passes through an intraocular lens. The SLSP operates by rotating a photodiode sensor 360 degrees around an IOL that is exposed to a light source, see Figure 1a. We chose a green laser source (543 nm) to best represent the known photopic maximum and to agree with the international standard specifications13. Here, an IOL is adapted onto a rotational and translational holder where a photodiode sensor can circle around and observe light scattering off of the lens. As a result, the SLSP has the unique capability to quantitatively measurement the magnitude and directionality of scattered light. However, although not described here, for better predictive capabilities, experiments should be conducted within a controlled environment using an appropriate eye model. The distance between the IOL and the optical sensor (as well as the size of the sensor element) will determine the resolution capabilities of the device; however, there will be a tradeoff between resolution and signal strength that will need to be adjusted, as needed.
To accurately describe the principles of the SLSP platform we define three types of rotational angles, see Figures 1b and 1c. Specifically, the rotation angle (&#730;R) represents the rotation of a photodiode sensor as it rotates around an IOL. Here, 0&#730;R would represent when the sensor is behind the lens (backward scattered light) and 180&#730;R represents when the sensor is in front of the lens (forward scattered light). Angles of 90&#730; and 270&#730; represent the transition points between forward and backward scattered light. The sensing angle (&#730;S) represents degrees that the sensor is pivoted (in the up and down direction) so that it can detect more than one plane of scattered light. Here, 0&#730;S means the sensor surface is parallel to the IOL (and light source). Finally, the angle of incidence (&#730;I) represents the angle that the light source is approaching the IOL from. Here, 0&#730;I corresponds to when the incident light is on the optical axis of the IOL and 90&#730; would represent when the light source is perpendicular to the Meridional plane.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>PD300 series Photodiode Sensor</td>
			<td>Ophir-Spiricon Corp</td>
			<td>7Z02410</td>
			<td>PD300-1W, RoHS</td>
		</tr>
		<tr>
			<td>URS Series Precision Rotation Stage</td>
			<td>Newport Corp.</td>
			<td>URS75BCC</td>
			<td></td>
		</tr>
		<tr>
			<td>ESP301 1-Axis Motion Controller and Driver</td>
			<td>Newport Corp.</td>
			<td>ESP301-1N</td>
			<td></td>
		</tr>
		<tr>
			<td>LabView Software</td>
			<td>National Instruments Corp.</td>
			<td>776671-35</td>
			<td></td>
		</tr>
		<tr>
			<td>Origin</td>
			<td>OriginLab Corp.</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Single Mode FC/APC Fiber Optic Patch Cables</td>
			<td>ThorLabs Inc.</td>
			<td>P3-460B-FC</td>
			<td></td>
		</tr>
		<tr>
			<td>10X Olympus Plan Achromat Objective</td>
			<td>ThorLabs Inc.</td>
			<td>RMS10X</td>
			<td>RMS10X - 10X Olympus Plan Achromat Objective, 0.25 NA, 10.6 mm WD&#160;</td>
		</tr>
	</tbody>
</table>

scanning light scattering profiler (slps) based methodology to quantitatively evaluate forward and backward light scattering from intraocular lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Goniophotometry measurements can produce 360&#730;R of signal when the sensor is not located on the plane of the light source. However, to collect measurements from scattered light on the plane of the light source (0&#730;I) the sensor will need to eclipse the light source, resulting in less than 360&#730;R of signal. In our experiments, it was determined that ~20&#730;R of signal was blocked as the sensor eclipsed the light source.
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Watch this Scientific Journal Video about Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses at JoVE.com

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

The overall goal of this Scanning Light Scattering Profiler is to quantitatively evaluate the intensity and directionality of scattered light, as it passed through an intraocular lens. This test matter can help addressing key questions in the field of intraocular lenses, such as, if a particular design or material is more sensitive to introducing unwanted light scattering. The main advantage of this technique is that it's quantitative, and can be used to detect directionality of light scatter.A test procedure will be demonstrated by Claudine Krawczyk, a technical associate in my lab. The experimental setup is assembled on a bench top. At its core is a goniophotometer designed around this programmable 360 degree rotation, and linear translation stage.The stage rests on a platform that enables translation and tilt adjustments. A photo diode mounted at the end of the stage's extendable arm, is the goniophotometer sensor. It is supported on a mount that can be adjusted by at least 45 degrees, to measure different planes of scatter.Construct a platform to hold the intraocular lens above the goniophotometer. Use three or four 18-inch long, half-inch diameter cylindrical posts and post stands, to support an 18-inch by 18-inch prep board. The prep board serves as the base for a three-axis translation stage that is suspended below it.Next, obtain the intraocular lens for the experiment. This multifocal optical lens will serve for this demonstration. Note the structure's intraocular lenses have to hold them in place.Use these structures and a clamp to attach the lens to the platform. Here, the lens is attached and ready for use in the protocol. Use a narrow line width laser source for the goniophotometer light source.Choose a 10Xinfinity corrected objective lens to focus the beam into a single-mode delivery optical fiber. Position the fiber at the focal point of the objective lens, to columnate the light source. Next, position an iris aperture in front of the light source to adjust the diameter of the Gaussian beam.The aperture diameter should be representative of a human eye, one to six millimeters. Align the light source so the intraocular lens is directly in front of it, and the lens's plane of focus is perpendicular to the beam. The most important step is ensuring that the intraocular lens is appropriately aligned with the light source.The intraocular lens should be adjusted so that the light does not change directions as it passes through its center. Intraocular alignment can be done using a pinhole aperture behind the intraocular lens, to identify the directionality of the light source before passing through the lens. The lens position can be adjusted with the platform stage.Now, position the motorized stage so its axis of rotation is directly underneath the intraocular lens. This ensures the intraocular lens is at the center of the goniophotometer trajectory. Use the linear translation arm to adjust the photo diode to intraocular lens distance, to balance signal and resolution needs.In this case, the distance chosen is 6.75 centimeters. Before gathering data, ensure the apparatus is configured for the experiment. Check that the angle of incidence of the light on the intraocular lens is zero degrees.Next, turn attention to the iris, and be sure the aperture is consistent with a typical iris diameter. Also check that the distance from the intraocular lens to the photo diode, as well as the photo diode angle, are correct. At this point, finalize the automation of the data collection.During the experiment, the rotation stage will sweep the photo diode 360 degrees around the intraocular lens to allow collection of data at different angles. The angle step size is an input to the automation program. Before performing the experiment, block light to the apparatus by enclosing it with a container with non-reflective internal coating.Be sure to provide an opening for the light source. When ready, perform the experiment with all unnecessary lights off. There is a direct correlation between the beam diameter and the intensity of the scattered light, as a function of rotation angle.Two iris apertures are represented in this data for a mono-focal lens. The black curve is for an iris diameter of one millimeter. The red curve is for an iris aperture of 4.64 millimeters.Qualitatively the difference is clear. The data allowed for a quantitative study of the change in signal intensity. The light scatter intensity is also affected by the angle of incidence.In this plot, data for four different angles of incidence are provided for a mono-focal lens. As the angle of incidence increases to approach the grazing angle, the scattering intensity increases as expected, since most light is reflected off the lens. Compare the data from a mono-focal lens with those of a multi-focal lens.The data correspond to the same angles of incidence. Note the broadening of the multi-focal peaks as the angle of incidence increases. The most intense peak, at the 80 degree incidence angle, is at the boundary between the front and back scattered light.This could be identified as glare. Although this test matter was developed for testing intraocular lenses, it has a broader impact and can be applicable for testing of contact lenses and other optical components. After watching this video, you should have a good understanding of how to replicate the goniophotometer concept to the quantitative evaluation of light scatter after passing through intraocular lenses.Don't forget that working with lasers can be extremely hazardous, and precautions such as wearing safety glasses should always be taken when running the experiment.

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