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.
