Measurement of Carotenoids in Perifovea using the Macular Pigment Reflectometer

A device that can objectively provide levels of macular pigment optical density as well as the measurements of lutein and zeaxanthin represents a major breakthrough in the field of macular pigment measurement. The current study developed the technical ability to modify the reflectometry to obtain carotenoid levels in the parafovea and parafoveal regions without any alteration to the reflectometry optics. In our current study, we developed the technical ability to modify reflectometry so that we can obtain carotenoid levels in the parafovea and parafoveal regions.

We do this without any alteration to the reflectometer's optics. Ensure the subject understands the need for proper convergence during the calibration step. Lubricating eyes increases subject comfort.

Regulating subject blinking and providing a final countdown improves compliance. Visual demonstration is crucial since this is a prototype and significantly different from existing technology. It can be confusing to operate without having witnessed the proper procedure being performed.

Begin this procedure with participant recruitment as described in the text protocol. Obtain a slidable track with an approximate one meter long aluminum rail that contains a hollow indent with space for a slidable track such as a door weather strip. Mount the track 6.1 meters from the subject seated at the macular pigment reflectometer, or MPR, for the reflectometry measurements to be performed.

Ensure that the track is 1.5 meters off the ground to be at the same height as the participant's eye during the reflectometry measurement. Mount three one-centimeter-by-one-centimeter remote-controlled LED lights on the slidable track so that the centers of the lights are spaced 10.7 centimeters away from each other. This value was determined from the distance each LED light is from the participant.

To perform the central measurements using the reflectometer, input the participant information into the reflectometer software. Then click the Run Eye Test tab. Perform the calibration of the spectrometer within the reflectometer device to full spectrum white sample once a day when the device is turned on by the technician.

A participant is not needed for this step. Click the White button next to Calibrate. Insert the white calibration tube onto the reflectometer after the message instructing the user to insert the white calibration tube is displayed on the screen.

Click OK once the white calibration tube is inserted to begin the white calibration. After the white calibration successful message has appeared on the screen, ensure the Black button next to Calibrate has been enabled. To perform black calibration, first instill a drop of artificial tears into the participant's eyes.

Then have the participant place their chin onto the chin rest. Instruct the participant to place their eye close to the eye cup. Using the joystick, gently position the system so the eye cup presses against the participant's eye socket and blocks the room light from the system.

Click the Black button to select Calibrate, and align the system to the participant's pupil. Proper alignment is achieved when the pupil is centered in the circle displayed on the touchscreen monitor. So you're just gonna be turning the little knob, and you're trying to find Instruct the participant to adjust the rotating knob on the front of the system to obtain a clear target.

Click OK once the participant has properly adjusted the system to their vision. The system will automatically carry out a black calibration sequence. Once black calibration has been successfully completed, the Left Eye and Right Eye buttons will be enabled, and a black calibration successful message will appear on the screen.

To start the measurement, click the Left Eye or Right Eye button on the screen depending on which eye is being measured. Ensure that the system displays the message Align System to Subject's Eye. Ensure that the system is aligned to the participant's pupil.

Use the joystick to make fine adjustments. Click the OK button on the screen to start the macular pigment optical density, or MPOD, measurement. The measurement time is 30 seconds, with a minimum of 10 seconds needed to obtain the parameters and results.

A countdown timer will appear on the top of the screen displaying how much time is left for the measurement. Make sure that you only blink when I tell you, okay? Ask the participant to look at the fixation light and encourage them to only blink when necessary.

Use the joystick during the measurement to ensure the system stays in alignment with the participant's pupil. Ensure the system displays a message stating Measurement Successful once the measurement is completed. Click the OK button to finish.

Repeat the black calibration and measurement steps to test the other eye if needed. The entire process takes about two to three minutes. After the white and black calibration is performed, begin peripheral track calibration by pressing the Left Eye or Right Eye button on the screen depending on which eye is to be measured.

The system will display a message Align System to the subject's eye. Ensure that the system is aligned to the participant's pupil. Use the joystick to make fine adjustments.

Turn on the LED light on the track system that is farthest right from the participant. At this time, the participant should be able to see both the light from inside the reflectometer with their right eye and the red LED light with their left. All right, so for this next section, you're gonna go ahead and tell Shorty to either move it left, move it right.

Instruct the participant to direct the trained observer to adjust the peripheral track until they can superimpose both stimuli to the best of their ability. Variability in the distance of the superimposed calibration point is due to anatomical differences. To start the measurement, turn off the LED light and switch on the next LED light to carry out the next one degree eccentric measurement.

So now we're gonna go ahead and move that red light. So I know the light's gonna move but just Explain to the participant that they need to look at the new red LED light throughout the entire measurement. Click the OK button on the screen to start the MPOD measurement.

The measurement time is 30 seconds. A countdown timer will appear on the top of the screen displaying how much time is left for the measurement. Ask the participant to look at the appropriate red LED light and encourage them to only blink when necessary.

Use the joystick during the measurement to ensure the system stays in alignment with the participant's pupil. Ensure the system displays a message stating Measurement Successful once the measurement is completed. Click the OK button to finish.

Repeat these steps to retake a measurement. Two measurements are recommended for each degree to allow for the comparison. To repeat measurements at a different retinal eccentricity, change the degree separation.

Shown here are the main results of MPOD obtained by both the devices as well as L-OD and Z-OD of all participants involved in the study at various eccentricities. The mean MPOD obtained by the heterochromatic flicker photometer was 0.480 and that obtained by the reflectometry technique was 0.593. The Z-OD was larger centrally compared to the L-OD measured in the foveal region.

The Z-OD to L-OD ratio centrally was 2.61:1. The Z-OD decreased as a function of eccentricity at the center of the fovea. At one degree from the central fovea, the concentration of Z-OD measured by reflectometry decreased significantly with an increase in L-OD.

The Z-OD to L-OD ratio at one degree from central fixation was 1.0:1.38. In the parafoveal region at two degrees from central fixation, the lutein became the predominant carotenoid and the Z-OD to L-OD ratio was 1.0:2.08. Data obtained from all eight subjects are shown here.

Examining the table, it is obvious that there is significant inter-individual variability of L-OD, Z-OD, and MPOD values indicating that the physiological limits of normality can be large. If the calibration step is not properly followed, results will be unreliable. Therefore, subject and technician education is vital.

There are no risk or hazardous materials used in this procedure. However, the risk of a general eye exam still apply, such as tropicamide 1%being used to dilate the eyes, which can cause increased intraocular pressure if the angles are narrow. The reflectometry device brings advantages of measuring macular pigment optical density in an easy-to-use objective fashion that is without patient input and can also provide levels of lutein and zeaxanthin.