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Initiate a Scan

To position the patient module for scanning, you must initiate a scan. First, select a scan acquisition protocol using the Scan Tab, below.

  • If not in the MAIN WINDOW, click the Go to Scan Acquisition button to display is, as pictured below. If necessary, click the Scan Tab to bring it to the front.

  • From the MAIN WINDOW, select a scan acquisition protocol from the Scan Tab. You can either click the protocol and then click the New Scan button at the bottom, or double-click the protocol. This activates the SCAN ACQUISITION window, as pictured below.

  • The SCAN ACQUISITION window allows you to adjust video and scan parameters from a single interface, enabling the acquisition of high quality scans.
  • The Repeat button to the left of the Scan button allows you to repeat any saved scan group using the same parameters.

Alignment and Acquisition Scan Mode

The Mode button, at lower left of the window, toggles between alignment and acquisition scan modes.

  • Alignment Mode: The scanner activates by default in Go to Scan Alignment mode. In this mode, the scanner traces an aiming pattern rapidly and continuously, which you can see in the video monitor. Alignment mode is useful for scan placement on the desired retinal feature.
  • Acquisition Mode: Click the Go to Scan Acquistion button to switch to scan acquisition mode. In this mode, the scanner traces the actual scan pattern to be used more slowly. Th3e scanner must be in acquisition mode to acquire scans.

In preparation for the next step, the important features to note are the scan image (left side) and video image (upper right). The other functions available in this window will be detailed in the usual sequence of their application.

Center Line Display

Right click anywhere in the scan image and a vertical line appears in the center of the scan image.

Once the SCAN ACQUISITION WINDOW is active, you can begin to position the patient module for scanning.

Caution: The optimal position of the patient module ocular lens is ~9mm or ~3/8″ from the study eye. When positioned properly, the ocular lens may touch the eyelashes or the nose. Practice the utmost care to avoid contact with the patient’s eye.

Tools to Position the Patient Module

Use the following tools to position the patient module for scanning:

(1) The joystick to make gross and fine adjustments of the patient module in the horizontal plane – side to side, forward and back. The joystick is located on the rear (operator side) of the patient module.

(2) The joystick knob makes fine vertical adjustments. The joystick spins in either direction to move the patient module up or down slowly and smoothly. It works whether or not the joystick is locked. Turn the joystick clockwise to raise the patient module, counter-clockwise to lower it.

(3) The focus adjustment knob retracts and extends the ocular lens. It should be set at the number that corresponds to the patient’s refractive correction, in diopters, if known. Focus adjustment knobs are located on both sides of the patient module at the patient’s eye level. From the operator side, turn the know toward you to extend the lens toward the patient. Turn it away from you to retract it. This adjusts the focus of the video camera whose black and white image you see on your monitor.

How to Position the Patient Module

The immediate goal of positioning is to acquire a video image and a scan image of the desired retinal feature. The black and white video image aids you in accurately positioning the instrument and placing the scan, but the final goal is to acquire a high quality scan image.

You must position the patient module manually, using the joystick to make adjustments in the three dimensions. It is a reiterative process of positioning with the joystick, focusing the ocular lens and positioning further. All the while, use the live video image to observe the position and focus with respect to the study eye.

(1) At the outset, focus on the study eye from a distance before moving the patient module. Instruct the patient to look straight ahead. Then press the joystick button to unlock the patient module and move it toward the study eye. Place it so that the ocular lens is approximately 25mm (one inch) from he study eye.

(2) Manipulate the joystick – move the lateral adjustments and twist for vertical adjustments – to center the video image on the pupil. Then, using the joystick, gently push the patient module toward the eye so the video image moves through the pupil and the fundus comes into view.

(3) Instruct the patient to look at the green target light. With the joystick, carefully continue to push the patient module toward the eye and make vertical adjustments until the Stratus OCT beeps, which is a signal that the patient module is the correct distance from the eye of scanning. It beeps when it begins to acquire a retinal scan image, which is visible as a band of contrasting color (green, yellow, red) against the blue background noise on the monitor.

(4) Instruct the patient to continue to fixate on the green target light. If necessary, further adjust there patient module position from side to side, up and down, until the retinal image fills the screen and is evenly illuminated. Shadows from the edge of the pupil should be eliminated, if possible, for best scanning results. Press the joystick button to lock the patient module in place.

While the patient module is locked, you can still adjust the focus and twist the joystick to adjust height. With experience, you may find that you have condensed steps 2 through 4 into one continuous step.

Note: It is not necessary to spend a long time trying to get the best possible view of the fundus. It is more important to have a strong scan image signal than an excellent fundus video image.

In the usual cause of a scan, the first thing you do after positioning is adjust the Z-offset (axial position) of the scan. The axial length of the Stratus OCT scan image is 2mm while the eye length is 10-fold larger. So, if the axial range is not correct, the retina is not scanned, and you see nothing bu noise in the live scan image. The 2mm axial “window” must be position to bracket the retina, making it visible in the scan image.

Once you bring the retina into range for the first scan, it is likely to be visible subsequently. Still, you are likely to adjust Z offset from scan to scan to center the retinal scan image.

During patient module positioning, the Stratus OCT beeps when it begins to scan the retina. If the retinal image is already visible on the monitor, you can skip step 1 below.

To bring the scan image into view along the Z-axis, follow these steps:

  1. Click the Optimize Z-offset button on the Scan Parameter Tab (pictured below).
  2. Click the Z-offset arrow buttons (to the right go the Optimize button) to bring the entire retinal scan image into view.
  3. Shift-Click (hold down the Shift key and click) the arrows to move in larger increments.
  4. The up arrow searches posteriorly (lower in the scan image), and the down arrow searches anteriorly (higher in the scan image).
  5. These methods are operative in both Alignment and Acquisition Scan Modes, but they are usually done in scan alignment mode right after position the patient module.
  6. It is not necessary fro the retinal scan image to be centered. The important issue is that none of the image be cut off.

Optimize Polarization

Polarization is adjustable so you can optimize the interferometer signal strength by matching the polarization of light reflected from the retina. This optimizes the scan image, which results in more yellow and red color in the image. It is necessary to adjust Z offset before polarization so the retina is visible in the color scan image while you adjust polarization.

Once you have a retinal scan image on the screen, click the Optimize Polarization button on the Scan Parameter Tab.

You can incrementally adjust the polarization using the Polarization arrow buttons. If you do, you may note that there are several local maxima in the 180-degree range of polarization. These optional polarization settings may yield scan signals comparable to and occasionally better than the signal achieved using the Optimize button.

Polarization should be adjusted when initiating scanning on each new eye. It need not be readjusted when performing a series of consecutive scans on an eye if it has been done at the beginning of the series.

You can use the Optimize Polarization button in both Alignment and Acquisition Scan Modes. The results of adjusting the polarization may be better appreciated when the scanner is in slow mode.

Accurate scan placement on the desired retinal feature is nearly automatic with the Stratus OCT, because:

(1) The instrument detects which eye is being scanned and,

(2) It automatically places the fixation target in the correct location for the eye and scan acquisition protocol you have selected.

Still the SCAN ACQUISITION WINDOW offers two intuitive and easy methods to precisely adjust scan placement, so you can scan the exact part of the retina you want.

Note: Both the scan placement methods described below work in both alignment ent and acquisition scan modes.

Click and Drag

You can simply click and drag the scan pattern and put it exactly where you want it. As long as the video image is live, scan placement is always adjustable.

Note: Right-click anywhere in the scan image and a vertical line appears in the center of the scan image. Click again to remove it. This is useful to determine if you have centered the desired retinal feature, e.g., the fovea.

Move the Scan Pattern

By default, the click and drag method works on the scan pattern. To drag the scan pattern, position the pointer near the center of the scan pattern until the four-headed arrow appears. Then click and drag.

The two-headed arrow appears when the pointer is near the edge of a scan pattern. Click and drag with this arrow to adjust the scan size, and the angle if available.

Move the Fixation LED

Click and drag works on the fixation LED if it is sufficiently separated from the scan pattern, or if you select Move Fixation LED from the drop-down list as illustrated below. After you save the first scan in a related series, you can no longer move the fixation LED.

Why move the fixation target? – Aside from changing between fovea and disc locations, it may not be clear why one would want to adjust the fixation target location. The usual reason is to bring another portion of the retina into view or into the center of view so that the scan pattern may be applied to it. For example, there be a particular area of pathology away from the macula or the optic disc.

When freezing the view image of the macula, you may observe better contrast when you move the fixation LED to bring part of the optic disc into view on the edge of the video image. It may also help in orienting your observations.

Scan, Landmark and Fixation LED Controls

The upper right portion of the Scan Parameter Tab contains on-screen controls to move the scan, landmark and internal fixation LED (light-emitting diode). The default position for the scan and landmark is the center of the video image. The default fixation LED location is either the center (fovea mode) or 15° nasally (disc mode), depending on the scan protocol.

Click the triangle on the drop down list and select what you want to move. The default is to move the scan.

The Details Tab in Scan Acquisition Window shows the x and y positions of the scan, landmark and fixation LED, in mm, relative to 0.0 at the center of the video image.

Click the arrow buttons to move the selected feature in the indicated direction. One click moves the feature 0.1mm. Click the central circle button to return it to the default position

Landmark

The landmark is a pulsating point of light that appears in the video monitor in addition to the scan pattern. you can move it independently or together with the scan pattern. To move the landmark, use the menu options on the Scan Parameter Tab.

Fixation can be challenging in pattens with significant pathology or poor visual acuity. The Landmark tool can aid in positioning the scan pattern relative to anatomical landmarks. For example, it may be placed on the edge of the optic nerve head and used in centering a Fast Macular Thickness Map scan pattern on the fovea. When using the Repeat Scan function, the prior image shows the landmark position. The operator can align the new scan with this position.

Disc and Fovea Buttons

In most cases, the fovea and/or the optic disc are the primary points of clinical interest. Carl Zeiss Meditex designed most of its scan acquisition protocols for scans on one or the other location by default, although they may be used in other locations. Thus, the Stratus OCT places the fixation target either central (fovea mode) or approximately 15° nasally (disc mode), depending on the scan protocol. On the Scan Parameter Tab you can click the Disc or Fovea button to select one or the other default location.

 

There are three steps to acquire Stratus OCT scans:

(1) Switch to scan acquisition mode, if you have not already done so.

On-Screen: Click Go to Scan Acquisition Mode button.

Blue Patient Module Buttons: Press the left button once.

(2) Freeze the scan, with or without flash.

On-Screen: Click the Freeze with Flash button, except with highly photosensitive patients, for whom you should click the Freeze without Flash button.

Blue Patient Module Buttons: Again, press the left button once. Flash is used unless you uncheck the Freeze With Flash option in the Scan menu (click Scan>Freeze with Flash)

(3) Save the scan

On-Screen: if you are satisfied with the quantity of the scan image frozen on screen, click the Save button. The video and scan images will be saved to the hard disk drive. If not, click Cancel to return to scan acquisition mode and acquire another scan.

Optional Scan Review: The Stratus OCT continuously scans and saves up to eight scans in temporary memory. Therefore, you can review the last several scan images and select which one to save. Click the Review button to so to the SCAN REVIEW WINDOW.

Blue Patient Module Buttons: Press the right blue button to save the scan image frozen on screen. The right blue button is only active when a scan is frozen, and saving scans is its only use. Press the left blue button to cancel saving and return to scan acquisition mode.

Note: If you click the Cancel button before saving, you will be asked if you want to save