Software Protocol

The software protocol will be different, depending upon the maker of the instrument, but some general guidelines can be helpful:

1. Once you become familiar with what the instrument can produce in terms results and reports, you will want to standardize the scanning protocol so that every operator will know what scans need to be captured, saved, and reported.  This can vary for each doctor who makes use of the instrument, or there can be one general protocol for macula scans and one general protocol for glaucoma scans. 

There are three advantages to standardization.  The first is that the operator knows what is expected.  The second is that the patient will get a sense of professionalism instead of incompetence or experimentation.  The third is that all the information needed for future evaluation and comparison to subsequent scans will have been saved.

A good example is the protocol that we use with the Opko SLO/OCT for macula scans.   We routinely capture three different scan types, because they yield different information.  Each scan type takes less than 30 seconds to perform with a cooperative patient.

A report from the 3D topography scan is pictured below.  The 3D imaging can be viewed in Section 2.

Generally, retinal topography maps are based upon retinal thickness measurements.  Retinal thickness is defined as the vertical distance between the top of the retinal nerve fiber layer (RNFL) to the top of the retinal pigment epithelial layer (RPE).  In the image below, the top arrow points to a red line that is tracing the RNFL.  The bottom arrow is pointing to a green line that is tracing the RPE layer.

An image from an individual raster scan is pictured below.  A slide show of an entire raster scan can be viewed in Section 2.

The image of an individual line scan is pictured below.

The software procedures with the Opko SD SLO/OCT are easily learned and performed.   As with most ocular imaging procedures, the key to good results is good patient management.  Although the scanning speed is much improved with spectral domain technology, the best results are still obtained when the patient's eye remains motionless.  Here are some helpfull hints:

1. It is best to work with a dilated eye.  Because of the scanning laser technology, the Opko instrument can capture beautiful images through an undilated pupil, but dilating the pupil gives you more lateral operating room.  You don't have to continually chase after the pupil if the patient's eye is moving.
2. Having the patient's head firmly planted in the headrest is critical.  The Z axis window is very narrow.  The Z axis is the forward and back distance between the retina and the instrument lens.  Remember that the structure that you are imaging is less than 2mm thick.  Be sure that the headrest does not move, if so, figure out how to tighten it up (loose screws?).  Be sure that the patient understands the importance of keeping the chin in the chinrest and the forehead against the bar.
3. Good fixation by the patient is very helpful, although with the high speed technology and eye tracking (on RNFL scans), acceptable images can be captured even with an eye that has wandering fixation.  The Opko instrument has a large internal fixation cross, as well as an external fixation light for the fellow eye.
4. Scan acquisition times for raster protocols are from 1 to 4 seconds, so warn the patient to not move or blink just before the scan starts.  Have the patient blink before each scan.  A good tear film is important for good image resolution, so keep some artificial tears handy.
5. If there are lens opacities present, the scanner can be moved around in the X and Y axis inside the pupil to improve the scan image.  Good dilation helps.
6. Just as with the OCT 3, a good OCT scan has no motion artifacts, no blink artifacts, and has a high signal to noise ratio.  A high signal to noise ratio is evident by good reflection from the structure.  If you are viewing the OCT scan in grayscale, the best scans are the bright, dense scans.  If you are viewing the OCT is false color, then the bests scans have a higher percentage of hot colors (red, orange, yellow).  The display has a signal indicator, but it is distracting to have to look back and forth.  The same information can be had by just observing the quality of the scan in the window.  The scanner runs continuously until you initiate a capture, so adjustments can be made in alignment to optimize the scan. Below are screen shots from the scan acquisition window, in grayscale and in false color.

1.  The patient is aligned with window #1.  The three "snowball" dots on the cornea are focused on the cornea by moving the instrument along the Z axis.  The small square in the center is aligned inside the pupil by moving the instrument on the X and Y axis with the joystick.

2. The graphic at #2 is the position of the internal fixation cross, which is centered by default, but can be moved anywhere, or aligned for optic nerve scans.

3.  Once the eye is aligned, the SLO image of the fundus appears in window #3.  The operator then clicks on the "autofocus" button at the top left.  The instrument then focuses on the retina (no diopter adjustment is needed), and then brings the scan image into window #4.

4. With the scan image in window #4, the operator uses software adjustment to tweak the alignment in the window.  The joystick is used to adjust the scan in the pupil to optimize the scan signal.  When the scan looks optimized in the window, the scan is acquired with a mouse click.

With a cooperative patient, the complete alignment process is very fast, taking about 30 seconds.