University of Iowa Health Care

Ophthalmology and Visual Sciences

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PROFESSIONALISM COMPENTENCY: The PASCAL (PAttern SCAn Laser) Argon Laser: Getting Started

Alex Cohen, MD, Gina Rogers, MD, Thomas A. Oetting, MD

March 2, 2009

Learning to use the PASCAL (Pattern Scan Laser) photocoagulator, as part of on-going professional development.

Introduction:

Becoming proficient in performing retinal laser treatments is an important part of ophthalmology residency. At the University of Iowa, we routinely use the PASCAL (Pattern Scan Laser) photocoagulator for performing panretinal photocoagulation, focal laser, and treating retinal breaks or tears. The PASCAL uses 532 nm laser pulses and can be set to rapidly deliver energy in a predetermined pattern, thus allowing for decreased patient discomfort and treatment time.

As part if our training program, residents are required to become familiar with the set up and operation of this laser and demonstrate proficiency in the delivery of safe treatment prior to performing laser surgery on patients. To do this, a simulated retina is drawn on a black backed (to facilitate laser uptake) paper. Two situations are simulated, PRP in a virgin eye, and demarcation of a posterior flap tear.

Getting Started:

Turn on the laser using the provided key. The computer and the laser will boot up and eventually the default screen will appear which displays a variety of parameters including power, spot size, and duration. Recommended starting parameters for common situations are listed in Table 1. Input the desired settings by using the touch screen and selecting from those available in the drop down menu. For example, spot size can be set at 60µm, 100µm, 200µ, or 400µm depending upon the task. The PASCAL is unique in that the laser can be set to deliver a predetermined pattern of treatment. This is accomplished by touching the “Pattern” menu on the screen which will bring up a new window. From here select a pattern depending upon the type of treatment desired.

Simulated Exercises:

For the first simulated exercise, treating a posterior flap tear, input the parameters as outlined in Table 1. Select the circular pattern from the “Pattern” menu. The number of spots to be delivered can be adjusted by touching adjoining spots until a 360-degree circumferential pattern is selected. The radius of the circle can also be adjusted as needed to surround the tear. The laser aiming bean is not visible until the “Standby” button is pressed. This changes the mode to “Treat” and the laser is now active. Align the aiming beam so that the simulated tear is outlined and adjust the radius as needed. Next, the laser power needs to be titrated until an appropriate burn is achieved. For this, touch “Titrate” which will change the pattern to a single spot. The power can be adjusted by using either the touch button on the screen or by rotating a knob on the actual slit lamp. Audible clicks are heard as he laser power is increased or decreased. With the simulated paper retina, much more power is required to achieve a burn than would normally be required when treating actual retina. Once an appropriate burn has been achieved, press “Titrate” again and the full pattern will return. Now the laser is ready to deliver the selected pattern of treatment. The simulated flap tear should be treated with three consecutive circumferential rows. The radius of he circle should be enlarged after each treatment. Any insufficiently treated areas should be filled in by selecting a single spot from the “Pattern” menu and applying laser where needed.

For the second simulated exercise, panretinal photocoagulation, adjust the global settings as described in Table 1 and select either a 3x3 or 4x4 grid from the “Pattern” menu. Use the titrate function again to achieve appropriate burns. One this is accomplished, press “Titrate” again to switchback to the full grid of treatment. Apply panretinal photocoagulation around the periphery of the simulated retina. Change patterns as needed to fill in any missing areas. It is important to realize that the laser does not apply all of the spots of a pattern at once; rather each is delivered over the set time. Thus, if the patient moves, the spots of the grid will become distorted. Letting up on the foot pedal can abruptly terminate laser delivery during any point of the pattern treatment.

The real patient:

When treating patient, the recommendations apply as those outlined above. However, delivering laser to a patent requires the use of a direct contact lens and a coupling agent such as Hypomellose 2.5% (GONAK). Various lenses are available for each type of laser application (see Table 1). Generally, lenses such as the Super Quad or Rodenstock are used for PRP or treating a retinal tear. Lenses such as the Area Centralis or Super Macula 2.2 are used for focal laser treatments. The patient should be given a drop of topical anesthetic prior to placing the lens on the eye. A coupling agent should be applied to the lens, being careful to avoid air bubbles. Once the lens is placed on the patient’s eye and the surgeon has oriented himself to the desired area of treatment, he above outlined protocol should be followed. It is important to remember that patients may experience pain during laser treatment and this can be minimized by limiting the duration of treatment, lowering the power, or in some instances decreasing the number of spots being delivered at one time. A retrobulbar block can also be used as needed for anesthesia.

Shutting down:

Once treatment has been terminated, place the laser in “Standby” mode. The specific parameters of treatment, including spot size, spot number, spot duration and power used, should be recorded. The coupling agent can be cleaned from the patient’s eye with sterile saline if needed The laser is turned off by selecting “Shut Down” from the screen menu or just turning the key to the “Off” position.

Table 1: Recommended Starting Parameters for Various Treatments
  Power (mW) Spot Size (µm) Duration (ms) Pattern Lens
PRP 350 200 20 3x3 Super Quad 160
Rodenstock
FOCAL 100 100 20 Single Super Macula 2.2
Area Centralis
HST 350 200 20 Circle Super Quad 160
Rodenstock

 

last updated: 03-02-2009
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