Treating Retinal Disease with FPGA Controlled Lasers
- Friday, 01 May 2009
More than 50 percent of Americans diagnosed with diabetes are at risk of developing diabetic retinopathy, a retinal disease that can lead to blindness. The condition is a result of diabetes affecting the circulatory system of the retina and causing abnormal new blood vessel growth. It has become the leading cause of new blindness among U.S. adults.
Since the 1970s, ophthalmologists have used a standard treatment called laser photocoagulation to treat diabetic retinopathy. The method, which has changed little since its inception, involves the controlled destruction of the peripheral retina using targeted laser pulses. This can free up oxygen to the rest of the eye and slow down or even prevent the blindness caused by the disease. While this type of treatment has proven effective at reducing the chances of vision loss by as much as 50 percent, it can require as many as 2,000 burns and ophthalmologists can deliver only one burn at a time. A full course of treatment typically requires two to four sessions, each lasting 12 to 15 minutes in which physicians administer the laser burns using a joystick and foot pedal to aim and fire. The procedure is so painful that some patients do not return for follow-up visits, even though they are fully aware that the untreated condition can eventually lead to blindness.
OptiMedica Corporation recognized the need for improved safety, precision, comfort, and speed of the photocoagulation procedure. Using a technique that was originally developed at Stanford University, they created the PASCAL Photocoagulator, which semi-automates a series of patterned laser shots and cuts the entire procedure to less than five minutes. The system provides significantly improved performance for the physician administering the treatment, as well as an enhanced therapeutic experience for the patient.
The PASCAL Photocoagulator uses a pattern scan laser to treat the condition using a single shot or predetermined pattern array. By automatically delivering multiple, shorter pulses rather than a series of manually placed lesions, the PASCAL system greatly reduces the risk of inadvertent application of the treatment to the fovea, which can result in localized vision loss. Physicians using conventional methods of photocoagulation must manually attempt to avoid this critical region of central vision. Furthermore, the PASCAL system significantly reduces the overall procedure time, as well as the amount of discomfort felt by the patient. This is achieved by reducing the laser pulse time from 100 milliseconds to just 10 milliseconds and then automating multiple spots with each depression of the foot pedal.
To precisely control the laser for pattern arrays, a control system applies a voltage proportional to the desired location of a beam to a galvanometer, an analog electromechanical transducer that produces a rotary deflection in response to voltage. The galvanometer is used as a high-speed, ultra-sensitive, limited rotation motor and when attached to a small mirror, precisely controls the position of a laser. OptiMedica needed hardware-timed decision making to meet these high-performance control requirements. The option to design a custom application specific integrated circuit (ASIC) chip would have required long lead times due to the fabrication process. Using field-programmable gate array (FPGA) technology, OptiMedica was able to meet all requirements with commercial off-the-shelf hardware.