Laser therapy has been used to treat many pathologies in the eye for decades. A xenon arc laser was developed in the 1950s by the Carl Zeiss Laboratory. It was used clinically in the early days of retinal therapy. The argon laser was discovered in 1964 by William Bridges. However, an official study to investigate the effects of laser treatment via PRP was not conducted until the 1970s.
This study, the Diabetic Retinopathy Study (DRS), examined the impact of pan-retinal photocoagulation (PRP) through both xenon arc laser and argon laser treatments on patients with proliferative diabetic retinopathy (PDR) to determine whether it was more beneficial than no treatment at all.
The study showed that laser therapy was indeed helpful to patients with PDR and showed that argon lasers created less adverse effects for patients than xenon lasers while retaining similar efficacy. This study also set forth the first detailed treatment parameters for PDR. As a result, xenon arc laser therapy is now primarily discontinued in favor of argon laser (or modern equivalent continuous-wave millisecond laser systems).
The Early Treatment Diabetic Retinopathy Study (ETDRS), conducted shortly after the DRS, examined PRP’s effects on non-proliferative diabetic retinopathy (NPDR) and determined the exact stage in the disease course at which a Doral Health & Wellness Ophthalmologist can administer laser therapy. Currently, more advanced laser delivery systems and other methods of combating diabetic retinopathy are emerging. However, PRP remains the mainstay of treatment for PDR.
PRP is typically delivered through either a slit lamp system or an indirect laser ophthalmoscope (headlamp/BIO).
Slit-lamp: The laser is attached to the typical ophthalmic slit lamp. The laser energy is delivered in a coaxial fashion. The patient is placed in a seated position, and the chin is placed on the chin-rest. A contact lens, which focuses the laser onto the retina, is set against the cornea with a clear coupling agent. Typically a wide-angle or mirrored lens is used. The laser goes through the cornea, anterior chamber, and lens and focuses on the retina by the contact lens.
Headlamp: The patient may be supine or seated. The doctor wears the standard indirect headlamp with the laser attached coaxially. A handheld lens is used to view the retina and focus the laser on the retina. The doctor’s head movements control the aiming beam. In both cases, the doctor or surgeon will place topical anesthesia, usually proparacaine or tetracaine, into both eyes. For infants or patients with compliance problems, stronger anesthesia, such as systemic anesthesia or sedative, may be administered. Both methods make approximately 1500-5000 typical-sized burns across 1-4 treatment sessions (variable with treatment protocol). According to the DRS protocol using a standard argon-type laser PRP, settings include burns that range approximately 200μ to 500μ in size, pulse durations of 100 milliseconds, and 200-250 mW power. The goal is to produce burns that are grey in color and avoid dense white burns. Depending on the protocol being used, all settings may be adjusted for the desired effect.
Information on this treatment was written by Sejal Jhawer, Peter A. Karth, MD.