Subjects and Medical Procedures

The study was a prospective randomized controlled trial. We compared the pain perception at laser treatment of peripheral retinal degenerations with green and infrared wavelengths.

Sequential patients with indications for photocoagulation of bilateral peripheral retinal degenerations were invited to participate in the study. The indications for treatment were horseshoe tears and dialyses, besides operculated holes and lattice degeneration in symptomatic patients (photopsias) or patients with history of retinal disease (RD in the fellow eye, high myopia, or intraocular surgery). Exclusion criteria for the study were severe liver disease, pregnancy, patients on regular analgesics, previous laser photocoagulation, and age less than 18 years.

Thirty patients (60 eyes) were enrolled in the study ( Figure 1 ). Each patient was randomly assigned to 1 of 2 arms: group 1, right eye treated with infrared laser (diode, 810-nm wavelength) and left eye treated with green laser (frequency-doubled solid-state laser, diode-pumped, with 532-nm wavelength); or group 2, right eye treated with green laser and left eye treated with infrared laser. Block randomization was performed at the time of enrollment (blocks of 4 patients; 2 of each group). The right eye was the first treated in all cases regardless of the wavelength arrangement. One ophthalmologist performed the photocoagulation.

Consort flow diagram: Pain perception at laser treatment of peripheral retinal degenerations with green and infrared wavelengths.

The treatment of each eye was standardized as follows: slit-lamp delivery system, total of 200 burns, 250-μm spot size, duration of pulse 0.1 seconds, pulse interval 0.3 seconds, avoiding the horizontal midlines, aiming for a moderately gray burn with green laser (100 to 400 mW) and a light gray burn with infrared laser (200 to 800 mW). Anesthetic drops (proparacaine 0.5%) were used for topical anesthesia before contact lens use.

Immediately after photocoagulation, the patient was asked to grade pain perception according to an 11-point (ie, 0–10) numerical rating scale (NRS), accompanied by the instructions “Please rate your pain by indicating the number that best describes it.” This NRS is represented as a straight line (10 cm in length). The numbers between 0 and 10 are spaced at regular intervals along the line; at either end of the line are 2 poles that are defined as the extreme limits of the response to be measured, with 0 meaning “No pain” and 10 meaning “Pain as bad as you can imagine.”

The interval between the treatment of the first and the second eye was 1 week. After grading of pain perception the patient was offered a single dose of a short-action painkiller (paracetamol 750 mg). In case of intolerable pain, the patient received peribulbar anesthesia. In case of persistent pain, the patient would be assisted by an anesthetist (fortunately, no patients needed such assistance). Patients were offered the option to suspend treatment after first eye. Although pain relief was not offered for the second eye, all patients completed the treatment of both eyes.

Data Collection and Outcomes

Data were collected by a standardized form that included gender, age, eye, pain perception, mean time to apply treatment, laser power, and wavelength, completed by the physician at the time of preoperative medical examination. Pain perception and complications of laser photocoagulation were recorded on a standardized form by a member of the medical staff. One of the study’s researchers reviewed the relevant medical records in order to determine whether 1 of the study’s definitions was met. These reviewers were not informed of the study-group assignment of the patients.

The primary outcome of the study was the assessment of pain immediately after photocoagulation. The secondary outcome was complications of laser photocoagulation (vasovagal episode, break in Bruch membrane, choroidal effusion, and vitreous hemorrhage).

Sample Size and Statistical Analysis

A sample size of 30 patients (total of 60 eyes; 30 eyes in each group) was planned. With an assumption of a mean pain perception of 2.5 (NRS) in the green-wavelength group, this sample size provided an 80% probability of detecting a difference as small as 2 (NRS) of pain perception in the infrared-wavelength group. Results of these analyses were considered statistically significant when the P values were < .05. For continuous variables, 1-way analysis of variance (ANOVA) tables were used.