Subthreshold (retinal pigment epithelium) photocoagulation in macular diseases: a pilot study

Abstract

Background: Subthreshold (retinal pigment epithelium) photocoagulation is a new photocoagulation method, which treats the retinal pigment epithelium (RPE) and avoids damage to the neural retina. The initial results in this prospective pilot study on various macular diseases are presented.

Methods: 12 patients with diabetic maculopathy (group I), 10 with soft drusen (group II), and four with central serous retinopathy (CSR) (group III) were treated and followed up for 1 year. Treatment was achieved using a train of repetitive short laser pulses (1.7 micros) of a green Nd:YLF laser (parameters: 527 nm, 100 and 500 pulses, repetition rate: 500 Hz, spot size: 160 microm, energies: 70-100 microJ). Laser energy was based on the visibility of test lesions on fluorescein angiography (50-130 microJ). Patients were examined at various times by ophthalmoscopy, fluorescein and ICG angiography, and infrared imaging.

Results: After 6 months hard exudates disappeared in six out of nine patients in group I and leakage disappeared in six out of 12 diabetic patients. In group II drusen were less in seven out of 10 patients. In group III serous detachment disappeared in three out of four cases. Visual acuity was stable in all cases. None of the laser lesions was clinically visible immediately. After 1 day most lesions were visible as yellowish RPE depigmentation. After 3 months some of the lesions were visible as hyperpigmented areas but most were not. Fluorescein angiography showed leakage only in the first week. Infrared imaging showed that most lesions can be visualised in groups I and II after a period longer than 1 week as hyperreflective areas.

Conclusion: This study showed that subthreshold (RPE) photocoagulation is effective in some cases of diabetic maculopathy, drusens, and in CSR. Visibility of laser burns is not always necessary in the treatment of macular diseases presented here. Infrared imaging is an effective and non-invasive way of visualising subthreshold (RPE) laser burns.

Figure 1

Early (A) and late (B) phase of test exposures in the lower part of the macula with various number of pulses and energy, showing RPE disruption.

Figure 2

Fundus picture of a 48 year old diabetic patient with hard exudates (A). The corresponding fluorescein angiogram shows diffuse leakage (B). Angiogram 2 hours after a grid and a focal treatment to the area of hard exudates was performed (C). Fundus image 6 months after photocoagulation (D). Apart from two areas of hyperpigmentation (arrows) no laser scars can be seen.

Figure 3

Late phase (10 minutes) of a diabetic patient showing clinically significant exudation before treatment (A). The corresponding angiogram 1 day after treatment (B) shows RPE disruption due to the laser effects. Early (C) and late (D) phase of the angiogram 6 months later: no exudation is detectable in the late phase (10 minutes) (D), however microaneurysms are still visible.

Figure 4

Fundus image of a patient with soft drusen before (A) and 2 hours after a grid treatment has been applied to the temporal macula (B). Fundus image 1 year after treatment (C). Most drusen have disappeared. The photocoagulation pattern is shown in Figure 7B, visible as bright hyperfluorescent areas due to disruption of the outer blood-retinal barrier.

Figure 5

Fundus image before (A) and 6 months after subthreshold RPE treatment (B). A change in the drusen pattern is notable (arrows).

Figure 6

Fundus image of a patient with recurrent central serous retinopathy before (A) and 2 weeks (B) after photocoagulation Corresponding fluorescein angiogram before (C), 2 hours (D), and 2 weeks (E) after photocoagulation. Exudation has disappeared after 2 weeks. Note laser scars (arrow) of previously done conventional treatment.

Figure 7

Fluorescein angiogram 2 hours (A) and 4 hours (B) after photocoagulation. Test exposures (parameters: 500 pulses each 70 µJ and 100 pulses each 70 µJ) have been applied to the test area. While 2 hours after treatment (A) one laser exposure (parameter: 500 pulses, 70 µJ) is visible (arrow), 4 hours after treatment (B) all four laser exposures have led to disruption of the RPE barrier (arrow).

Figure 8

Fundus image of a patient treated for soft drusen 6 months after treatment (A). The photocoagulation pattern is shown in (B). Corresponding infrared images 1 day (C) and 1 week (D) after treatment. While no laser lesions are visible after 1 day all laser exposures can be visualised after 1 week (D).