Focal and grid macular laser have been a cornerstone treatment of various retinal diseases for decades. The most common applications over the years have been diabetic macular edema (DME), macular edema due to branch retinal vein occlusions (BRVO), and central serous retinopathy (CSR). The first solar photocoagulator was developed by Meyer-Schwickerath in the 1940s. He and Littman later developed the xenon arc photocoagulator, which was used for both anterior and posterior segment applications.¹

Since being described for the treatment of clinically significant DME (CSDME) in the Early Treatment of Diabetic Retinopathy Study (ETDRS) in 1985,² focal laser had been the first-line treatment modality for this condition until it was supplanted by intravitreal anti-vascular endothelial growth factor (anti-VEGF) therapy in the mid-2000s. That notwithstanding, focal laser still has a role as it remains the preferred treatment for non-center-involved DME (NCI-DME) and is sometimes used to augment anti-VEGF treatment in cases of center-involved DME (CI-DME). Recent clinical trials suggest that while anti-VEGF monotherapy for macular edema from diabetic retinopathy is effective for a large portion of patients, combination therapy with laser treatment is required to achieve the best possible outcome for many patients (approximately 50% of patients in the Diabetic Retinopathy Clinical Research Network [DRCR.net] protocol T study)³ and may potentially reduce the frequency of anti-VEGF injections.

Macular laser treatment for BRVO was found to be effective for macular edema in the landmark Branch Vein Occlusion Study (BVOS) trial in 1984.⁴ Treatment of this condition has also transitioned from macular grid laser to intravitreal anti-VEGF therapy much like DME, but laser still plays a useful role in some clinical scenarios (i.e., focal leakage from capillary breakdown, persistent and/or diffuse leakage despite anti-VEGF therapy, and treatment in patients who wish to forego or minimize injection therapy).

Macular focal laser also has a pertinent role in the treatment of CSR.⁵ Additionally, focal laser has demonstrated efficacy in the treatment of several other retinal conditions such as retinal arterial macroaneurysms (RAM),⁶ Coats’ disease,⁷ retinal capillary hemangiomas,⁸ and optic disc pit maculopathy.⁹

The mechanism of action of laser photocoagulation involves light energy being absorbed and converted into a thermal burn at the level of the pigmented tissues of the retinal pigment epithelium (RPE) and choroid, triggering local protein denaturation. The mechanism by which this process leads to beneficial physiologic and anatomical effects in the macula is speculative, but there are numerous theories. The direct effect from destruction of the RPE and photoreceptors leading to reduced oxygen consumption and increased oxygenation of the inner retina is one proposed mechanism.¹⁰ Another is the direct effect on retinal blood vessels, inducing closure and a corresponding reduction in leakage.¹⁰ A third theory asserts that photocoagulation induces the release of transforming growth factor-beta 2 and other cytokines from RPE cells, which in turn suppresses the proliferation of vascular endothelial cells contributing to macular edema.¹¹ Other speculated mechanisms are that focal laser increases the RPE pump action¹² and/or induces recruitment of healthy RPE cells as a healing response.¹³

This chapter focuses on guidelines and treatment parameters for conventional macular lasers (532-nm argon green and 577-nm yellow), which are widely available and have been the standard for decades. It does bear mentioning that there are numerous other laser types (various multicolor lasers, subthreshold) and delivery systems (pattern scanning laser, camera-navigated contactless lasers with retinal landmark tracking), each of which has its own specific unique applications, benefits, and shortcomings. It is beyond the purview of this chapter to explore each of these laser technologies individually, but further discussion on the basic science of lasers can be found in Chapter 3. The treating clinician should have a comprehensive understanding of the laser unit itself (laser parameters, computerized algorithms if available), how the laser functions with the associated delivery device (slit lamp), and the properties of the selected laser wavelength prior to embarking on treatment.