Panretinal Photocoagulation
Alan R. Hromas
Retinal ischemia is a common manifestation of a number of vascular diseases causing impairment of retinal circulation, including diabetic retinopathy, retinal arterial and venous occlusion, and inflammatory vasculitis. Ischemia and the resulting retinal tissue hypoxia upregulate the production of vascular endothelial growth factor (VEGF), which in turn may lead to deleterious effects on vision via increased vascular permeability or neovascularization. Neovascularization may manifest on the optic nerve head or elsewhere on the retina, leading to tractional elevation and detachment, or vitreous hemorrhage. Anterior segment neovascularization may produce a secondary angle closure, leading to neovascular glaucoma.
Diabetic retinopathy has long been recognized as a common cause of retinal ischemia via progressive hyperglycemia-mediated damage to the retinal microcirculation. The landmark Diabetic Retinopathy Study (DRS, 1979) demonstrated a significant reduction in the risk of severe vision loss in patients with proliferative diabetic retinopathy (PDR) treated with panretinal photocoagulation (PRP).1,2,3 The subsequent Early Treatment of Diabetic Retinopathy Study (EDTRS, 1991) further refined the indications and thresholds for treatment.4 Over the last 15 years, intravitreal injections of anti-VEGF drugs have gradually begun to emerge as an alternative treatment for many of the situations previously treated with PRP, and the Diabetic Retinopathy Clinical Research Network (DRCR.net) protocol S (2016) confirmed that intravitreal injections of the anti-VEGF drug ranibizumab was a viable, and sometimes superior, treatment option as compared to traditional laser.5
Though the research and data regarding PRP are most robust in the case of diabetic retinopathy, many of the findings have been extrapolated to other ischemic retinal diseases. The effectiveness of PRP in causing reduction or regression of neovascularization is believed to be related to its ability to improve oxygenation of the ischemic inner retina and downregulate the production of VEGF. The resulting reduction in circulating VEGF generally leads to stabilization or regression of existing neovascularization.6,7
Treatment generally involves the administration of multiple individual laser spots throughout the ischemic area, ideally using preoperative fluorescein angiography to delineate the areas of nonperfusion. PRP can be performed in-office with a slit-lampmounted laser or laser indirect ophthalmoscope (LIO), as well as in the operating room, with an endolaser, in conjunction with pars plana vitrectomy. Though the principles are similar regardless, this chapter will focus on in-office treatment.
INDICATIONS
Key Indications
PDR
Branch retinal vein occlusion (BRVO) or central retinal vein occlusion (CRVO), when associated with neovascularization8,9
Branch retinal artery occlusion or central retinal artery occlusion (CRAO), when associated with neovascularization10
Sickle cell retinopathy11
Inflammatory retinal vasculitis with neovascularization
Radiation retinopathy
Inherited or genetic abnormalities causing retinal ischemia and neovascularization
Familial exudative vitreoretinopathy
Eales’ disease
Incontinentia pigmenti
Though the most common indications for PRP are listed here, treatment may be indicated for any condition producing ischemia with neovascularization. Neovascularization may be found in multiple locations, including on the optic disc (NVD), elsewhere on the retina (NVE) (Figs. 19.1 and 19.2), on the iris (NVI), or within the iridocorneal angle (NVA).
 FIGURE 19-1 Fundus photograph showing neovascularization elsewhere. |
 FIGURE 19-2 Fluorescein angiogram showing neovascularization elsewhere with peripheral ischemia. |
Because of the potential for significant side effects resulting from PRP, extensive research has been undertaken to determine the optimal timing to perform treatment; that is, whether treatment should be performed at the first sign of neovascularization, only in more high-risk cases, or even prior to neovascularization developing (DRS, ETDRS). In brief, the authors concluded that PRP during the mild and moderate preproliferative stages tended to produce untoward side effects such as peripheral vision loss without significant benefit. In general, PRP can reasonably be performed in cases of severe non-PDR, particularly when the treating physician determines that there is high risk of progression to proliferative disease or if there are socioeconomic factors that may prevent the patient from following up on the recommended schedule for monitoring.4,12
When PDR is present (defined as the presence of NVD, NVE, NVI, or NVA), treatment is generally recommended. Some treating physicians may elect to delay treatment until “high-risk characteristics” develop, including neovascularization over one third of the optic disc, NVD associated with vitreous hemorrhage, or NVE greater than half of the disc area in size associated with vitreous hemorrhage.13,14
Note: Ablative laser to peripheral avascular retina is widely used for the treatment of advanced stages of retinopathy of prematurity. The principle is similar to that employed in acquired retinal vascular diseases, but there are important differences in the laser technique that are beyond the scope of this chapter.15
CONTRAINDICATIONS
Key Contraindications
Media opacity preventing clear view of posterior segment
Patient inability to cooperate
Performing safe PRP requires an adequate view of the posterior segment. By nature of the conditions being treated with PRP, the fundus view is often compromised by vitreous hemorrhage; other conditions such as corneal opacities,
cataract, or inadequate mydriasis may be compounding factors. If the view is inadequate to safely aim the laser, treatment is best deferred until circumstances have improved spontaneously (i.e., via natural reabsorption of vitreous hemorrhage) or through other methods (cataract surgery or vitrectomy as indicated). Intravitreal injections of anti-VEGF medications can often be used to induce rapid regression of neovascularization and control neovascular complications in the meantime.
cataract, or inadequate mydriasis may be compounding factors. If the view is inadequate to safely aim the laser, treatment is best deferred until circumstances have improved spontaneously (i.e., via natural reabsorption of vitreous hemorrhage) or through other methods (cataract surgery or vitrectomy as indicated). Intravitreal injections of anti-VEGF medications can often be used to induce rapid regression of neovascularization and control neovascular complications in the meantime.
PRP is frequently employed in an in-office setting on patients who are awake and alert. For patients that are unable to cooperate with treatment due to age or mental status, treatment in an operating suite while under sedation administered by an anesthesiologist is an option. Patients who are awake during the procedure require some degree of cooperation to facilitate treatment and decrease the risk of inadvertent laser damage to the macula and optic nerve. This is particularly important when treatment is being administered via LIO, as compared to treatment via a slit-lamp-mounted laser with contact lens. In-office cooperation is facilitated by ensuring the patient receives adequate anesthesia preoperatively and ensuring that the patient is in a comfortable position, whether at the slitlamp or in a reclining chair.
INFORMED CONSENT CONSIDERATIONS
Key Informed Consent Adverse Events
Decrease in peripheral vision
Nyctalopia
Inadvertent laser damage to optic nerve or macular area with resulting scotoma
Contraction of neovascular tissue with tractional elevation of the retina
Vitreous hemorrhage
Discomfort during the procedure
Failure to adequately induce regression of the neovascularization
Worsening cataract
Worsening macular edema
Transient choroidal effusion
Informed consent should include a description of the procedure to be performed, as well as the purpose, in plain language. For instance, “laser treatment to cause regression of abnormal blood vessels on the retina,” which is intended to “decrease the risk of bleeding in the eye and retinal detachment” or “decrease the risk of glaucoma (high eye pressure)” as indicated.
In addition to the proposed benefits of the procedure, the risks listed previously should be addressed. In particular, some degree of peripheral vision loss and decreased low-light vision (nyctalopia) is very common among patients following PRP16,17 and may be especially problematic for patients in certain professions (e.g., truck drivers). If the eye is being anesthetized with retrobulbar injection, the rare but potentially fatal complication of brainstem anesthesia should also be discussed.
As noted previously, the goal of treatment via PRP is to induce regression of neovascular tissue. It is important to discuss with patients preoperatively that, in the process of regression, neovascular tissue will sometimes contract, causing anterior traction on the retina and hemorrhage into the vitreous or progression of tractional retinal detachment. As patients are often asymptomatic or minimally symptomatic from a visual acuity perspective prior to treatment (despite having what may be heavy neovascularization), failure to adequately explain the risks of these outcomes beforehand may lead to them placing the blame on the surgeon or procedure itself.
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