Retreatment with scatter laser was indicated for the redevelopment of high-risk characteristics at which time a minimum of 500 scatter laser burns were given between previous laser scars, anterior to the equator, and the macula. Factors considered in the decision to retreat included the following: (1) change in NV since last treatment, (2) appearance of NV (caliber, degree of capillary network, extent of fibrous tissue), (3) frequency and extent of VH since last treatment, (4) extent of laser scars, and (5) extent of fibrous tissue/ TRD. Additionally, ETDRS protocol recommended local confluent or scatter laser treatment to newly occurring small flat NVE.68 Since the publications by the ETDRS, scatter laser of the macula is usually avoided to minimize visual side effects.185 However, focal macular laser has been shown to reduce the rate of progression of PDR and scatter laser to ischemic temporal macula seems appropriate when active NV is present despite adequate peripheral retinal treatment.67 In cases of recurrent vitreous hemorrhage, retreatment with laser reduces the rate of future VH.186 The risk factors predictive of the need for retreatment include the presence of NVD and the severity of diabetes (e.g., younger age at onset of DM and short time from diagnosis of DM to development of high-risk characteristics).187 Over the course of a year following initial PRP for proliferative diabetic retinopathy, retreatment may be anticipated in about a third of patients.187

There is disagreement on the issue of determining end point in the application of PRP. There are proponents of high-intensity, high-density photocoagulation and this pattern may be most appropriate for severe

proliferative diabetic retinopathy as seen in some patients with severe PDR from type 1 diabetes.188,189

However, both the benefits and the adverse effects of scatter laser are dose dependent.67 Therefore, if vitreous traction rather than progressive NV growth is the primary cause of VH, vitrectomy surgery is more

appropriate than exhaustive laser retreatment leading to peripheral retinal ablation.20,164,189–191

9.2.3 Complications

Complications of laser photocoagulation of PDR

are important to identify, treat promptly, and prevent when possible.185,192 A potentially serious

anterior segment complication is corneal epithelial trauma.142 Diabetic eyes are predisposed to abrasion due to poor adhesion of the epithelium to the basement membrane, which may relate to corneal neuropathy. Friction from the contact lens creates a shear force that overcomes the pathologic adhesion.142 Rarely, severe thermal damage to the cornea may be caused by pigment, such as mascara, on the corneal surface during treatment.193 Anterior segment breakdown of the blood–aqueous barrier may be more long lasting in eyes with darker color irides, but appears to be clinically insignificant.194 Lenticular burns may occur in cataractous eyes treated with small-diameter, high-power, longduration argon photocoagulation.195 Posterior segment adverse effects due to breakdown of the blood–ocular barrier include macular edema, serous macular/retinal detachment, contraction of preretinal membranes, and choroidal detachment, which may lead to shallowing of the anterior cham-

ber, transient myopia, and secondary glau- coma.160,196–199 These complications were reported

by the ETDRS and were found to be less common in eyes randomized to less extensive scatter laser.67 In ETDRS protocol, PRP was not applied over fibrous tissue to minimize the risk of preretinal fibrous contraction and TRD.67 Despite this precaution, vitrectomy surgery may be required for the treatment of traction retinal detachment following PRP.120 Ciliochoroidal effusion is common after PRP and usually asymptomatic; however, it may

cause angle closure in hyperopic eyes with shallow chambers (Fig. 9.11).177,199 Treatment involves the

use of topical and oral glaucoma medications and steroids. Iridotomy is not typically helpful in these cases.200 Inadvertent direct photocoagulation of the macula may result in permanent scotoma and may be best prevented by following a strict regimen beginning with photocoagulation posteriorly and working anteriorly.68 Rupture of Bruch’s membrane with associated risk of hemorrhage and neovascularization secondary to laser photocoagulation is uncommon and appears to be related to highly intense,

small spot-size burns, and the red spectrum of laser light.201–206 Even without direct macular photocoa-

gulation, multifocal ERG of the macula may show reduced amplitudes after PRP despite good acuity and lack of increase in thickening on OCT.207 Inadvertent photocoagulation of the long posterior ciliary