Complications of Photocoagulation
The most serious complications of photocoagulation are caused by the use of excessive energy or misdirected light. Complications that may be associated with photocoagulation include inadvertent corneal burns, which can lead to opacities. Treatment of the iris may cause iritis and create zones of atrophy. Pupillary abnormalities may arise from thermal damage to the long ciliary nerves in the suprachoroidal space or the iris sphincter muscle. Absorption by lens pigments may create lenticular burns and resultant opacities. Optic neuropathy may occur from treatment directly to or adjacent to the optic nerve head, and nerve fiber damage may follow intense absorption in zones of intraretinal hemorrhage, increased pigmentation, or retinal thinning. Chorioretinal complications include foveal burns, Bruch membrane ruptures, creation of retinal or choroidal lesions, and exudative choroidal or retinal detachment. Retinal nerve fiber layer damage resulting from laser treatment can have more widespread vision loss than the local area. For example, if the damage occurs in the peripapillary retinal nerve fiber layer, arcuate scotomas can develop; when the papillomacular bundle is damaged, central vision loss can result.
Accidental foveal burns
Great care should be taken to identify the fovea by means of biomicroscopy; this step may be aided by comparing the appearance with recent fluorescein angiography images. Frequent reference to the foveal center throughout the procedure is helpful to maintain orientation. In some instances, the risk of foveal burns may be reduced by immobilizing the globe with peribulbar or retrobulbar anesthesia, especially when juxtafoveal treatment is being performed.
Bruch membrane ruptures
Small spot size, high power, and short duration of applications all increase the risk of a rupture in Bruch membrane, which may subsequently give rise to hemorrhage from the choriocapillaris and development of CNV.
Intense photocoagulation may cause full-thickness retinal holes. Similarly, intense treatment may create fibrous proliferation, striae, and foveal distortion, with resultant metamorphopsia or diplopia. Focal treatment with small-diameter, high-intensity burns may cause vascular occlusion or perforate blood vessels, leading to preretinal or vitreous hemorrhage. In addition, extensive panretinal treatment may induce or exacerbate macular edema, particularly in patients with diabetes mellitus.
Treatment of CNV may be complicated by subretinal hemorrhage, choroidal ischemia, and additional CNV or chorioretinal anastomosis. If active subretinal hemorrhage occurs during treatment, it should be addressed immediately by increasing digital pressure on the contact lens while continuing to treat the remaining portions of the CNV lesion in order to minimize obscuration of landmarks by hemorrhage. Progressive atrophy of the RPE may develop at the margin of photocoagulation scars, resulting in enlarged scotomas. Also, photocoagulation may precipitate tears of the pigment epithelium.
Exudative retinal and choroidal detachment
Extensive, intense photocoagulation may lead to massive chorioretinal edema and resultant serous retinal and choroidal detachment (Fig 19-3). The latter, in turn, can lead to narrowing of the anterior chamber angle from forward rotation of the ciliary body, resultant elevated intraocular pressure, and, rarely, aqueous misdirection. This reaction peaks 1–3 days after treatment and resolves spontaneously within a few weeks. Corticosteroids may be helpful to treat massive exudation.
Avoiding laser photocoagulation complications
As discussed, awareness and avoidance of the fovea during laser treatment is paramount. Selection of proper wavelength, power, exposure time, and spot size is also important. Proper titration of laser power and exposure time may be necessary to achieve the desired tissue effect. Waiting for proper pupillary dilation can help limit iris damage. Careful preoperative explanation of the laser procedure to the patient and comfortable positioning of the patient will facilitate cooperation and steady fixation, thereby improving safety.
Palanker D, Lavinsky D, Blumenkranz MS, Marcellino G. The impact of pulse duration and burn grade on size of retinal photocoagulation lesion: implications for pattern density. Retina. 2011;31(8):1664–1669.
Figure 19-3 Color fundus photograph shows choroidal detachment that occurred following panretinal scatter photocoagulation for diabetic retinopathy.
(Courtesy of M. Gilbert Grand, MD.)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.