Who is more prone to scotomas after photocoagulation (laser treatment)?

Patients at Higher Risk for Scotomas After Photocoagulation

Patients with preexisting diabetic retinopathy who are pregnant or planning pregnancy are at significantly higher risk of developing scotomas after laser photocoagulation treatment. 1

Risk Factors for Scotomas After Photocoagulation

Certain patient populations have increased vulnerability to developing scotomas (blind spots) following laser photocoagulation:

1. Pregnant women with diabetes:

   • Pregnancy can aggravate retinopathy in patients with preexisting diabetes
   • The progression rate of diabetic retinopathy during pregnancy is substantial:
     • New diabetic retinopathy development: 15.0 per 100 pregnancies
     • Worsening of nonproliferative diabetic retinopathy: 31.0 per 100 pregnancies
     • Progression from nonproliferative to proliferative diabetic retinopathy: 6.3 per 100 pregnancies
     • Worsening of proliferative diabetic retinopathy: 37.0 per 100 pregnancies 1

2. Patients with advanced baseline disease:

   • Those with disc neovascularization or vitreous hemorrhage
   • Patients with high-risk proliferative diabetic retinopathy (PDR)
   • Individuals with severe nonproliferative diabetic retinopathy 1

3. Patients receiving conventional threshold laser treatment:

   • Traditional panretinal photocoagulation creates permanent structural changes in the retina
   • Approximately 40% of the treated retinal area is destroyed during conventional treatment 2
   • Threshold laser treatments are more likely to produce paracentral scotomas than subthreshold techniques 3

Mechanism of Scotoma Formation

Scotomas after photocoagulation occur because:

• Laser burns create permanent structural changes in the retina
• Panretinal photocoagulation involves multiple laser burns in the peripheral retina
• These structural changes are expected outcomes rather than complications of the procedure 2

Prevention Strategies

To minimize the risk of scotomas, especially in high-risk populations:

1. Consider alternative treatments:

   • Anti-VEGF therapy is now recommended as first-line treatment for diabetic macular edema 1
   • Intravitreous injections of anti-VEGF ranibizumab are not inferior to traditional panretinal laser photocoagulation for PDR 1

2. Use modified laser techniques:

   • Subthreshold (invisible) diode laser modified grid photocoagulation can reduce the objective and subjective effect on the paracentral visual field 4
   • Subthreshold laser is as effective as conventional threshold laser in reducing diabetic macular edema while better preserving contrast sensitivity and photo stress recovery time 3

3. Avoid treating near the fovea:

   • Maintain at least 500 μm distance from the center of the macula
   • Avoid foveal vasculature to prevent central vision damage 2

Monitoring and Follow-up

For patients who have undergone photocoagulation:

• Monitor for changes in pattern or size of perceived scotomas
• Conduct annual comprehensive eye examinations
• Perform OCT imaging to assess for potential complications like macular edema
• Consider fluorescein angiography to detect leakage or neovascularization 2

Clinical Implications

Despite the risk of scotomas, laser photocoagulation remains beneficial in reducing the risk of severe vision loss in appropriate patients. The DRS showed that panretinal photocoagulation reduced the risk of severe vision loss from PDR from 15.9% in untreated eyes to 6.4% in treated eyes 1.

The benefits of treatment must be weighed against the risks, particularly in high-risk groups such as pregnant women with diabetes, who require close monitoring throughout pregnancy and for one year postpartum 1.