What causes a flickering or shimmering patch in vision after laser photocoagulation?

Flickering or Shimmering Vision After Laser Photocoagulation

Flickering or shimmering patches in vision after laser photocoagulation are primarily caused by the permanent structural changes from discrete burns created in the retina, which manifest as visual disturbances that typically improve over time. 1

Mechanism and Prevalence

Laser photocoagulation works by creating discrete burns in the retina that result in:

• Permanent structural changes to retinal tissue
• Disruption of the choriocapillaris beneath laser spots
• Alterations to the retinal pigment epithelium (RPE)

These changes manifest visually as:

• Grainy or spotty vision
• Multiple scotomas (blind spots)
• Visual field defects
• Temporary blurry vision

According to the American Academy of Ophthalmology, approximately 60-70% of patients develop multiple scotomas after laser photocoagulation treatment, with the percentage varying based on the type of laser procedure and underlying condition being treated 1.

Timeline of Visual Symptoms

The visual disturbances follow a predictable pattern:

• Begin immediately after treatment
• Approximately 70% of maximum treatment response is seen at 1 week
• Visual symptoms generally diminish over time, sometimes requiring several months for complete adaptation 1

The choriocapillaris beneath laser spots is disrupted immediately (within 1 hour) following photocoagulation but begins to restore at week 2, with some spots still showing alterations at 1 year. Meanwhile, the outer retina and RPE remain disrupted at the 1-year mark 2.

Types of Visual Disturbances Based on Treatment Type

The nature and extent of visual disturbances depend on the type of laser treatment:

1. Panretinal photocoagulation (PRP):

   • Causes more widespread visual changes
   • Used for proliferative diabetic retinopathy and retinal artery occlusions
   • Higher risk of visual field defects and night vision problems 1, 3

2. Focal/grid photocoagulation:

   • Typically causes more localized visual disturbances
   • Used for conditions like central serous chorioretinopathy 1

Risk Factors for Persistent Visual Disturbances

Certain factors increase the risk of more severe or persistent visual symptoms:

• Increased laser duration and power
• Intensive treatment in a single sitting
• Excessive thermal energy dispersion within retina and choroid 3
• Treatment close to the macula or fovea
• Extensive treatment of peripheral retina 4

Monitoring and Management

For patients experiencing flickering or shimmering vision after laser photocoagulation:

1. Regular follow-up examinations as recommended by the American Academy of Ophthalmology:

   • Visual acuity testing
   • Undilated slit-lamp biomicroscopy
   • Pupillary assessment
   • IOP measurement
   • Stereoscopic examination of the posterior pole 1

2. Diagnostic assessment should include:

   • OCT imaging of the macula
   • Consideration of fluorescein angiography to detect leakage or neovascularization 1

3. Patient education about:

   • Expected timeline for symptom improvement
   • Signs of complications requiring immediate attention

Complications to Monitor

Patients should report any:

• Significant worsening of symptoms
• New floaters or flashes
• Sudden decrease in vision
• Pain and redness in the eye 1

Potential complications include:

• Macular edema (8% incidence after PRP)
• Choroidal effusions
• Exudative retinal detachments
• Subretinal fibrosis (rare but serious complication causing persistent visual loss) 5
• Transient loss of accommodation (even after limited peripheral retinal treatment) 4

Clinical Perspective

While visual disturbances after laser photocoagulation can be concerning for patients, it's important to note that the benefits of preventing severe vision loss from conditions like diabetic retinopathy or retinal vein occlusions generally outweigh the risk of these visual disturbances 1.

The advent of newer laser delivery systems, such as multispot pattern lasers, has significantly reduced but not eliminated these visual side effects 3.