How often should retinal nerve fibre thickness and ganglion cell layer thickness be monitored in patients with myopia?

Monitoring Retinal Nerve Fiber Layer and Ganglion Cell Layer Thickness in Myopia

Patients with high myopia should have their retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) thickness monitored more frequently than those with low to moderate myopia due to the significant negative correlation between myopia severity and these retinal parameters. 1, 2

Impact of Myopia on RNFL and GCL Thickness

Myopia, particularly high myopia, has significant effects on retinal structure:

• High myopia (≤-6.0 diopters) is associated with thinner RNFL and GCL/GCIPL measurements compared to low and moderate myopia 2
• A negative correlation exists between RNFL/GCL thickness and:
  • Increasing severity of myopia
  • Increasing axial length 3, 1
• For every 1 diopter increase in myopic refractive error:
  • RNFL thickness decreases by approximately 3.67 μm
  • GCIPL thickness decreases by approximately 1.68 μm 1

Monitoring Recommendations Based on Myopia Severity

Low to Moderate Myopia (>-6.0 diopters)

• Annual monitoring is sufficient as these patients show less significant thinning of RNFL and GCL
• Both RNFL and GCL measurements remain relatively stable in this group 2

High Myopia (≤-6.0 diopters)

• More frequent monitoring (every 6 months) is warranted
• High myopia shows significant thinning in:
  • Average, superior, inferior, and nasal RNFL quadrants
  • Average, superior, and inferior GCL measurements 2, 4
• Special attention to nontemporal parameters of both RNFL and GCIPL, which show more pronounced thinning in high myopia 4

Measurement Considerations

• Use spectral domain optical coherence tomography (SD-OCT) for consistent measurements
• When evaluating glaucomatous changes in highly myopic patients:
  • Macular GCC thickness measurements may be a good alternative or complementary to RNFL assessment 5
  • Consider both parameters as GCC thickness showed a strong correlation with RNFL thickness (correlation coefficient=0.763) 5

Clinical Pitfalls and Caveats

• Optic disc area influences RNFL thickness but not GCIPL thickness:
  • Larger disc areas are associated with thicker RNFL measurements
  • GCIPL measurements are not significantly affected by disc area 1
• Temporal RNFL thickness may remain relatively stable across different myopia groups 2
• When monitoring for glaucomatous changes in myopic patients:
  • Consider that baseline RNFL and GCL thickness will be thinner in high myopia
  • Use both RNFL and GCL measurements for more accurate assessment 5, 4
• In children with myopia, early monitoring is important as thinning correlates with increasing severity of myopia and axial length 3

Algorithm for Monitoring

1. Determine myopia severity (low: >-3.0D, moderate: -3.0D to -6.0D, high: ≤-6.0D)
2. Establish baseline RNFL and GCL measurements using SD-OCT
3. For high myopia: Monitor every 6 months
4. For low to moderate myopia: Monitor annually
5. If patient has additional risk factors for glaucoma: Consider more frequent monitoring regardless of myopia severity
6. Pay special attention to nontemporal parameters in high myopia patients
7. Consider both RNFL and GCL measurements for comprehensive evaluation