What is the effect of allergic conjunctivitis on retinal nerve fibre layer thickness?

Effect of Allergic Conjunctivitis on Retinal Nerve Fibre Layer Thickness

Allergic conjunctivitis, particularly vernal keratoconjunctivitis (VKC) treated with long-term topical corticosteroids, is associated with significant thinning of the retinal nerve fiber layer (RNFL). 1

Findings from Research

Impact of Allergic Conjunctivitis on RNFL

The most recent and highest quality evidence demonstrates that VKC patients under long-term topical corticosteroid therapy (mean duration 23.8 ± 9.09 months) show:

• Significantly thinner mean global RNFL thickness
• Reduced superior and inferior RNFL thickness
• Negative correlations between duration of topical corticosteroid use and RNFL thickness (global, superior, and temporal regions) 1

These differences remained significant even after correction for ocular magnification effects, suggesting that the thinning is not merely due to changes in axial length or refractive error.

Potential Mechanisms

Two possible mechanisms may explain this RNFL thinning:

1. Direct effect of allergic inflammation: Chronic inflammatory processes in allergic conjunctivitis may affect retinal structures

2. Corticosteroid-induced changes: Long-term topical corticosteroid therapy (commonly used to treat allergic conjunctivitis) appears to have a significant impact on RNFL thickness 1

Clinical Implications

Monitoring Recommendations

• Regular RNFL thickness measurements should be incorporated into the follow-up of allergic conjunctivitis patients, particularly those on long-term corticosteroid therapy
• This is especially important since:
  • Visual field testing in pediatric patients (common in VKC) is difficult to perform
  • IOP measurements may be unreliable in detecting early glaucomatous damage 1

Confounding Factors to Consider

When interpreting RNFL measurements in allergic conjunctivitis patients, be aware of these factors:

• Refractive error: Myopic children have thinner RNFL (99.17 μm) compared to emmetropic (100.81 μm) and hyperopic children (102.45 μm) 2
• Axial length: Longer axial length correlates with thinner RNFL 2
• Optic disc parameters: Smaller disc area, larger cup area, and smaller rim area are associated with thinner RNFL 2

Clinical Pearls and Pitfalls

• Pitfall: Relying solely on IOP measurements to monitor for corticosteroid-related complications in allergic conjunctivitis patients

  • Solution: Include RNFL thickness measurements in routine follow-up

• Pitfall: Attributing RNFL changes solely to refractive error or axial length

  • Solution: Consider the duration of corticosteroid use as an independent risk factor for RNFL thinning

• Pearl: The normal RNFL thickness follows a "double hump" configuration with the thickest regions in the inferior (266±64 μm) and superior (240±57 μm) quadrants, followed by nasal (220±70 μm) and temporal (170±58 μm) quadrants 3

In conclusion, clinicians should be vigilant about monitoring RNFL thickness in allergic conjunctivitis patients, particularly those requiring long-term corticosteroid therapy, as significant thinning may occur that could impact visual outcomes.