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Editors Selection IGR 24-4
Anatomical Structures: Fine-tuning the assessment of RNFL and disc rim
Comment by Miriam Kolko & Niklas Telinius on:
117105 Progressive Changes in the Neuroretinal Rim and Retinal Nerve Fiber Layer in Glaucoma: Impact of Baseline Values and Floor Effects, Tomita R; Rawlyk B; Sharpe GP et al., Ophthalmology, 2024; 131: 700-707
This study by Tomita et al. investigates the impact of baseline values on the detectability of structural changes in the optic nerve using optical coherence tomography (OCT).
Methods and Participants:The data originates from a longitudinal cohort study conducted at the Nova Scotia Health Eye Care Centre, which followed 97 patients with open-angle glaucoma and 42 healthy controls over a median period of seven years. Participants underwent biannual OCT imaging for a minimum of five years. Baseline minimum rim width (MRW) and peripapillary retinal nerve fiber layer thickness (RNFLT) measurements were categorized into three groups: within normal limits (WNL), borderline (BL), and outside normal limits (ONL). Linear mixed-effect models were applied to quantify global and sectoral rates of change, while the follow-up period for each participant was divided into two equal halves to examine temporal changes in progression rates.
Key Findings:Statistically significant changes in MRW and RNFLT were observed across all baseline damage categories, underscoring the value of OCT imaging even in patients with baseline values outside the normal limits. However, the magnitude of these changes diminished as baseline values decreased. Among glaucoma patients with ONL baseline MRW, 73% demonstrated measurable progression, with an average reduction of 2.74 µm/year, a rate significantly faster than the rate observed in healthy controls. Similarly, 64% of patients with ONL baseline RNFLT showed measurable changes, with an average reduction of 0.89 µm/year.
The study revealed a more pronounced floor effect in RNFLT compared to MRW. Over the follow-up period, RNFLT progression rates slowed significantly in the second half, while MRW rates remained consistent. Globally, RNFLT slopes became less negative during the latter period, indicating reduced detectability of change as RNFLT values approached the measurement floor. In contrast, MRW changes remained consistently detectable, even at lower baseline values. These findings suggest that MRW is less affected by the floor effect, making it potentially more reliable for monitoring disease progression in advanced stages of glaucoma.
Limitations:Most participants had mild to moderate glaucoma, limiting insights into the progression patterns in more advanced stages. Additionally, while the study focused on MRW and RNFLT, it did not include macular imaging or ganglion cell complex thickness, which could provide complementary insights into glaucomatous changes. Lastly, the study did not identify a threshold for glaucomatous damage beyond which MRW or RNFLT would no longer be useful as diagnostic metrics.
Conclusion: This research underscores the importance of MRW and RNFLT as tools for monitoring glaucoma progression while highlighting notable differences in their sensitivity to baseline damage and susceptibility to floor effects. Although both parameters remain clinically valuable, MRW may offer greater reliability due to its reduced dependence on baseline values and its floor effect occurring later in the disease course. These findings support the use of OCT imaging, even for patients with baseline values outside the normal range.
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