Upon conducting an extensive literature review, this study appears to be one of the first prospective studies aimed at longitudinally evaluating the natural history and evolution of RNFL-OCT in patients with radiologic chiasmatic compression syndrome, without clinical manifestations. The objective was to understand the true role of RNFL-OCT and its impact during the pre-clinical phase of chiasma compression syndrome in NFPA, as well as to assess any changes over time.
Based on the analysis of 20 patients, it was observed that alterations in OCT, whether at diagnosis or during follow-up, did not correspond to visual impairments in terms of visual acuity (VA) and visual field (VF) dysfunction. Existing literature contains several studies that investigate the prognostic role of OCT, typically involving patients with visual disturbances at diagnosis and a clear indication for decompressive surgery. These studies have demonstrated the prognostic value of OCT in terms of post-surgical improvement of visual impairments [5, 15].
Two previous retrospective studies by Blanch et al. and Yum et al. [2, 16], which focused on patients in the pre-clinical phase, did not provide conclusive evidence regarding the role of RNFL-OCT in early detection of visual disturbances and did not evaluate its evolution over time.
In the current study, the eight patients with altered RNFL-OCT at diagnosis, despite having radiological optic chiasm compression, did not present any VA or VF disturbances. Interestingly, in all eight patients, the RNFL-OCT alteration was localized in the nasal sector, consistent with the anatomical correspondence between compressed chiasm involvement and OCT alterations described in the literature [1].
Based on this hypothesis, supported by available literature, that OCT alteration could serve as an early marker of VA and VF dysfunction, we conducted comprehensive and consistent ophthalmological follow-up of our patients [1]. Our analysis demonstrates that the eight patients with mild and moderate baseline RNFL-OCT thickness alterations did not develop visual signs or symptoms over time, with a mean follow-up of 60 months (SD: 19; ranging from 36 to 96 months). Furthermore, the four patients who had normal RNFL-OCT at diagnosis but developed moderate and severe alterations during follow-up did not experience any VA or VF dysfunction, with a mean follow-up of 60 months (SD: 19; ranging from 36 to 96 months). Additionally, all twenty pituitary adenomas remained globally stable in size during the average follow-up period of 60 months (SD: 19; ranging from 36 to 96 months).
If the reduction in RNFL-OCT thickness corresponds to axonal death or morphological alteration, one could argue that a structural alteration at this level is associated with objectively functional visual impairments. However, the present study did not demonstrate this correlation, neither at diagnosis nor during a relatively long follow-up period. Furthermore, our analysis revealed a statistically significant relation between RNFL thickness and tumor height (p = 0.0012), as well as a tendency between RNFL thickness and chiasma thickness at the median line level (p = 0.053). Therefore, the question arises regarding how to interpret an OCT alteration when managing a patient with radiological compression of the optic anterior pathway. Based on our study, the presence of RNFL-OCT alteration does not appear to be an early marker of visual dysfunction.
Study limitation
The main limitation of our study, despite its prospective and longitudinal nature, as well as the relatively long follow-up period (mean 60 months; SD: 19; ranging from 36 to 96 months), is the limited sample size. We believe that further prospective multicenter studies involving a larger number of patients are necessary to assess the true role of RNFL as an early marker of visual dysfunction in compressed anterior optic pathways. Additionally, exploring other parameters such as the ganglion cell complex (GCC), as recent studies have suggested its potentially better sensitivity and specificity, would be valuable. Furthermore, establishing a clear cutoff value for RNFL/GCC to aid in the decision-making process for surgical management is worth considering.