Correlation between Retinal Nerve Fiber Layer and Clinical Grading of Papilledema in Patients with Idiopathic Intracranial Hypertension

DISCUSSION

Papilledema is edema of the optical disc caused by elevated intracranial pressure, and it is one of the main common causes of optic disc edema. Classically, edema is bilateral, with early indications and symptoms like headache, tinnitus, transitory vision obscuration, and diplopia, as well as the maintenance of visual acuity. When treating a patient with papilledema, it's critical to use neuroimaging to rule out the existence of intracranial expanding lesions or ventriculomegaly. If a neuroimaging examination finds no blockage of the cerebral venous flow system or exhibits evidence of obstruction, the identification of idiopathic intracranial hypertension (IIH), frequently referred to as pseudotumor cerebri disorder, should be considered.¹⁰

The evaluation of visual function, generally by measuring visual acuity and automated perimetry and fundoscopic variations, is critical for the diagnosis and management of these individuals. Many people think that an eye fundus exam, particularly when combined with retinography, is sufficient for assessing these individuals. However, in addition to being subjective, examiner-dependent, and non-quantitative, the intensity of edema determined only by fundoscopy may be vulnerable to inaccuracies.¹¹

Even among expert examiners, studies have revealed that there is little agreement on the categorization of papilledema. Furthermore, less skilled physicians may have difficulty identifying more subtle edemas, as well as effectively tracking whether the edema is diminishing or not.^{12, 13}

In this situation, noninvasive imaging methods such as optical coherence tomography may be a suitable alternative for improving diagnosis and patient follow-up.¹⁴

In fact, earlier research has revealed that OCT may be used to measure the thickness of the peripapillary retinal nerve fiber layer (RNFL) to determine optical disc edema.¹⁵

However, in cases of extreme edema (grade 3 or greater on the Frisén scale), the quantification of papilledema using OCT measurements of the thickness of the peripapillary RNFL may be subject to errors due to flaws in the demarcation of the rising and falling boundaries of the peripapillary RNFL, preventing a more reliable estimation of the edema severity.¹²

 Recent advancements in SD-OCT enabled the segmentation and evaluation of the retina's inner layers. As lately indicated by Afonso et al., lowering the overall macular thickness and its inner layers identified by SD-OCT, particularly by evaluating the  retinal ganglion cell (RGC) layer and the inner plexiform layer (IPL), is an essential observation in patients with chronic papilledema, and this decrease would relates to the loss of vision activity and responses from the RGC obtained by pattern reversal electro retino gram (PERG) .¹⁶

Other researchers believe that in individuals with papilledema, the diminution of the inner layers of the retina (RGC + IPL) acquired by SD-OCT might disclose early symptoms of neuronal and axonal death, even in the existence of optic disc edema. This would enable more aggressive therapy measures to be used in order to prevent or reduce additional vision loss.¹⁷

        This study includes 48 eyes ,the mean of  their BCVA (0.79 ± 0.16)  showing insignificant relation between visual acuity  and RNFL thickness with (p=.883)

According to results the mean of inferior RNFL quadrant is (213.75 ± 99.16), superior (210.58 ± 108.80), nasal (131.98 ± 70.51) and temporal (92.29 ± 33.67). The mean of RNFL thickness in 4 quadrants show increased RNFL thickness inferiorly > superiorly > nasally and > temporal quadrant (following the ISNT rule). So, in mild papilledema , RNFL thickness of nasal and temporal quadrant is important to confirm the diagnosis.

 In this study, clinical grades of papilledema is classified as mild  (41.7%), moderate (27.1%) and severe (31.2%) when analyzing values of median RNFL thickness and RNFL in all quadrants showing highly significant Correlation between severity of papilledema and RNFL thickness (P value< 0.01).

According to statistical data, in mild papilledema the mean of inferior quadrant is (131.05 ± 47.65), superior (119.60 ± 35.55), nasal (74.55 ± 29.41), temporal (67.55 ± 14.97) and average RNFL thickness is (98.30 ± 24.97). In moderate papilledema the mean of inferior quadrant is (206.38 ± 54.26), superior (221.23 ± 62.10), nasal (134.62 ± 62.94), temporal (88.00 ± 17.83) and average RNFL thickness is (162.69 ± 36.96). In severe papilledema the mean of inferior quadrant is (330.40 ± 54.83), superior (322.67 ± 96.60), nasal (206.27 ± 38.59), temporal (129.67 ± 28.31) and average RNFL thickness is (247.40 ± 37.69).

When analyzing the values of average RNFL thickness and its relation with papilledema severity under ROC curve give cut off point which help in diagnosis.  Mild papilledema is diagnosed with (≤ 118) µm, moderate severity with range (>118 – 188) µm and severe papilledema with (>188) µm. This study shows that OCT and MFS are complementing approaches for following up patients with papilledema. However, as disc edema worsens, OCT failure rates rise, indicating that OCT can be more beneficial at low levels of papilledema using existing methods. The greater relationship between MFS grade and RNFL thickness implies that RNFL thickness measures should be prioritized.

As a result, the OCT may be a highly differential diagnosis in instances of papilledema in a variety of ways, including quantifying optic disc edema, assessing response to established therapies, aiding in the differential diagnosis with other edematous optic neuropathies, and detecting axonal loss and knowing the processes regarding loss of vision, particularly through ultrastructural evaluation of the macula

Our study has significant limitations, including a limited sample size, particularly at the higher levels of papilledema. With high degrees of papilledema, measuring error may develop, and OCT algorithm failure rates can become considerable. Disc hemorrhages may also damage accuracy by affecting reflectivity in an unpredictable way.

CONCLUSION

OCT has the ability to be a useful imaging tool for the identification and monitoring of IIH, especially when combined with other clinical data. It is now being used in concert with other imaging techniques and clinical factors to detect early variations in the ONH and retinal layers before and after intracranial hypertension therapy. It's also a valuable investigative tool for studying the pathogenesis of papilledema and evaluating papilledema by verifying or supplementing a clinical examination, particularly in low grades. The importance of OCT in the treatment of IIH will rise as more research is done to enhance picture quality and categorization, as well as big human investigations are completed.