The pathogenesis of papilledema in IIH is mainly due to the mechanical effect. Vascular affection occurs secondary to these mechanical changes. The optic nerve and brain share the same leptomeninges. When CSF pressure increases, it compresses the optic nerve leading to stasis of axoplasmic flow of the optic nerve fiber layer and the optic disc. This stasis in the axoplasmic flow leads to swelling of nerve fiber, and subsequently the optic disc. This swelling secondarily compresses the optic disc venules leading to leakage of extracellular fluid. Thus, vascular changes in papilledema are secondary and not primary [9].

The visual impairment most likely is not due to axoplasmic stasis only because the impulses are conducted through the axon membrane and not through the axoplasm. Thus, vascular changes play a role in the visual impairment [7].

So, we can use the secondary vascular changes that occur in papilledema to evaluate the effect of intracranial pressure reduction after shunt surgery.

The sure method to detect intracranial pressure is by measuring the CSF opening pressure but it is an invasive method. So, many non-invasive methods were used to detect increasing intracranial pressure [10].

We can use papilledema resolution as an indicator of the reduction of CSF opening pressure. However, Sinclair et al [11] reported that papilledema was completely resolved only in 44% of patients, which means that about 56% of patients may have residual optic disc elevation.

After normalization of ICP by medical treatment or surgery, papilledema resolves within week or months. However, some patients have residual disc elevation which may occur as a result of gliosis in the optic disc [1]. The delay in the resolution of disc oedema may be due to congenital variation in the distance of the intracanlicular part of the optic nerve and the size of the lamena creprosa opening [7].

Fundus examination and fundus photography are good methods to detect papilledema resolution. However, in some situations, depending on them is difficult. In cases with optic disc morphological abnormality (eg. Tilted disc) it is difficult to distinguish between disc oedema and blurring of the disc margin. In longstanding papilledema, gliosis of the optic disc occurs making the optic disc margin irregular which subsequently leads to difficult papilledema recognition by fundus examination [12] In recurrent and relapsed IIH, detection of papilledema by fundus examination is difficult as a result of the gliosis and thinning of RNFL that occurred from the previous attack [8].

In those patients, we need to find a method to ensure that optic nerve is in a safe condition as a confirmatory method with measurement of CSF opening pressure by lumber puncture and in the future it may replace the invasive lumber puncture.

Depending on clinical follow up alone isn’t conclusive as in some patients they suffer postoperative headache of low intracranial tension but the patient usually fails to declare it obviously. In cases this headache is associated with residual papilledema it is crucial to investigate thoroughly to be sure that intracranial tension is normal. Normal CSF opening pressure by Lumber puncture alone indicates that intracranial tension is normal but it is invasive method and in case of residual papilledema .it is a must to ensure that optic nerve is in a safe condition.

MRI optic nerve is crucial in the diagnosis of IIH. However, the morphological signs of MRI become clearly visible only in advanced disease stages on conventional MRI. So, it can’t be used in early detection or follow-up of patients [13, 14]. Ultrasound is useful in differentiating papilledema from psudopapilledema. It can measure the morphological changes in optic nerve like MRI [15]. However, these changes have low specificity and need highly expert examiners [9]. Moreover, measuring the retinal nerve fiber layer thickness by OCT can be used to detect papilledema. However, depending on it in papilledema follow-up is somewhat problematic. Decreasing the RNFL thickness may be due to a true reduction of the optic disc oedema. Yet, it may be due to atrophy of RNFL that may occur during the course of the disease [7].

In this study, we performed shunt surgery for patients with IIH. Then we divided the patients after surgery into a completely resolved papilledema group and a residual disc elevation group. Both groups have successful surgery proved clinically by resolution of preoperative symptoms of headache, blurring of vision and vomiting, fundus examination which revealed resolution of papilledema in 15 cases and residual papilledema in 6 patients, those 6 patients were submitted to measuring the post-operative CSF opening pressure by lumber puncture which was normal for all patients.

In the residual disc elevation group, the optic disc vessel density was significantly reduced after surgery. The normal CSF opening pressure indicates resolution of IIH. So, the reduction in optic disc vessel density can be used as an indicator for the resolution of IIH in cases with residual disc elevation.

In this study, the grade of papilledema in the residual disc elevation group is higher than the completely resolved papilledema. Thus, it may take a longer duration to resolve.

The absence of significant differences between the two groups as regard the post-operative optic disc vessel density; indicates that the vessel density can help in cases of residual disc elevation.

To our knowledge, this is the first study that detects the reduction of optic disc vessel density after shunt surgery for patients with IIH having a residual elevation of the optic disc.

There are some limitations of measuring the optic disc vessel density by OCT-A. In severe degrees of papilledema and a high degree of myopia; the quality of the image is poor; making the quantitative measure of vessel density difficult. Also, media opacity can hinder light from reaching the retina, (fundus examination can’t be done in these cases also). Moreover, pregnancy, smoking, and some medications can affect vessel density measurement. However, we can depend on the difference between the pre and postoperative values.

In conclusion, in cases of residual optic disc swelling after shunt surgery, we may detect the reduction of intracranial pressure by the reduction in the optic disc vessel density which is a safe non-invasive technique. That may replace the invasive CSF opening pressure measurement. Still we need more patients and more studies to prove this evidence.