There are two main categories of shunts used in the treatment of chronic cerebrospinal fluid (CSF) increased intracranial pressure, i.e. cerebral shunts and lumbar shunts (extracranial shunts). Shunts are used in many neurological disorders, in cases of chronic increased intracranial pressure to drain excess CSF from the subarachnoid cavity associated with different conditions such as hydrocephalus and swelling of the brain due to the excess build-up of CSF. The increase in intracranial pressure (ICP) can lead to an intracranial hematoma, cerebral edema, crushed brain tissue or herniation.

A ventriculo-peritoneal shunt (VP-shunt) is a cerebral shunt, which consists of a valve housing connected to a catheter, the end of which is placed in the peritoneal cavity, to channelize the CSF and alleviate or prevent problems in patients that suffer from hydrocephalus or other related diseases. Subsequent complications may arise, which require immediate shunt revision (i.e. the replacement or reprogramming of an already existing shunt) to avoid new symptoms. The over-drainage is one of the possible complications in these patients.

The purpose of this case report is to describe a patient with a ventriculo-peritoneal shunt for the treatment of chronic increased intracranial pressure that developed a subacute and progressive bilateral ON, which appeared to be similar to normal tension glaucoma, associated with loss of right peripheral visual field and left nasal defects and other systemic symptoms. All symptoms improved significantly, and some even regressed after removal of the VP-shunt.

The case report is based on a 46-year-old Caucasian woman that resided both in Japan and Italy. The patient did not smoke, assume alcohol or drugs and did not have any food or environmental allergies. There was no history of trauma. She was taking oral medication for minor gastroesophageal reflux. In 2000, the patient underwent implantation of a ventriculo-peritoneal shunt (VP shunt) to resolve hydrocephalus after hemorrhagic rupture of a subarachnoid aneurysm. In 2010, following an eye examination, she was diagnosed with borderline intraocular pressure. Due to the Fukushima disaster, the patient did not undergo ophthalmological examinations while residing in Japan for about two years.

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Figure 1. Visual field damage progression.

In October 2012, due to an initial loss of peripheral vision in the right eye, associated with other neurological and systemic symptoms (i.e. fever above 37°C, photophobia, polyuria, dizziness in switching from upright to supine position, etc), the patient performed an eye examination in Japan and was diagnosed a rapidly progressive normal tension glaucoma. The patient was put on topical therapy with a prostaglandin analogue (latanoprost eye drops).

Several months later, the patient decided to come for a second opinion in our glaucoma clinic. The study was in compliance with the tenets of the Helsinki’s Declaration, and informed consent was obtained from the patient prior to testing. The study was in compliance with the Institutional Review Boards (IRBs) and HIPAA requirements, and was approved by the IRB of the Azienda Ospedaliero-Universitaria “S. Maria della Misericordia”, Udine, Italy. The complete eye examination showed:

• - well corrected bilateral mild myopia with visual acuity of 20/20 in both eyes
• - normal color vision
• - no evidence of afferent pupillary defect
• - intraocular pressure during medical treatment of 14 mmHg in both eyes;
• - pachymetry 538 micron and 560 micron in the right and left eye, respectively;
• - progressive temporal visual field defect in the right eye and slight nasal defect in left eye (Humphrey 30-2 SITA standard) [Fig. 1];
• - reduction of the thickness of the retinal nerve fiber layer (RNFL) and of the ganglion cells complex (GCC) at OCT examination (worse in the right eye) [Fig. 2, Fig. 3];
• - right optic nerve head with increased cupping and pallor and left optic nerve head within normal limits.

The patient later performed Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scans, which were both negative for compressive pathologies. She also underwent echo colour doppler of supra-aortic trunks, electroretinogram, polysomnography, 24-hour blood pressure holter, cardiac assessment; which all were found to be within normal limits.

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Figure 2. GCC thickness map and Nerve Head RNFL thickness progression.

Based on these results, she was discharged and diagnosed with isolated subacute bilateral chronic progressive optic neuropathy (worse in the right eye). We hypothesised that the disease could be related to low CSF tension.

In 2013, the patient returned to Japan where she continued with her regular follow-up ophthalmological visits. She was diagnosed with progressing glaucoma at the Tomakomai Civil Hospital, based on the subsequent visual field deteriorations despite medical therapy. A trabeculectomy was then proposed, however, the patient refused to undergo surgery.

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Figure 3. Right eye GCC thickness map progression.

During subsequent examinations (CT and neurosurgical checks), it was found that the VP shunt was well-positioned, but with possible over-drainage. The patient underwent pressure adjustments of the valve of the VP shunt on several occasions. The value of the pressure was initially raised from 70 to 100 mmH2O, then to 130 and then to 160 mmH2O and, finally, reached the maximum value with closure of the valve at 200 mmH2O.

In January 2014, the VP shunt was definitively removed. After surgery, the next visual fields remained almost stable (some slight improvement in a single point) and photophobia disappeared. With regards to the systemic symptoms, the body temperature returned to normal values, below 37°C; the dizziness disappeared, even during clino-orthostatic position changes, and her urination was normal, both with regards to frequency and quantity.

Eyes with both normal-pressure and high-pressure glaucoma can usually show similar optic disc alterations, however, eyes with vascular optic neuropathies tend to show a different optic disc appearance. Factors in addition to intraocular pressure (IOP) may play a role in the pathogenesis of glaucomatous optic neuropathy [3, 5, 7]. Clinical and experimental studies have shown that there are physiologic associations between CSF pressure, systemic arterial blood pressure, IOP and body mass index; patients with normal IOP glaucoma have significantly lower CSF pressure and a higher trans lamina cribrosa pressure difference when compared to normal subjects. Patients with normal pressure glaucoma have a significantly narrower orbital CSF space as compared with patients with high-pressure glaucoma [4, 6, 7].

According to several studies, [1, 2, 4, 5, 7] decreased cerebrospinal fluid pressure (CSFP) has been shown to be a new risk factor in the development of the glaucomatous damage. This concept is based on the notion that a differential pressure exists across the lamina cribrosa, which separates the intraocular space from the subarachnoid fluid space. The trans-lamina cribrosa pressure difference is dependent on the intraocular pressure and the retrobulbar cerebrospinal fluid pressure [5, 7]. An increased translaminar pressure difference can occur in eyes with a relative increase in IOP or a reduction in CSFP. This net change in pressure may act on the tissues within the optic nerve head, potentially contributing to glaucomatous optic neuropathy. Similarly, patients with ocular hypertension and elevated CSFPs, would benefit from a relatively protective effect from glaucomatous damage [3].

In 1976, Volkov pointed out that a low cerebrospinal fluid pressure could pathogenetically be associated with glaucomatous optic neuropathy. Similarly, in 1979, Yablonsky, Ritch and Pokorny postulated that an abnormally low cerebrospinal fluid pressure around the optic nerve may be the reason for barotraumatically induced optic nerve damage in normal-pressure glaucoma [2].

The lamina cribrosa of the optic nerve head forms the border between the intraocular space that has a higher pressure than the retrobulbar space. The difference between IOP and the pressure in the retrobulbar cerebrospinal fluid and optic nerve tissue space creates a pressure gradient across the lamina cribrosa that can negatively affect the eye [5, 7]. An abnormal pressure gradient influences the physiology and pathophysiology of the optic nerve head, including the orthograde and retrograde axoplasmic flow [2, 4]. The IOP, usually assessed with Goldmann applanation tonometry or similar devices, reports the transcorneal pressure difference. For the optic nerve health, however, the trans-lamina cribrosa pressure difference and the trans-lamina cribrosa pressure gradient are also very important factors [2].

The trans-lamina cribrosa pressure gradient is dependent on the distance between both compartments and, consequently, on the thickness of the lamina cribrosa. With this in mind, thinning of the lamina in myopic eyes may be a further reason for greater susceptibility to glaucoma [6, 7].

The case report is based on a rather unique and difficult interpretation of clinical signs, symptoms and results within a neuro-ophthalmologic framework, which entails multiple etiopathogenesis. The progressing visual field defects could have been primarily due to a circulatory origin, glaucomatous cause, or a combination of both conditions. Based on the clinical improvement of the patient after device removal, the most probable diagnosis of this patient was glaucomatous-like ON secondary to decreased cerebrospinal fluid pressure due to a possible VP shunt over-drainage.