In life, most of us should count our blessings that we are able to see. Sadly, a rare tragedy can occur leaving one in a blind world. This article will focus on two patients, one young and one old, who lost their sight in a split second.
Case 1
A 34-year-old male, GH, was a fortnight from getting married back in August 2017 when he was admitted to hospital for a third routine heart operation, this time a valve replacement. Unfortunately, during the procedure he suffered bilateral posterior cerebral artery territory branch occlusion, thought to be due to possible rogue emboli, which blocked both the right and left side (figure1). The consequence was bilateral occipital lobe cytotoxic oedema due to vascular infarcts and stroke which meant weeks of physiotherapy, speech and memory training and rehabilitation.
His fiancée had been our patient since she was little and she was instrumental in GH coming to see me. It was a truly humbling experience to see such a very young man who had to be led from a car and into the consulting room. The wedding was postponed and his fiancée became his carer. Their dream of an internet-wine business and life together was now put on hold.
Figure 1 Cytotoxic oedema of both occipital poles along with involvement of the right thalamus and resultant, due to acute infarction within the posterior cerebral artery territory (top left). The vascular image (top) shows patent, fully perfused right and left posterior cerebral arteries (PCAs) and normal anterior and middle cerebral arteries – the areas of infarct are labelled as ‘?’ The sagittal image (top right) shows the impact to be greater on the right side. Amsler grids (bottom left) show tiny windows of vision in each eye, approximately 10 by 14 degrees left and 11 by 11 degrees for the right. The fundus images (bottom right) show no retinal or foveal abnormality to account for the constricted field.
Ocular Examination
• Unaided vision; initially, no light perception was reported. With encouragement, GH found that by raising his chin he could achieve 6/7.5 binocularly
• Gross perimetry; a small window of vision centrally – automated central fields were not attempted
• Amsler; revealed around 10 degrees of vision in both the right and the left eye (figure 1) with surrounding absolute scotoma
• Pupil reactions; recorded as PERLA for both eyes
• Fundus examination; no optic disc or macular abnormalities – healthy fundus right and left eye
• OCT; no nerve fibre or macula defect in either eye
• VEP; low amplitude for both the high and low contrast stimuli
Amplitude reduction on visually-evoked potential (VEP) can indicate axonal loss or dysfunction along the visual pathway, and in our patient’s case the left eye showed much lower amplitude at both the high and low contrast settings. Amplitude can also be related to lower acuity, and GH’s significant vision loss may have contributed to the amplitude values. Latency is a term used to describe the time it takes for a signal from the optic nerve to reach the striate cortex. Generally, it should be in the range of 100 milliseconds. In this case, the latency showed a slight delay in the left eye for low contrast stimuli (113 compared to 101 milliseconds in the right eye). Latency represents demyelination of the nerves and in our patient’s case, once again, there were no indications of any dramatic slowing down of nerve conduction.
In summary, the VEP indicated that there were no issues at the retinal level. Nor were there any significant problems along the visual pathway affecting the nerve fibres, except a slight delay in the conduction of message from the optic nerve to the striate cortex in the left eye. The lack of change, especially with low contrast stimuli more so than high contrast stimuli, indicated the inner foveal based parvocellular neural pathway was not affected. I have summarised the way the neurones are packed within the optic tract with the foveal cells being central whilst the magnocellular neurones arising from the non-foveal region are situated on the outer layer (see figure 2).
Figure 2 (a) Parvocellular neurones (P in red) are bunched centrally and arise predominantly from the fovea. They respond to colour and fine detail. Magnocellular neurones (M in blue) arise outside the foveal region and respond to movement and low spatial frequency information. (b) The VEP amplitude indicates the presence of healthy retinal cells and for our patient the amplitude is seen to be depressed for each eye, though this can sometimes be due to reduced acuity or uncorrected refractive error. The latency is normal with high contrast stimuli for each eye, but the left eye shows reduced latency (113.3ms) for low contrast suggesting the magnocellular neurones are feeling the impact of the occipital lobe infarct on this side
Management
The patient was taught to learn to lift his head while focusing on objects and, once he had mastered the technique, was able to again use the computer. It was at this stage that we received a personalised bottle of wine as proof that he had started the online wine business!
Discussion
The occipital lobe is largely supplied by the posterior cerebral arteries which are terminal branches of the basilar artery (figure 3). Posterior cerebral artery infarction (tissue death due to ischaemia- the term infarct describes the lesion that results) can lead to occipital lobe infarction (or stroke). The resulting visual field defect will usually be a homonymous hemianopia, perhaps with a measurable area of central macula sparing, the field loss being on the opposite side to the that of the affected lobe. If both the occipital lobes are affected, there is a complete loss of visual field, except for, sometimes, a small area of macular field that is spared. Studies have shown that up to 12% of patients who suffer a stroke develop visual field loss, with homonymous hemianopia in 54% of cases.
Figure 3 (a) The posterior cerebral arteries (P1 and P2) radiate from the basilar artery (BA) and the deep posterior cerebral artery branches go on to supply the occipital region. The middle cerebral artery (MCA) branches from the internal carotid artery and deep branches perfuse part of the striate cortex. (b) An infarct of the right and left occipital lobes. (c) Visual field loss associated with the infarcts shown in (b)
Macula sparing describes the situation where the central 10 degrees of visual field is unaffected, and one theory to explain this suggests that there is dual blood supply to the occipital lobe. The posterior cerebral artery constitutes most of the blood supply to the occipital pole, but a deeper branch of the middle cerebral artery also perfuses some parts of the striate cortex related to foveal function and may preserve macular function when the posterior cerebral artery fails.
Case 2
A 68-year-old Asian male diabetic, GK, was on holiday in Tanzania when he experienced acute visual loss and headache. He was seen at a local eye hospital and soon returned back to the UK by private plane. He had immediate surgery for a pituitary tumour that had bled. The surgery was carried as a trans-sphenoidal procedure (with nasal entry) and debulking of the haemorrhagic adenoma completed. The surgery involved endoscopic excision of the sellar lesion (meaning one within the sellar turcica, the bony-walled box that houses and protects the pituitary gland; the name derives from a Turkish word for a saddle thought by early anatomists to be of a similar shape) followed by a graft of adipose tissue from the abdomen. GK suffered complete functional loss of vision for two weeks following the surgery.
Two months later, however, GK was able to make out the consultant’s outline, shirt colour and tie, and could interpret some larger images on the television. This change in his vision raised hope that there would be further improvement over the next few months and years.
There were other reported symptoms, such as him feeling thirsty and needing to drink around four to five litres a day, passing water five to six times during the night and every two hours during the day. His urine was also dilute. Blood tests revealed sodium levels to be in the upper range of normal (at 144mEq/L) indicating that he had diabetes insipidus.
Figure 4 Pituitary gland within the sella turcica also noting the hormones from the posteior gland
He was prescribed desmopressin (a synthetic anti-diuretic hormone) which helped reduce his urine output. The pituitary function was compromised post-surgery, so he was prescribed levothyroxine. To prevent Addison’s crisis (shock, seizure or coma caused by low levels of cortisol hormones from the adrenal glands due to reduced pituitary control), hydrocortisone 10mg was prescribed. Figure 4 shows the pituitary gland and table 1 summarises the endocrine role of the pituitary gland.
Follow-up examination
Three months after his operation, GK attended for his annual diabetic eye examination. His medications were:
• Metformin
• Sitagliptin
• Furosemide
• Ramipril
• Ferrous sulphate (iron)
• Atorvastatin
• Amlodipine
• Doxazosin.
The newly added drugs were:
• Desmopressin
• Hydrocortisone
• Levothyroxine
• Sando-K (potassium)
Vision; right and left hand movements only
Six months later, the vision showed a slight improvement;
R. -2.00 / -1.25 X 80 (6/24, N14)
L. hand movements only
Clinical findings
• Slit lamp; bilateral posterior subcapsular cataracts
• Fundoscopy; Optic discs; pale R and L. Vasculature; narrowing of arterial blood vessels (left eye worse – see figure 5)
• OCT; total loss of ganglion cells in both eyes
Figure 5 Fundoscopy and OCT at follow-up assessment. (a) Top left shows the right eye showing thick retinal nerve fibres (blue arrow and RNFL circle), and also thickened ganglion cell complex (inset plot). Top right images shows loss of nerve fibres (marked as ‘?’) and complete loss of ganglion cells. Note the pale optic disc subsequent to pituitary apoplexy. (b) Bottom left shows left eye with thick nerve fibres (blue arrow) and prominent arteries (right arrow), with relatively thick ganglion cell complex (inset). The right image shows complete loss of nerve fibres, barely visible arteries with cattle-trucking (double arrow), optic disc pallor and total loss of ganglion cells.
Pituitary apoplexyApoplexy comes from a Greek word ‘apoplexia’ meaning ‘struck down’ and plexe in Greek means a stroke. It describes the sudden bleeding of an organ or tissue, such as the pituitary, ovary or cerebrum. Pituitary apoplexy (or pituitary tumour apoplexy) occurs when a pituitary adenoma (a benign tumour of glandular tissue) has either bled within the gland or causes an impaired blood supply to the gland causing a sudden neurological impairment (figure 6).
Figure 6 Top; axial, coronal and sagittal views of a haemorrhagic pituitary apoplexy. The white arrows show the optic chiasm being pushed upwards and appearing swollen. Bottom; coronal and axial 2.5mm images showing remnants of pituitary tumour (R) and a deflated pituitary after surgery. The white arrows show the chiasm settled back down and relatively thin.
The characteristics of a pituitary adenoma include:
• sudden onset of visual symptoms
• headaches
• altered mental state
• hormonal dysfunction
The visual symptoms are due to the impact on the optic nerve (affecting visual acuity), the optic chiasm (affecting the visual fields) and the cranial nerves (causing nerve palsies and double vision).
Some 80% of patients who present with pituitary apoplexy have an undiagnosed pituitary tumour that has outgrown its blood supply. The anterior and posterior pituitary lobe have the same venous drainage (hypophyseal veins) but the arterial supply is different.
The superior hypophyseal artery is a branch of the internal carotid artery and supplies the anterior pituitary. The increase in size can compress the vein and cause a bleed or it can compress the artery and cause an infarct. Hence. pituitary apoplexy can be divided into haemorrhagic or infarction.
The posterior pituitary receives blood supply from many arteries including superior hypophyseal artery, infundibular artery and inferior hypophyseal artery.
Management
Treatment usually involves the following:
• Rapid administration of high dose corticosteroid such as hydrocortisone
• Careful monitoring of fluid and electrolytes – desmopressin is prescribed initially if the patient is passing water very frequently and also feeling thirsty. Diabetes insipidus if the urine is very dilute.
• Urgent trans-sphenoidal surgery.
Kirit Patel is an optometrist in independent practice in Radlett, Hertfordshire.