|Year : 2020 | Volume
| Issue : 3 | Page : 194-196
Chiasmic blindness: Hunted down
J P Justin Prashanth1, Hannah Ranjee Prasanth1, Renuka Srinivasan1, Ramesh Kannan2
1 Department of Ophthalmology, Pondicherry Institute of Medical Sciences, Kalapet, Puducherry, India
2 Department of Neurology, Pondicherry Institute of Medical Sciences, Kalapet, Puducherry, India
|Date of Submission||09-Mar-2020|
|Date of Acceptance||01-May-2020|
|Date of Web Publication||14-Sep-2020|
Dr. J P Justin Prashanth
T2 A Block, Akshara Apartments, Vallalar Nagar, Kalapet, Puducherry - 605 014
Source of Support: None, Conflict of Interest: None
We report a rare case of the left-sided anterior chiasmal lesion causing junctional scotoma. A 50-year-old female presented with sudden, painless complete loss of vision in the left eye with no perception of light and Grade IV relative afferent pupillary defect. The rest of the anterior segment and fundus of both eyes were normal. Visual fields of the right eye showed temporal hemianopia. Computed tomography of the brain plain and contrast showed a space-occupying lesion in the suprasellar region extending into the left optic canal compressing the left anterior chiasma. A junctional scotoma due to compression of the left anterior chiasma was diagnosed which is usually caused by lesions such as pituitary adenoma, meningiomas, cerebral aneurysms, and ischemic anterior chiasmal lesions. This usually resolves after intracranial decompression surgeries but the ischemic etiology carries a poor prognosis.
Keywords: Anterior chiasma, junctional scotoma, temporal Hemianopia
|How to cite this article:|
Prashanth J P, Prasanth HR, Srinivasan R, Kannan R. Chiasmic blindness: Hunted down. TNOA J Ophthalmic Sci Res 2020;58:194-6
| Introduction|| |
Lesions of the anterior chiasma cause blindness in one eye with temporal quadrantanopia/hemianopia of the other eye. It usually involves fibers of the ipsilateral optic nerve causing ipsilateral central scotoma and anterior chiasmal fibers containing the nasal fibers of the contralateral eye producing temporal hemianopia in the other eye. Such a lesion is called a junctional scotoma. This type of lesion is usually present in only 10% of patients with pituitary tumors. Our case is a very rare case of junctional scotoma causing blindness in the left eye with temporal hemianopia in the other eye which is caused by an arterial aneurysm or a thrombosed vessel compressing the anterior chiasm which is a rare etiology.
| Case Report|| |
A 50-year-old female presented to our outpatient department with loss of vision in the left eye for the past 1 week along with loss of left field of vision in her right eye, sudden in onset, which progressed rapidly to the present state of blindness in the left eye. There is no history of trauma to either of the eyes. There is no history of redness, pain, or watering of the eyes. There was no history suggestive of a sensory, motor, cranial nerve, or autonomic dysfunction. On elaborating her medical history, she revealed that she had undergone mitral valve replacement surgery 15 years back for rheumatic heart disease. She has been on tablet Warfarin 4 mg once daily since then but has been irregular with her medications. There was no other significant personal or family history.
On examination, she was moderately built and moderately nourished with a fair general condition. Her pulse rate was 84 per minute, and blood pressure was 120/80 mmHg with 100% oxygen saturation in room air. Her cardiovascular system was normal apart from a pronounced S1 sound due to the artificial valve. The examination of the central nervous system revealed no focal neurological deficits.
On ocular examination, the right eye had a vision of 6/6, while in the left eye, she denied perception of light. Anterior segment of the right eye was within normal limits, while the left eye showed Grade IV relative afferent pupillary defect (RAPD) with the rest of the anterior segment remaining within normal limits. On examination of the fundus, both eyes had an optic disc with a cup-disc ratio of 0.6 withHealthy Neuro Retinal Rim (HNRR) with the rest of the retina remaining within normal limits [Figure 1]. Humphrey field analyzer was used to check the visual field of the right eye, which showed temporal hemianopia [Figure 2]. An urgent neurologist opinion was sought and a computed tomography (CT)-brain with contrast was taken which revealed a space-occupying lesion of 1.4 cm × 1.4 cm in the suprasellar region extending into the left optic canal for 1 cm compressing the left anterior chiasmal junction with the optic nerve [Figure 3] and [Figure 4] which correlated with the left eye blindness and right eye temporal hemianopia leading us to a diagnosis of the junctional scotoma.
|Figure 3: Computed tomography brain showing a space occupying lesion in the suprasellar region|
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|Figure 4: Same space occupying lesion at a higher cut showing extent of the lesion|
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| Discussion|| |
The junctional scotoma is a visual field defect that occurs because of the lesion compressing the junction of the optic nerve and the optic chiasma typically producing a visual field defect of central scotoma in the ipsilateral eye with contralateral temporal quadrantanopia. This is because of the arrangement of the nerve fibers in the optic chiasma where the junction of the optic nerve and the chiasm consists of fibers of the entire retina of the ipsilateral eye with the inferonasal fibers of the contralateral eye which travel low and anteriorly after decussation. Anterior chiasmal lesion producing a junctional scotoma is the second most common chiasmal lesion contributing to 13% of chiasmal lesions, according to a study by Schiefer et al. In our patient, there was an absence of light perception in the left eye with Grade IV RAPD and temporal hemianopia in the contralateral eye, which indicates the extent of compression/ischemia of the junction which is a very rare phenomenon with the etiology being a vascular one. Based on the CT brain plain and contrast, we suspected a thrombosed vessel, most probably a thrombosed giant aneurysm compressing the junction of the left optic nerve with that of the chiasm, which is also called as the Willebrand's knee.
Walsh and Hoyt reported a patient with dolichoectasia of the right internal carotid artery compressing the Willebrand's knee of the corresponding side of the chiasm producing an inferior field defect in the ipsilateral eye with a contralateral superotemporal quadrantanopia. This they attributed to compression of the distal right optic nerve near its junction with the optic chiasma. Meadows had reported a case series of 15 patients who presented with carotid artery aneurysm in the cavernous sinus, out of whom six had developed optic atrophy, which he attributed to the aneurysm compressing the optic nerve.
Bird had described in his study of eight patients with the anterior chiasmal syndrome that a central scotoma was present in the ipsilateral eye, i.e. the lesion compressing the corresponding side of the anterior chiasma with a temporal field loss in the contralateral eye. Among them, five cases had contralateral superior temporal field defect along with central scotoma in the ipsilateral eye, and in two of these five cases, the peripheral field was normal by kinetic perimetry. In the remaining three cases, there was contralateral paracentral temporal field loss along with ipsilateral central scotoma, without preferential loss above or below the horizontal meridian.
A number of authors as well have described anterior chiasmal lesion caused by cerebral aneurysm majorly producing a nasal field defect, which often presents as the first sign of the underlying pathology.,,,,
The extensive literature search was done, which showed a few cases with compressive etiology for junctional scotoma and only two cases with ischemic cause, which our patient had presented with. In cases with sudden, painless loss of vision due to neurological causes, visual field analysis must be done whenever possible as it may lead to the anatomic diagnosis.
| Conclusion|| |
In the above-said references, they have mentioned about a central scotoma with contralateral superotemporal field defects which are quite typical in the case of an anterior chiasmal lesion. While in our case, it presented with complete blindness in the ipsilateral eye with a Grade IV RAPD and contralateral temporal hemianopia, which is one of the first kinds to be reported to the best of our knowledge. In our case, it further requires imaging investigations to rule out the specific etiology causing this type of a field defect such as a T2 waited for magnetic resonance imaging of the brain along with magnetic resonance angiography to confirm the vascular etiology of our case which we suspect to be a thrombosed giant aneurysm which could be a compressive lesion and as well might include a component of ischemia of the left anterior chiasma which will explain the large extent of the lesion in the Willebrand's knee producing such a gross visual defect.
Therefore its important to assess a patient neurologically, especially the ones presenting with profound loss of vision, which could not be justified by a thorough ophthalmic examination.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]