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Optic nerve
Chapter 10
Optic nerve
10.1 Optic neuritis® Optic neuritis generally presents as sudden blindness and as such the differential diagnosis includes sudden acquired retinal degeneration and central blindness. Here the clinical feature allowing a diagnosis to be made is optic nerve swelling. The problem is that the appearance of optic nerve head swelling is very difficult, if not impossible, to differentiate from the papilloedema which can be seen with a space-occupying lesion that could present as central blindness.
Emergency management of optic neuritis 1. Perform full ophthalmic examination 2. Specifically evaluate pupillary light reflexes and swinging light test 3. Evaluate other neurological parameters with suspicion of diseases such as GME 4. Give systemic steroid at 1–2 mg/kg Prognostic indicators in optic neuritis 1. Duration of blindness an important prognostic sign, more than five days poor 2. Degree of optic nerve swelling and haemorrhage potentially a poor sign although can resolve on aggressive treatment 3. Degree of optic disc pallor an important sign as this suggests the onset of optic atrophy
Generally, however, the difference is that optic neuritis produces visual dysfunction, whereas papilloedema does not unless resulting from an intracranial lesion which concurrently causes blindness. Optic nerve head swelling is characterized by a domed enlargement of the optic papilla with a fuzzy indistinct border to the disc and surface haemorrhages. It is the authors’ experience that optic neuritis is more likely to present with haemorrhage at the optic disc than is papilloedema, although vessels of the optic disc are engorged in both. To date, however, we have no definitive evidence that this is the case. The big question centres around what other neurological inflammatory foci may be present. A full neurological examination is mandatory and the use of computerized tomography (CT) or magnetic resonance imaging (MRI) is invaluable to show if other inflammatory lesions are occurring intracranially. Optic neuritis occurs in humans as part of multiple sclerosis and in dogs as a manifestation of granulomatous meningoencephalitis (GME). It is thus essential that other manifestations of GME be investigated. Whether other neurological lesions are found or not, the treatment is systemic steroid at an anti-inflammatory dose and this may need to continue for a significant time if recurrence of blindness on cessation of treatment is to be avoided. If the patient cannot be seen by a veterinary ophthalmologist for electroretinography, or referral for
Optic nerve
CT/MRI, the veterinary surgeon has the vision of the animal to gain and nothing to lose by using anti inflammatory agents. Retrobulbar optic neuritis has the same effects on vision without the fundus changes seen where the optic nerve head is involved; high resolution retrobulbar ultrasound can be useful in defining it. The incidence of this condition is not clear, but apparently low.
10.2 Central blindness® Blindness not associated with disease of the globe or the extracranial optic nerve can be
85
associated with intracranial mass lesions. These may have effects on vision predominantly through two mechanisms. One is a rise in intracranial pressure while the other is direct effect on the visual pathways. The most common lesion producing an acute decrease in vision is a tumour at the level of the optic chiasm causing chiasmal compression. Most often these are pituitary macro-adenomas which may, or may not be associated with hormonal imbalances and such obvious changes as polydipsia and polyuria. All these intracranial lesions require a neurological as well as an ophthalmological, and quite possibly also an oncological referral.
Optic nerve
10.1 Optic neuritis® Optic neuritis generally presents as sudden blindness and as such the differential diagnosis includes sudden acquired retinal degeneration and central blindness. Here the clinical feature allowing a diagnosis to be made is optic nerve swelling. The problem is that the appearance of optic nerve head swelling is very difficult, if not impossible, to differentiate from the papilloedema which can be seen with a space-occupying lesion that could present as central blindness.
Emergency management of optic neuritis 1. Perform full ophthalmic examination 2. Specifically evaluate pupillary light reflexes and swinging light test 3. Evaluate other neurological parameters with suspicion of diseases such as GME 4. Give systemic steroid at 1–2 mg/kg Prognostic indicators in optic neuritis 1. Duration of blindness an important prognostic sign, more than five days poor 2. Degree of optic nerve swelling and haemorrhage potentially a poor sign although can resolve on aggressive treatment 3. Degree of optic disc pallor an important sign as this suggests the onset of optic atrophy
Generally, however, the difference is that optic neuritis produces visual dysfunction, whereas papilloedema does not unless resulting from an intracranial lesion which concurrently causes blindness. Optic nerve head swelling is characterized by a domed enlargement of the optic papilla with a fuzzy indistinct border to the disc and surface haemorrhages. It is the authors’ experience that optic neuritis is more likely to present with haemorrhage at the optic disc than is papilloedema, although vessels of the optic disc are engorged in both. To date, however, we have no definitive evidence that this is the case. The big question centres around what other neurological inflammatory foci may be present. A full neurological examination is mandatory and the use of computerized tomography (CT) or magnetic resonance imaging (MRI) is invaluable to show if other inflammatory lesions are occurring intracranially. Optic neuritis occurs in humans as part of multiple sclerosis and in dogs as a manifestation of granulomatous meningoencephalitis (GME). It is thus essential that other manifestations of GME be investigated. Whether other neurological lesions are found or not, the treatment is systemic steroid at an anti-inflammatory dose and this may need to continue for a significant time if recurrence of blindness on cessation of treatment is to be avoided. If the patient cannot be seen by a veterinary ophthalmologist for electroretinography, or referral for
Optic nerve
CT/MRI, the veterinary surgeon has the vision of the animal to gain and nothing to lose by using anti inflammatory agents. Retrobulbar optic neuritis has the same effects on vision without the fundus changes seen where the optic nerve head is involved; high resolution retrobulbar ultrasound can be useful in defining it. The incidence of this condition is not clear, but apparently low.
10.2 Central blindness® Blindness not associated with disease of the globe or the extracranial optic nerve can be
85
associated with intracranial mass lesions. These may have effects on vision predominantly through two mechanisms. One is a rise in intracranial pressure while the other is direct effect on the visual pathways. The most common lesion producing an acute decrease in vision is a tumour at the level of the optic chiasm causing chiasmal compression. Most often these are pituitary macro-adenomas which may, or may not be associated with hormonal imbalances and such obvious changes as polydipsia and polyuria. All these intracranial lesions require a neurological as well as an ophthalmological, and quite possibly also an oncological referral.