Ischemic optic neuropathy (ION) is a group of common optic nerve diseases that seriously endanger visual function.
At present, there are many differences in the pathogenesis, clinical manifestations, and especially the treatment of each type of disease. Non-arteritic anterior ischemic optic neuropathy is the most common type, with an incidence of 0.23/10,000~1.02/10,000, and can develop at any age, accounting for 89% of the cases above 45 years old.
I. Classification of ION
ION is divided into two types according to the lesion site: anterior ION (AION) and posterior ION (PION), AION involves the optic papilla, while PION involves the optic nerve after the optic papilla.
AION is further classified according to the cause, AION is divided into arteritic AION (A-AION) due to giant cell arteritis and non-arteritic AION (NA-AION) due to causes other than giant cell arteritis; PION also includes arteritic inflammatory AION due to giant cell arteritis PION also includes arterial inflammatory PION (arteriticPION, A-PION) due to giant cell arteritis, non-arteritic PION (NA-PION) due to causes other than giant cell arteritis, and surgical-derived PION as a complication of many surgical procedures.
II. Pathophysiological changes of NA-AION
(I) Pathogenesis
NA-AION is caused by acute ischemia of the optic papilla. This ischemia is usually due to transient nonperfusion or hypoperfusion of the short posterior ciliary artery supplying the optic papilla, and rarely NA-AION is due to embolization of the artery or small arteries supplying the optic papilla.
The vast majority of nonperfusion or hypoperfusion of the optic papilla is due to a temporary drop in blood pressure, most commonly due to nocturnal hypotension during sleep or other causes of systemic hypoperfusion. Ocular ischemia and localized ocular hypoperfusion due to severe stenosis or obstruction of the common carotid artery, internal carotid artery, and/or ophthalmic artery are less common. A rapid increase in intraocular pressure can also result in a temporary decrease in ocular perfusion pressure (perfusion pressure = mean blood pressure – intraocular pressure). A drop in the perfusion pressure of the optic papilla capillaries below the threshold of its own regulatory range can lead to ischemia of the optic papilla and consequently to the development of NA-AION in some sensitive individuals.
(B) Risk factors
1, systemic factors: hypertension, nocturnal hypotension, diabetes, ischemic heart disease, hyperlipidemia, atherosclerosis, arteriosclerosis and arterial hypotension due to other causes (including shock, cardiopulmonary bypass surgery, etc.), sleep apnea, hemodialysis, severe and recurrent bleeding, easy embolism, migraine, cardiovascular self-regulatory dysfunction, type A personality, carotid endarterectomy, etc.
2. Local ocular factors: no-vision cup, small vision cup, crowded optic disc, glaucoma or other causes of significantly elevated intraocular pressure, any cause of significant optic papillary edema, abnormal relative position of the short posterior ciliary artery watershed to the optic papilla, disorder of the trophoblastic vessels of the optic papilla, vitreous warts of the optic papilla and cataract extraction surgery.
III. Clinical manifestations of NA-AION
(A) Symptoms
1. Visual acuity: sudden and painless vision loss, mostly found in the early morning when waking up. When the edge of the visual field defect just passes the central gaze point, it may be accompanied by intermittent blurred vision. The initial visual acuity is 1.0 in 33% of cases, >0.5 in 51% of cases, and ≤0.1 in 21% of cases. When the ischemia is located on the nasal side of the optic papilla, the central vision may not be affected, so normal visual acuity does not completely exclude NA-AION.
2. Visual field: often complains of nasal, inferior or superior visual occlusion.
3. The onset is usually monocular, but can also be bilateral. Onset in the contralateral eye is often months or years later. Simultaneous onset in both eyes is very rare.
(B) Physical signs
1. Relative afferent pupillary dysfunction: may occur in monocular involvement or in those with inconsistent lesions in both eyes.
2. Optic papillary changes: At the beginning of the disease, there may be limited or diffuse optic papillary edema, which may be accompanied by optic papillary congestion and linear hemorrhage around the optic papilla. About 2~3 weeks after the onset of the disease, the color of the optic papilla starts to fade. The resolution of the optic papillar edema is approximately 6 to 12 weeks after onset. After the optic papillar edema has completely subsided, the optic papilla can be partially or completely pale.
The evolution of optic papillar edema and the corresponding visual field changes: the initial stage of the disease is mostly segmental optic papillar edema, and the corresponding visual field appears defective; after a few days of diffuse optic papillar edema, the color of the first involved part of the optic papilla begins to fade, and the edema gradually subsides, at which time the latter part of the involved optic papillar edema may be more obvious, and the corresponding visual field may be normal or appear relatively dark.
4.Other fundus changes: Mild plasma retinal detachment may appear between the optic papilla and macula. Due to the optic papilla edema, some retinal veins are dilated. In some patients, some lipid deposits may appear around the optic papilla or in the macula after the optic papillary edema subsides.
(C) Visual field examination
Visual field examination is an important and necessary method to evaluate impaired visual function. The most common visual field change is a quadrantal visual field defect connected to the physiological blind spot around the central gaze point, mostly on the nasal side and below.
(iv) FFA examination
In the early phase of onset (usually within 4 weeks), impaired circulation and its sites can be seen early in the FFA artery, manifesting as limited or diffuse filling retardation of the optic papilla and filling defects and retardation of the peripapillary choroid and/or choroidal watershed area, which may be accompanied by prolonged brachial retinal circulation time.
(E) Visual electrophysiological examination
Visual evoked potential examination often shows decreased amplitude and prolonged latency, mostly with decreased amplitude. The electroretinogram is often not abnormal.
(F) Other examinations
1.Checking erythrocyte sedimentation rate and C-reactive protein is recommended to exclude the possibility of A-AION.
2.Carotid ultrasonography, postbulbar vascular flow ultrasonography, 24 h ambulatory blood pressure monitoring, sleep monitoring, etc.
3.OCT can clearly show the nerve fiber changes and plasmatic detachment of the retina.
(VII) Prognosis
1. Prognosis of the affected eyes: 41%-43% of the affected eyes improve their visual function during the natural course of the disease in 6 months. The progression or recurrence of NA-AION is almost always associated with nocturnal hypotension, especially low diastolic blood pressure.
2. Onset in the contralateral eye: The proportion of NA-AION occurring in the contralateral eye within 5 years is about 15% to 17%. The mean time to involvement of the contralateral eye is 6.9 years in patients with combined diabetes and 9.1 years in non-diabetic patients.
IV. Diagnosis and differential diagnosis
(A) Diagnostic criteria
1. Sudden onset of visual field defects and/or painless visual acuity loss;
2, Visual field examination shows a quadrant visual field defect connected with the physiological blind spot that bypasses the central gaze point, mostly located on the nasal side and below;
3. Restricted or diffuse optic papillary edema, often with peripheral linear hemorrhage;
4. The presence of relative afferent pupillary dysfunction and/or abnormal visual evoked potentials;
5. The presence of systemic or ocular local risk factors;
6, except for other optic neuropathies.
(II) Differential diagnosis
Optic nerve diseases that need to be differentiated from NA-AION include optic neuritis, other causes of optic papillary edema, compressive, infiltrative, traumatic, toxic, nutritional-metabolic and hereditary optic neuropathies. It is important to understand the clinical features of various optic neuropathies, and to take a thorough history and select the appropriate ancillary tests for differential diagnosis.
Idiopathic demyelinating optic neuritis often presents with subacute progressive vision loss within 2 to 4 weeks, whereas NA-AION usually does not present with continuous progressive worsening after acute vision loss. Visual cross and central optic lesions mainly present as bilateral temporal hemianopia or different types of isotropic hemianopia (vertical hemianopia) rather than horizontal hemianopia and are generally not easily confused with NA-AION, although misdiagnosis may occur in rare cases.
V. Treatment
1, glucocorticoid treatment for those with disease duration within 2 weeks, systemic glucocorticoid treatment can significantly improve visual acuity and visual field, and the absorption of optic papilledema can also be significantly accelerated. Oral administration is recommended, and intravitreal injection of tretinoin and other treatments are not advocated.
2.Control of systemic diseases and other risk factors emphasizes the need to prevent and control the occurrence of nocturnal hypotension, especially for patients whose blood pressure is located at the low limit of normal and for hypertensive patients who are prone to medically induced hypotension due to irregular medication (e.g., nocturnal medication, excessive medication, etc.).
3.Other adjuvant treatment
(1) Improving microcirculation drugs may have some auxiliary effect on NA-AION treatment, such as camptothecin. The blood supply condition of the eye should be clarified before use. They should not be used in patients with hypotension, carotid hypoperfusion or ocular hypoperfusion.
(2) Drugs that reduce capillary permeability or promote edema absorption can be used to reduce optic papillary edema.
(3) Nutritional drugs may have an adjunctive effect on NA-AION treatment, such as B vitamins.