3 Cranial Nerve II: Visual Disorders
Abstract
This chapter focuses on the different types of optic nerve (cranial nerve II) disorders; how optic neuropathies may present to the general physician; and recommendations regarding diagnosis, referrals, and some cost considerations. It may be important to take into consideration the limitations on care imposed by the presence of insurance coverage, the type of insurance, the types of procedures covered under various insurance plans, and a general sense of the average cost of various procedures. For the purposes of this chapter, average estimated costs will be used, but geographic and other variations may occur locally, and prices may vary significantly based on local, regional, and state market differences. Ophthalmology consultation is recommended for each of the visual disorders discussed. Some procedures that are performed frequently for patients with CN II disorders include magnetic resonance imaging, computed tomography scans, orbital ultrasound, fluorescein angiography, Humphrey visual field and other automated perimetry, optical coherence tomography, electroretinography, and visual evoked response. Some sample, estimated costs for these procedures are listed in the text.
3.1 Initial Evaluation and General Considerations
3.1.1 History
The clinical history and physical examination are important aspects of the clinical workup that provide useful insight for reaching an accurate diagnosis. Clinicians should note the following when eliciting the history: presence of existing eye defects including but not limited to glaucoma or cataracts; age of the patient; medical history with special attention to diabetes, hypertension, or visual changes; use of corrective eyewear and if this is up to date; notable changes pertaining to the eye including but not limited to pain, redness, tearing; diplopia, specifying monocular versus binocular diplopia; and other changes in vision including hyperopia, myopia, scotomas, or flashes/specks/spots in the visual field. If blurry vision is the main complaint, careful attention should be placed for onset, duration, triggers, time of day, bilaterality, and whether central or peripheral vision is affected. Additionally, it is important to note whether the blurry vision is more pronounced at a given distance (far vs. near).
3.1.2 Physical Examination
Comfort and familiarity with techniques for physical examination of the visual and oculomotor systems are essential. An example script for how a basic ocular examination may be performed by the front-line provider is as follows:
Assess visual acuity: ask the patient to read the lowest line they are able to read from any vision testing chart (from the appropriate distance) with one eye and then the other and with and without corrective prescription. Near cards should be held at approximately 14 inches from the patient or at a normal reading distance. Patients may have blurry vision secondary to ocular dryness, which may be improved simply by administering an artificial tear solution. If a pinhole mask is available and utilized, the blurry vision from a refractive error is expected to improve. If not available, an easy way to test for refractive error is by making a hole with a pencil tip on a card and asking the patient to read through it.
Assess visual fields: facing the patient at an arm’s length, ask the patient to cover one eye and look toward the physician’s nose without moving. Cover your contralateral eye (the one in front of the patient’s covered eye) and move your free hand to all corners of visual quadrants and extend any number of fingers, asking the patient to state the number of fingers shown. Repeat in all four quadrants and in both eyes.
Assess extraocular movements: facing the patient, ask the patient to look directly at the physician and hold their head steady. Have the patient follow your extended finger (about 1 ft away) with only the eyes as you slowly move in an “H” pattern. Conclude by bringing your finger toward the patient’s nasal bridge to test convergence. Evaluate for smooth pursuit, nystagmus, and difficulty in completing movements.
Examine eyes: look at the color and fullness of the eyelids and the periorbital skin. Observe any asymmetry of the eyelids and their distance from the center of the pupil. Examine the light reflex position for alignment. Spread the eyelids to examine the eye surface for discharge or hemorrhage, and assess the corneal surface for abrasion.
Test orbicularis oculi: ask the patient to close their eyes tightly. Have them resist as you attempt to open the eyelids with your fingers.
Test intraocular pressure (rough approximation): ask the patient to close their eyes and gently press over the eyelids toward the center of the eyeball. Compare this to the tip of your nose—the eyeball should be softer or equally soft to the tip of your nose.
Examine pupils: note the size of the pupils and presence of red reflex. Test pupillary responses (both direct and indirect) by first decreasing the room light and then asking the patient to look into the distance as you shine light into the pupils, waiting a few seconds between eyes. Also note for the presence of a relative afferent pupillary defect.
Fundoscopic examination: decrease the room light and ask the patient to look into the distance. Hold ophthalmoscope in the right hand for examination of the right eye and vice versa. Check for red reflex from 12 to 18 inches away and approach to within 2 to 3 inches. Evaluate any opacity of the cornea or vitreous. Examine the retina and retinal vasculature. Examine the optic disc for color, contour, edema, and cupping.
3.1.3 Indications for Urgent Referral and Diagnostic Testing
Patients presenting with the following symptoms should be referred immediately to an ophthalmologist:
Physical wound of the eye including a scratch, cut, puncture, or concern that something is stuck in the eye.
If the patient uses contacts and reports they may be “stuck” underneath their lids.
Sudden acute loss of vision with or without pain.
Painful binocular diplopia.
Presence of flashing light or floaters even if only part of the visual field is affected.
Acute and unexplained pain or redness of the eye. Chronic symptoms may be referred as a routine visit to the ophthalmologist.
Eye pain that is concurrent with nausea, headache, or vomiting.
Exposure of chemicals to the eye.
Infectious conditions, such as herpes simplex or zoster or acute dacryocystitis.
Other changes in vision may not be emergent but may still warrant referral to an ophthalmologist for observation. When referring or ordering diagnostic testing, physicians should consider the cost of common procedures and imaging as summarized in ▶Table 3.1. These estimated prices are for reference only, as actual prices may vary significantly based on insurance coverage and market differences.
3.2 Vascular
3.2.1 Anterior Ischemic Optic Neuropathy
Nonarteritic
Etiology and Pathophysiology
Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute, unilateral optic neuropathy in adults. Proposed risk factors include hypertension, diabetes, atherosclerosis, past surgeries with major blood loss, prothrombotic conditions, obstructive sleep apnea, nocturnal hypotension, use of amiodarone derivatives, and erectile dysfunction drugs. 1 , 2
Presenting Symptoms and Signs
The presentation is usually an acute, unilateral, painless vision loss. Patients with NAION usually have a small cup-to-disc (C:D) ratio, which is a proposed predisposing structural risk factor. The visual acuity loss is variable. Ophthalmoscopy reveals optic disc edema in the acute phase. 3 Optic atrophy (sector or diffuse) may develop over time (▶Fig. 3.1).
Clinical Considerations
Diagnosis
The diagnosis of NAION is primarily clinical because there is no diagnostic laboratory or imaging finding for NAION. The diagnosis is made based on older age, the presence of vasculopathic risk factors, visual loss patterns, optic disc edema, and a small C:D ratio. Patients with NAION typically do not require neuroimaging. In older patients (e.g., older than 50 y), giant cell arteritis (GCA) may need to be ruled out with clinical examination and laboratory testing (see below).
Current Treatment
Eliminating or adjusting the risk factors listed earlier may be beneficial. There is currently no evidence-based treatment for NAION. Optic nerve decompression and aspirin have not been shown to improve vision and the use of corticosteroids remains controversial (http://quarkpharma.com/?p=12476). 4 , 5 Clinical trials are currently underway for NAION (http://quarkpharma.com/?p=12476).
Cost considerations a | |
Not recommended | MRI, lumbar puncture not indicated for typical NAION |
Recommended | ESR/C-reactive protein (CRP) if GCA is suspected |
Practice option | Complete blood count (CBC) and platelet count |
a Authors’ opinions, not consensus statement. | |
Giant Cell Arteritis/Arteritic
Etiology and Pathophysiology
Arteritic anterior ischemic optic neuropathy (AAION), or GCA, is a systemic granulomatous vasculitis, affecting medium to large-sized arteries. GCA is considered an ophthalmic emergency due to its aggressive course. 4
Presenting Symptoms and Signs
The most common ocular manifestation of GCA is acute unilateral painful vision loss that can initially present with episodes of transient vision loss. 5 In addition, patients with GCA may complain of jaw claudication, scalp tenderness, headache, hip and shoulder arthralgia, malaise, and fevers (see ▶Fig. 3.2). 6
Clinical Considerations
Diagnosis
The gold standard for diagnosis is a temporal artery biopsy (TAB), but note that TAB sensitivity ranges from 70 to 90%. 7 Studies also suggest the use of temporal artery ultrasound for diagnosis of GCA, which may present with a positive “halo sign” (inflammation around the artery). Some studies have shown high specificity and moderate sensitivity, but ultrasound has not yet reached the level of replacing the TAB for the diagnosis of GCA.89
Current Treatment
The current treatment of GCA remains high-dose corticosteroids. 10 Treatment courses vary but may be as long as 1 to 2 years of chronic steroids and given the need to taper steroids slowly to prevent a GCA relapse. 6 In addition, recent studies have shown the potential for tocilizumab to be therapeutic for GCA. 11 The cost of tocilizumab is $355 for a prefilled syringe of 162 mg of drugs. 12 Consultation with rheumatology is recommended for most cases of GCA but especially for those cases requiring consideration for steroid-sparing regimens including tocilizumab.
Cost considerations | |
Not recommended | Lumbar puncture |
Recommended | ESP/CRP, TAB, steroids |
Practice option | CBC and platelet count, ultrasound, MRI, fractional anisotropy (FA) |
3.2.2 Posterior Ischemic Optic Neuropathy
Etiology and Pathophysiology
Posterior ischemic optic neuropathy (PION) is an optic nerve disorder resulting from an infarction of the retrobulbar portion of the optic nerve. This form of neuropathy is less common than anterior ischemic optic neuropathy (AION) and can be distinguished from AION by the normal-appearing optic nerve head. 8 Etiology of PION is typically divided into three groups: perioperative (surgical), arteritic (GCA), and nonarteritic (idiopathic). 9
Presenting Symptoms and Signs
Patients with PION typically present with acute central or peripheral vision loss. 8 Other symptoms are based on the type of PION.
Clinical Considerations
Diagnosis
PION is a diagnosis of exclusion. It is recommended to rule out GCA, perform a thorough ophthalmologic examination, and consider a brain MRI to rule out other causes of retrobulbar optic neuropathy. 9
Current Treatment
Treatment depends on the mechanism of PION. There is currently no treatment for perioperative PION and nonarteritic PION that can significantly improve vision loss. Patients with arteritic PION may be treated with corticosteroids if GCA is suspected. 13
3.2.3 Hypertensive Retinopathy
Etiology and Pathophysiology
Hypertensive retinopathy (HR) is a condition found in hypertensive patients characterized by retinal vascular signs. 14
Presenting Symptoms and Signs
The traditional classification system of HR is known as the Keith–Wagener–Barker (KWB) scale and classifies HR as mild, moderate, or malignant depending on the extent of the disease. Malignant cases involve severe grade 4 retinopathy and papilledema. 15 Patients with hypertension may also experience NAION.
Clinical Considerations
Diagnosis
Early detection of HR is beneficial because some studies have suggested an association between retinopathy and long-term stroke risk. Fundoscopic examination and retinal photography have been recommended to determine the presence and severity of retinopathy in hypertensive patients. 16
Current Treatment
HR treatment is focused around the goal of reducing systemic blood pressure. 17 Consultation with a retinal specialist may also be sought for further treatment.
3.2.4 Diabetic Papillitis
Etiology and Pathophysiology
Diabetic papillitis (DP) is a rare finding in patients with type 1 or type 2 diabetes presenting with optic disc edema. 18 The pathophysiology of the disease is undetermined, but evidence does suggest that duration of diabetes is not a risk factor for DP. 19
Presenting Symptoms and Signs
In patients with DP, the optic nerve function is typically intact and either unilateral or bilateral hyperemic disc swelling may be present. Patients may occasionally present with decreased visual acuity but for the most part are asymptomatic. 18 In 70 to 100% of patients with DP, macular edema may be a comorbid finding. Other signs of diabetic retinopathy may be found in 35 to 90% of patients. 19
Clinical Considerations
Diagnosis
DP is a diagnosis of exclusion. The current criteria listed for DP diagnosis are as follows: (1) patient must have confirmed diagnosis of either type 1 or type 2 diabetes; (2) present with optic disc edema; (3) have largely intact optic nerve function; (4) have normal intracranial pressure; and (5) be clear of inflammation, infection, and/or infiltration of the optic nerve. MRI of the brain and orbits and lumbar puncture may be performed in order to rule out other conditions. 18
Current Treatment
No treatment is recommended for most patients with DP since the disease usually self-resolved. Use of corticosteroids is currently debated as to whether it is effective in curbing progression of the diseases. Other treatment options such as vascular endothelial growth factor (VEGF) inhibitors to resolve swelling and improve visual acuity have been reported but require further testing to confirm their efficacy. 19
3.3 Infectious
3.3.1 Infectious Neuroretinitis
Etiology and Pathophysiology
Neuroretinitis may be involved in the presentation of infections. Common etiologic agents may include Bartonella, syphilis, and Lyme disease.
Bartonella neuroretinitis, also known as cat scratch disease (CSD), is the ocular manifestation of infection by Bartonella henselae, which is the most common infectious cause of neuroretinitis, contributing to up to 64% of all cases. 20
Syphilis is a chronic, sexually transmitted infection of the spirochete Treponema pallidum that may affect any part of the body, including the eyes. Syphilitic infection of the eye is uncommon but can occur in later stages of the disease. 21 , 22
Lyme disease is an Ixodes tick–transmitted infection caused by the spirochete Borrelia burgdorferi. The localized infection begins with erythema migrans “bull’s eye” rash. After the infection becomes disseminated and in the absence of treatment, up to 15% of patients may develop neurological complications. 23
Presenting Symptoms and Signs
Patients may present with decreased visual acuity. Optic disc edema with a macular star figure may be noted. 20 , 24 Panuveitis is the most common ophthalmic finding in ocular syphilis (see ▶Fig. 3.3). 25
Clinical Considerations
Diagnosis
Diagnosis is based on history, and physical and serologic testing.
Current Treatment
Consultation with an infectious disease specialist may be considered to assist with medical management. For bartonella neuroretinitis, data suggest use of doxycycline with rifampin for adults for 4 to 6 weeks under observation by an ophthalmologist. For children younger than 8 years, a 4- to 6-week course of rifampin and either azithromycin or trimethoprim/sulfamethoxazole can be considered. 26
For ocular syphilis, parenteral penicillin is currently the drug of choice for treatment, typically resulting in visual improvement and management of inflammation within 1 month. Corticosteroids are typically not used, but may be considered if additional inflammatory complications, such as macular edema, arise. 25
For treatment of early Lyme disease, oral doxycycline, amoxicillin, and cefuroxime have all demonstrated equal effectiveness. Of these antimicrobial choices, doxycycline was noted to have superior central nervous system (CNS) penetration. 27
Cost considerations | |
Not recommended | – |
Recommended | Serologic testing |
Practice option | Lumbar puncture, MRI, infectious disease referral |
3.4 Compressive/Neoplastic
3.4.1 Compressive Optic Neuropathy
Optic Nerve Glioma
Etiology and Pathophysiology
Optic nerve glioma is the most common tumor of the optic nerve. 28 Benign optic nerve gliomas may present at any age, but most become symptomatic within the first two decades of life. 24 Malignant optic nerve glioma is less common, occurring predominantly in males older than 20 years. 28 Patients may also have evidence of neurofibromatosis type I (NF1). 29
Presenting Symptoms and Signs
Patients with optic nerve gliomas may present with progressive decreased visual function, proptosis, optic disc swelling, and/or strabismus. Typically, ocular and orbital pains are both absent. 28
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