11.3: Eyes

In the IHS Classification of Headache, separate categories are given to headache associated with acute glaucoma (11.3.1), refractive errors (11.3.2), and heterophoria or heterotropia (latent or manifest squint) (11.3.3). The comment is made that uncorrected refractive errors and heterophoria may cause headaches, but their importance is widely overestimated. However, ocular disease clearly causes headache and pain in and around the eyes. This section is meant to describe these conditions.

Ocular and Retrobulbar Pain Associated With Ocular Disease

The response of a patient to an intrinsic or extrinsic ocular lesion that causes the symptom of pain is infinitely varied as is the description of the pain itself. Nevertheless, clinical ocular and orbital conditions associated with pain in the eye may be grouped according to the anatomic site of the lesion (Hitchings, 1980). These sites and their associated conditions include: (1) the cornea--erosion, foreign body, ulcer, bullous keratopathy; (2) the sclera--scleritis; (3) the iris--iritis, miotics, iridectomy, photocoagulation, anterior segment ischemia, acute angle closure glaucoma; (4) the ciliary body--photocoagulation; (5) the retina and choroid--photocoagulation, extreme glare; (6) the optic nerve--optic neuritis; and (7) the orbit--inflammation, tumors, injury. In addition to the discussion that follows, the reader may be interested in the reviews of this subject by Behrens (1976, 1978).

The sensation of pain may result from direct stimulation of pain nerve endings or from excessive stimulation of sensory terminals that usually transmit other sensations.

The extensive network of sensory nerves that innervate the cornea and sclera is described in detail elsewhere. Bergmanson (1977) studied denervation within the monkey eye after section of the ophthalmic division of the trigeminal nerve. He found minimal evidence for sensory innervation of the choroid and little innervation of the iris. The ciliary muscle had no sensory nerves, but the ciliary body adjacent to the base of the iris and the trabecular meshwork had a rich sensory plexus. Bergmanson was unable to identify specific sensory nerve terminals from the sections that he studied; however, there did not appear to be any proprioceptors. Thus, sensations carded by the plexus could include pain, temperature, and tactile stimulation.

The sensation of pain can be generated by direct mechanical stimulation or by a combination of one or more of the following: tissue distortion, vasodilation, heat perception, and chemoreceptor awareness of inflammatory products that affect sensory terminals.

The nature and severity of pain produced by extrinsic or intrinsic ocular diseases vary depending on the region of the eye being damaged and the underlying cause.

Cornea and Sclera
Superficial Corneal Disease

Mechanical stimulation after loss (foreign body, erosion, ulceration) or disease (bullous keratopathy) of corneal epithelium produces directly a sensation of pain. The pain from a corneal foreign body, abrasion, or disease of the external portions of the eye producing irritation of the conjunctiva and cornea is so characteristic as to be described as a foreign body sensation. It differs entirely from the deep seated neuralgic pain of iritis or iridocyclitis. The pain from a corneal foreign body or abrasion is accompanied by profuse lacrimation, photophobia, conjunctival injection, blepharospasm, and radiation of pain to the forehead. Foreign body sensation is not referred to the cornea but instead is routinely interpreted as a localized scratching sensation beneath the upper lid (Burton, 1981). Experimental evidence by several groups of investigators (Bill et al., 1979; Nicholl et al., 1980) suggests that after direct pain has occurred, subsequent antidromic impulses cause release of substance P, a polypeptide that consists of 11 amino acids, from the iris, resulting in inflammation and further pain. This experimental evidence is in agreement with the clinical observation that severe ocular pain with miosis and anterior chamber ``inflammation'' may follow delayed healing of a corneal erosion.

Limbal Disease

Inflammation affecting either the cornea or sclera will cause pain through tissue distortion, vasodilation, and stimulation of chemoreceptors.

Posterior Scleritis

There is little direct sensory innervation of the posterior sclera. The pain from posterior scleritis may occur from direct involvement of the short posterior ciliary nerves or from inflammation of adjacent extraocular muscles or orbital structures.

Iris
Iritis

The pain of anterior uveitis can be severe, but is usually less overwhelming than that of acute angle closure glaucoma (see below). It is frequently widespread in its reference, and patients may complain of earache, pain in the teeth, or pain over one of the sinuses. It is usually described as throbbing or neuralgic in character, and is often associated with photophobia that may be severe enough to overshadow other aspects of the pain. Excessive lacrimation and blepharospasm are frequently observed. The eye is likely to be tender upon palpation. According to Burton (1981), the deep, throbbing pain is always worse at night and in the early morning hours. Breakdown of the blood-aqueous barrier probably allows a release of kinins and prostaglandin E1 from polymorphonuclear leucocytes, while substance P and other polypeptides (together with prostaglandin E2) are released from the iris itself. These chemicals are believed to stimulate chemoreceptors in the ciliary body nerve plexus and may also cause miosis (Cole and Unger, 1973; Unger et al., 1974).

Mechanical Stimulation

Manipulation of the iris during an iridectomy causes pain by tugging at the root of the iris rather than by cutting iris tissue. In addition, pulling on the iris root and iris prolapse also cause inflammation and further pain. Photocoagulation (laser) burns generate heat and will cause pain if the duration of the burn is long. Although burns of short duration (2---3 µsec) do not generate sufficient heat to produce pain, they may set up a shock wave that produces an ill-defined sensation that has been described as ``like a blow'' (Unger et al., 1977).

Chemical Stimulation

Ocular pain after the instillation of pilocarpine is associated with but is probably not caused by iris sphincter or ciliary spasm. The most likely cause of this pain is traction of the ciliary muscle on the scleral spur with distortion of the adjacent ciliary plexus.

Acute Angle Closure Glaucoma

Severe head pain localized within and around the involved eye is the symptom that most often draws attention to the presence of acute angle closure glaucoma. However, many patients are seen in whom the associated pain is minimal, vague, and variable in location. Teeth have been extracted and presumed sinus infections treated with antibiotics because of misinterpretation of pain actually arising from a glaucomatous eye. At the other end of the clinical spectrum is the patient whose pain is excruciating and directly localized to the orbit. Such pain is unremitting, and may or may not have a pulsatile quality. The associated symptoms of nausea, vomiting, and abdominal pain can be attributed to spread of pain impulses from trigeminal nuclei to other brainstem nuclei. Severity of the nausea and vomiting, the degree of prostration, and the patient's inability to cooperate during history taking and physical examination may result in unnecessary laparotomy. Fortunately, most patients are able to indicate the eyeball itself as the source of the pain. Many patients describe aching as the essential quality of their pain. We have seen three patients with intermittent angle closure glaucoma who were referred with the diagnosis of migraine. Indeed, the history of pain was suggestive of migraine; however, slit lamp biomicroscopy confirmed the presence of occludable anterior chamber angles, and the correct diagnosis was made. Patients with acute angle closure glaucoma also complain of visual loss during the episode. We have examined two patients whose combination of episodic visual loss associated with pain were initially interpreted as ``painful amaurosis fugax.'' One of these patients had already undergone cerebral arteriography, and the other was scheduled for a complete cerebrovascular disease evaluation when the correct diagnosis became evident (see also Ravits and Seybold, 1984).

The pain that occurs in acute angle closure glaucoma may be caused by the associated intraocular inflammation. Whether elevation of intraocular pressure alone can cause pain is less clear. Certainly, chronic elevation of intraocular pressure may persist for years without symptoms.

Ciliary Body

Photocoagulation of the ciliary processes is usually painless although prolonged photocoagulation of the iris root may be quite painful.

Retina and Choroid

Short duration photocoagulation may be painful depending upon the instrument used. Argon laser photocoagulation is usually painless, while krypton laser photocoagulation may cause some pain.

Optic Nerve

About 80% of patients with optic neuritis experience tenderness of the globe or pain on eye movement (Perkin and Rose, 1979; McDonald, 1980). The pain may be described as a sharp or a dull, aching sensation. It may occur prior to, coincident with, or following the onset of visual dysfunction. It has been suggested by Rose (1972) that the pain of optic neuritis occurs from distention of the optic nerve sheath with irritation of its trigeminal sensory fibers. That the optic nerve is indeed swollen has been confirmed by ultrasonography (Coleman and Carroll, 1972) and by computed tomography (Howard et al., 1980).

Orbit
Inflammation

Inflammatory orbital conditions such as orbital cellulitis, orbital pseudotumor, and extension of sinusitis are generally associated with moderate to severe pain, presumably from involvement of the major trigeminal sensory nerves.

Tumors

As a general rule, neoplasms that involve the orbit are not painful; however, when pain is present, the tumors are likely to be malignant (Grinberg and Levy, 1974; Jones et al., 1979; McDonald, 1980; Trobe et al., 1982). Tumors that spread to the orbit from the paranasal sinuses are usually associated with late pain. In some cases, however, pain may be the earliest sign of a tumor involving the orbital apex and cavernous sinus. The pain is severe, continuous, and associated with facial dysesthesia. It has been described as chronic, burning, and intermittently stabbing, and it involves one or more divisions of the trigeminal nerve. When this type of pain is present, it is evidence of intraneural infiltration by neoplastic cells, usually from basal cell, squamous cell, or nasopharyngeal carcinoma (Jefferson, 1953; Ballantyne et al., 1963; Moore et al., 1976; Trobe et al., 1982). When the pain is combined with involvement of one or more ocular motor nerves, it confidently predicts neural infiltration within the cavernous sinus (Mohs and Lathrop, 1952; Willis, 1952; Ballantyne et al., 1963; Moore et al., 1976; Unsöld et al., 1980; Trobe et al., 1982).

The differential diagnosis of painful ophthalmoplegic migraine with cranio-orbital lesions is shown in Table 3.

Trauma

Non-neoplastic proliferation of neural tissue may occur in the orbit after injury or surgery, producing severe pain (Biette, 1900; Lohlein, 1910; Bäbel and Valerio, 1945; Blodi 1949; Wolter and Benz, 1964; Johnson et al., 1966; Jakobiec and Jones, 1979; Sutula and Weiter, 1980; Folberg et al., 1981). These ``amputation neuromas'' represent abortive regenerative attempts on the part of severed nerves. In such lesions, the connective tissue components of the nerve--endoneurium, perineurium, and Schwann cells--all proliferate. Axon cylinders elongate, branch, and ramify from the proximal to the distal portion of the nerve (Hogan and Zimmerman, 1962; Henderson, 1973). Removal of the offending structure is usually followed by prompt relief of pain.

Postoperative Pain

Pain that occurs after ocular surgery is not infrequent, and ocular surgical procedures including cyclocryotherapy, circular buckling for retinal reattachment, or evisceration, may cause severe and persistent pain that is not relieved even by the more potent analgesics. Michels and Maumenee (1973) recommended postoperative administration of retrobulbar alcohol in seeing eyes to prevent unnecessary suffering. Ticho et al. (1980) have obtained excellent pain relief with subcutaneous electric stimulation using a portable, battery-operated apparatus, while Jolson (1982) has advocated transcutaneous electric nerve stimulation for ocular pain control. These systems apparently act through stimulation of endogenous opiates. Finally, selective percutaneous radiofrequency thermocoagulation of the trigeminal ganglion has been used to treat some patients with chronic ocular pain with good success and no serious complications (Rosenberg et al., 1981).

Ocular and Retrobulbar Pain Without Ocular or Orbital Disease

The complaint of mild, localized intraocular retrobulbar pain when no obvious corneal, intraocular, or orbital disease exists is a common problem to ophthalmologists as well as to internists, neurologists, and neurosurgeons. Many of the patients who seek ophthalmologic consultation for such pains are middle aged women. In many cases, the symptoms seem to be magnified by the patient's unfounded anxiety regarding the possibility of glaucoma, impending blindness, or brain tumor. Occasionally, such pains are mentioned as an afterthought by the patient who came only for a routine ophthalmologic examination and for the prescription of glasses. Some patients are able to give a rather precise description of their pain while others are vague and have difficulty conveying any accurate impression of their discomfort. Some describe stabbing pains, others dull continuous pain, and others a feeling of pressure in their eye. We have been impressed with the rarity of positive findings when these patients are fully evaluated. Only rarely has it been possible to find any plausible ocular, orbital, or intracranial explanation. Now and then an obvious lacrimal insufficiency as indicated by a Schirmer's test seems to be responsible. Desiccation of the cornea and minor epithelial change may initiate the symptoms that some patients describe as pain. Relief of symptoms with the use of various tear replacement solutions or ointments seems to support the diagnosis but by no means establishes its validity.

Patients with cervical arthritis may complain of ocular pain. This pain may originate from the upper cervical nerve roots from whence it is referred to the eye. Conceivably, some of these pains could arise from other structures innervated by the ophthalmic nerve (nasal mucosa, orbital vessels, or the intracranial dura), but proof of the source is rarely possible. Exhaustive radiologic studies and consultation with other specialists are seldom required as they are rarely of help. A sympathetic, reassuring physician and routine analgesics are, in most cases, all that the patient requires.

Lansche (1964) described a type of pain for which he suggested the term ophthalmodynia periodica. This pain is an intermittent, single stab or jab of local, ocular pain that strikes without warning and often causes the patient to quickly place a hand over the involved eye. The pain leaves as quickly as it comes and causes no tearing or nasal stuffiness. A second pain may immediately follow the first, but rarely is there a third or a fourth. The pain may not recur for weeks or months; however, some patients have a series of attacks and then are free of symptoms for long periods. Lansche (1964) had no plausible explanation for these apparently genuine symptoms, although transient ischemic pain from an embolus is an interesting possibility.

Bilateral ocular or retrobulbar aching and tenderness is a common finding associated with the so-called tension headache.

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