Shawn C. Richards and Richard S. Davidson

Introduction

Superior limbic keratoconjunctivitis (SLK) is a rare disorder of the superior cornea and conjunctiva, that was first fully described by Frederick Theodore in 1963.¹ He suggested the term SLK to describe a series of patients with the following presenting signs: (1) inflammation of the superior tarsal conjunctiva, (2) inflammation of the superior bulbar conjunctiva, (3) fine punctate staining of the superior cornea, limbus, and the adjacent conjunctiva, and (4) filaments on the superior limbus or upper fourth of the cornea.

Presentation

Patients with SLK can present with a variety of non-specific complaints. The most common symptoms are irritation, burning, foreign body sensation, redness, photophobia, mucoid discharge from the eyes, and even an inflammatory ptosis. These symptoms are usually much more severe if the patient has corneal filaments. Often, the irritation is mild in the morning but worsens throughout the day.² The symptoms can be vague and intermittent and often are mistaken for other ocular surface disease, such as dry eye and blepharitis. Due to the fact that the clinical findings are often missed because the superior conjunctival is frequently not examined, SLK patients can be misdiagnosed or not diagnosed for many years.

In untreated patients, the natural course of the disease is one of episodic relapses and gradual improvement over several years, with eventual resolution of symptoms. Most patients are affected bilaterally (Fig. 21.1), but asymmetric and unilateral disease occurs. The female to male ratio is variable but is roughly 2 : 1.³ Presentation typically occurs in the fourth or fifth decades of life.⁴ A familial association has rarely been reported but is not the norm.

Clinical Examination

The classic physical finding associated with SLK is superior bulbar conjunctival injection. Vital stains, such as rose bengal or lissamine green are the most effective way to highlight abnormal conjunctiva (Fig. 21.2). These stains are especially beneficial in cases where the conjunctival injection may be subtle. Caution should be taken though, as vital staining of the superior bulbar conjunctiva does not guarantee a diagnosis of SLK. Bainbridge et al. looked at 93 consecutive patients who presented to an eye clinic for any reason, that were subsequently stained with rose bengal. While none of them carried a diagnosis of SLK, 25% of them exhibited staining of the superior bulbar conjunctiva.² This study reinforces the fact that a diagnosis of SLK should only be made after a thorough patient history is obtained and physical examination is performed. Other clinical findings of SLK include injection and redundancy of the superior bulbar conjunctiva, filaments of the superior cornea and conjunctiva, and a papillary reaction on the superior tarsal conjunctiva. The inferior tarsal conjunctiva is typically normal. Corneal hypoesthesia is also sometimes present.¹ The presence of filaments on the superior cornea should alert the clinician to the diagnosis of SLK, as this is the most common cause of this finding. When evaluating a patient for SLK, the upper lid should be everted to look for the common papillary reaction that is often seen in this condition. Key to the diagnosis of SLK is the willingness of the clinician to examine the superior bulbar conjunctiva. Many clinicians do not elevate the upper lid to examine the superior part of the eye. If the upper lid is not elevated, the diagnosis of SLK is missed. It is prudent to include lid elevation as part of the examination steps in any patient with ocular surface symptoms. Another factor in missing the diagnosis of SLK, is the fact that the superior bulbar conjunctival injection may be subtle. If the clinician looks at the superior conjunctiva with the biomicroscope on high magnification only, subtle findings may be unrecognized. It is useful in the SLK patient to simultaneously elevate both upper lids and look at the superior conjunctiva with the unaided eye. This simple technique may often be the most useful way to see the conjunctival injection.

Etiology

While there have been many theories about the etiology of SLK, some uncertainty remains. Some have suggested a viral cause, but cultures have been universally negative. In other studies, bacterial cultures have been shown to be positive but mostly for normal ocular flora. An autoimmune etiology has also been proposed, but this is also less likely, due to the lack of immunoglobulin deposition noted on direct immunofluorescence, a lack of increase in eosinophils, and the variable response to topical steroids. The most popular theory is that of mechanical trauma.