Dr Priyanka Doctor, MS and Dr Rahul Doctor, MS, are from the BayView Clinic, Mumbai
Leprosy remains one of the world’s major blinding diseases and yet few ophthalmologists are aware of the spectrum of ocular complications. Cross-sectional studies of the eye changes in leprosy patients have shown that up to 20% of leprosy patients develop sight-threatening lesions and between 5% and 7% are blind (depending on the definition of blindness). Visual impairment in leprosy needs special consideration by leprologists and ophthalmologists, not only because much of it is preventable, but also because it is a severe burden to be added to the problems of morbility and social stigma that characterise this ancient disease.
The ocular lesions of leprosy can be classified into 4 categories:
M. leprae invade the eye only on the lepromatous end of the spectrum. The organisms are generally bloodborne, and therefore generalised, affecting both eyes almost equally. The tissues affected are from the anterior segment of the eye, since M. leprae is known to invade and multiply in the cooler regions of the body, which may account for the selective involvement to the anterior segment of the eye. Another unusual feature in lepromatous disease is the absence of reaction to M. leprae and their unhindered growth, so unlike that evoked by M. tuberculosis.
The 3 common lesions are
The cornea is richly supplied by nerves from the nasociliary branch of the ophthalmic division to the 5th cranial nerve and has no blood supply. These two peculiarities aid detection of thickening and beading of the corneal nerves on a slit-lamp, and this is considered to be a common and characteristic presenting sign of early leprosy. Since there are no blood vessels in the cornea, M. leprae can invade the structure only by direct extension from surrounding tissues. Some believe that bacilli may move in along the nerves and form micronodular swellings. Since the cornea is transparent, these changes are detected early when they appear in the upper outer quadrant as faint discrete and later dense white grains of chalk.
These are called ‘corneal pearls’. Appearing in other parts of the cornea, these form diffuse superficial punctuate keratitis. These lesions are characteristic of lepromatous leprosy. As lepromatous leprosy advances, the corneal lesions get aggravated. The cornea gets vascularised and lepromatous granuloma form in the ciliary body / episclera. Macrophages containing M. leprae aggregate around invading capillaries forming perivascular microgranulomas. The granuloma may infiltrate deeper into the stroma forming interstitial keratitis which may seriously affect vision.
Lepromatous iridocyclitis is one of the commonest causes of blindness in leprosy. With bacillemia a common feature of leprosy and the iris and ciliary body being highly vascular, it is highly likely that they are infected by the hematogenous route. The sphincer muscles of the iris which are surrounded and infiltrated by lepromatous granuloma gradually undergo destruction.
Miliary lepromas or iris pearls near the pupillary margins, which are spherical yellowish opaque micronodules upto 2 mm in size, are said to be pathognomonic. They are small clumps of macrophages packed with M. leprae. The anterior surface of the iris when infiltrated by lepromatous granuloma, ulcerates and loses its lining layer of fibroblasts and melanocytes thus exposing the foam cells to the anterior chamber. Impairment of autonomic nerves supplying the iris and ciliary body cause early dysfunction of the pupillary muscles.
The granulomatous lesion of the iris with ulceration may produce an exudate composed of fibrin and polymorphs and the pupillary margins may adhere to the anterior capsule of the lens causing posterior synechiae. The constricting action of the sphincter muscle may already have been lost, resulting in a fixed, narrow, non-reacting pupil.
Eventually, destruction of the tissues of the iris and ciliary body causes atrophy and shrinkage of the globe known as pthisis bulbi.
Usually the granulomatous inflammation resolves with antileprosy treatment, but in some cases there may be continued presence of inflammatory cells resulting in persistent chronic silent iritis. Further, the chronic inflammation may be the result of persisteng M. leprae or its antigens and they may be responsible for maintaining the disease process.
A mild conjunctival inflammation with edema and dilated blood vessels may be seen. Pterygium, with collections of macrophages containing M. leprae, has been reported.
This involvement is common in untreated lepromatous patients, presenting with nodules up to 5 mm in diameter at the sclerocorneal junction. Scleritis is mostly seen in advanced untreated lepromatous patients and may weaken the globe.
The choroid and retina are not ordinarily involved in leprosy. There have been a few anecdotal reports of extensions of lepromatous lesions form the ciliary body to the choroid which appear as minute nodular lesions.
Chronic iridocyclitis may be responsible for the early formation of cataract. Steroids, used in the treatment of lepra reactions may hasten the formation of subcapsular cataract.
Acute iridocyclitis is a common complication of erythema nodosum leprosum reactions. In this, there is an exudate of polymorphs and fibrin in areas already having macrophage granulomas. This may aggravate the destructive granulomatous involvement of the ciliary body and iris. Keratic precipitates of neutrophils and fibrin may be deposited in the anterior chamber.
Acute uveitis has been considered to be an immune complex disease within uveal vessels, but such a pathogenesis is unclear.
Involvement of the ophthalmic branch of the V cranial nerve produces impairment of sensations in parts of the face including conjunctiva and cornea. Corneal sensory involvement, for some unknown reason, is essentially partial. Infiltration of the VII nerve - more frequently in the zygomatic branch – may produce paralysis of the orbicularis oculi that closes the eyelids. This impairment, too, is found to be partial.
In polar lepromatous leprosy, involvement of both V and VII cranial nerves is bilateral but total paralysis is rare. In borderline leprosy undergoing upgrading reactions, bilateral and fairly complete involvement of the VII nerve is seen. In tuberculoid types, the involvement of both nerves is usually unilateral and depends on location of the skin lesion.
The V nerve involvement results in impairment of corneal sensibility predisposing to corneal ulcers.
If only the VII nerve is involved, there is classical lagophthalmos. Severe involvement of the nerve results in permanently open lids and the centre of the cornea and its lower portion are exposed to wind and dust. This, combined with the absence of blinking, leads to dryness of the corneal epithelium making it prone to ulceration. This is known as ‘exposure keratitis’.
If both the V and VII nerves are involved, pathological changes in the cornea are seen including secondarily infected corneal ulcers.
The eyebrow, starting from its lateral aspect may lose hair (madarosis). Hair loss is due to hair root infiltration with lepromatous granuloma. Loss of eyelashes is not so common. Lagophthalmos often causes ectropion and sagging of the medial side of the eyelid margin, causing epiphora.
Bilateral granulomatous infiltration of the lacrimal and meibomian glands in lepromatous leprosy and lacrimal gland in tuberculous leprosy is seen. Chronic dacryocystitis by secondary organisms and destruction of the nasal bones resulting in obstruction of the nasolacrimal duct may be observed.
The eye is involved in all forms of leprosy, more in lepromatous than tuberculous leprosy. Considering the seriousness of eye complications, repeated and careful examination of the eye especially of those with lepromatous leprosy and those with nerve involvement affecting the eye cannot be overemphasized, especially since M. leprae can survive in the iris and ciliary body long after skin lesions have become negative.