enter the bloodstream and form cysts in target organs. Poor hygiene and poverty are risk factors for cysticercosis; therefore, the disease is mainly seen among low socioeconomic classes in China, Eastern Europe, India, Indonesia, Latin America, and Pakistan [1].

Although subcutaneous cysticercosis is probably the most common form of the disease, clinical symptoms are usually manifested only in patients with cerebral or ocular involvement [2]. Ocular structures are affected in 13–40% of infected patients, at times leading to impaired vision or blindness [3].

In 1830, Soemmering described the first case of ocular cysticercosis, which was localized to the anterior chamber. In 1854, von Graefe reported a case of cysticercosis in the vitreous cavity, which was surgically removed. Since then, there have been many reports of ocular cysticercosis published in the literature

Epidemiology

Taenia solium has a worldwide distribution, with higher incidence in Mexico, Africa, Southeast Asia, Eastern Europe, and South America. The parasite has also been found in pigs in Colorado and New Mexico, and native acquisition of the disease has been proven in the United States. The incidence of cysticercosis in developed countries has increased in the past 10 years, probably due to an increasing number of immigrants from endemic countries [4]. Even in orthodox Jewish communities with strict dietary habits and in vegetarians, neurocysticercosis has been reported [5, 6]. This is due to the fact that the development of the disease depends strictly on the ingestion of fertilized eggs, which are found in fecal contaminants and not from the ingestion of the larvae that are found in muscle tissues.

Ocular manifestations usually appear in the first four decades of life, without sex predilection and with higher incidence in the first two decades of life, compared with neurocysticercosis [7, 8]. The left eye seems to be more often involved than the right eye.

Etiology and Pathogenesis

The adult form of T. solium is 3 mm in length and usually lodges in the proximal portion of the jejunum, where it can live for decades. The globulous scolex or head of the worm has a peak or face with two crowns of hooks. The gravid proglottid measures 6–12 mm approximately, and the uterus has from 8 to 12 lateral branches. The eggs are infectious for both the pig and humans, with a fecal-oral transmission route. Humans can become autoinfected if the gravid portions containing fertilized eggs reach the stomach again through inverse peristalsis, as occurs during regurgitations.

In the intermediate host, the hexacanth embryo is released from the egg, traverses the intestinal wall, and is transported to distant places by the venous of lymphatic system, where it turns into a mature larva or cysticercus cellulosae in a period of 60–70 days [3, 9], with a mean survival of 5 years [4] (Fig. 3.1).

Ocular cysticerci can be localized in any part of the eye, such as the anterior chamber [10, 11], subconjunctival space [12] (Fig. 3.2), optic disc [13], subretinal space [14] (Figs. 3.3 and 3.4), vitreous cavity [15–17], and lacrimal gland or eyelids [18]. Some authors have reported parasites located in the lens [2] that migrate to the sclera [19]. It is hypothesized that the parasite reaches the posterior pole through the posterior ciliary arteries, because it is usually found in the macular subretinal space [20], where it can perforate the retina, spread to the vitreous cavity, and cause a retinal detachment [21] or an inflammatory response with the formation of a macular hole or chorioretinal, scar depending on the exit site [22] (Fig. 3.5). The central retinal artery is the most likely route through which the parasite reaches the optic disc. The ocular adnexa are involved via the anterior ciliary arteries [23]. Some authors suggest that the damage to the ocular structures by ocular cysticercosis is produced by a great amount of toxins released when the parasite dies [2]. Nevertheless, signs of inflammation have been noted even in patients with living parasites.

It has been reported that the inflammatory response associated with ocular cysticercosis is produced by the host immunologic reaction rather than by the cysticercus itself, with a greater

response if the parasite is located in the vitreous cavity than if it is found in the subretinal space [24, 25]. In some cases, the inflammatory response can be so intense that it can simulate the

Fig. 3.4 Subretinal cysticercus at the level of the fovea

clinical appearance of endophthalmitis or so indolent that it might cause neovascular glaucoma [26].

In the last 20 years, ocular cysticercosis has shown the following distribution: subconjunctival, 62.7%; intraocular, 26.3%; orbital, 7%; and lid, 4%. A significant decrease has been noted in subconjunctival cases (85% vs. 28%) with a significant rise in intraocular cysticercosis (6% vs. 60%) [27].

Systemic Manifestations

Systemic manifestations of cysticercosis include subcutaneous cysts and inflammatory nodules, seen as calcium deposits in soft tissues on radiographic

The diagnosis of ocular cysticercosis is to be suspected in those patients living in endemic areas who suffer from uveitis, leucocoria, and neurologic symptoms, as well in those with eyelid nodules and subconjunctival cysts [29].

Indirect ophthalmoscopy and biomicroscopy are of great help in diagnosing the disease. The parasite in the vitreous cavity has a cystic translucent appearance. If it is alive, undulation, contraction, and expansion movements can be seen as a light beam illuminates the cyst [30]. In early stages, when a cyst is located in the macular subretinal space, it may manifest as an acute retinitis with edema and subretinal exudates [31], showing a pearl-like cyst containing the mobile parasite. Retinal holes made by the cysticercus can be observed in the area. If the parasite is located in the subretinal space, the macular area is more commonly involved (80%), likely because of the regional vascular features [20] and thickness.

The diagnosis is more difficult if the parasite is located in the retinal periphery or if there is significant vitreous inflammatory response that precludes adequate visualization [32]. In the latter situation, as well as when a retinal detachment is

Fig. 3.5 Sequence of a subretinal posterior pole cysticercus migrating to the vitreous cavity. (a) Subretinal living cysticercus. (b) The macula seems to be the most usual location

and the favorite exit site (80%), likely because of regional vascular features and thickness. (c) Intravitreal live cysticercus. (d) Residual macular hole created by the cysticercus

suspected, imaging techniques become an invaluable diagnostic tool to detect the parasite. The appearance of ocular cysticercosis depends on the site and living status of cysticercus. For diagnosis, B-ultrasonography should be selected first for diagnostic purposes. As a second line, magnetic resonance imaging (MRI) can be used to visualize living cysticerci and CT for nonliving calcified cysticerci [33].

Because ultrasonography is the gold standard, it is important to mention that in the A-mode, two high-reflective spikes showing the anterior and posterior walls of the cyst are seen with an additional 100% reflectivity spike seen inside the cyst, representing the scolex, which usually has an eccentric position. In the B-mode, a cystic mass with high-reflectivity eccentric structure showing undulatory movements can be observed [34] (Figs. 3.6 and 3.7).

Laboratory tests have limited value in the diagnosis of the disease. Immunoelectrotransference

testing reaches 100% specificity and 95% sensitivity. ELISA serum testing achieves 63% specificity and 65% sensitivity. ELISA cerebrospinal fluid (CSF) immunotransference testing has 86% specificity and 62% sensitivity [35].

Late-stage histopathology findings as reported by Gomez-Leal [36] include the presence of a central eosinophilic mass with some parasitic elements, surrounded by a polymorphonuclear infiltrate and a layer of granulomatous-type inflammatory responses. These findings are contained in a fibrous capsule infiltrated by chronic inflammatory cells (Fig. 3.8). Other intraocular changes include choroidal infiltration with lymphocytes and plasma cells, retinal detachment with gliosis and atrophy in some areas, lens opacification adherent to the inflammatory process in the vitreous cavity through a cyclitic membrane, iris atrophy with anterior synechiae closing the anterior chamber angle, and partial atrophy of the ciliary body (Fig. 3.9).