Whereas Hodgkin lymphoma very rarely causes ocular disease, non-Hodgkin lymphoma (NHL) is the most common type of ocular lymphoma. Depending on the site of involvement, ocular lymphoma can be either intraocular or orbital and adnexal.
The most common presentation of intraocular lymphoma is decreased vision with nonresolving uveitis. Diagnosis is often based on obtaining an intraocular biopsy specimen. Optimal management is not yet realized. Chemoradiation is the most effective treatment, but significant ocular and cerebral morbidity is associated with its use.
Lymphoma has been described as the most common malignant orbital tumor, representing 55% of cases in adults  and 10% of cases in older patients. [2, 3] Lymphoproliferative disease of the orbit usually presents later in life and causes symptoms due to gradually increasing mass effect. Proptosis and visible conjunctival mass are the common modes of presentation. It tends to be localized to the orbit at the time of diagnosis and responds well to local or systemic therapy. 
Orbital and adnexal lymphoma is associated with systemic lymphoma in 30-35% of cases. Hence, all patients with ocular lymphoma should have a complete workup to rule out systemic lymphoma. 
Over the years, different systems have been used to classify lymphomas, including the Rappaport Classification (used until the 1970s), the Working Formulation, the National Cancer Institute Working Formulation, and the Revised European-American Lymphoma Classification (REAL). In 2001, a modern comprehensive classification system was published under the auspices of the World Health Organization (WHO); this represents the first worldwide consensus document on the classification of lymphoma. 
The prognosis for ocular lymphoma depends on the tumor’s histologic type and stage, as well as on the treatment employed. In general, with modern treatment of patients with NHL, the overall survival rate at 5 years is approximately 60%.
Recent molecular studies demonstrating viral DNA in the ocular lymphoma cells suggest a role for infectious agents in the pathogenesis of intraocular lymphoma.
Extramarginal zone lymphomas, which account for most primary orbital and adnexal lymphomas, are characterized by an indolent natural history with frequent, continuous extranodal relapses.  Follicular lymphoma, diffuse large B cell lymphoma, mantle cell lymphoma, B-cell chronic lymphocytic leukemia, peripheral T-cell lymphoma, and natural killer cell lymphoma have also been reported to affect the orbit.
Several hypotheses explain the increasing incidence of non-Hodgkin lymphoma (NHL). Better imaging techniques, improved biopsy techniques, and newer classification systems are likely to have contributed to the apparent increase in the incidence of lymphoma. The aging population, the increasing number of immunosuppressive drugs, and the AIDS epidemic have also contributed to the increased incidence of NHL.
Chlamydia psittaci is associated with ocular adnexal mucosa-associated lymphoid tissue (MALT) lymphoma, and this association varies across different geographical areas. [8, 9] In South Florida, orbital and adnexal lymphomas are not associated with C psittaci infections. 
The National Cancer Institute Surveillance, Epidemiology, and End Results program estimated that in 2008, 2,390 US men and women (1,340 men and 1,050 women) would be diagnosed with eye cancer and 240 people would die of this disease. [10, 11]
The lifetime risk of being diagnosed with non-Hodgkin lymphoma (NHL) is 2.08%. From 1975-2001, a rapid and steady increase occurred in the incidence of ocular NHL, with annual increases of 6.2% and 6.5% among white males and white females, respectively. 
The incidence of lymphoproliferative ocular diseases, especially malignant lymphoma, has increased over the years. Lymphoma is the most common primary malignant orbital tumor in Asian countries like Japan and Korea [12, 13, 14] as well as in Europe. 
Intraocular lymphoma is rare, with fewer than 200 cases being reported. This type of lymphoma is estimated to represent 1% of NHLs, 1% of intracranial tumors, and less than 1% of intraocular tumors.  However, over the past 20 years, a steady rise has occurred in the number of reported cases  in both immunocompetent patients and immunocompromised patients. 
Incidence of ocular lymphoma increases with advancing age.  Intraocular lymphoma typically affects elderly patients, with reported series having mean ages in the seventh decade of life. The median age at presentation for orbital and adnexal lymphoma is older than 60 years. In a study conducted in the United States, malignant lymphoma was the most common orbital tumor in the elderly age group, accounting for 24% of cases. 
No sex predilection was noted for ocular lymphomas in some studies.  However, in cases of intraocular lymphoma, women are known to be affected up to twice as often as men. Orbital lymphoma was found to have a female preponderance.  During 1992–2001, ocular NHL rates per 100,000 person-years for both sexes were highest among Asians/Pacific Islanders, lower in whites, and lower still in blacks. 
The symptoms reported differ according to whether the lymphoma is intraocular or orbital and adnexal.
There are 2 distinct forms of intraocular lymphoma. When the ocular disease appears to be a subset of primary central nervous system (CNS) lymphoma (PCNSL), the term “primary CNS lymphoma with ocular involvement” (PCNSLO) is used. In these cases, intraocular lymphoma can precede CNS involvement by months or years. The second form of intraocular lymphoma arises outside the CNS and metastasizes to the eye.
Intraocular lymphoma has been divided anatomically into vitreoretinal and uveal forms. The vitreoretinal form is associated with PCNSL and is typically a large B-cell tumor (intermediate-grade lymphoma). In contrast, the uveal form is associated with systemic NHL and also with involvement of orbital structures. It is typically small B-cell proliferation (low-grade lymphoma) and usually occurs with advanced systemic disease. Rare cases of T-cell lymphoma with ocular involvement have been reported.
On initial presentation, PCNSLO may be either unilateral or bilateral, but ultimately, 80-90% of patients have bilateral involvement. Intracranial disease occurs in 56-85% of patients with ocular disease, and estimates suggest that 15-25% of patients who present with CNS disease have ocular disease—hence the distinction between PCNSL and PCNSLO. [20, 21, 22, 23, 24]
The typical clinical profile is an elderly patient with uveitis that is refractory to treatment. The most common subjective symptoms are painless decreased vision, photophobia, red eye, and floaters. In some patients with known PCNSL, ocular disease may be discovered on routine screening. Because of its insidious onset and ability to simulate other conditions, delay in diagnosis is common.
Vision loss is frequent in PCNSLO and may range from mild to severe. With extensive disease, circulating tumor cells can appear in the anterior chamber in as many as 75% of patients. The cells simulate iridocyclitis and can even form a pseudohypopyon. Secondary anterior segment changes include neovascularization of the iris and iridocorneal angle with possible glaucoma. In rare circumstances, PCNSLO can form a mass in the iris or angle.
In the posterior segment, vitreous cells are a typical finding and are present in most cases. The characteristic fundus lesion is a low-lying, yellow-to-white mass deep to the sensory retina. Lesions may be single or multiple, confluent or discrete. They may even appear as multiple punctate lesions.
Lesions may be infiltrative and involve all layers of the retina. Retinal hemorrhage is rarely seen. The deep location of the infiltrates can give rise to exudative retinal detachment. If chorioretinal lesions regress, scarring and atrophy of the retinal pigment epithelium may be the only remaining fundus findings. Optic neuropathy may also be a feature. [20, 21, 22, 23, 24]
PCNSLO appears to occur with increased frequency in persons who are severely immunosuppressed.
Metastatic systemic lymphoma, like other metastatic ocular tumors, is usually confined to the uvea—in particular, the choroid. Compared with PCNSLO, metastatic systemic lymphomas are much less prevalent, have a better prognosis, and are less likely to create a diagnostic dilemma. 
Orbital and adnexal lymphoma
Orbital and ocular adnexal lymphoma has an insidious onset and can progress slowly for over a year before producing symptoms. Symptoms are usually secondary to pressure effects on surrounding structures. Clinical features include painless proptosis with or without motility disturbances, double vision, ptosis, and, rarely, decreased vision. The lesions can be unilateral or bilateral. Lymphomatous lesions can involve the preseptal portion of the eyelid.
Orbital lymphomas present with painless proptosis, the lesions being more common in the anterior superior orbit. The mass is usually rubbery to firm on palpation with no palpable bony destruction. The lacrimal gland, lacrimal sac, and extraocular muscles can also be similarly involved.
Conjunctival lymphoma has a characteristic salmon-pink appearance (see the image below). It may be an extension of orbital or intraocular lymphoma.
Simultaneous occurrence of intraocular and orbital lymphoma does occur but is rare. 
The presence of cervical or preauricular lymphadenopathy, parotid gland swelling, or an abdominal mass can signify systemic disease. Hence, a thorough physical evaluation should be carried out in all patients with ocular lymphoma.
The differential diagnosis for primary central nervous system lymphoma with ocular involvement (PCNSLO) includes reactive lymphoid hyperplasia (RLH), spread of systemic lymphoma, primary uveitis, infection, metastatic tumor, and amelanotic melanoma. All of these (except uveal melanoma) may not uncommonly have central nervous system (CNS) involvement.
Primarily vitreoretinal involvement supports the diagnosis of PCNSLO, whereas primarily choroidal involvement and evidence of other non-Hodgkin lymphoma (NHL) supports metastatic spread to the choroid. Large cell intraocular lymphoma with retinal involvement can mimic cytomegalovirus retinitis.
Conjunctival lymphoma should be included in the differential diagnoses of chronic conjunctivitis. Persisting signs and symptoms of conjunctivitis not responding to standard treatment should prompt biopsy. 
The differential diagnosis for orbital lymphoma include idiopathic inflammatory pseudotumor, orbital lymphoid hyperplasia, orbital sarcoidosis, Wegener granulomatosis, and chronic dacryoadenitis.
Laboratory studies are required to address the differential diagnosis of primary central nervous system lymphoma with ocular involvement (PCNSLO) and orbital lymphoma. They include the following:
Complete blood count (CBC) with differential
Serum immunoprotein electrophoresis
Rapid plasma reagin (RPR) screening
Erythrocyte sedimentation rate (ESR)
Fluorescent treponemal antibody absorption (FTA-Abs) test
Antinuclear antibodies (ANA) test
Angiotensin-converting enzyme (ACE)
Cytomegalovirus (CMV) titers
A tuberculosis skin test is advisable. The serum lactate dehydrogenase (LDH) level is a prognostic indicator, with higher levels being indicative of a poorer prognosis. Enzyme-linked immunosorbent assay (ELISA) for HIV is also recommended.
B-scan ultrasonography can show the presence of an intraocular mass. In addition, retinal detachment may be seen. Computed tomography (CT) and magnetic resonance imaging (MRI) have a low sensitivity for intraocular lymphoma and do not facilitate differentiating the diagnosis against uveitis or ocular melanoma.  Evaluation of patients with intraocular lymphoma includes high-resolution neuroradiologic imaging of the central nervous system (CNS) with contrast to look for lesions elsewhere.
Orbital and adnexal lymphoma
CT scan and MRI have made it possible to make a strongly presumptive diagnosis of orbital lymphoid tumors. They are more reliable than B-scan ultrasonography in the diagnosis of orbital lymphoma. Positron emission tomography (PET) is useful in selected settings as well.
CT scan of the orbits is a sensitive investigation that facilitates the diagnosis of orbital and adnexal lymphoma. On CT scan of the orbits, orbital lymphomas are seen as well-defined, lobulated or nodular, homogeneous masses of relatively high density and sharp margins. The lesions mold themselves to preexisting structures without eroding the bone (see the image below). 
The following 4 patterns are commonly seen:
Lacrimal gland involvement
Extension of a lymphomatous lesion
The lesion is usually extraconal but can extend intraconally as well. Lacrimal gland disease may involve both orbital lobes and palpebral lobes. The lacrimal sac  and extraocular muscles  may also be involved. A streaky appearance may be seen, which represents irregular infiltration of the microfascial structure of retrobulbar fat.  Calcification is rarely seen. Heterogeneous lesions with bony destruction are indicative of high-grade lymphomas.  Bilateral lesions are possible and can signify systemic disease.
MRI of the orbits possesses good soft tissue definition; however, it lacks the ability to delineate bone destruction, which can be seen in high-grade lymphomas. MRI may miss conjunctival disease. 
Orbital lesions are usually hypointense  or isointense on T1-weighted MRI and hyperintense on T2-weighted images. Gadolinium enhancement is seen on T1-weighted images.  This is indicative of high cellularity.
Fluorine-18 deoxyglucose PET (FDG-PET) can sometimes find systemic extranodal lymphomatous sites that are not detected with conventional imaging studies. This ability yields valuable information in patients with ocular lymphoma, which may result in important changes in staging and also in patient management. [37, 38, 39] PET has been found to have a higher sensitivity than CT scan (86% vs 72%) in detecting distant disease. 
Lumbar puncture is indicated to obtain cerebrospinal fluid (CSF) for cytology if the patient is believed to have CNS lymphoma. Bone marrow aspiration is used for staging systemic lymphomas. CT scans of the chest and abdomen are obtained to rule out retroperitoneal lymphoma. Bone scans may also be done.
Vitreous biopsy remains the mainstay of diagnosis for primary central nervous system lymphoma with ocular involvement (PCNSLO). Vitreous aspiration biopsy is a safe technique whose advantage is that it best preserves the cytomorphology. Material is aspirated directly through a 25-gauge needle into a syringe.
A mechanical vitrector provides better management of the tissue during the procedure and also allows more specimens to be obtained. However, specimens are often diluted and appear to undergo some artifactitious change, since malignant lymphocytes are fragile to the effects of mechanical disruption. Material may also be lost in the tubing.
If vitreous samples do not provide diagnostic tissue in the presence of retinal lesions, retinal and chorioretinal biopsies or subretinal aspiration may be done. Either an intraocular approach or a transscleral approach can be used.
Biopsy of the lesion is essential to confirm the diagnosis and also to help grade the lymphoma. The diffuse infiltrating nature of lymphomas may make their complete excision difficult. Also, their excellent response to irradiation obviates the need for complete excision.
The route of biopsy is chosen depending on the site of the lesion. Direct approach is possible for conjunctival and lid lesions, whereas orbitotomy is needed for lesions involving the lacrimal gland or posterior orbit. In the case of bilateral disease, only 1 orbit need undergo biopsy.
A key factor in obtaining an accurate diagnosis of intraocular lymphoma is a cytopathologist with experience in intraocular specimens.
Mucosa-associated lymphoid tissue (MALT) lymphoma, diffuse large cell lymphoma, and small lymphocytic lymphoma are some common types of intraocular lymphoma. Because of the fragility of neoplastic lymphocytes, a specimen may contain numerous abnormal-appearing but uninterruptable cells.
Tumor cells can involve the vitreous, retina, optic nerve, or choroid. They are found less often in the anterior segment. Choroidal involvement by primary central nervous system lymphoma with ocular involvement (PCNSLO) is typically diffuse, whereas retinal involvement may be more perivascular. When present, retinal necrosis can be extensive.
Molecular analysis detecting immunoglobulin gene rearrangements and ocular cytokine levels showing elevated interleukin (IL)–10 (IL-10), with an IL-10–to–IL-6 ratio greater than 1.0, are helpful adjuncts to cytology for establishing the diagnosis of PCNSLO.  CDR3 polymorphism analysis is recommended to confirm clonality.
Extranodal marginal zone B-cell lymphoma represents the most common orbital lymphoma subtype. [41, 42] Most patients with ocular adnexal lymphoma have stage IE disease. Immunohistochemical staining with CD markers helps classify lymphomas.
Gross specimens appear salmon-colored with a fish-flesh consistency. Hypercellular proliferations are seen with sparse stroma. Immunologic identification of cell surface markers on lymphocytes can be used to classify tumors as containing T or B cells and as being monoclonal or polyclonal in origin.
The vast majority of orbital lymphomas are of B-cell origin with monoclonal proliferation from a single neoplastic cell. Well-differentiated monoclonal lesions have associated systemic disease in 20% of cases, while the association increases to 60% with less well-differentiated lesions.
The MIB-1 proliferation rate and p53 positivity may aid in the prediction of disease stage and disease progression, whereas polymerase chain reaction (PCR) testing can support the diagnosis and reduce the number of histologically indeterminate lesions. 
Treatment & Management
Because of the high recurrence rate and refractory nature of primary central nervous system lymphoma with ocular involvement (PCNSLO), treatment is difficult.  However, treatment of intraocular lymphoma underwent a significant advance with the introduction of chemoradiation to the central nervous system (CNS) and ocular radiation.
Radiation (3500-4000 cGy) alone to the eyes and CNS gave high rates of initial response, but patients usually succumbed to recurrent disease. With multimodality therapy, including a boosted radiation dose (5000-10,000 cGy) to the spinal cord and intrathecal methotrexate, vision can be improved and life can be prolonged, with some patients alive at 9 years after treatment. In selected cases, patients with isolated ocular disease have been treated with ocular radiation alone, with some longer-term survivors. [44, 45, 46]
Innovations in treatment include multiagent primary chemotherapy. This approach was designed to reduce the radiation-associated cognitive defects that can occur in up to 40% of patients older than 50 years. The regimen includes methotrexate and procarbazine, vincristine, thiotepa, or both vincristine and cytarabine. Complete remission has been seen for as long as 30 months. [44, 45, 46]
Radiotherapy for PCNSLO is highly effective, and complications are generally acceptable. Complications of radiotherapy include cataract, dry eye, corneal ulcer, neovascular glaucoma, radiation retinopathy, and optic neuropathy. [47, 48] In the absence of a clear advantage to intravitreal chemotherapy, which involves repetitive injections and associated risks, radiotherapy may still be the most appropriate first-line treatment in most cases. 
Research is ongoing to determine if lower doses of local radiation are effective and still reduce associated complications.
Orbital and adnexal lymphoma
The recommended therapy for stage IE tumors is radiotherapy, whereas disseminated disease is treated with chemotherapy. 
Lymphoid tumors of the conjunctiva have traditionally been treated with local radiation therapy. Some cases of conjunctival lymphoma were seen to spontaneously regress after biopsy; hence, follow-up without radiation has been considered an option for patients with mucosa-associated lymphoid tissue (MALT) lymphoma of conjunctival origin after the pathologic diagnosis by biopsy.  Cryotherapy for certain conjunctival lymphomatous tumors has been suggested because of fewer ocular and systemic complications and lower cost. 
Radiotherapy alone is a highly effective modality in the curative management of primary orbital lymphoma.  Bilateral orbital disease itself, in the absence of systemic disease, is not an indication for chemotherapy.
Approximately 50% of orbital lymphomas are confined to the orbit at the time of diagnosis. In such cases, where there is no evidence of systemic lymphoma, local orbital low-dose (1500-3000 cGy) irradiation in fractionated doses is advised. High-grade tumors may require up to 4000 cGy. Appropriate shielding of the globe (lens-sparing technique) is recommended to minimize ocular complications of radiotherapy. 
In cases of massive orbital involvement, both chemotherapy and radiation therapy can be simultaneously given.
Because secondary orbital lymphomas often exhibit widespread systemic involvement and usually have a more aggressive histologic classification than primary orbital lymphomas do, treatment of these lesions with systemic chemotherapy or systemic immunotherapy is warranted. In some cases, combining such systemic therapy with local radiation treatment is beneficial.  After radiotherapy, local control was achieved in 97-100% of patients. [47, 53, 54]
Lymphomas respond well to monoclonal antibody (mAb) therapy, and research is ongoing to determine if such therapy can replace chemotherapy. Rituximab, ibritumomab, and epratuzumab are examples of mAbs that either are already in use or are being tested for use in lymphoma treatment. Intravenous rituximab has been used to treat low-grade lymphoma, with good results. [55, 56]
Antiangiogenic drugs, such as thalidomide, are also being researched for use in lymphoma treatment, as they are shown to slow the growth of cancer cells.
Neurologic evaluation is required in patients with intraocular lymphoma to rule out CNS involvement. Patients with ocular lymphoma should be referred to the clinical oncologist for evaluation of systemic lymphoma.
Further outpatient care
Despite usually demonstrating an indolent course, extranodal marginal zone B-cell lymphomas are renowned for recurrence in extranodal sites, including other ocular adnexal sites.  These sites can also include the lung, parotid gland, and bone marrow. 
Close clinical follow-up every 6 months for 2 years upon completion of treatment and annually thereafter is recommended. The evaluation should include neuroimaging studies (eg, ultrasonography, computed tomography [CT], or magnetic resonance imaging [MRI] of the orbits) to look for residual or recurrent local disease.
Serial imaging can be a very useful tool for detecting recurrence. Residual fibrosis of involved extraocular muscles or other orbital structures can appear similar to tumor. Whether re-biopsy or exploration is indicated should be a clinical decision, often aided by serial imaging.
A clinical oncologist should also follow up with the patient for a thorough systemic evaluation every 6 months for 2 years and annually thereafter.
Death can occur as a result of the systemic spread of lymphoma.  Prior or concurrent systemic disease has been noted as the most significant predictive factor for lymphoma-related death, but tumor-related death was also found to be more common and earlier with bilateral disease. Tumor-related death is slightly less where symptoms have been present for more than a year and slightly greater in the elderly.
Patients with primary central nervous system lymphoma with ocular involvement (PCNSLO) have a poor prognosis even with chemoradiation, and many succumb to central nervous system (CNS) disease within 2 years. Yet, median survival of primary central nervous system lymphoma (PCNSL) has increased from 1-1.5 years to over 3 years with newer therapies. Features affecting the prognosis of PCNSLO are not well understood.  Death ensues by CNS dissemination. Ocular lymphoma may be the initial manifestation of PCNSL.
In a study of patients with ocular adnexal lymphomas, age, sex, and anatomic location of the lymphomas did not have prognostic significance during a follow-up period of 6 months to 16.5 years.  The major prognostic criteria for ocular adnexal lymphomas include anatomic location of the tumor, stage of disease at first presentation, subtype of lymphoma, immunohistochemical markers determining factors such as tumor growth rate, and the serum lactate dehydrogenase (LDH) level. 
The extent of disease at the time of presentation was the most important clinical prognostic factor. Advanced disease correlated with increased risk ratios of having persistent disease at the final follow-up and lymphoma-related death. 
The longest survival has been seen in patients with low-grade lymphomas (ie, marginal zone lymphoma, follicular lymphoma).  However, T-cell lymphomas are associated with high mortality with conventional treatment, as there is a high incidence of systemic involvement. 
The overall prognosis for ocular adnexal lymphoid tumors is excellent; when lumped together, 67% are not found to be associated with systemic disease with a mean follow-up of over 4 years. Over the course of follow-up, it could be anticipated that 20-25% of patients not known to have systemic lymphoma develop evidence of disseminated disease within 5 years. 
Conjunctival lymphoma is known to have the lowest rate of extraorbital spread and lymphoma-related death, the rate of these 2 events being sequentially greater for patients with predominantly deep orbital lymphoma, lacrimal gland lymphoma, or eyelid lymphoma. [61, 60]
With radiotherapy for orbital disease, the 5-year disease-free survival and overall survival rate has been between 65-73.6% and 65.5-78%. [47, 53] Most relapses occur in the first 2 years after therapy. The risk of late relapse is higher in patients with a divergent histology of both indolent disease and aggressive disease.
Intraocular lymphoma can lead to blindness due to damage of the intraocular structures involved. Orbital lymphoma can cause blindness in untreated or aggressive cases with severe proptosis leading to corneal complications or optic neuropathy. Local irradiation can also cause reversible blindness due to cataract and irreversible blindness in cases of radiation-induced optic neuropathy and retinopathy.