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Birdshot C Pavesio Euretina 2012 Birdshot Chorioretinopathy Carlos Pavesio MD, FRCOphth Consultant Ophthalmologist Moorfields Eye Hospital London, UK Background: Birdshot Chorioretinopathy (BCR) can be defined as a chronic, bilateral, inflammatory condition, which affects the posterior segment of the eye with involvement of the choroid and retinal vessels. BCR is an uncommon condition, being diagnosed in 0.6-1.5% of patients with uveitis referred to tertiary centers, accounting for 6-7.9% of patients with posterior uveitis. Females are more frequently involved and the mean age at disease onset is reported as being 53 years. The youngest reported patient was 25 years old, and the oldest 79. It is found more frequently in white people of northern European origin. It seems to be much less frequent in Asia, which may be related to the low prevalence of HLA-A29 among Asian populations. There has been only one report of one Hispanic and one black individual with this condition. Ocular Picture: The presenting symptoms may vary and while some patients may present reporting significant night blindness, others will complain of fluctuation in vision, floaters, photopsia, glare and reduction of peripheral vision. These symptoms give a good indication of the fact that in the early stages of the disease there is involvement of the peripheral retina, more likely due to the retinal vasculitis than to the choroidal disease, which is not matched by changes in central vision. Patients do not present with symptoms of pain and redness, which reflects the fact that the examination of these patients reveals an anterior chamber with no or minimal inflammation, and typically no posterior synechiae. A study looking into laser flare photometry has shown no significant elevation of aqueous humor protein content. 1 Birdshot C Pavesio Euretina 2012 The vitreous shows cellular infiltrate in nearly all patients, which tends to be more marked in the posterior portion, but also shows variation in its intensity tending to be more intense during early stages of the disease. The typical birdshot lesions, which may take as long as 8 years to appear after onset of symptoms, are usually round or oval in shape, measuring from a quarter to half a disc diameter, but they can become confluent and form linear lesions(Fig 1). They are normally seen as if radiating from the optic disc to the periphery, most commonly nasally and inferiorly to the disc. Figure1: colour photograph, deep cream-colored elongated spots located predominantly nasally and inferiorly to the disc. In typical cases they appear bilaterally and tend to be quite symmetric, but striking asymmetry can also be found. The lesions, at least initially, seem to be located in the choroidal stroma and are associated with the large choroidal veins. The indistinct appearance of the lesions, the lack of pigmentary changes involving the retinal pigment epithelium (RPE), and the angiography behavior of the lesionssupport this deep location in the choroidal stroma. The macula may also show lesions, but it is most frequently spared, which may be related to the relative absence of large choroidal veins in this location. In later stages the 2 Birdshot C Pavesio Euretina 2012 lesions tend to take a more atrophic appearance and enlarge, also involving outer retina and producing RPE pigmentary disturbance. At this stage the functional abnormalities have become irreversible and therapy is unlikely to be of any benefit. The involvement of the retina appears in the form of retinal vasculitis leading to hyperpermeability of capillaries and retinal edema, especially cystoid macular edema (CME). Peripheral vision disturbances, seen quite early in the course of the disease, seem to be related to inner retinal abnormalities, secondary to vasculitis and possibly diffuse retinal edema, different from late disease when the outer retina becomes affected by progressive choroidal disease. Other findings include diffuse narrowing of retinal arterioles, vascular tortuosity, perivascular hemorrhages and optic disc swelling. The most common symptoms related to central vision are blurring of vision and floaters, but visual acuity tends to be fairly good in the majority of patients at presentation (better than 20/40 in 61.8% of eyes), even if they are already showing significant complaints related to their peripheral vision. Most patients show symmetric visual acuity disturbance, but striking asymmetry can also be found. The most important reason for loss of central vision is the development of CME. Until recently this finding represented the main reason to treat patients with BCR, but the understanding that peripheral retinal insult is happening independent of this abnormality has led to a change in treatment strategy.The relapsing and remitting nature of the CME may lead to permanent macular damage and permanent loss of visual acuity in later phases of the disease. The diffuse inner retinal involvement produces symptoms of reduction of peripheral visual field and nyctalopia, which are usually seen quite early, even before any other abnormalities become apparent. They may be reversed by therapy. 3 Birdshot C Pavesio Euretina 2012 Problems with color vision have also been reported in as many as 76% of the patients, mainly affecting both the blue-yellow and red-green axis, which is the result not only of the retinal disease, but also of the optic disc involvement, which is frequently overlooked.The optic neuropathy can be present without any signs of papillitis or optic disc edema. The optic disc margins remain sharp and the pallor of the optic nerve appears insidiously. Visual field testing is mandatory, particularly if the visual impairment cannot be explained by the retinal involvement. Glare, photopsia, photophobia, metamorphopsia and decreased depth perception have also been reported. Etiology/Pathogenesis: Even though the exact role of specific HLA associations has not been determined, a strong association with HLA-A29 has been found. No associations were found for HLA-DR in one study. The HLA-A29 genotype or phenotype is found in up to 7% of Caucasians and in more than 95% of individuals with BCR. Only 4.3% of the cases of BCR reported have been HLA-A29 negative. It must be kept in mind that the use of HLA-A29 as a defining criterion for the diagnosis of BCR may have influenced this strong association.The relative risk of BCR among HLA-A29 positive individuals has been estimated to be between 50 and 224. There are six described subtypes of the HLA-A29 (HLA-A*2901 through HLA-A*2906). The HLA-A29.2 serotype has been strongly associated with the risk of developing BCR, while it has been shown in one study that the HLA-A29.1 serotype might have a protective role. It is interesting to note that the HLA-A29 phenotype has also been associated with idiopathic retinal vasculitis. 4 Birdshot C Pavesio Euretina 2012 Diagnosis: a. Diagnostic Criteria The criteria initially formulated by Ryan and Maumenne include: 1. Minimal, if any, anterior segment inflammation; 2. diffuse vitritis without snowbanking; 3. retinal vascular leakage, particularly in the posterior pole, which may be associated with macular edema and optic disc edema; 4. distinctive, discrete, cream coloured or depigmented spots throughout the postequatorial fundus; and 5. a painless eye. In the largest reported series to date of 102 cases, Priem and Oosterhuis used the criteria of: 1. bilateral birdshot spots plus 2. retinal vasculopathy or disc edema or optic atrophy or vitreous cells. A recent publication has reported on the research criteria for BCR, designed mainly to facilitate clinical studies. The required characteristics included: 1. Bilateral disease; 2. Presence of at least three peripapillary “birdshot lesions” inferior or nasal to the optic disc in one eye; 3 Low-grade anterior segment intraocular inflammation; 4. Low-grade vitreous inflammatory reaction. Supportive findings include a positive HLA-A29 test, retinal vasculitis and CME. It is important to stress these criteria were created for research purposes. The finding of keratic precipitates, posterior synechiae and the presence of infectious, neoplastic, or other inflammatory diseases that can cause multifocal choroidal lesions, represent exclusion criteria. These criteria showed high specificity and sensitivity as reported by the same authors. b. Ancillary Tests 1. Fundus Fluorescein angiography (FFA): angiographic studies with sodium fluorescein are particularly useful for the study of retinal circulation, but are limited when assessing lesions located primarily in the choroidal stroma. The choroidal birdshot spots are described as 5 Birdshot C Pavesio Euretina 2012 showing early hypofluorescence and late hyperfluorescence. In reality, considering the deep location of these lesions, most of them are actually not well demonstrated by FFA, and we actually see fewer lesions than those apparent by ophthalmoscopy. The profuse leakage of fluorescein at the level of choriocapillary tends to hide the deeper lesions from sight. FFA shows the vascular leakage from retinal vessels and also CME and disc edema, which are very common findings (Fig 2). Fig 2: late phase of the fluorescein fundus angiography : Cystoid Oedema of the posterior pole with CMO. Another finding reported during FFA in BCR is a prolongation of the arteriovenous transit time, which was initially described by Gass [13]. The transit time was found to be prolonged by about 20 seconds, which was felt to be due to the extensive leakage of fluorescein into the retina from compromised blood-retinal barrier associated with vasculitis, delaying the appearance of the dye in the venous circulation. 2. Indocyanine green angiography (ICG): the birdshot lesions appear hypofluorescent on ICG and are associated with medium-to-large choroidal vessels. Hypofluorescence in ICG could mean either an inflammatory infiltrate (space occupying lesion), or non-perfusion of the choroid. The histopathologic report of an eye of a 49 year old man supports the first by demonstrating the presence of multiple foci of predominantly lymphocytes, located at various 6 Birdshot C Pavesio Euretina 2012 levels of the choroid, occasionally occupying the full thickness. The choroidal lesions are actually more visible by ICG than clinically, especially in lightly pigmented fundus (Fig 3). Fig 3:: intermediate phase of the ICG-A (12 minutes) during active inflammation: numerous dark spots are distributed throughout the fundus (nodular choroidal inflammation). Active lesions tend to be become isofluorescent in the later phase of the angiogram, indicating penetration of the dye in to the affected areas, while lesions which have become atrophic will continue to show hypofluorescence. Another feature is the presence of a fuzzy indistinct appearance of the stromal vessels of the choroid. Early treatment will have a marked effect on the choroidal lesions, which tend to resolve. This finding can be used to assess response to therapy. This is in contrast to the response of the retinal vasculopathy and is likely to be due to a much higher concentration of the therapeutic agent in the richly perfused choroid. 3. Electrophysiology: abnormal electroretinograms (ERG) have been found in nearly 90% of the cases. Early reports suggested possible inner retinal dysfunction, as suggested by the finding of a negative ERG which indicates abnormal function of the neural retina with relative sparing of outer retina-inner choroidal complex. In later disease there is also involvement of the outer retina, which is demonstrated by progressive decrease in a-wave and b-wave amplitudes. It is a very useful test especially considering that the functional status of 7 Birdshot C Pavesio Euretina 2012 the retina cannot be reliably inferred either from subjective symptoms or clinical signs. The most sensitive parameter for dysfunction was the 30Hz cone derived flicker response. It seems to be quite helpful for the decision to initiate therapy and also for monitoring efficacy of treatment. 4. Visual Fields: the observed visual fields abnormalities include peripheral constriction, generalized diminished sensitivity, enlarged blind spot, and central or paracentral scotomas. It is likely that visual field findings reflect what is seen by electrophysiological studies and that in the early stages of the disease they are related to inner retinal dysfunction and that later on an outer retinal component also plays a role. It would certainly be much simpler to use visual fields for monitoring purposes, but there are issues regarding standardization, both of hardware and testing strategies, which make interpretation more difficult. Proper studies are required to establish its value, especially in comparison to electrophysiology tests. 5. Optical Coherence Tomography (OCT): this test has been quite widely used to study the macula and for monitoring CME and atrophic changes. Ultrahigh resolution OCT and depth enhancement imaging may become interesting adjuncts to the study of the retinal changes in different stages of BCR. Differential Diagnosis: It is important to remember that BCR behaves in a very special way it involves both the choroid and the retina as primary targets. Most inflammatory processes involving the eye tend to primarily affect one or the other. There are two other conditions which can lead to a similar dual involvement, tuberculosis and sarcoidosis, but they usually also present with systemic manifestations, not present in BCR. 8 Birdshot C Pavesio Euretina 2012 Theoretically one can list all entities producing white dots in the fundus as part of the differential diagnosis for BCR. The concept of white dot syndromes needs be revised since the conditions put under this heading actually involve different layers of retina/choroid and do nothave much in common. This has been brought about by studies of these conditions using ICG angiography. Conditions such as APMPPE (Acute Posterior Multifocal Placoid Pigment Epitheliopathy), PIC (Punctate Inner Choroidopathy) and MEWDS (Multiple Evanescent White Dot Syndrome)involve the inner choroid. Conditons such as VKH and sympathetic ophthalmia, which truly involve the choroidal stroma, are also associated with significant anterior segment involvement, not a feature of BCR. Conditions such as sarcoidosis, tuberculosis, mentioned above, and syphilis, apart from potential anterior segment inflammation, tend to show systemic manifestations, not a presentation proven in BCR. It is important not to forget the possibility of a masquerade presentation, as in the case of intraocular lymphomas, which may present with vitritis. The subretinal lesions seen in this condition, at least initially, are located in a sub-RPE location and not in the deep choroid. Treatment: An important development in the management of BCR has been the recognition that we should not wait for changes in central vision to initiate therapy. Peripheral retinal abnormalities may be well advanced by the time visual acuity suffers a decline, which is reflected by symptoms of peripheral field loss and nyctalopia reported by the patients and by the findings in ERG and visual field tests. This is important because early and aggressive management may produce reversal of these abnormalities before they become chronic and irreversible. Also it has been proposed that serial ERGs may be useful in monitoring response to therapy and in guiding decisions to taper medications. Sequential 9 Birdshot C Pavesio Euretina 2012 visual field testing may also be an alternative for monitoring these patients as mentioned above. Considering that BCR is a chronic, progressive disease, the objective of therapy should be of maximum control of inflammatory activity. Steroids, either systemically or locally, have been used, especially for the treatment of CME, but also for the management of abnormalities in ERG and CNV. This type of treatment is likely to produce some improvement in early stages, but will not provide sufficient control. Even though long-term control may be achieved with low doses of systemic steroids, this is likely to be more an exception and they should be used more to manage acute exacerbations. Periocular injections and intravitreal triamcinolone have a temporary effect and do not achieve overall control. A more stable delivery of intraocular steroids is achieved by the use of intraocular devices, such as the fluocinolone acetonide device (Retisert). Unpublished data shows also good control of the implanted eyes but with high risk of cataract and ocular hypertension, requiring filtering procedure. Agents such as cyclosporine, mycophenolate mofetil, azathioprine, oral methotrexate and daclizumab have been used with reported success, but no data regarding superior efficacy of any strategy is currently available.Their use is actually recommended early in the management so as to provide the best chance of maintaining long-term retinal function and visual acuity. Another form of therapy reported deals with the use of intravenous immunoglobulin in 18 patients previously treated with systemic steroids but not with immunosuppressive agents. The results showed favorable response in terms of resolution of macular edema, visual acuity, visual fields and lowering of the corticosteroid-dependence threshold. Even though it is an interesting option, it must be kept in mind that it is a small series and patients had better initial vision when compared to other reports, not allowing us to conclude that this represents an option in poorly responsive cases. 10 Birdshot C Pavesio Euretina 2012 Prognosis: The most common complication seems to be chronic CME, affecting around 50% of the cases. Epiretinal membranes occur in nearly 10% of cases and may progress with significant contraction. Choroidal neovascular membranes are uncommon occurring in less than 6% of cases. Neovascularization of the retina and disc are uncommon. Most patients reported in the literature show progressive decline in vision, mainly due to chronic CME. Other causes of decreased vision include: CNV, progressive choroidal atrophy, vitreous opacity, cataract, epiretinal membrane, optic atrophy and central retinal vein occlusion. A final visual acuity of 20/40 or better, in the better-seeing eye, was reported in 75.1% of patients. Legal blindness as defined by visual acuity of 20/200 or worse was found in 9.8% of patients. Longfollow-up of these patients show that there is progressive enlargement of the choroidal lesions, which is associated temporally with visual loss. There are progressive pigmentary changes involving the RPE, and consequently photoreceptors, and in later stages, due to vasculitis, it may result in a pale disc and attenuated retinal vessels, reflecting the loss of retinal function. 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