Chorioretinal Folds
Any condition causing a reduction in the area of the inner surface of the sclera (scleral thickening or scleral shrinkage) will cause the inner portion of the choroid, including Bruch’s membrane, the overlying retinal pigment epithelium (RPE), and the outer retinal layers, to be thrown into a series of folds or wrinkles. Indentation of the sclera by scleral depression or by an orbital tumor in the absence of scleral thickening or shrinkage does not produce chorioretinal folds. Choroidal thickening by congestion alone or by choroidal inflammatory or neoplastic infiltration may or may not cause chorioretinal folds. The terms “choroidal folds,” “choroidal striae,” or, more accurately, “chorioretinal folds” are used to refer to those folds that produce a characteristic ophthalmoscopic, biomicroscopic, and fluorescein angiographic appearance in the fundus ( Figures 4.01–4.05 ). Figures 4.01F , 4.02B and C ; and 4.03 H illustrate diagrammatically and photomicrographically the histopathologic configuration of these folds.
Acutely acquired chorioretinal folds usually produce visual dysfunction caused by distortion by the overlying retinal receptors. Most patients with long-standing idiopathic folds, however, are typically asymptomatic, have excellent visual acuity, and may show no evidence of metamorphopsia on the Amsler grid ( Figure 4.01A–D ). Chorioretinal folds produce alternate yellow and dark streaks, which often involve the posterior pole of the eye ( Figure 4.01 ). These folds may have a horizontal, oblique, or vertical orientation ( Figure 4.01 ) and are generally roughly parallel to each other. They may, however, have an irregular ( Figure 4.01H ) or a radiating pattern ( Figure 4.04D–F ). The longer the duration of the folds, the more prominent they appear. Biomicroscopy reveals that the elevated portion, or crest, of the folds appears yellow in contrast to the darker appearance of the relative narrow trough between the folds. The retina, particularly its outer layers, may or may not mirror precisely the contours of the choroidal and RPE folds. The retina in the central macula is often thrown into a stellate pattern of folds.
Characteristic changes in the background choroidal fluorescence are caused by folding of the choroid and RPE ( Figures 4.01 and 4.03–4.06 ). Figure 4.02 depicts schematically the histopathologic changes occurring in the RPE and choroid that account for the various angiographic patterns seen in chorioretinal folds. Intensification of the choroidal fluorescence occurs along the crest of the choroidal and RPE folds and produces a series of relatively hyperfluorescent streaks that are evident as early as the arterial phase. The hyperfluorescent streaks are caused by the relative normality or slight thinness of the RPE on the crest, the greater thickness of the pool of choroidal dye beneath the crest, and the shorter course of the incident blue and reflected yellow-green light through the RPE on the crest compared to that in the trough. This pattern of fluorescence remains constant, but the degree of fluorescence gradually fades along with the background fluorescence, usually within 1 hour. The troughs of the folds appear hypofluorescent. In some cases the choroidal folds are quite broad and the troughs between them may be narrow ( Figures 4.03B and E and 4.04B ). This results in the angiographic finding of narrow dark lines running within a background of normal or slightly intensified background choroidal fluorescence ( Figures 4.01E and 4.03B and E ). Indocyanine green angiography also demonstrates the lines; however the hyperfluorescent lines appear to be broader than they appear on fluorescein angiography.
Angiography is helpful in demonstrating these folds, which, if only mildly developed, may be overlooked. It is also helpful in detection of proliferative and metaplastic RPE changes ( Figure 4.01E ), drusen formation, focal RPE leaks, and choroidal neovascularization that may occur occasionally along these folds ( Figure 4.01I and J ). Angiography is also useful in differentiating folds of the choroid and RPE from folds in the retina, which do not alter background fluorescence ( Figure 4.06E and I ). Autofluorescence imaging also demonstrates the chorioretinal folds with the color of the lines being most often opposite to the lines seen on angiography. The crests appear dark or hypoautofluorescent due to stretching of the pigment epithelium and spread of the RPE pigment while the troughs appear hyperautofluorescent due to crowding of the pigment in the pigment epithelium ( Figure 4.02J and K ). Autofluorescence is rapid and noninvasive and can replace fluorescein angiography. It is especially useful in monitoring folds that are expected to resolve, such as after correction of hypotony, resolution of choroidal detachments, and so forth.
Ultrasonography usually demonstrates some flattening and thickening of the posterior sclera and choroid in the area of extensive chorioretinal folding ( Figure 4.04G ). Atta and Byrne studied 31 eyes with folds in 24 patients and found that over 60% had flattening of the posterior ocular wall, 40% had thickening of the retinochoroidal layer, and 25% had distended optic nerve sheaths. Computed tomography of patients with idiopathic acquired folds also reveals flattening of the posterior globe and mild to moderate enlargement of the optic nerve sheaths.
Causes of Chorioretinal Folds
Idiopathic Chorioretinal Folds
Idiopathic chorioretinal folds are most frequently encountered as an incidental finding in predominantly male patients, who are seen because of presbyopia and who have normal or near normal visual acuity. These patients typically have hyperopia that may vary from 1 to 6 D or more. When the folds occur in the macular region, they are often roughly horizontal in their course or may radiate outward from the optic disc ( Figure 4.01 ). They may involve most of the posterior pole of the eye. Frequently, they are confined to an area either above or below the macula and optic disc. In such cases their course is often irregularly oblique. Their distribution in both eyes is usually symmetric. They may be confined to one eye in some cases. Acquisition of folds in the second eye may occur during observation. Idiopathic central serous retinopathy occasionally occurs in these patients ( Figure 4.02F–K ; see Chapter 3 for discussion of associated findings in ICSC). Since in the embryonic development of the eye, the choroid should adapt itself to developing sclera in such a way that folds do not occur and since most patients with high hyperopia do not have chorioretinal folds, it is probable that these folds are acquired. Some patients experience rather sudden change in vision, suggesting that scleral shortening may occur abruptly in some cases in the absence of any other signs of orbital inflammatory reaction. It is likely that some inflammatory process affecting the posterior sclera, either in late prenatal life or some time during childhood in the absence of clinical signs or symptoms, causes shrinkage of the fibrous tunic of the eye. This would account for the hyperopia, the flattening of the posterior sclera, and the folds that remain as a permanent residue of this inflammation.
Retrobulbar Mass Lesions
Benign and malignant orbital tumors, including Erdheim–Chester disease, lymphangioma, hemangioma, orbital pseudotumor and others, as well as orbital implants for repair of orbital wall fractures, may cause only an indentation of the globe or in some cases may cause scleral edema, choroidal congestion, and chorioretinal folds ( Figure 4.03A–C and 4.04 A and B ). The pattern and location of these folds may or may not be helpful in defining the site of the tumor. Intraconal tumors often induce hyperopia, and extraconal tumors often induce astigmatism. Broad yellow chorioretinal folds should be differentiated from the finer retinal folds that may occasionally be produced by a retrobulbar mass. These latter folds produce no changes in the angiographic picture. If the retrobulbar mass is removed or otherwise treated successfully, the chorioretinal folds usually disappear ( Figure 4.03A–F ).
Scleral Inflammation
Thickening and inflammation of the sclera in thyroid eye disease, inflammatory pseudotumor of the orbit, and rheumatoid posterior scleritis may cause chorioretinal folds ( Figure 4.03A–F ).
Scleral Buckle
Thickening of the sclera in the vicinity of a scleral buckle for a rhegmatogenous retinal detachment may occasionally produce chorioretinal folds, which are usually present near the posterior slope of the buckle.
Choroidal Tumors
Choroidal tumors, particularly malignant melanomas and metastatic carcinomas, may produce folds in the choroid and retina surrounding the base of the tumor ( Figure 4.03G–I ). These folds are produced by mechanical displacement of the surrounding choroid by the expanding tumor, as well as by vascular engorgement, choroidal edema, and scleral thickening.
Hypotony
In some instances patients with intraocular hypotony, usually caused by a wound leak, cyclodialysis cleft, or excessive filtration after a glaucoma-filtering procedure, will develop loss of central vision secondary to marked irregular folding of the choroid, RPE, and retina. Initially, these folds are broad and are not sharply delineated. They tend to radiate outward in a branching fashion from the optic disc temporally, whereas nasal to the disc they tend to be arranged concentrically or irregularly ( Figure 4.04F and H ). This difference in the pattern of the folds is probably determined partly by traction exerted nasally by the optic nerve as the eye moves. There may be a broad area of swelling of the choroid surrounding the optic nerve head, which together with circumpapillary retinal folding produces a picture simulating marked papilledema. The sensory retina may be arranged into irregular folds that do not exactly parallel the choroidal and RPE folds. The sensory retina is often thrown into a series of radiating or stellate folds around the center of the fovea ( Figure 4.04H ). This unusual central stellate retinal wrinkling is caused by the central displacement of the normally very thick retina surrounding the very thin foveola by the thickened posterior scleral wall and engorgement of the choroid. The retinal vessels are often tortuous and sometimes engorged. Cystoid macular edema is not usually present. The primary cause of loss of visual acuity in most patients is the marked folding of the retina centrally. Shallowing of the anterior chamber caused by ciliochoroidal edema and detachment may occur. A postoperative wound leak or a cyclodialysis cleft, produced either inadvertently during an iridectomy at the time of cataract extraction or intentionally for the correction of glaucoma, were formerly the most important causes of these changes. With the development of improved techniques of wound closure and controlled trabeculectomies the incidence of hypotony maculopathy decreased dramatically during the 1980s. With the introduction of mitomycin C and 5-fluorouracil to improve the effectiveness of glaucoma-filtering procedures; however, there has been an increase in the incidence of hypotony maculopathy. Patients with chronic hypotony caused by cyclodialysis are at risk of developing permanent anterior synechiae and intractable glaucoma after surgical closure of the cyclodialysis cleft. Early detection of the characteristic fundoscopic picture of hypotony and its causes is important because surgical correction of the cause will usually result in visual improvement. As the intraocular tension becomes normalized, the choroidal folds become flattened and may completely disappear. In cases of prolonged hypotony, however, permanent, irregularly dark, pigmented lines caused by changes in the RPE remain. These changes are often present nasally as well as in the macular area. Early in the course of hypotony, fluorescein angiography shows an irregular increase in background choroidal fluorescence corresponding to the crest of the choroidal folds and also shows some evidence of leakage of dye from the capillaries on the optic nerve head but usually not from the retinal capillaries. Permanent alterations in the RPE may be demonstrable with angiography after resumption of normal intraocular pressure and marked improvement in the degree of chorioretinal wrinkling. It is not known why most eyes with the acute development of hypotony fail to develop chorioretinal folds. The maculopathy is most likely to occur in young myopic patients. It is possible the sclera in young patients is more susceptible to swelling and contraction, which reduce intraocular volume and cause the redundant folds of choroid and retina to develop. The pattern of the folds cannot be explained on the basis of uveal edema alone.
Choroidal Effusion
Choroidal folds are also seen posterior to choroidal elevation in patients with both serous and hemorrhagic choroidal detachments. The rapid rise in choroidal volume throws the retina and choroid posterior to this into folds that run parallel to the elevation ( Figure 4.03I–K ; see Chapter 3).
Choroidal Neovascularization
Contraction of a sub-RPE choroidal neovascular complex and the underlying Bruch’s membrane occurring either spontaneously or after photocoagulation may cause a radiating pattern of chorioretinal folds around the membrane ( Figure 4.04C–E ). Contraction of the superficial part of a sub-RPE neovascular complex may produce a series of parallel hyperpigmented folds in the RPE overlying the neovascular complex (see discussion of occult choroidal neovascularization in age-related macular degeneration in Chapter 3). Radial chorioretinal folds are sometimes seen in association with a pigment epithelial rip following treatment with antivascular endothelial growth factor agents ( Figure 4.04C–E ).
Vogt–Koyanagi–Harada Disease
The earliest manifestation of Harada’s disease is congestion and thickening of the choroid visible as choroidal folds or striations, followed by exudative retinal detachment. These striations are usually seen in the less or later involved fellow eye when the patient presents with symptoms in one eye, and can also be seen further in the disease course in areas outside the pockets of SRF (subretinal fluid). C-scan optical coherence tomography (OCT) shows these undulations on the RPE layer, which resolve once the retina flattens (see Chapter 11).
Focal Chorioretinal Scars
Occasionally contraction of deep focal chorioretinal scars from a variety of causes at the retinal choroidal interface may cause a pattern of radiating folds. Johnson et al. observed the development of radiating folds around what they believed was a scar induced by the operating microscope.
Optic Nerve Head Diseases Associated with Chorioretinal Folds
The changes in the posterior sclera responsible for shrinkage and flattening of the posterior sclera in patients with chorioretinal folds may also be responsible for reducing the diameter of the perioptic scleral ring and dura. This change may be responsible for the frequency of the “crowded disc” appearance or pseudopapilledema ( Figure 4.04A and B ) in these patients and for predisposing them to the development of optic disc hyaline bodies (drusen), juxtapapillary subretinal neovascularization, ischemic optic neuropathy ( Figure 4.04J–L ), and papilledema. The small diameter of the optic disc unassociated with chorioretinal folds has been implicated in the pathogenesis of pseudopapilledema, ischemic optic neuropathy, and hyaline bodies of the optic nerve head.
Chorioretinal folds may occur in association with pseudopapilledema in patients with Alagille’s syndrome (arteriohepatic dysplasia) ( Figure 4.05 ; see Chapter 5).
Chorioretinal folds often showing a horizontal course in the macula but converging on the nasal side of the optic disc have been described in association with papilledema caused by raised intracranial pressure. The mechanism for how papilledema causes folds that extend well away from the optic disc is difficult to explain. The fact that these folds may persist after resolution of papilledema suggests that in some cases they may have been present before the development of the papilledema. Because chorioretinal folds occur with such frequency, their association with other diseases may or may not be pathogenically related.
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