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CLINICAL CASES

Various SD-OCT Features of Focal Choroidal Excavations

Kou, Sandra*; Rett, Doug

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Optometry and Vision Science: April 2015 - Volume 92 - Issue 4S - p S59-S66
doi: 10.1097/OPX.0000000000000530
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Abstract

Focal choroidal excavation (FCE), an anomalous excavation of the choroid in the macula, was first detected by Jampol et al.1 in 2006 using time domain optical coherence tomography (OCT). Since then, 165 cases (188 eyes) have been detected using spectral domain OCT (SD-OCT).1–7,10–16 Focal choroidal excavation can be unilateral or bilateral and typically involve the foveal or perifoveal region of the macula. The funduscopic appearance of FCE can present as punctate pigmentary changes, yellowish-white lesions, or a diffuse hyperpigmented and hypopigmented area. Although these subtle abnormalities can be observed during a routine retinal examination, the actual structure of the FCE can only be visualized with OCT. Although time domain OCT is able to image FCE lesions, SD-OCT imaging is preferred because of improved visualization of the retinal layers and features such as enhanced depth imaging (EDI). Enhanced depth imaging OCT (EDI-OCT), a feature of SD-OCT with improved visualization of the entire choroid up to the sclera, is helpful in studying FCE cases to rule out a staphylomatous excavation of the sclerochoroidal junction. Enhanced depth imaging OCT typically reveals a focal attenuation of the outer choroid that is bordered by an undisturbed sclerochoroidal junction below and normal retinal layers above. Because OCT imaging localizes the lesion to the choroid layer, it is hypothesized that FCE is linked to central serous chorioretinopathy (CSC)2 or caused by a structural developmental anomaly.3

Focal choroidal excavations are classified as the conforming type or nonconforming type,3 based on the interaction between the overlying retinal layers and the excavated choroid. The conforming type describes cases where the outer retinal layers conform to retinal pigment epithelial alterations within the excavation; the nonconforming type refers to cases where the outer retina is separated from the retinal pigment epithelium (RPE) within the excavation, with presumably subretinal fluid filling the space between. Margolis et al.3 hypothesized that the elasticity of the retina allows the photoreceptors to remain attached to the RPE initially in conforming FCE. Although the progression from conforming FCE to nonconforming FCE has not been previously reported in the literature, it is thought that conforming FCE could eventually progress to nonconforming FCE as the stress on the outer retina leads to a separation of the photoreceptor tips from the RPE. Further enlargement of a nonconforming FCE over time may be exacerbated by the additional retinal ischemia and atrophic changes related to the normal thinning of the choroid with age.

Although FCEs are localized to the macula, they are generally associated with good visual acuity. Patients can be asymptomatic or may experience mild symptoms of metamorphopsia. With more and more eye care providers incorporating OCT into their practices, it is possible that the number of FCEs detected may increase. This article reports two cases of unilateral FCE to demonstrate its multiple SD-OCT features and to specifically document the first reported progression of a conforming FCE to a nonconforming FCE.

CASE REPORTS

Case 1

A 68-year-old African American man presented for a routine examination without ocular complaints. The patient denied history of eye trauma. Best-corrected visual acuity was 20/20 in each eye with a mild hyperopic refractive error. Although the patient lacked visual complaints, the Amsler grid test showed positive results in the left eye for metamorphopsia 5 degrees from fixation in all directions. A dilated fundus examination showed a focal area of pigment disruption superonasal to the fovea of the right eye. The left eye showed a focal area of hypopigmentation one disc diameter temporal to the fovea (Fig. 1).

FIGURE 1
FIGURE 1:
A 68-year-old man with FCE of the left eye. The left eye shows a subtle diffuse hypopigmented area underneath a vessel temporal to the macula. The right eye shows disruption of the macular pigment superonasal to the fovea.

Macular SD-OCT (Spectralis OCT, Heidelberg) scans were performed in each eye. Disruption of the RPE was confirmed superonasal to the fovea of the right eye. The scan of the left eye showed a nonconforming FCE temporal to the fovea (Fig. 2C), corresponding to the same area of hypopigmentation seen on fundoscopy (Fig. 1). The superficial retinal layers from the retinal nerve fiber layer to the external limiting membrane remained intact overlying the FCE. The inner/outer segment line was disrupted across the FCE, with likely subretinal fluid filling the space above the dipped down RPE. Interestingly, a scan was done in the same area just a year prior (Fig. 2B), and comparison showed progression of the FCE from the conforming type (Fig. 2B) to the nonconforming type (Fig. 2C). Fundus photographs were not taken previously to allow for comparison. Enhanced depth imaging OCT (Spectralis OCT) of the presenting nonconforming FCE showed a disrupted choriocapillaris and attenuated outer choroid (Fig. 3). The adjacent outer choroidal vessels appeared enlarged. Additionally, a solid hyperreflective band of tissue beneath the choroid represented an unaltered sclerochoroidal junction.

FIGURE 2
FIGURE 2:
Optical coherence tomography (A) shows an FCE temporal to the fovea in the left eye. The excavation demonstrates progression in a 1-year period, changing from the conforming type (B) to the nonconforming type (C), and then staying stable at 6-month follow-up (D).
FIGURE 3
FIGURE 3:
Enhanced depth imaging suggests absent or thinned outer layers of the choroid directly beneath the FCE. The small- to medium-sized vessels in the choriocapillaris appear unaffected, as well as the sclerochoroidal junction and overlying retinal layers. In the areas directly adjacent to the excavation, the outer choroidal vessels appear enlarged. The FCE appears broader in the vertical scan (bottom) than in the horizontal scan (top).

Short-wavelength autofluorescence (Spectralis OCT), traditionally used to highlight RPE abnormalities, was relatively unremarkable except for a very subtle area of diffuse hyperfluorescence inferior to the FCE lesion and a separate focal area of hypofluorescence nasal to the fovea (Fig. 4). Near-infrared autofluorescence, a technique that highlights choroidal lesions better, more clearly showed the full extent of the FCE in the left eye (Fig. 5B). The lesion was hypofluorescent centrally with mild surrounding hyperfluorescence concentrated inferiorly. Near-infrared autofluorescence also picked up focal peripapillary areas of choroidal abnormalities in the left eye that were not as apparent on fundoscopy and OCT. The uninvolved right eye also showed few focal perifoveal and peripapillary areas of hyperfluorescence and hypofluorescence with near-infrared autofluorescence imaging (Fig. 5A) despite the absence of an FCE on OCT. The FCE lesion of interest was found to be stable at 6 months follow-up on OCT (Fig. 2C, D), as well as the fundus appearance.

FIGURE 4
FIGURE 4:
Short-wavelength autofluorescence imaging of the FCE of the left eye is relatively unremarkable except for trace hyperfluorescence of the area inferior to the lesion.
FIGURE 5
FIGURE 5:
Near-infrared autofluorescence imaging (A) shows hypofluorescence in the center of the FCE (B), with surrounding areas of increased hyperfluorescence. Few smaller scattered hyperfluorescent and hypofluorescent peripapillary lesions are present in both eyes.

Case 2

A 57-year-old white man presented to the eye clinic for a consult for new glasses. Ocular history was significant for macular RPE disruption in the right eye of unknown etiology. Best-corrected acuities were 20/20 in each eye with a mild myopic refractive error. The Amsler grid test showed negative results in each eye for metamorphopsia or scotoma. The dilated fundus examination revealed a 1.5-disc-diameter circular area of pigment disruption and small drusen at the fovea of the right eye without hemorrhage or subretinal fluid (Fig. 6). The macula of the left eye was flat with trace drusen.

FIGURE 6
FIGURE 6:
A 57-year-old man with FCE of the right eye. Both eyes are unremarkable on fundus examination except for pigment mottling in the macula of the right eye.

Spectral domain OCT imaging confirmed a subfoveal focal conforming choroidal excavation of the right eye (Fig. 7B). This excavation corresponded with the area of pigment disruption seen on funduscopic examination (Fig. 6). All superficial retinal layers overlying the lesion, from the retinal nerve fiber layer to the outer plexiform layer, remained undisturbed. Additionally, there was no disruption of the inner segment/outer segment junction, the photoreceptor outer segments, or the RPE as all layers conformed to the excavation. Enhanced depth imaging OCT demonstrated a compressed outer choroidal layer directly under the lesion but seemingly enlarged choroidal vessels adjacent to the lesion (Fig. 8A, B). The inner choroid layer and sclerochoroidal junction appeared intact. The vertical line scan (Fig. 8A) demonstrated that the excavation covered a much larger area than seen on the horizontal scan (Fig. 8B). Short-wavelength autofluorescence imaging (Spectralis OCT) of the FCE lesion in the right eye (Fig. 9A) was relatively unremarkable. Short-wavelength autofluorescence of the fellow eye (Fig. 9B) showed scattered punctate areas of hypofluorescence within the superior arcade. Near-infrared autofluorescence images were unable to be obtained. The lesion was found to be stable and visually insignificant upon follow-up at 6 months (Fig. 7C).

FIGURE 7
FIGURE 7:
Optical coherence tomography imaging through the macula of the right eye (A) shows a subfoveal FCE (B) that is stable at 6 months follow-up (C).
FIGURE 8
FIGURE 8:
Enhanced depth imaging of the FCE in vertical (A) and horizontal (B) scans. The vertical scan shows that the lesion involves a much larger area compared with the excavation seen on the horizontal scan. The overlying retinal layers as well as the sclerochoroidal junction remain intact at the lesion site.
FIGURE 9
FIGURE 9:
Short-wavelength fundus autofluorescence does not highlight the area of FCE in the right eye (A). Autofluorescence imaging of the left eye (B) shows multiple punctate hypofluorescent lesions scattered throughout the superior arcades.

DISCUSSION

These two reported cases are consistent with existing literature in their location, appearance, and the fact that they fall into the two defined classifications of conforming and nonconforming FCE. There is a wide patient demographic for FCE. Earlier studies were performed on predominantly Asian populations where FCE was found in patients with an average age of 45 years who had myopic refractive errors.2,4 Subsequent studies, including this one, have shown that FCE can occur across a wider spectrum of races and refractive errors and without sex predilection or inheritance pattern.3,6

Most of the reports show stability of FCE to follow-up, with a longest follow-up of 36 months.4 In a few cases, however, the conversion between the two different types of FCE can be observed. Focal choroidal excavation lesions in patients with active CSC have previously been reported to demonstrate conversion from the nonconforming to the conforming type as the subretinal fluid resolved.2,5 Although it has been previously hypothesized that conforming FCE could convert to nonconforming FCE,3 case 1 represents the first reported case to demonstrate this conversion. Although it is possible that the patient may have had active CSC in the interim follow-up, the patient was asymptomatic and thus the presence of active CSC was not detected. It is possible that the mechanical stress of the excavation over time caused the photoreceptor tips to separate from the RPE, as previously hypothesized by Margolis et al.3 Despite this progression, the patient presented without complaint and the new report of metamorphopsia was noted only upon Amsler grid evaluation during the examination. It remains unclear what the clinical implications are for this progression seen on OCT. Although the literature does not indicate the necessity of fluorescein angiography or indocyanine green angiography (ICGA) in all cases of nonconforming FCE, these studies may be indicated in cases of nonconforming FCE with larger areas of subretinal fluid to rule out choroidal neovascularization (CNV) or CSC.

Rare complications of CNV have been reported in patients with FCE. It has been suggested that choroidal excavation can affect the structure of the RPE and the underlying choroidal layers, resulting in ischemic changes and CNV formation.2 A series of 12 eyes with CNV and FCE was reported by Xu et al.6 In this study, all eyes had CNV formation at the site of the choroidal excavation. Choroidal neovascularization occurred regardless of conforming or nonconforming type, shallow or deep lesions, and foveal or eccentric location. In some cases, the CNV occurred in a nonconforming FCE, and after treatment with intravitreal anti–vascular endothelial growth factor, the CNV regressed and became a conforming-type FCE. Fortunately, the cases of CNV appeared to respond well to anti–vascular endothelial growth factor treatment, with regression after a single injection in most affected eyes. This indicates the importance of following patients with FCE more closely. Fluorescein angiography and ICGA may be warranted especially in cases of nonconforming FCE to rule out CNV.

It is generally agreed upon that FCE is a choroidal abnormality, as multiple studies using EDI-OCT2,3,5 and B scan4 demonstrate integrity of the retinal layers above and the sclerochoroidal junction below these lesions. It remains unclear, however, whether it is a congenital malformation or an acquired insult. More recently, FCE has been suggested to be associated with CSC. Ellabban et al.2 found that FCEs were present in 7.8% (9 of 116) of eyes with CSC. Lee et al.5 found an even higher occurrence of CSC in FCE eyes (24.4%). Indocyanine green angiography studies performed in eyes with FCE3–5,7 have shown corresponding areas of choroidal venous dilation, choroidal hyperpermeability, punctate hyperfluorescence, and focal areas of hyperfluorescence—all of which are findings also similarly found in CSC. The similarities in choroidal vascular disturbances between CSC and FCE are notable, but a direct relation between the two conditions remains unclear.

To look more closely at the choroid in studying FCE, it is helpful to use the EDI feature of SD-OCT. Enhanced depth imaging has been shown to visualize the choroid better compared with standard OCT because it involves setting the choroid adjacent to the “zero-delay” line, a set reference point where the image capture is optimal.8 In standard OCT, the zero-delay line is normally set at the vitreous inner retina junction and provides excellent visualization of retinal details. Moving away from the zero-delay line, however, decreases the resolution from structures within the choroid. Thus, the EDI technique allows for enhanced visualization of the choroid up to the sclera.

Visualization of the choroid in the two reported cases with EDI-OCT suggests an absence or compression of the larger-caliber vessels directly beneath the FCE lesions. It is still unclear why this occurs, but perhaps the RPE then sags over the excavated area. The choriocapillaris appears preserved in these lesions with the hyperfluorescent small-diameter blood vessels bridging the bottom of the excavation and the sclera (Figs. 3 and 9). The imaging studies agree with the existing literature in that there is no apparent disruption of the sclerochoroidal junction.2,5 Although the outer choroid appears diminished directly under the excavation, the surrounding areas adjacent to the excavation demonstrate enlarged choroidal vasculature. This corresponds with the venous dilation and choroidal hyperpermeability seen in ICGA studies of FCE lesions.4,5 Thus, EDI is a helpful tool practitioners can use in addition to ICGA to image lesions involving the choroid like FCE.

Fundus autofluorescence also offers unique imaging of FCE lesions (Figs. 4, 5, and 8). There are two autofluorescence modalities that can be used to image the fundus: short-wavelength (488 nm) or near-infrared autofluorescence (ICG mode, 790 nm). Although RPE lipofuscin is the principal source of traditional short-wavelength autofluorescence, it is thought that near-infrared autofluorescence largely originates from melanin.9 Melanin is present in higher concentrations in both the choroid and foveal RPE. Lipofuscin is commonly present in lysosomes of the RPE. Thus, each type of image provides slightly different information. There will be an area of high autofluorescence centered on the fovea in near-infrared imaging because of the increased RPE melanin at the fovea. This is the opposite of traditional short-wavelength autofluorescence, in which the fovea appears dark because the RPE melanin and foveal pigment attenuate the signal. Lesions involving the deeper choroidal layers such as FCE will therefore be better visualized by the near-infrared autofluorescence versus the traditional short-wavelength autofluorescence, as evidenced in case 1.

Thus far, existing studies have found little to mild hyperautofluorescence or hypoautofluorescence of FCE lesions and a lack of abnormality in the fellow eye when using traditional short-wavelength autofluorescence.2,4 The near-infrared autofluorescence imaging in case 1 (Fig. 5) shows that it has an improved ability to highlight lesions corresponding to areas of pigment disruption seen on the funduscopic examination compared with short-wavelength autofluorescence. Furthermore, it can reveal additional bilateral peripapillary chorioretinal lesions (Fig. 5A, B) that are not as easily seen on fundus examination or traditional OCT. More cases in the future should be studied using near-infrared autofluorescence to elucidate whether the bilaterality of these deeper chorioretinal disturbances is a constant feature of FCE.

Patients with FCEs often present with mild visual disturbances or no symptoms at all. Consistent with this finding, a 10-2 Humphrey visual field analysis performed on 21 eyes with FCE failed to detect any abnormalities.4 Both reported cases lacked presenting visual complaints. Only upon Amsler grid testing during the examination did the patient in case 1 note mild metamorphopsia in the eye with FCE. Kumano et al.10 suggested that metamorphopsia is present if the lesion is at the fovea and the photoreceptor outer segments are disrupted, as in cases of nonconforming FCE. Consistent with this observation, the patient in case 1 denied metamorphopsia when the FCE was the conforming type and only noticed metamorphopsia when it had progressed to the nonconforming type with disruption of the photoreceptor outer segments. It remains unclear why the patient reported metamorphopsia in all directions from fixation, however, because the photoreceptor outer segments were only disrupted at the lesion site temporal to the fovea. Katome et al.11 described a patient symptomatic for bilateral metamorphopsia that was found to have bilateral subfoveal conforming FCE with preservation of the inner segment/outer segment junction and photoreceptor outer segments. Therefore, positive symptoms of metamorphopsia may only be partially attributed to the disruption of the photoreceptor outer segments at this time. Regardless of type of FCE, it is helpful for FCE patients to monitor visual symptoms with a home Amsler grid. Perhaps future studies using microperimetry or the multifocal electroretinogram can also be done to further explore the functional impact of FCE lesions.

In summary, FCE is a rare choroidal anomaly of the macular region of undetermined etiology. It is clinically visualized as RPE or choroidal abnormalities, and OCT shows its structure. Imaging techniques such as EDI and near-infrared autofluorescence are helpful in studying FCE. Fluorescein angiography and ICGA are useful in cases that may be complicated by CSC or CNV. Central serous chorioretinopathy has been implicated in some FCE cases, but the association between the two conditions is still uncertain. Larger studies with longer follow-up are needed to increase our understanding of the etiology and visual prognosis of eyes with FCE, as the clinical implications remain unclear for this condition.

Sandra Kou

VA Boston Healthcare System

150 S. Huntington Ave.

Boston, MA 02130

e-mail: [email protected]

Received July 7, 2014; accepted January 27, 2015.

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Keywords:

SD-OCT; enhanced depth imaging; autofluorescence; focal choroidal excavation

© 2015 American Academy of Optometry