Characteristics of Exudative Age-related Macular Degeneration Determined In Vivo with Confocal and Indirect Infrared Imaging

Characteristics of Exudative Age' related Macular Degeneration Determined In Vivo with Confocal and Indirect Infrared Imaging M. Elizabeth Hartnett, MD,I,2 Ann E. Elsner, PhD 1,3 Purpose: To evaluate the current and future interventions in age-related macular degeneration (AM D), it is essential to delineate the early clinical features associated with later visual loss. The authors describe the retinal pigment epithelium (RPE)/Bruch membrane region in ten patients with advanced exudative AMD using current angiographic techniques and a noninvasive method: infrared (IR) imaging with the scanning laser ophthalmoscope. Methods: Ten patients with exudative AMD, evidenced by choroidal neovascularization (CNV), fibrovascular scar formation, pigment epithelial detachment, or serous subretinal fluid, were examined using IR imaging, fluorescein angiography, indocyanine green angiography, and stereoscopic viewing of fundus slides. The authors determined the number and size of drusen and subretinal deposits and the topographic character of the RPE/Bruch membrane area and of CNV. Results: In all patients, IR imaging yielded the greatest number of drusen and subretinal deposits. Sheets of subretinal material, but few lesions consistent with soft drusen, were seen. Infrared imaging provided topographic information of evolving CNV. Choroidal neovascularization appeared as a complex with a dark central core, an enveloping reflective structure which created a halo-like appearance in the plane of focus, and outer retinal/subretinal striae. Conclusions: Infrared imaging provides a noninvasive, in vivo method to image early changes in the RPE/Bruch membrane. It offers advantages over current imaging techniques by minimizing light scatter through cloudy media and enhancing the ability to image through small pupils, retinal hyperpigmentation, blood, heavy exudation, or subretinal fluid. It provides additional information regarding early CNV, and the character of drusen and subretinal deposits. Ophthalmology 1996;103:58-71

Originally received: October 6, 1994. Revision accepted: July 3, 1995. I

Harvard University, Cambridge.

2

Schepens Retina Associates, Boston.

3

Schepens Eye Research Institute, Boston.

Presented at the ARVO Annual Meeting, Sarasota, May 1994. Supported by DOE DE-FG 02-91ER61229, EY08794-01A1, and the Perkin Fund, New Canaan, Connecticut. The authors have no proprietary interest in the equipment or technology used in this study, other than grant support for research.

58

The clinical features of patients with age-related macular degeneration (AMD) have been classified to determine early findings predictive of later sight loss, namely choroidal neovascularization (CNV), retinal atrophy, and pigment epithelial detachments. I - 3 Yet, many classification schemes fail to provide reliable and repeated information predictive of the subsequent anatomic and visual outcomes in all patients. Greater understanding of the Reprint requests to M. Elizabeth Hartnett, MD, Schepens Retina Associates, 100 Charles River Plaza, Boston, MA 02114.

Hartnett and Elsner . In Vivo Infrared Imaging in Exudative AMD pathophysiology of AMD is needed. Further insight into the nature of drusen and subretinal topography may help to differentiate among the varying precursor stages in AMD and their corresponding outcomes. Appropriate medical intervention then can be determined and tested for effectiveness. Information about size, extent, and composition of drusen and the choroidal vasculature may be masked in clinical examination and stereoscopic fundus photography by the overlying retina, retinal pigment epithelium (RPE), or by the lack of contrast in heavily or lighdy4 pigmented fundi. In fluorescein angiography, masking occurs because of the melanin and xanthophyll pigments, blood, heavy exudation, dense subretinal fluid, or overlying retinal vascular hyperfluorescence. The choroidal circulation and choriocapillaris are not well resolved. Through indocyanine green angiography (ICGA), some drusen are imaged, 5 but most drusen are not demonstrated, and the choriocapillaris is not well visualized. Recent clinicohistopathologic correlations suggest that clinical definitions of drusen do not correspond to their presumed histopathologic determinants. 6 There is a need to obtain a better image of the RPE/Bruch membrane region in a noninvasive way in vivo and to define and follow the early precursor lesions of patients with AMD longitudinally. Many patients with AMD and visual impairment have other concomitant ocular disorders, such as glaucoma, cataract, or pseudophakia. Such patients may be rejected from studies because of the technical inability to image their maculas adequately. Yet, their eyes may provide valuable information and are representative of eyes typically found in this age group and in AMD. We chose a group of patients seen consecutively by the same retinal specialist, all of whom had AMD with visual impairment. Although small in number, this population represents a realistic cross-section of patients referred to retinal specialists for visual loss secondary to AMD. We used infrared (IR) imaging with the scanning laser ophthalmoscope (SLO) in direct confocal and indirect modes7- 9 to compare drusen and the subretinal topography seen in these patients with clinical evaluation and more standard methods of imaging, fluorescein angiography (FA), stereoscopic fundus slides (FS), and, in some cases, ICGA. We found that drusen seen on clinical examination correspond to some elevated, discrete subretinal deposits seen with IR imaging. Yet, we were able to see a greater number of similar-appearing subretinal deposits and of the RPE/Bruch membrane topography with IR imaging than what we saw by clinical evaluation. We believe that IR imaging may be a valuable in vivo method that provides greater information and thus a greater understanding of the RPE/Bruch membrane region.

Patients and Methods Patients Our study population included ten consecutive patients referred for retinal evaluation because of visual impair-

ment from AMD (Table 1). All patients had wet AMD diagnosed because oflarge confluent soft drusen,l pigment epithelial detachment (PED), CNV, subretinal fluid, and/ or fibrovascular scar formation in one or both eyes. In two patients, the less-involved eye had either presumed pigment (case 1) or large confluent drusen (case 3). In case 1, there was initially no clinical suspicion of wet AMD in the fellow, less-involved eye before IR imaging. In the remaining eight patients in whom extensive pathology in one eye precluded the imaging of drusen and subretinal deposits in the macula, only the fellow, less-involved eye was studied. In these eight study eyes, wet AMD manifested by drusen, PED, CNV, or subretinal hemorrhage. No patient was excluded due to media opacity, small pupil, or intraocular lens (lOL) because these conditions often coexist with AMD in this age group. A sampled macular region of each of the study eyes allowed viewing of drusen and subretinal deposits by the greatest number of methods possible by avoiding areas masked by the exudative process. The imaging data were collected prospectively and analyzed at a later time. No patient had a previously known allergy to fluorescein. No patient with an allergy to ICG or iodine underwent ICGA. Written informed consent before participation was obtained from all patients. The protocol was reviewed and approved by the Institutional Review Board of the Schepens Eye Research Institute and included confidentiality of results.

Clinical Examination and Angiography All patients underwent a thorough ophthalmologic examination, including funduscopic biomicroscopy of both maculas. Stereoscopic color FS, FA, and, in seven eyes in which FA alone failed to provide adequate clinical information, ICGA using the SLO, were performed. In patients referred from outside areas, photographs and imaging studies were requested. Testing was performed at this institution based on the individual clinical need of the patients to be cost effective in today's healthcare environment. Photographic FAs were performed in standard fashion with an intravenous, antecubital injection of 5 ml 10% sodium fluorescein, followed by sequential fundus photographs using a Zeiss (Oberkochen, Germany), Topcon (Tokyo, Japan), or Kowa (Tokyo, Japan) fundus camera. Stereo pairs of the macula were taken during the transit phases. Scanning laser ophthalmoscope FAs (cases 7 and 9; Table 1) were performed using 488-nm excitation light, 160 JL W at the cornea, and a Schott OG 515 filter (Glass Technologies, Inc, Duryea, PA). Scanning laser ophthalmoscope ICGAs were performed in seven patients using an 805-nm excitation light, 0.7 to 1 mW at the cornea, and an 81 O-nm long-pass filter. Indocyanine green, reconstituted with 3 to 5 ml diluent, was given as a 3-ml injection into the antecubital vein, followed by a saline flush, and viewed as a 40° field of view. A repeat injection of 2 ml was given for a 20° field of view after allowing sufficient time for recirculation of the original bolus of ICG. This was done only in those patients in whom minimal pooling of dye was present, and the additional bolus

59

Ophthalmology

Volume 103, Number 1, January 1996

Table 1. Demographics of Patients· Case No.

Age (yrs)

Sex

1

59

M

2 3

79 73

M M

4 51'

86 92

F F

6

79

F

7

74

F

8 9 10§

86 91 81

F F M

PED

=

Hypertensiont

Eye

+

OD OS OD OD OS OS OS

+

OD OD OD OS OD

+

pigment epithelial detachment; CNV

=

Clincal Macular Appearance Pigment CNV TreatedCNV Drusen Subretinal fluid PED Subretinal fluid, occult CNV PED, occult CNV Drusen, shallow PED Subretinal heme Occult CNV PED, subfoveal occultCNV

Indocyanine Green Angiography

+ + + + + + +

choroidal neovascularization.

• The fellow eyes of cases 2 and 4 through 10 had fibrovascular scars precluding adequate viewing of drusen and subretinal deposits; therefore, only one study eye in each of these patients was included in the study.

t All hypertension was controlled with medications. t Patient had glaucoma. § Patient had a history of cardiovascular disease.

was believed to be needed for information in the 20° field after the 40° videoangiogram was reviewed. Indocyanine green angiography was not performed in three patients. Case 1 had a well-defined CNV in the left eye, and ICGA was not required for diagnosis. Cases 3 and 9 had iodine allergies. All patients underwent IR imaging using the SLO. Infrared imaging was performed before ICGA when both were to be performed.

Stereoscopic Fundus Photographs Color stereo pairs of FS were viewed on a light box with stereo viewers (X4 magnification) by the same observer, with the room lights off to achieve the best contrast possible. The more focused slide of the stereo pair from the FS, or red-free slide when the FS was not available, was viewed on a slidex (approximately X8 magnification). A transparent grid with I-mm2 boxes was superimposed onto the image on the slidex. Outlines of the drusen, optic nerve, and blood vessels were drawn onto the overlay. A sampled macular region was determined and drawn in to represent the largest area of the macula that provided the best available quality data by all methods. From this area, counting of drusen and subretinal deposits was performed. The approximate area of the sampled macular region in deg2was calculated by dividing the area in each slide (number of millimeter-squared boxes from the transparent grid overlays) by the normalized area of the entire slide (number

60

of millimeter-squared boxes per deg2 of field; 30°, Zeiss; 50°, Topcon or Kowa). The sampled macular region in relation to the center of the foveal avascular zone for each eye was superotemporal in three eyes of three patients, superonasal in one eye or one patient, superior hemimacular in one eye of one patient, temporal in one eye of one patient, inferior nasal in four eyes of four patients, and included the entire macula in two eyes of one patient. The mean ± standard deviation for the sampled macular region was 152 ± 79.6 deg2 • The slide then was projected using a Kodak slide projector (Rochester, NY) (approximately X33 magnification). Red~free Fundus Photographs and Fluorescein Angiography

Red-free photographs and FA were viewed in a similar manner to FS slides. Drusen were seen either as subretinal low-density lesions (on red-free photographs) or as early hyperfluorescing or late staining subretinal lesions (on FAs). In two eyes (cases 7 and 9; Table 2), drusen were counted from a red-free or FA still frame from a videoangiogram.

Infrared Imaging Video images were obtained using the SL07 with a tuneable infrared laser (Ti:Sapphire SEO, Concord, MA; 795-

Hartnett and Elsner . In Vivo Infrared Imaging in Exudative AMD

Table 2. Subretinal Deposit and Drusen Characteristics and Number by Different Imaging Techniques Case No.

2 3 4 5 6 7 8 9 10

Eye

Lens Status

OD* OS* aD aD as as as aD ODt aD OSt aD

Phakic Phakic IOL Phakic, NS Phakic, NS Phakic, NS 10L Phakic, NS Phakic, NS Aphakic IOL Phakic

FA Fluorescence Late

(4X)

(4X)

(4X)

8x

33 X

IR

>80~m

Sampled Macular Region (degZ)*

+ +

+ + +

0 2

0 1 9 28 21 12 0 24 9 21 56 0

8 37 15 0 0

0 2 28 62 80 8 24 45

0 6 45 82 92

NA

NA

15 43 188 125 104 35 53 87 384 77 79 69

2 5 6 3 12 3 4 19 17 7 7 1

237 293 93 136 79 156 274 102 121 96 50 190

+

NA

NA

+ + + +

+ + + + +

FS

Red-free

Early

NA

76 64 8 20 42 NA

19 NA NA

FA

3

10

24

7t 38 32 7 24

21

30

NA

3

3

NA NA

42

FA = fluorescein anigiogram; FS = fundus slide; IR = infrared image; OD = right eye; OS = left eye; lOL NS = nuclear sclerosis. • Based on fundus slide field of view 30° (Zeiss), 50° (Topcon, Kowa).

t t

= intraocular lens; NA = not applicable;

Subretinal deposits and drusen counted from FA videoangiogram. Poor-quality FA secondary to small pupil and lOL precluded adequate imaging.

895 nm).9,10 Typically, 805-, 835-, 865-, and 895-nm wavelengths were used with powers from 40 to 200 j.J.W. This is noninvasive and not uncomfortable or fatiguing to the patient. Although parametric data were collected in this article, clinically useful data could be obtained quickly. Confocal imaging was performed initially (Fig IA). Focusing was determined at the optical plane of the major retinal blood vessel walls for each wavelength tested. The light reflected from the macula was allowed to return through a central annulus of200 or 800 j.J.m. In the highly confocal image (200-j.J.m aperture) light focused at the desired optical plane returned to the detector with little light from other tissue planes. In the direct mode, a larger aperture of 400 to 800 j.J.m allowed a higher proportion of light from deeper layers of the retina to return to the detector. This direct mode was helpful in determining the optical plane desired for viewing subretinal structures and pathologylO and will represent the aperture used when the term confocal is used. Highly confocal will indicate the 200-j.J.m aperture. We found that 835- and 865-nm wavelengths were the most helpful in evaluating the RPE/Bruch region membrane and deep retinal region. Once the desired optical plane was set, indirect mode imaging ofthe macula was performed (Fig IB). Here, the aperture was of a larger diameter with the central circular area occluded. Directly reflected light was blocked, allowing light scattered from the deeper retinal layers to return to the detector. The central occluded areas were 200 or 800 j.J.m in diameter. The 800-j.J.m diameter stop was used in this article to count subretinal deposits in digitally stored images.

Each transparent grid overlay derived from the slidex ( X8 magnification) indicating the drusen in the sampled macular region of a study eye was compared with captured computer videoimages indicating subretinal deposits seen on IR imaging.

Determination of the Number of Drusen and Subretinal Deposits Drusen and subretinal deposits were counted separately using color FS, FA, red-free slides, and IR imaging from the sampled macular region as described. Subretinal deposits, were defined as areas of elevation viewed on IR images that mayor may not correspond directly to clinical drusen. Those subretinal deposits seen on IR images that corresponded directly to subretinal deposits viewed by FS and defined as clinical drusen also were referred to as subretinal deposits in the IR images. Other subretinal deposits, viewed on IR imaging, although similar in appearance to deposits corresponding to clinical drusen, were not called drusen if no clinical counterparts were noted, but were included with subretinal deposits. Therefore, drusen was retained as a clinical term and used in describing subretinal structures with FS, red-free slides, and FA. Subretinal deposits described clinical drusen and other small, discrete, elevated lesions seen on IR imaging alone. All drusen and subretinal deposits were counted and recorded. Drusen and subretinal deposits were counted by the same individual (MEH) three times. The variability of counts was 2% or less for FS, FA, and red-free slides and 4% or less for IR videoimages. On FS, FA, and red-free

61

A

.

~;:.oHt:r'"-;' p.);~.:.n

B

Top, Figure 1. A, confocal imaging, direct mode. Directly reflected light enters central annulus. Fibrin at the edges of the choroidal neovascularization (CNV) complex reflects more light (thick arrow). Less light is reflected from the active neovascular areas because hemoglobin absorbs light (thin arrow). We believe the halo-like appearance seen at the plane of focus represents the greater reflected light and the central dark area represents neovascular channels. B, indirect mode. Scattered light from deeper layers (small diagonal arrows) passes through the annular aperture, whereas reflected light is blocked by the central stop. Little light is reflected from the center of the CNV because it is absorbed by hemoglobin (thin arrows). A higher degree of scattering of light is likely where fibrin density is greatest (thick arrows). Center and bottom, Figure Z. Fundus photography (center left) and late frame of fluorescein angiogram (center right) of case 1 (right eye), initial evaluation, show a pigmented, deep, flat area inferior to the fovea. Bottom left, an indirect infrared image (865 nm) of the same eye, visit I, shows an elevated lesion with a dark central core and a surrounding elevated lighter halo-like appearance in the plane of focus. Bottom right, fluorescein angiogram of case 1 (right eye), visit Z, 4 months later, shows choroidal neovascularization. Note similarity of this fluorescein angiogram to the previous infrared image, visit 1.

62

Hartnett and Elsner . In Vivo Infrared Imaging in Exudative AMD slides, there was minimal confluence of drusen. The greatest obstacles in counting drusen were small pupils and media opacities precluding good-quality photographs. Although small pupils and media opacities did not present obstacles to imaging the macular area by IR imaging, the confluence of clinical drusen made it more difficult to appreciate individual subretinal deposits. Statistical determination of the number of drusen and subretinal deposits and the effects of magnification or imaging method were determined using nonparametric methods. Where two eyes were quantified, results were averaged so that sample sizes were determined by the number of patients. No data were pooled across method, so that the sample size for each data analysis depended on the number of patients who had good-quality images for each method in the analysis.

Determination of Subretinal Deposit Size and Character (elevation, fluorescence) Approximate size of subretinal deposits was determined by counting the pixels on the computer images of captured IR indirect images and multiplying by 20 JLm/pixeC (based on optical data from Rodenstock (Ottebrunn-Riemerling, Germany) and our calibration for the emmetropic eye}. The IR indirect images provided the best views from which to count elevated subretinal deposits. Small subretinal deposits were designated as having diameters 80 JLm or less, because this was the smallest diameter believed to accurately reflect the size of the deposit, given the resolution of the IR images, and to meet the definition of hard drusen less than 63 JLm in diameter. II The borders of clinically apparent drusen on FS were appreciated easily on IR images. However, the distinct borders of smaller subretinal deposits that were not visible on FS are not always well appreciated by IR imaging because of the small size of the deposits (the accuracy in quantifying size of small subretinal deposits is 20% or lower). The characteristics of drusen and subretinal deposits were evaluated as follows. Size determination was used to define hard drusen (~80 JLm in diameter}. I I The presence of elevation was determined using the stereo viewers when viewing stereo pairs of FS, FA, and red-free slides, and by shadows cast by thickened regions or motion parallax in video using IR imaging in the indirect mode. The fluorescence characteristics of drusen were determined as early hyperfluorescence occurring during the arteriolar to venous flow stages, and late fluorescence as that occurring after arteriolar-venous phases. Drusen were counted as hyperfluorescent only if their fluorescence was greater than the background choroidal fluorescence. 3

Case Reports Case 1. A 59-year-old man noted gradual blurring of his central vision in the left eye I month previously. His medical history included a previous cholecystectomy and appendectomy. Otherwise, he had good health. He had two siblings with AMD.

Figure 3. Top, fluorescein angiogram of a well-defined subfoveal choroidal neovascularization (CNV) in the left eye of case I, with surrounding window defects, some of which correspond to fundus slide drusen and infrared (IR) subretinal deposits. Bottom, indirect IR image (865 nm) of subfoveal CNV in the left of case 1 shows a dark central core with a surrounding elevated halo-like area with an additional dark area surrounded by a lighter area. This appearance suggested a multilayered CNV complex. Also notice that subretinal deposits nasal to the CNV appear as elevated lighter lesions. The window defects noted on fluorescein angiography are outlined in black. Notice good correspondence but a greater number of subretinal deposits noted by IR imaging, as evidenced by elevated areas of the same size with shadowing.

Visual acuity was 20/20 in the right eye and 20/200 in the left. Intraocular pressures were 11 mmHg in the right eye and 12 mmHg in the left. Anterior segment showed no inflammation and mild nuclear sclerosis in both eyes. Results of fundus examination of the macula in the right eye showed a welldemarcated, deeply pigmented area abutting the fovea and extending inferior to it (Fig 2, center left). There was no associated

63

Figure 4. Top left. red-free image of the right eye shows a treated area below the fovea (visit 1. case 2) with few drusen-like deposits noted in the macula. Top right. late frame of fluorescein angiogram in the right eye shows areas of previous photocoagulation and faint fluorescence at the boundary between the earlier treated area (rounder, lower area of hypo/luorescence) and most recent treatment area (upper, triangular area). Also notice hyperfluorescence in the earlier area of treatment (lower). Center left. "highly confocal" infrared (IR) image (835 nm) of case 2 (right eye) shows fine, deep, radiating striae extending superonasal from the foveola. Notice the dark central core and halo-like appearance in the plane of focus above the area of treatment. This appeared elevated, unlike the clinical appearance. Also notice numerous surrounding elevated subretinal deposits. An 835-nm IR image was used for this image to show subretinal features and maintain retinal landmarks for comparison. Center right. indirect

64

Hartnett and Elsner . In Vivo Infrared Imaging in Exudative AMD IR image (865 nm) of the same eye. Notice the appearance of elevated, discrete, subretinal deposits and of sheets of subretinal material. Bottom left, early phase indocyanine green angiogram shows no clear, lacy filling of choroidal neovascularization. Bottom right, late-phase indocyanine green angiogram without evidence of a late hot spot. Notice inferior hypofluorescence of an earlier treated area and superior triangular hypofluorescence, corresponding to the most recent area of treatment as seen on the fluorescein angiogram (Fig 4, top right). Any faint hyperfluorescence is believed to represent staining between these two areas.

elevation, exudation, hemorrhage, or drusen. The macula in the left showed an area of retinal elevation involving the fovea with a few drusen located near it. Neither eye had vitreous cells, histolike spots, or peripheral streaks. Both eyes had mild peripapillary atrophy. A late frame of the FA in the right eye showed a welldemarcated hypofluorescent area with surrounding staining but no definite leakage, corresponding to the area of pigmentation seen clinically (Fig 2, center right). In the left eye, there was a lacy area of early hyperfluorescence with leakage consistent with a well-defined CNV (Fig 3, top). There were a few window defects believed to be drusen, because they corresponded to clinical drusen seen surrounding the membrane. Infrared imaging of Bruch membrane area by confocal, direct, and indirect modes showed numerous subretinal deposits that were small and elevated, located temporal to the optic nerve and throughout the macula. The area, believed to be pigment in the right eye, was elevated on indirect viewing with a halo-like appearance in the plane of focus (Fig 2, bottom left). The left eye showed a multilayered structure with concentric dark and lighter, thickened areas. The surrounding macula showed numerous elevated subretinal deposits as seen on IR indirect imaging (Fig 3, bottom). These appeared to be small, discrete areas determined to be elevated by motion parallax and shadowing. The drusen apparent on FS, and FA corresponded to a number of subretinal deposits seen on IR imaging. However, many more subretinal deposits were seen on IR imaging. The patient desired no laser treatment and was requested to return in I month. He was lost to follow-up until 4 months later. Visual acuity in the right eye had worsened to 20/30. The FA showed a well-defined subfoveal CNV (Fig 2, bottom right) in the area noted to be elevated by IR imaging on previous evaluation. Here, the diagnosis was not clearly AMD, although the history and results of clinical examination did not support an alternative diagnosis. Infrared imaging supported the diagnosis of AMD based on a greater number of subretinal deposits/drusen than that appreciated clinically on FS or FA. It also imaged the core and surrounding halo in the right eye, which had a similar appearance to the subfoveal CNV only appreciated on FA 4 months later (compare Fig 2, bottom). Case 2. A 79-year-old man who had had focal laser treatments three times in the right eye for CNV and subsequent recurrences secondary to AMD presented for a second opinion. His initial CNV occurred approximately 2 months after uneventful cataract surgery with IOL implantation. He was first seen at our laboratory approximately 2 weeks after his last laser. He had no further distortion. His left eye had lost central vision 7 years earlier from subfoveal CNV successfully closed with photocoagulation. On examination, visual acuity was 20/30 in the right eye and counting fingers in the left. Intraocular pressures were 15 mmHg in the right eye and 18 mmHg in the left. Anterior segment biomicroscopy was significant only for a well-positioned posterior chamber IOL in the right eye and nuclear sclerosis in the left. The clinical appearance and red-free slide

showed a flat, dry, atrophic area with few surrounding drusen (Fig 4, top left). The FA showed an early hypo fluorescent area inferior to the foveola extending into the foveal avascular zone, representing previous photocoagulation and faint fluorescence at the boundary between the earlier treated area and the most recent treatment area. In the late phases of the FA, there was an area of hyperfluorescence in the center of the earlier treated area inferior to the fovea (Fig 4, top right). Small, discrete, hyperfluorescing drusen were viewed early in the FA surrounding the treatment area. There was leakage from a fibrovascular scar in the left eye. Highly confocal IR imaging showed the treatment area with an elevated area superiorly. Fine, radiating, retinal striae were noted off the superior aspect of the treated area (Fig 4, center left). The indirect mode showed a halo-like appearance surrounding the treatment area. Surrounding this halo-like appearance were sheets of elevated subretinal deposits throughout the macula (Fig 4, center right). Indocyanine green angiography showed a dark area corresponding to previous laser and to the hypofluorescent area on FA. An area offaint hyperfluorescence between early laser treatment and the most recent treatment corresponded to a similar area on FA, but no hyperfluorescence was noted inferior to this within the old treatment scar where an area of hyperfluorescence was of concern on FA (Fig 4, bottom). The patient was followed. He returned 2! months later with a drop in visual acuity to 20170. Results of his clinical examination showed the dry scar as noted previously, with retinal elevation and a subretinal hemorrhage extending under the fovea in the foveal avascular zone. Confocal imaging showed elevation above the treatment scar with fine, radiating striae extending superior and nasal to the scar (Fig 5, top left). On ICGA, a subfoveal CNV with a feeding vessel extending from within the scar was appreciated (Fig 5, top right). Treatment of the feeding vessels and recurrent CNV was only initially successful. The patient returned I! months later with another recurrence. Note the red-free image with recurrence through the fovea with subretinal hemorrhage in Figure 5, bottom left. Highly confocal IR imaging showed deep retinal striae, elevation of subretinal deposits, and thickened areas (Fig 5, bottom right), which appeared more expansive than the IR image from the previous examination. Here, IR imaging provided earlier topographic information of a questionable area of recurrence of CNV within the laser treatment area on visit 1.

Results We studied ten patients (6 women, 4 men), ranging in age from 59 to 92 years (mean, 80 years). Three patients had medically controlled hypertension and one had a history of cardiovascular disease (Table 1). A total of 12 eyes (7 right eyes and 5 left eyes) are described. One patient had glaucoma. Six patients were phakic (7 eyes), 3 patients had IOLs (3 eyes), and 1

65

Ophthalmology

Volume 103, Number 1, January 1996

patient was aphakic (Table 2). One patient (1 eye) had asteroid hyalosis. These reflectile particles were noted at the shorter IR wavelengths (e.g., 805 nm) but did not interfere with FA, IeGA, or IR imaging at longer wavelengths.

Subretinal Deposit Number Drusen defined by clinical FS, FA, and red-free images corresponded in location with some subretinal deposits seen on IR imaging, and we therefore believe that these deposits represent the topographic appearances of drusen (Table 2). Although we do not know the nature of the other subretinal deposits seen on IR imaging that did not correspond to clinical drusen, we were able to note a sim-

ilarity in size, elevation, and reflectance to those subretinal deposits that corresponded to clinical drusen. We did not call these other subretinal deposits drusen because drusen is a clinical term. However, we believe the subretinal deposits seen on IR imaging probably represent subretinal deposits identical or similar to drusen, or material under the RPE or within Bruch membrane. Drusen and subretinal deposits viewed by IR imaging were counted together, because there were no distinguishing characteristics noted to separate them. These were all referred to as subretinal deposits. In all eyes imaged, IR imaging enabled us to see a greater number of subretinal deposits than any other method used (Fig 6, top left). When the numbers of drusen and subretinal deposits determined by FS, FA, red-free, and IR imaging were compared using the Krus-

Figure 5. Top left, 21 months later, a confocal infrared image (830 nm) of case 2 shows enlargement of area with striae, best seen superiorly radiating from the core of the choroidal neovascularization (CNV), suggesting expansion of it. An 830-nm infrared image was used for this image to show subretinal features and maintain retinal landmarks for comparison. Top right, indocyanine green angiogram shows an area of hyperfluorescence extending into the fovea (cross). Bottom left, red-free image of the same eye shows striae present at visit 3, 11 months later. Bottom right, indirect infrared image (805 nm) of the same eye, visit 3, shows striae of deeper retinal layers. Striae were visible at all wavelengths, but were seen most clearly at 805 nm.

66

Hartnett and Elsner . In Vivo Infrared Imaging in Exudative AMD 400~----------------------~ x

300

.~

Figure 6. Top left, number of drusen and subretinal deposits counted in sampled macular area versus the method used. circles = fundus slide (FS); squares = red-free images; triangles = fluorescein angiogram; crosses = infrared imaging. Bottom left, effect of magnification of FS on the proportion of drusen counted. Triangles = FS (X4); circles = X8 magnification; squares = X33 magnification. Bottom right, proportion of subretinal deposits counted more than 80 /Lm in diameter as measured from captured indirect infrared videoimages. In all graphs, X axis refers to case number (see Tables 1 and 2).

c

Q)

(/):J 200

x

~

"C

x

100

x

•

x

x

x

• I x l •• , ! • • o +-.....~J-.....-t--I.......-+-~•..-~.F--....-+--' o

2

x

6

4

8

10

patient

0.3 -r-------------------,

100~----------------------~

• • 50 •

•

• 2

E

c5CXJ

••

•

o

•

0.2

4

1\

• •

• 6

8

0.1 .-

• •

10

patient kal-Wallis H Test, significant differences were found (P < 0.005). When we compared IR imaging to the next most sensitive method used clinically to determine the presence of drusen (FS), IR imaging showed a significantly larger number of subretinal deposits than FS (sign test, P = 0.0156). In most patients, we also were able to determine qualitatively large, thickened areas that may have represented diffuse drusen or a sheet of material in the sub-

• • •

• • •

• o ~-----+----~~----~+-----~-----+-:~ 10 o 4 8 2 6 patient RPE space, described previously as basal linear deposits, 12 or basal laminar deposits. 6 Magnification of the FS or red-free image enabled us to see the same or a greater number of drusen than with stereo viewing of FS or red-free alone (Fig 6, top right). When the three magnifications of color slides (FS, X8, X33) were compared in those patients with color FS, significantly more drusen were counted as

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magnification was increased (Friedman rank-sum test,

P < 0.0017).

appearance showed no hypo fluorescence or hyperfluorescence of these lesions, but the quality of the FA was poor because of nuclear sclerosis of the lens.

Subretinal Deposit Size The predominant types of drusen and subretinal deposits in our patients were hard drusen, defined as discrete, subretinal deposits 80 ~m in diameter or less, or confluent sheets of subretinal material (Table 2). All patients had a low percentage of subretinal deposits of more than 80 ~m (Fig 6, bottom).

Subretinal Deposit Character: Fluorescence In six eyes (5 patients), drusen demonstrated early hypertluorescence by FA (Table 2). Five eyes of four patients showed drusen with only late hyperfluorescence. No fluorescence of deposits was seen in one patient (2 eyes). In five eyes of four patients, nuclear sclerosis precluded excellent viewing of the macular area clinically, by FS or FA, and in another patient the quality of the angiogram was too poor secondary to a small pupil and IOL to determine early versus late hyperfluorescence.

Aid in Determining Choroidal N eovascularization In case 2, early FA and ICGA images in the area of a treated CNV failed to show definite evidence of residual or recurrent CNV. The FA (Fig 4, top right) showed two areas of hypertluorescence, one within the earlier treatment scar and one between the earlier and most recent areas of treatment. The ICGA also had fluorescence at the interface of the earlier and most recent laser treatment noted in the late phases (Fig 4, bottom right). This area was believed to be staining associated with laser treatment. Infrared images provided greater detail and showed radial striae, a dark central core surrounded by a lighter halolike appearance in the plane of focus in the confocal mode,

Subretinal Deposit Character: Elevation In no eye did stereo viewing of stereo pairs ofFS, red-free images, or FA show elevation of subretinal deposits. Infrared imaging differentiated flat lesions from elevated ones in all patients, as seen in the macula in the left of case 3 (Fig 7). In case 3 (Fig 8), other lesions believed to be drusen on clinical examination and FS were found to be flat and highly reflective by IR imaging. Fluorescein angiographic

Figure 7. Indirect infrared image (835 run) of the left eye (case 3) shows a central area of diffuse elevation with surrounding elevated lesions. No definite halo-like appearance was noted in the center. This 835-nm infrared image showed subretinal features while maintaining retinal landmarks for comparison.

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Figure 8. Top, color photograph of case 3 (left eye) with flat lesions believed to be drusen. Bottom, indirect infrared image (865 run) shows flat. highly reflective lesions associated with the presumed drusen. Notice the numerous smaller. elevated subretinal deposits nasal to these reflective lesions that were not noted on clinical evaluation.

Hartnett and Elsner . In Vivo Infrared Imaging in Exudative AMD and an elevated corresponding area in the indirect mode (Fig 4, center). We believe this dark, central core and surrounding halo-like appearance in the plane of focus represents the topographic appearance of CNV. Several months later, this patient returned with a clearly imaged CNV by ICGA (Fig 5, top right) and FA in the same area as seen by IR imaging previously. The new IR images showed the striae and halo-like appearance surrounding the dark central core in the confocal mode (Fig 5, top left) and the elevated area in the indirect mode to be more advanced, indicating evolution of the CNV. The presence of outer retinal or subretinal striae (Fig 5, bottom) were also features of CNV seen in our patients. Such striae were not noted readily in typical red-free photographs. Although these could represent contraction of the CNV complex in some patients, this patient's CNV expanded over time. In this patient, striae may represent traction from increased volume of edematous tissue. Case 6 had a large area of sub foveal thickening imaged by IR, which the FA failed to show. Only an occult CNV outside the fovea was imaged on FA. The decision not to treat was made, because the patient maintained foveal fixation in this better eye. Although a definitive diagnosis of CNV cannot be made in this case without histopathologic examination, the diagnosis of occult CNV by FA and the similarity in appearance of this IR image with that of one demonstrating well-defined CNV (case 1) led us to believe this represented a large subfoveal CNV. Case 1 was believed to have an area of pigmentation in his good eye on the first clinical examination, FS, FA, and red-free photographs. Infrared imaging showed an elevated halo-like appearance with a dark central core in the plane offocus (Fig 2, bottom left). This area developed into a classic subfoveal CNV noted on FA 4 months later (Fig 2, bottom right). In contrast, case 3 in the left eye (Fig 7) has an elevated area in the fovea. There was no dark central core or surrounding halo-like appearance in the plane offocus. Follow-up of this patient showed resolution of the fluid and no development of CNV. In four other patients (cases 5, 6, 9, and 10), IR imaging showed regions of thickening with dark centers suggestive ofCNV. The ICGAs showed CNV in three patients (cases 5, 6, and 10). Cases 3 and 9 did not undergo ICGA because of allergies to iodine. Case 4 had a large PED which did not show well-defined characteristics of CNV by FA, ICGA, or IR imaging. Cases 7 and 8 did not have evidence of CNV by any method.

Conclusions The pathogenesis of AMD remains unclear. The clinical features associated with differing anatomic and visual outcomes are unknown. Clinical studies suggest that the risk factors for the development ofCNV include confluent soft drusen, focal hyperpigmentation,2 hyperfluorescence. of drusen,3 and soft membranous drusen,4 whereas confluent hard drusen 13 ,14 and choroidal perfusion delay de-

termined byFA 15 are associated with geographic atrophy. These clinical studies have the strength that the followup anatomic and visual outcomes of patients with varying clinical features can be determined. However, the actual pathology of the clinical features at any given point in time is unknown. Histopathologic studies conclude that deposits beneath the RPE cell membrane and anterior to its basal lamina are associated with CNV. 12,16 Histopathologic studies obviously are limited as to the ultimate visual and anatomic outcomes of patients whose early clinical changes are being studied histopathologically. A recent clinicohistopathologic study demonstrated the difficulty in having current clinical data and angiograms at the time of histopathologic study.6 This study concluded that clinical features, such as soft drusen and calcified drusen, did not correspond to their histopathologic counterparts. Such lack of agreement in terminology and understanding of the actual pathologic features believed to be correlated with clinical findings in eyes with AMD remains a problem in studying AMD. A recent clinicohistopathologic study described a type of soft drusen with indistinct borders, soft membranous drusen, associated with CNV, but also pointed out that these drusen may be difficult to distinguish from confluent soft clusters of hard drusen, 4 associated with geographic atrophy. The presence of basal laminar deposit4,6 determines the distribution of soft membranous drusen and may be an important feature to note clinically. A means of evaluating the topography of the RPE/Bruch membrane region in vivo is needed to determine longitudinally the outcomes of various early changes. Through IR imaging, we were able to view the greatest number of subretinal deposits and drusen in all eyes examined (Fig 6, top) even when FS and red-free images were magnified (Fig 6, bottom). In case 1, IR imaging supported the diagnosis of AMD by showing topographic information suggesting RPE/Bruch membrane changes, despite relatively few drusen seen clinically and on FS. Lesions believed to be drusen by clinical evaluation corresponded to some ofthe subretinal deposits in IR images in most patients (Fig 3, bottom). In case 3, the clinically apparent yellow, subretinallesions believed to be drusen, appeared not to be subretinal elevations on IR imaging. Rather, they were flat and highly reflective when viewed with IR imaging (Fig 8). They varied substantially from neighboring elevated subretinal deposits which were the type that corresponded to clinical drusen found in the IR images from other patients. These latter elevated subretinal deposits were not present clinically in case 3. It is unclear what the flat, highly reflective lesions represented, whether greater expanses of deeper deposits within Bruch membrane, or early atrophy. This eye had a mixed population of subretinal deposits, suggesting that several disorders may affect the pigment epithelium, photoreceptor, and choriocapillaris simultaneously or that the characteristics of subretinallesions change over time. Possibly, the flat, reflectile lesions may be unrelated to AMD and represent an entirely different process. Stereoscopic viewing of FS, red-free slides, or FA did not provide a sense of depth of the drusen. Although ste-

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reoscopic pairs of FS often allow one to see the elevation oflarger drusen, media opacities may limit the quality of good stereoimages. We found that IR imaging provided more topographic information of the RPE/Bruch membrane region than standard clinical and angiographic evaluation. A three-dimensional sense is possible through motion parallax, shadowing, and focusing. lo We do not believe that individual subretinal deposits represent atrophy or pigment as pigmentary changes do not provide depth information. Sheets of deep material (Fig 4, center right) were also apparent in eyes that did not demonstrate drusen on clinical evaluation in most patients. Smaller deposits were sometimes present on top of or adjacent to these extensive sheets. These sheets may have represented diffuse deposits between the RPE and its basement membrane,12,16 which have been shown to be associated with CNV in histopathologic studies, although there is controversy whether these provide a stimulus for CNV. 4 Infrared imaging may provide one of the only means of imaging diffuse deposits in patients at risk for CNV. Although all our patients were selected as having exudative AMD, few had a high percentage of subretinal deposits of more than 80 JLm (Fig 6, bottom), and only half of the eyes had early hyperfluorescing drusen (Table 2). Both larger, soft drusen and early hyperfluorescing drusen are reported as clinical risk factors of CNV. I ,3 The finding of sheets of elevated material may be an additional and important finding in determining eyes at risk for CNV. Infrared imaging provided greater information regarding the extent ofCNV than did FA, FS, or ICG in three of our patients (cases 1 [right eye], 2, and 6). It also provided topographic clues in cases 3, 5, 6, and 10 with occult CNV. In case 2, previous laser treatment made the interpretation of the ICGA difficult. Direct imaging (Figs 4, center left, and 5, top left) and indirect imaging (Figs 2, bottom left, 4, center right, and 5, bottom right) showed deep striae that were inapparent clinically, and a dark central core surrounded by a lighter, elevated, halo-like appearance in the plane of focus. The dark area may represent the vascularized portion of CNV (Fig 1). The subtle halo-like appearance in the plane offocus may correspond to fibrin, described by Lopez et all? and Grossniklaus et al,18 in excised surgical CNV specimens. The region surrounding the dark central core may have good sensitivity and specificity for detecting early CNV that is well defined by FA (Staurenghi et aI, presented as a poster at the 1994 ARVO Annual Meeting) or could represent prospective regions of recurrence (Brant et al, presented at the 1994 ARVO Annual Meeting). Using the criteria ofa dark central core thickening and striae, the CNV appeared to be of greater extent and was detected earlier by IR imaging compared with the correspondent FA (Elsner et al, presented at the 1993 ARVO Annual Meeting). This larger area of CNV viewed by IR may represent areas of vascularized components and of avascular areas within the membrane complexes, consistent with recent histopathologic studies of surgically excised CNV. 18,19 The avascular areas may represent more fibrous components of the membrane or areas where the RPE was able to modulate the activity of the CNV20 ,21 and prevent frank neovas-

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cularization. From IR images, we postulate that the CNV may be three-dimensional within the volume of the RPE/ Bruch membrane/neurosensory subretinal space (Fig 1). This may explain the multi-levels of elevation we viewed with IR imaging (Fig 3, bottom). It also may help explain why treatment of well-defined CNV with adjacent RPE disturbance on FA may result in later recurrence of the CNV in the previous ill-defined hyperfluorescence. Photocoagulation of the well-defined CNV may lead to hypoxia which may act as a stimulus for clinically inapparent deeper occult CNV to arise. This also may, in part, explain recurrences seen after some subretinal surgery to remove CNV, because removal of only one component of a larger, multilayered CNV complex may not eradicate deeper CNV connections. We believe the characteristics of CNV on IR imaging include the presence of a dark central core and surrounding halo in the plane of focus with or without deep retinal or subretinal striae. This may be present in occult CNV, CNV that has not evolved to the size recognizable on standard imaging, as well as well-defined CNV. In our experience, thickening is first appreciated. If no dark central core is present, which we believe represents blood vessels, the thickened area should be followed and not treated, because thickening alone may not represent early evolving CNV. The thickening may represent existing CNV that is quiescent or subretinal fluid from another pathology that may not be improved by photocoagulation. Topographic information viewed on IR imaging comes from textural cues, such as shadowing. Indocyanine green angiography, though using an IR wavelength, does not provide topographic information regarding the extent or evolution of the CNV. With ICGA, we see only fluorescent structures. Because ICG typically stays within vessels and rarely leaks, only individual vessels and not entire structures are seen. The choriocapillaris is not well resolved in ICGA, and the larger choroidal vessels are too far apart to provide such topographic information, although some topographic information is present with staining in the late phases of some ICGAs. Infrared video images provide the greatest contrast and ability to appreciate drusen and subretinal deposits. Photographic processing causes loss of some contrast and depth information. With the current ease of using videotapes in clinical medicine, the clinical use of IR imaging does not appear to pose a substantial problem. Infrared imaging minimizes masking from ocular pigmentation as noted in case 1 whose subretinal deposits were not discerned easily by clinical evaluation alone. Blood and subretinal fluid, which may preclude visualization clinically or by FA, have much less effect on the ability to image with IR wavelengths. Images at 865 nm provided the best visualization of subretinal deposits and drusen while maintaining some retinal landmarks. Generally, shorter IR wavelengths provided less subretinal information and more retinal information, and the converse was true for longer wavelengths. We believe a number of factors need to be investigated further, including visualization through exudation and ocular media.

Hartnett and Elsner· In Vivo Infrared Imaging in Exudative AMD Standard methods for imaging the eyes of elderly patients, such as FS and FA, may not always provide adequate quality images. Media opacity from nuclear sclerosis causes increased scattering oflight, particularly blue light used in FA. In five eyes offour patients, nuclear sclerosis was present and precluded excellent viewing of the macula. Glaucoma is more common in an elderly population, and miotic pupils from chronic muscarinic agonists prevent good stereo photographs because of small pupils. In three eyes of three patients, the posterior chamber IOL also interfered with the viewing. Patients with AMD often have concomitantly other ocular disorders that may limit the quality of standard means of imaging; therefore, IR imaging may be particularly suited for them. Infrared imaging offers an advantage, in that the scattering of light is limited and the narrow laser beam allows imaging even through small pupils. There are limitations with current methods used to determine the pathophysiology of the disorders comprising AMD. There is no entirely suitable animal model. Clinicohistopathologic studies are limited, in that the final anatomic or visual outcome is unknown if early lesions are sectioned and studied, or the clinical picture of early lesions is often unknown if a later anatomic outcome is sectioned and studied. It is often impossible to have current clinical slides tightly correlated with timely descriptions of pathologic sections. Infrared imaging may provide a noninvasive, in vivo method to image early changes in the RPE/Bruch membrane. It offers distinct advantages over current imaging techniques, namely, less scattering through clouded media and the ability to image through small pupils using lower light levels. These advantages prove particularly helpful in the elderly population. Acknowledgments. The authors thank Faruk Koreshi,

MD, for the clinical information and fluorescein angiograms on case 2. They also thank Charles Schepens, MD, Judy Lin, MD, Will Price, MD, and Martin Cutler, MD, for patient referrals.

References 1. Bressler NM, Bressler SB, Fine SL. Age-related macular degeneration. Surv Ophthal 1988;32:375-413. 2. Bressler NM, Bressler SB, Seddon JM, et al. Drusen characteristics in patients with exudative versus non-exudative age-related macular degeneration. Retina 1988;8:109-14. 3. PauleikhoffD, Barondes MJ, Minassian D, et al. Drusen as risk factors in age-related macular disease. Am J Ophthalmol 1990;109:38-43. 4. Sarks JP, Sarks SH, Killingsworth MC. Evolution of soft drusen in age-related macular degeneration. Eye 1994; 8(Pt3):269-83. 5. Scheider A, Neuhauser L. Fluorescence characteristics of drusen during indocyanine-green angiography and their possible correlation with choroidal perfusion. Ger J Ophthalmol 1992; 1:328-34.

6. Bressler NM, Silva JC, Bressler SB, et al. Clinicopathologic correlation of drusen and retinal pigment epithelial abnormalities in age-related macular degeneration. Retina 1994;14:130-42. 7. Elsner AE, Bums SA, Hughes GW, Webb RH. Reflectometry with a scanning laser ophthalmoscope. Appl Opt 1992;31(19):3697-3710. 8. Elsner AE, Bums SA, Kreitz MR, Weiter JJ. New views of the retina/RPE complex: quantifying subretinal pathology. Noninvasive assessment of the visual system. Technical Digest, Optical Society of America 1991; 1: 150-3. 9. Elsner AE, Jalkh AH, Weiter JJ. New devices in retinal imaging and function evaluation, In: Freeman WR, editor. Practical atlas of retinal disease and therapy. New York: Raven Press, 1993: 19-35. 10. Wolf S, Wald KJ, Elsner EA, Staurenghi G. Indocyanine green choroidal videoangiography: a comparison of imaging analysis with the scanning laser ophthalmoscope and the fundus camera. [letter; comment] Retina 1993;13:266-9. II. Klein R, Davis MD, Magli YL, et al. The Wisconsin agerelated maculopathy grading system. Ophthalmology 1991;98:1128-34. 12. Sarks SH. Ageing and degeneration in the macular region: a clinico-pathological study. Br J OphthalmoI1976;60:32441. 13. Sarks JP, Sarks SH, Killingsworth Me. Evolution of geographic atrophy of the retinal pigment epithelium. Eye 1988;2(Pt5):552-77. 14. Sarks SH. Drusen patterns predisposing to geographic atrophy of the retinal pigment epithelium. Aust J Ophthalmol 1982;10:91-7. 15. Piguet B, Palmvang IB, Chisholm IH, et al. Evolution of age-related macular degeneration with choroidal perfusion abnormality. Am J Ophthalmol 1992;113:657-63. 16. van der Schaft TL, Mooy CM, de Bruijn WC, et al. Histologic features of the early stages of age-related macular degeneration: A statistical analysis. Ophthalmology 1992;99: 278-86. . 17. Lopez PF, Lambert HM, Grossniklaus HE, Sternberg P Jf. Well-defined subfoveal choroidal neovascular membranes in age-related macular degeneration. Ophthalmology 1993; 100:415-22. 18. Grossniklaus HE, Hutchinson AK, Capone A Jr, et al. Clinicopathologic features of surgically excised choroidal neovascular mem branes. Ophthalmology 1994; 101: 1099-111. 19. Bynoe LA, Chang TS, Funata M, et al. Histopathologic examination of vascular patterns in subfoveal neovascular. membranes. Ophthalmology 1994; 10 I: 1112-7. 20. Glaser BM, Campochiaro PA, Davis JL Jr, Jerdan JA. Retinal pigment epithelial cells release inhibitors of neovascularization. Ophthalmology 1987;94:780-4. 21. Glaser BM, Campochiaro PA, Davis JL Jr, Sato M. Retinal pigment epithelial cells release an inhibitor of neovascularization. Arch Ophthalmol 1985; 103: 1870-5. 22. Elsner AE, Bums SA, Weiter JJ, Delori Fe. Infrared imaging of sub-retinal structures in the human ocular fundus. Vision Res 1996;36:191-205.

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