Topography of diabetic macular edema with optical coherence tomography.

OBJECTIVE: This study aimed to develop a protocol to screen and monitor patients with diabetic macular thickening using optical coherence tomography (OCT), a technique for high-resolution cross-sectional imaging of the retina. DESIGN: A cross-sectional pilot study was conducted. PARTICIPANTS: A total of 182 eyes of 107 patients with diabetic retinopathy, 55 eyes from 31 patients with diabetes but no ophthalmoscopic evidence of retinopathy, and 73 eyes from 41 healthy volunteers were studied. INTERVENTION: Six optical coherence tomograms were obtained in a radial spoke pattern centered on the fovea. Retinal thickness was computed automatically from each tomogram at a total of 600 locations throughout the macula. Macular thickness was displayed geographically as a false-color topographic map and was reported numerically as averages in each of nine regions. MAIN OUTCOME MEASURES: Correlation of OCT with slit-lamp biomicroscopy, fluorescein angiography, and visual acuity was measured. RESULTS: Optical coherence tomography was able to quantify the development and resolution of both foveal and extrafoveal macular thickening. The mean +/- standard deviation foveal thickness was 174 +/- 18 microns in normal eyes, 179 +/- 17 microns in diabetic eyes without retinopathy, and 256 +/- 114 microns in eyes with nonproliferative diabetic retinopathy. Foveal thickness was highly correlated among left and right eyes of normal eyes (mean +/- standard deviation difference of 6 +/- 9 microns). Foveal thickness measured by OCT correlated with visual acuity (r2 = 0.79). A single diabetic eye with no slit-lamp evidence of retinopathy showed abnormal foveal thickening on OCT. CONCLUSIONS: Optical coherence tomography was a useful technique for quantifying macular thickness in patients with diabetic macular edema. The topographic mapping protocol provided geographic information on macular thickness that was intuitive and objective.

Characterization of epiretinal membranes using optical coherence tomography.

OBJECTIVE: To evaluate optical coherence tomography (OCT), a novel noncontact and noninvasive imaging technique, for the diagnosis and quantitative characterization of epiretinal membranes. METHODS: Optical coherence tomography is similar to an ultrasound B-scan, except that light rather than sound is used, which enables higher resolution. Over a 2-year period, OCT was used to examine 186 eyes of 160 patients who had a diagnosis of an epiretinal membrane. Optical coherence tomograms were correlated with visual acuity, slit-lamp biomicroscopy, fluorescein angiography, and funds photography. RESULTS: Based on OCT, the epiretinal membrane was clearly separated from the retina with focal points of attachment in 49 eyes and globally adherent (no observed separation) in 125 eyes. Globally adherent membranes were associated with the following features: macular pseudohole (32 eyes), a difference in optical reflectivity between the membrane and retina (65 eyes), and/or a visible membrane tuft or edge (92 eyes). The membrane was undetectable on OCT in 12 eyes. The membrane thickness (mean +/- standard deviation) was 61 +/- 28 microns in the 169 eyes in which the thickness could be measured with OCT. Mean central macular thickness measured with OCT correlated with visual acuity (R2 = 0.73). CONCLUSION: Optical coherence tomography was able to provide a structural assessment of the macula that was useful in the preoperative and postoperative evaluation of epiretinal membrane surgery. Quantitative measurements and the assessment of membrane adherence with OCT may be useful in characterizing the surgical prognosis of eyes with an epiretinal membrane.

Reproducibility of nerve fiber layer thickness measurements using optical coherence tomography.

PURPOSE: Optical coherence tomography (OCT) is a new technology that uses near-infrared light in an interferometer to produce approximately 10-microns resolution cross-sectional images of the tissue of interest. The authors performed repeated quantitative assessment of nerve fiber layer thickness in individuals with normal and glaucomatous eyes, and they evaluated the reproducibility of these measurements. METHODS: The authors studied 21 eyes of 21 subjects by OCT. Each subject underwent five repetitions of a series of scans on five separate occasions within a 1-month period. Each series consisted of three circular scans around the optic nerve head (diameters, 2.9, 3.4, and 4.5 mm). Each series was performed separately using internal (fixation with same eye being studied) and external (fixation with contralateral eye) fixation techniques. The eye studied and the sequence of testing were assigned randomly. RESULTS: Internal fixation (IF), in general, provides a slightly higher degree of reproducibility than external fixation (EF). Reproducibility was better in a given eye on a given visit than from visit to visit. Reproducibility as measured by intraclass correlation coefficients were as follows: circle diameter (CD), 2.9 mm, 0.51/0.57 (normal/glaucoma) (IF), 0.43/0.54 (EF); CD, 3.4 mm, 0.56/0.52 (IF), 0.43/0.61 (EF); CD, 4.5 mm, 0.53/0.43 (IF), 0.42/0.49 (EF). CONCLUSIONS: Nerve fiber layer thickness can be reproducibly measured using OCT. Internal is superior to external fixation; each circle diameter tested provides adequate reproducibility.

Optical coherence tomography of age-related macular degeneration and choroidal neovascularization.

OBJECTIVE: The authors used optical coherence tomography (OCT), a new technique for cross-sectional imaging of the retina, to morphologically study eyes with nonexudative and exudative age-related macular degeneration (AMD). In patients with untreated exudative AMD, OCT was compared with fluorescein angiography in the identification and classification of choroidal neovascularization (CNV). METHODS: Optical coherence tomography imaging is analogous to ultrasound, except that the use of light rather than sound enables higher longitudinal resolution with a noncontact and noninvasive measurement. Optical coherence tomography was performed on 391 patients with the clinical diagnosis of AMD and was compared with conventional clinical examination to establish the cross-sectional morphology of different lesions and to develop a classification scheme for CNV. Optical coherence tomograms and fluorescein angiograms then were reviewed and correlated independently in 90 eyes of 86 patients who had exudative AMD without previous laser treatment. RESULTS: Pigmentary changes, soft drusen, and detachments of the neurosensory retina and retinal pigment epithelium all had distinct presentations on OCT. Subretinal and intraretinal fluid caused changes in retinal thickness or elevation that could be quantified directly from the images. Choroidal neovascularization was evident in the tomograms as a thickening and fragmentation of a reflective layer, which corresponded to the retinal pigment epithelium and choriocapillaris. Changes in the reflection from this layer were observed during the progression of neovascularization, and after laser photocoagulation treatment. Classic CNV consistently presented with well-defined boundaries on OCT, whereas occult CNV had a variable cross-sectional appearance. CONCLUSIONS: Optical coherence tomography was useful in quantitatively evaluating subretinal and intraretinal fluid, assessing possible subfoveal involvement of neovascularization, and in monitoring CNV before and after laser photocoagulation. Optical coherence tomography was unable to detect CNV beneath serous pigment epithelial detachments. Optical coherence tomography may have potential in accurately defining the boundaries in a subset of angiographically occult CNV.

Macular disease and optical coherence tomography.

Optical coherence tomography (OCT) is a new diagnostic tool for high-resolution cross-sectional imaging of the retina. By measuring the "echo" delay time of light as it reflects from tissue at different ranges and by performing multiple axial scans in the transverse direction, OCT generates two-dimensional images detailing retinal architecture. OCT is a powerful new modality because it has a longitudinal resolution of 10 microns in the retina, which is superior to other currently available imaging techniques. Examinations are exceptionally tolerable for patients because OCT is noninvasive, the probe beam is near-infrared and thus not very bright, and scan acquisition time is only 2.5 seconds. OCT appears to be a useful device for evaluating a variety of retinal diseases, including macular holes, macular edema, and central serous chorioretinopathy.