Optical coherence tomography (OCT) is an optical acquisition method to examine biological tissues. In recent years, OCT has become an important imaging technology used in diagnosing and following macular pathologies. Further development enabled application of optical coherence tomography in evaluation of the integrity of the nerve fiber layer, optic nerve cupping, anterior chamber angle, or corneal topography. In this manuscript we overview the use of OCT in the clinical practice to enable corneal, iris, ciliary body, and angle evaluation and diagnostics.
Optical coherence tomography (OCT) systems use low-coherence, near-infrared light to provide detailed images of anterior segment structures at resolutions exceeding other systems like ultrasound biomicroscopy or conventional ultrasound [
The purpose of this paper is to present the various applications of the HD-OCT Cirrus device in the clinical practice to enable corneal, iris, ciliary body, and angle evaluation, for instance, examination of even fine structures like Descemet’s membrane, the trabecular meshwork, and Schwalbe’s line.
The Anterior Segment Cube
The Anterior Segment 5-Line Raster scans through 5 parallel lines of equal length that can be used to view high-resolution images of the anterior chamber angle and cornea. The line length is fixed at 3 mm, while the rotation and spacing are adjustable. Each line is composed of 4096 A-scans, and by default, the lines are horizontal and separated by 250
The HD-OCT device has been recently used as a noninvasive corneal imaging modality that was capable of in vivo differentiation of both corneal layers and demonstration of pathologic abnormalities in the cornea (Figure
High-definition OCT of the cornea enables localization of the interface between the corneal stroma and epithelial/Bowman’s layer.
Anterior Segment Cube
For refractive surgery corneal Cirrus OCT enables identification of the postoperative flap and unexpected changes as epithelial ingrowth. The thickness of eventual epithelial hyperplasia can be viewed by the Cirrus OCT. Postoperatively, OCT enables visualization of corneal flaps, as well as the integrity of the corneal layers.
For keratectomy the HD-OCT also allows various changes such as attachment of the implanted posterior Descemet in DMEK procedure or even wrinkle or fold within the DSEK. The OCT images also enable better clinical decision to conduct more accurate planning of treatments for corneal opacities.
Structural anatomies of the cornea like keratin precipitates secondary to uveitis can be monitored with the Cirrus OCT. Cases of intrastromal corneal foreign body can be viewed by the Cirrus. OCT accurately maps corneal thickness in clear and opacified corneas, allowing the examiner to precisely map the depth of corneal opacities, the degree of epithelial hyperplasia, and the thickness of the cornea, as well as corneal edema and thickening, scleral melts, corneal degenerations, and scars as well as corneal dystrophies [
Cirrus OCT of a 79-year-old patient who underwent cataract surgery. She developed postoperative corneal edema detected and monitored by the Cirrus OCT, characterized by diffuse hyperreflectivity interspacing lacunae of hyporeflectivity on corneal OCT scan. In addition, interruption of the endothelial layer can be documented.
Contact lens distance to the corneal epithelial can be measured with the Cirrus OCT. It enables to distinguish cases of thinner tear film thickness, which may be a sign of tight contact lens adaptation. Some of the limitations of the Cirrus in corneal analysis include not enough resolution for endothelial cell distinction, less precise pachymetry in comparison to the Pentacam, and little amount of publications on the topic in the medical literature.
An 86-year-old female underwent phacoemulsification surgery for therapy of cataracta rubra, advanced nuclear sclerosis. The surgery lasted 28 minutes while ultrasound time 3.02 minutes. Figure
Corneal imaging with the Cirrus OCT of an 86-year-old female patient who underwent lens phacoemulsification for therapy of dense nigra cataract. She developed focal microbullous keratopathy. OCT shows both the remarkable corneal edema, as well as interruption of endothelium layer. The patient was treated with topical steroids and experience improvement 4 weeks later.
A 77-year-old patient presents with nuclear lens cataract. Preoperative evaluation included specular corneal microscopy, fundus evaluation, and pachymetry. Figure
The Visante anterior segment OCT system (Carl Zeiss Meditec, Dublin, CA, USA) is a time-domain 1310 nm operating device that supports several modes, including high-resolution cornea, corneal pachymetry, and anterior segment at resolution of 18
Some properties and differences among Visante, Pentacam, and Cirrus OCT are described in detail. Courtesy of Zeiss.
(I) Visante anterior segment OCT |
(a) Anterior segment |
(i) 6 mm depth by 16 mm width 256 A-Scan per B-Scan |
(ii) 3 mm depth by 10 mm width 512 A-Scan per B-Scan |
(b) Wavelength 1310 nm (infrared, nonvisible light) |
(II) Cirrus HD-OCT |
(a) Anterior segment |
(i) Cube: |
(ii) 5-Line Raster: 3 mm, 4096 A-Scans |
(b) Posterior segment |
(i) Cube: |
(ii) 5-Line Raster: 9 mm, 4096 A-Scans |
(c) Wavelength 840 nm |
(III) Pentacam |
(a) Rotating Scheimpflug Imaging System |
(b) Wavelength 475 nm, blue LED (Info: Ziemer Galilei wavelength 470 nm) |
HD-OCT applies a scanning rate 50 to 60 times faster than time-domain OCT devices and with an axial resolution of 3 to 5
The Cirrus HD-OCT may enable identification of Schwalbe’s line (yellow arrow), scleral spur (green asterisk), and trabecular meshwork (red arrow).
A 45-year-old female underwent vitrectomy plus silicone oil for retinal detachment repair. She presented with postoperative corneal edema that impaired angle examination. Cirrus OCT disclosed open anterior chamber angle.
A 45-year-old female underwent vitrectomy plus silicone oil for retinal detachment repair. She presented with postoperative corneal edema and increase in intraocular pressure. The corneal edema impaired angle examination. OCT disclosed open anterior chamber angle (Figure
A 49-year-old female presents with a 1-week history of pain and visual loss OS. Her corrected visual acuity was 20/80 OS and 20/20 OD. Ophthalmic examination was unremarkable, except for angle alterations and intraocular pressure of 57 mmHg OS. There were OS areas alternating very narrow and close anterior chamber angle; OD the angle was narrow. OCT examination confirmed the anterior chamber angle morphology (Figure
A 49-year-old female presents with a 1-week history of pain and visual loss OS. Ophthalmic examination was unremarkable, except for angle alterations and intraocular pressure of 57 mmHg OS. There were OS areas alternating very narrow and close anterior chamber angle; OD the angle was narrow. (a) OCT examination confirmed the anterior chamber angle morphology (b) The patient underwent topical and systemic antihypertensive ocular therapy. Two days later, the intraocular pressure was 16 mmHg OS, the angle was open, confirmed by OCT exam.
Cirrus OCT provides relevant clinical data in regard to anterior chamber and corneal diagnosis. It enables detailed high-resolution corneal morphology analysis. It also allows anterior-chamber angle examination. OCT is a novel device to perform in vivo optical biopsies and a promising research and clinical tool for the evaluation of corneal pathologic features in a noninvasive manner. The future use of this novel technology should develop and increasingly is becoming important equipment in the clinical and surgical management of corneal, anterior chamber angle, and iridociliary diseases.