Role Of Optical Coherence Tomography In Management Of

A JOURNAL REVIEW ON

ROLE OF OPTICAL COHERENCE TOMOGRAPHY IN MANAGEMENT OF MACULAR DISEASES.

What is Optical coherence tomography ?  Devised by Tanno et al in 1990 & Introduced by

    

Huang et al 1991, Optical coherence tomography (OCT) is a new, non-contact, non-invasive, transpupillary technique for high resolution, crosssectional imaging of tissue. It is analogous to : computed tomography - which uses X rays, magnetic resonance - which uses spin resonance, and, ultrasound B scan - which uses sound waves. The operation of OCT is similar to that of ultrasound B-scan imaging except it utilizes near infra-red light (830nm) waves rather than acoustic sound waves. Because of this difference, the axial resolution of OCT is as high as 10 μm, compared with 150 μm of that of a conventional 10-MHz Bscan ultrasound.

Techniques of oct :  TIME DOMAIN OCT (STRATUS OCT) has an

axial resolution of 10 microns and a transverse resolution of 20 microns.  SPECTRAL/FOURIER DOMAIN OCT is capable of higher resolutions of 57microns(axial) & 10-20 microns(transverse) and acquires 512 vertical

scans. An experimental ultra high resolution OCT system has been developed using Ti-laser that provides an improved axial resolution of 2 to 3microns.

Scanning Tips 1. 2. 3. 4. 5.

Have a clear idea regarding the size and location of the pathology of interest. Refer to other images of the pathology, e.g. color photos and FA. Review past OCT exams and repeat scan types used before. Dilate the eye well. The patient must keep the forehead against the bar and the chin in the chinrest, with teeth together.  Use the marker on the headrest to align the patient vertically.  The outer canthus should be even with

6.Use the two buttons near the joystick for freezing and saving scans.  This saves you from having to juggle the joystick and the mouse.

7.Minimize patient fatigue by keeping scan time to a minimum.  Never scan an eye for more than 10 minutes (FDA regulation). 8.Keep the cornea lubricated.  Use artificial tears and have the patient blink when you are not saving a scan pass. 9.Move the instrument on the x and y axis

Principle : low coherence interferometry.

MICHELSON INTERFEROMETER

OCT Image of Normal Fovea

The OCT image above can be compared to what we know about retinal anatomy from conventional microscopic sections.  The vitreous is the black space on the top of the image.  We can identify the fovea by the normal depression.  The nerve fiber layer (NFL) and the retinal pigment epithelium (RPE) are easily identifiable.  These layers are more highly reflective than the other layers of the retina.  This higher reflectivity is represented by the "hotter" colors (red, yellow, orange, white) in the false color representation of the OCT .  The

Applications  (a) Follow up of the clinical

course, understanding the pathogenesis of the disease,  (b) For assessing the response to medical/surgical/ laser therapy,  (c) For documentation and explaining the prognosis of a particular disease.

Regions For purposes of analysis, the OCT image of the retina can be subdivided vertically into four regions:  the pre-retina  the epi-retina  the intra-retina  and the sub-retina

Profiles OCT retinal morphology (form and structure) can be subdivided into four "profiles":  Each profile has it's own set of deformations and anomalous structures.    

1. 2. 3. 4.

pre-retinal profile overall retinal profile foveal profile macular profile

The pre-retinal profile  A normal pre-retinal profile is black space, as

pictured below, because the normal vitreous space is translucent, meaning it has minimal reflective properties.  The small, faint, bluish dots in the preretinal space is "noise".  This is an electronic aberration created by increasing the sensitivity of the instrument to better visualize low reflective structures.

Anomalous structures that have been observed in the preretinal profile include the following:  1. pre-retinal membrane 2. epi-retinal membrane 3. vitreo-retinal strands 4. vitreo-retinal traction 5. pre-retinal neovascular membrane 6. pre-papillary neovascular membrane A pre-retinal membrane with traction on the fovea is pictured below.

The over-all retinal profile The normal over-all retinal profile has a slightly concave curvature that you would expect from observing the surface of a globe.  Abnormal profiles would include exaggerated concavity and convexity.  Retinal folds would also result in an abnormal over-all profile.

The following OCT image demonstrates an abnormal convexity in the over-all retinal profile.  In this case, a pigment epithelial detachment is causing the convexity.

The image below demonstrates an abnormal concavity to the over-all retinal profile.  Aside from the retinal detachment, notice the underlying concave curvature of the retina, suggesting the long eye of a significant myope.

The foveal profile The normal foveal profile is a slight depression in the surface of the retina, as pictured below.

Deformations that have been observed in the foveal profile include the following:   1. macular pucker 2. macular pseudo-hole 3. macular lamellar hole 4. macular cyst 5. macular hole, stage 1 (no depression, cyst present) 6. macular hole, stage 2 (partial rupture of retina, increased thickness) 7. macular hole, stage 3 (hole extends to RPE, increased thickness, some fluid) 8. macular hole, stage 4 (complete

macular cyst

The macular profile

  

 

The macular profile can, and often does,  include the fovea as it's center.  Therefore, a common OCT scan length of 6 mm would include 3 mm of the macula on   each side of the fovea. 

                                                                                                                                   

Deformations that have been observed in the macular profile include the following:  1. serous retinal detachment (RD) 2. serous retinal pigment epithelial detachment (PED) 3. hemorrhagic pigment epithelial detachment  A serous PED is pictured below.  We know that it is a PED because the fluid (black space around the arrow) is pushing up underneath the retinal pigment epithelium, identified by the relatively highly reflective (red and orange) line (arrow).  

Intra-retinal anomalies that have been identified in the macular profile include:   1. choroidal neovascular membrane(I & II) 2. diffuse intra-retinal edema 3. cystoid macular edema 4. drusen 5. hard exudates 6. scar tissue 7. atrophic degeneration 8. sub-retinal fibrosis

Cystoid Macular Edema

OCT is capable of detecting small, fluid-filled, cystic spaces within the macula.

Central Serous Chorioretinopathy

Central serous chorioretinopathy is characterized by the presence of fluid between the RPE and neurosensory retina.

Diabetic Retinopathy

Exudates appear as accumulation of dense material within the neurosensory retina.

Artifacts  Artifacts in the OCT scan are anomalies in the scan that are

not accurate images of actual physical structures, but are rather the result of an external agent or action.    Notice the large gap in the middle of the scan below.  This is

an artifact caused by a blink during scan acquisition.  This was a high resolution scan, which takes about a second for the scan pass, which is plenty of time to record a blink.

The scan below has waves in the retinal contour.  These are not retinal folds, but rather movement of the eye during the scan pass.

Various studies have been published in different journals to study ROLE OF OCT IN MANAGEMENT OF MACULAR DISEASES. A few of them are mentioned below. 1. The following study was conducted for Alberta Heritage Foundation for Medical Research (2003) Canada To evaluate the evidence on the use of OCT to diagnose retinal disease From 1995–July/August 2003 Cystoid macular oedema diagnosis:1 study compared OCT with FFA in patients with uveitis. 1 study compared OCT with FFA + slit-lamp biomicroscopy in patients with diabetic retinopathy.

Likelihood ratios indicate that OCT provided strong to convincing diagnostic evidence for detecting cystoid macular oedema and retinal blood vessel leakage. Resul ts: Accuracy for diagnosis of macular oedema OCT in patients with uveitis (FFA as reference standard) (1 study): • Sensitivity = 89%; specificity = 100% OCT in patients with diabetic retinopathy (FFA as reference standard) (1 study): • Foveal retinal thickness: Sensitivity = 81.5%; specificity = 94.1% (FFA as reference standard) • Average retinal thickness: Sensitivity = 73.1%; specificity = 100% (FFA as reference standard) • Foveal retinal thickness: Sensitivity = 88.8%; specificity = 96.0% (slit-lamp biomicroscopy as reference standard) • Average retinal thickness: Sensitivity = 80.2%; specificity = 100% (slit-lamp biomicroscopy as reference standard)

2.Optical coherence tomography to detect and manage retinal disease and glaucoma. Jaffe GJ, Caprioli J.2004,USA. PURPOSE: To review basic principles of optical coherence tomography, and to describe its use in the diagnosis and management of retinal diseases and glaucoma. DESIGN: Perspective. METHODS: Literature review. RESULTS: Optical coherence tomography is a noninvasive imaging technique that has been used increasingly to diagnose and manage a variety of retinal diseases and glaucoma. Optical coherence tomography (OCT) is based on the principal of Michelson interferometry. Interference patterns produced by low coherence light reflected from retinal tissues and a reference mirror are processed into an "A-scan" signal. Multiple A-scan signals are aligned to produce a two-dimensional image that can be thought of as a form of "in vivo histology." Optical coherence tomography has been used to identify macular holes, to differentiate macular holes from simulating lesions, to identify lamellar macular holes, macular cysts, vitreomacular traction, subretinal fluid, pigment epithelial detachment, and choroidal neovascularization. It can be used to identify and quantify macular edema, and to measure retinal thickness changes in response to therapy. Macular thickness measurements determined by OCT correlate well with visual acuity and with leakage observed by fluorescein angiography. Optical coherence tomography is an accurate and reproducible method to measure retinal nerve fiber layer thickness. Particularly, when used in combination with other optic nerve

Optical coherence tomography equipment is expensive, and not all insurance companies reimburse this procedure. Image quality is dependent on operator technique & degraded in the presence of

media opacity. Change analysis software for glaucoma applications is not fully developed, and there is a scarcity of age, gender, and racespecific normative data upon which to compare eyes with retinal disease and glaucoma. In the next few years, it is likely that the role of OCT as a method to diagnose and manage retinal disease and glaucoma will be further defined, and many of the current limitations will be overcome. CONCLUSIONS: Optical coherence tomography is a useful imaging technique to diagnose and manage a variety of retinal diseases and

Diabetic macular edema assessed with optical coherence tomography and stereo fundus photography. Strøm C, Sander B, Larsen N, Larsen M, Lund-Andersen H. Department of Ophthalmology, Herlev Hospital, University of Copenhagen, Copenhagen, Denmark. JAN 2002.To compare retinal thickening in PURPOSE:

diabetic macular edema assessed subjectively by evaluation of stereo fundus photographs with that assessed objectively by optical coherence tomography (OCT). CONCLUSIONS: The degree of agreement between subjectively and objectively assessed retinal thickening was very good, implying that

Optical Coherence Tomography versus Stereoscopic Fundus Photography or Biomicroscopy for Diagnosing Diabetic Macular Edema: A Systematic Review Gianni Virgili, Francesca Menchini, Andrea F. Dimastrogiovanni, Emilio Rapizzi, Ugo Menchini, Francesco Bandello, and Raffaella Gortana Chiodini

Rome, Italy in 2000. PURPOSE.

To review systematically the sensitivity and

specificity of optical coherence tomography (OCT) for diagnosing macular edema attributable to diabetic retinopathy compared with well-established gold standard tests such as fundus stereophotography or

RESULTS. Fifteen studies were considered eligible. These studies were of good quality for most items of the QUADAS checklist, but most studies did not report masking of examiners and did not describe how withdrawals and undetermined results were treated. Seven studies included healthy control subjects, which could have artificially enhanced OCT diagnostic performance. All but one study included both eyes of the patients without taking into account the withinsubject correlation in statistical analyses. Sensitivity and specificity data could be extracted from only 6 of 15 studies, because appropriate cross tabulations of index and reference tests were not reported by the others. In five of these studies, central retinal thickness cutoffs between 230 and 300 µm were adopted to define abnormal OCT results and considered the central type of CSME only, whereas in one study a complex algorithm accounting for extrafoveal CSME was used. The design of one study was case–control and was excluded from the meta-analysis. The expected operating point on the summary ROC, a pooled estimate of all studies, corresponded to a sensitivity of 0.79 (95% CI: 0.71–0.86), a specificity of 0.88 (95% CI: 0.80–0.93), a positive likelihood ratio of 6.5 (95% CI: 4.0–10.7), and a negative likelihood ratio of 0.24 (95% CI: 0.17–0.32). These values suggest a good overall performance of OCT for diagnosing CSME.

Purpose: To investigate the quantitative assessment of macular edema secondary to central or branch retinal vein occlusion with foveal thickness measurements by optical coherence tomography (OCT). Material and methods: Thirty eight eyes of 38 cases examined between October 2000-May 2002, with central or branch retinal vein occlusion were included in the study. At initial examination and during follow-up examinations at 3-6 month intervals, complete ophthalmic examination was done, color fundus photographs were taken and fluorescein angiography was performed. Foveal thickness measurements were taken in macular crosssection images obtained with optical coherence tomography. Control group included thirty-nine eyes of 33 healthy objects without eye pathology. Foveal thickness measurements were obtained from macular OCT images and compared with the values of study group.

Results: At initial examination, there was sponge-like retinal swelling in 34 %, cystoid macular edema in 34 %, serous macular edema in 19.2 % and mixed edema in 12.8 % of 38 cases (11 of them had central, 27 of them had branch retinal vein occlusion). In the study group, the mean foveal thickness at initial examination (590.2 ± 45 µm) was significantly higher than the mean value at last visit (403.1± 53 µm). These values were also significantly higher than the mean foveal thickness in control group (177.1 ± 19.4 µm). There was negative correlation between mean foveal thickness measurements and visual acuities at initial and final examinations.

Conclusion: Optical coherence tomography is a useful technique for noninvasive, objective and quantitative assessment of macular edema secondary to retinal vein occlusions with foveal

Purpose : To evaluate central serous chorioretinopathy (CSCR) with optical coherence tomography (OCT) during the acute and resolution phase. Method : 12 patients (8 men and 4 women) who were examined between October 2000 and May 2001 and diagnosed as CSCR were included in the study. Complete ophthalmologic examination was performed, color fundus photographs were taken and optical coherence tomography was performed. Fundus fluorescein angiography was performed in all cases except two pregnant women during initial examination. FA and OCT were repeated during the control examinations. The difference between the retinal thickness and serous

Results : 14 eyes of 12 patients had on acute phase of CSCR according to fundus examination and fluorescein angiography. 2 patients were pregnant and one of them had bilateral involvement. Fluorescein angiography  was not performed in these cases. Fluorescein angiograhy revealed one or more leakage points in 10 eyes, multiple pigment epithelial detachments (FED) in one eye. OCT scans showed neurosensory retinal detachment and increased retinal thickness  in 13 eyes, and PED's in one eye. FED in a pregnant woman was detected by OCT. During follow-up period, in the eyes without active leakage point in fluorescein  angiography, the neurosensory detachments resolved and retinal thickness decreased  In  OCT  scans.  

Conclusion: OCT is a useful and objective diagnostic technique  in  evaluating  FED,  neurosensory  retinal  detachment  and  retinal  thickness  in  CSCR.  It  may  be  an  alternative  diagnostic  tool  in  pregnant women.

Virgili et al. (2007) Italy : systematically the sensitivity and specificity To review of OCT for diagnosing macular oedema attributable to diabetic retinopathy compared with fundus stereophotography or contact and non-contact fundus biomicroscopy. OCT can be used to diagnose CSME, particularly its central type or CDME, and decide on laser photocoagulation in patients with intermediate suspicion of disease The strength of this conclusion is limited by the fact that data could be extracted from only a fraction of the published literature due to limitations in reporting. The precision of estimates is inflated by the within-patient correlation between Results : Sensitivity = 0.79 (95% CI: 0.71–0.86); specificity = 0.88 (95% CI: 0.80–0.93)

Comparison between optical coherence tomography and fundus fluorescein angiography for the detection of cystoid macular edema in patients with uveitis. ANTCLIFF R. J. ; STANFORD M. R. ; CHAUHAN D. S. ; GRAHAM E. M. ; SPALTON D. J. ; SHILLING J. S. ; FFYTCHE T. J. ; MARSHALL J. Department of Ophthalmology, Rayne Institute, St. Thomas'Hospital, London. Purpose: To compare optical coherence tomography (OCT) with fundus fluorescein angiography (FFA) for the detection of cystoid macular edema (CME) in patients with uveitis. Main Outcome Measures: Detection and distribution of macular edema. Results: One hundred eight eyes had similar results on both OCT and FFA in that 67 eyes had CME and 41 eyes had no CME. In 10 eyes subretinal fluid was detected on OCT but not FFA. Five of these eyes had CME on FFA but not OCT. Three other eyes had CME that was detected by FFA but not by OCT. Compared with FFA, the OCT sensitivity for detecting CME was 96% (including the eyes with subretinal fluid), and the OCT specificity was 100%.

Conclusions: OCT is as effective at detecting CME as is FFA but is superior in demonstrating axial

Conclusion : 1) OCT can detect very early macular disease changes. 2) It can be used to study, diagnose, monitoring & guiding retreatment decisions. 3) It is reproducible, accurate, sensitive and specific. Limitations: 1) Clear media needed,  2) Pupillary dimeter of approx. 4 mm,  3) Costly.

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