Op#c Nerve Head & Re#nal Imaging Dr Cesar Carrillo October, 2014 Vien#ane/NOC **Disclaimer** The images contained in this presenta5on are not my own, they can be found on the web
OUTLINE Indica5ons Confocal laser scanning tomography (Optos) Confocal laser scanning tomography with polarimetry (GDx) Confocal tomography (HRT) Op5cal coherence tomography (OCT) 2
Optic Nerve Head and Retinal Imaging - Indications Medically necessary for documen5ng the appearance of the op5c nerve head and re5na Pa5ents with :! glaucoma, glaucoma suspects! posterior vitreous detachment screening for:! chloroquine (Aralen)! hydroxychloroquine (Plaquenil)! vigabatrin (Sabril) toxicity! other diseases macular hole, diabe5c re5nopathy, and pseudotumor cerebri
Optic Nerve Head and Retinal Imaging Op5c nerve imaging for glaucoma more frequently than once per year is considered not medically necessary Methods: o Confocal laser scanning tomography (Optos) o Confocal laser scanning tomography with polarimetry (GDx nerve fiber layer tes5ng or analysis) o Confocal tomography (HRT) o Op5cal coherence tomography (OCT)
Confocal Laser Scanning Tomography (Optos) Ultra- Widefield (UWF) imaging Documen5ng Monitoring ocular pathology in the periphery > 80% view (200⁰) Non- contact
Confocal Laser Scanning Tomography with Polarimetry (GDx) GDx nerve fiber layer tes5ng or analysis Confocal laser scanning tomography with polarimetry
Confocal Tomography (HRT) Observa5on &documenta5on of the ONH Laser take 3- dimensional photo Area of the op5c disc and rim, volume of the cup
Optical Coherence Tomography (OCT)
Op5cal Coherence Tomography OCT Diagnos5c imaging technique that examines living 5ssue non- invasively. It is based on a complex analysis of the reflec5on of low coherence radia5on from the 5ssue under examina5on Real 5me cross sec5onal analysis
Op5cal Coherence Tomography OCT Qualita5ve and quan5ta5ve analysis of the re5na Qualita5ve analysis includes descrip5on by loca5on, a descrip5on of form and structure, iden5fica5on of anomalous structures, and observa5on of the reflec5ve quali5es of the re5na
OCT Quan5ta5ve analysis involves measurements of the re5na, specifically re5nal thickness and volume, and nerve fiber layer thickness. This is possible because the OCT so_ware is able to iden5fy and "trace" two key layers of the re5na, the NFL and RPE
OCT How does it work? o 128 to 768 axial samples (A- scans) in a single "scan pass o Each A- scan has 1024 data points and is 2mm long (deep)
OCT Resolu5on: When all of the A- scans are combined into one image, the image has a resolving power of about 10 microns ver5cally and 20 microns horizontally Compare that to the resolu5on of a good ophthalmic ultrasound at 100 microns
OCT Protocols: OCT has several built- in protocols for scanning the re5na and the op5c nerve head A protocol is simply a pre- determined procedure or method
OCT Scan Protocol Types: Line Circle Radial Lines
OCT The "line" scan simply scans in a single, straight line. The length of the line can be changed as well as the scan angle
OCT The "circle" scans in a circle instead of a line
OCT The "radial lines" scans 6 consecu5ve line scans in a star pagern
Re5nal Anatomy Compared to OCT The vitreous is the black space on the top of the image We can iden5fy the fovea by the normal depression The nerve fiber layer (NFL) and the re5nal pigment epithelium (RPE) are easily iden5fiable layers as they are more highly reflec5ve than the other layers of the re5na
Re5nal Anatomy Compared to OCT This higher reflec5vity is represented by the "hoger" colors (red, yellow, orange, white) in the false color representa5on of the OCT The middle layers of the re5na, between the NFL and RPE, are much less easily iden5fiable in the scan
Re5nal Anatomy Compared to OCT
Re5nal Anatomy Compared to OCT For purposes of analysis, the OCT image of the re5na can be subdivided ver5cally into four regions the pre- re5na the epi- re5na the intra- re5na the sub- re5na
The Pre- Re5nal Profile A normal pre- re5nal profile is black space Normal vitreous space is translucent The small, faint, bluish dots in the pre- re5nal space is "noise" This is an electronic aberra5on created by increasing the sensi5vity of the instrument to beger visualize low reflec5ve structures
The pre- re5nal profile Anomalous structures: pre- re5nal membrane epi- re5nal membrane vitreo- re5nal strands vitreo- re5nal trac5on pre- re5nal neovascular membrane pre- papillary neovascular membrane
The Over- All Re5nal Profile
A Pre- Re5nal Membrane With Trac5on on the Fovea
A Pigment Epithelial Detachment is Causing the Convexity
Aside from the re5nal detachment, no5ce the underlying concave curvature of the re5na, sugges5ng the long eye of a significant myopic
The foveal profile The normal foveal profile is a slight depression in the surface of the re5na
Deforma5ons in the Foveal Profile macular pucker macular pseudo- hole macular lamellar hole macular cyst macular hole, stage 1 (no depression, cyst present) macular hole, stage 2 (par5al rupture of re5na, increased thickness) macular hole, stage 3 (hole extends to RPE, increased thickness, some fluid) macular hole, stage 4 (complete hole, edema at margins, complete PVD)
Macular Cyst
Macular Hole - Stage 2
Macular Hole- Stage 3
Macular Hole- Stage 4 Operculum Suspended by the Hyaloid Membrane
The Macular Profile The macular profile can, and o_en does, include the fovea as it's center
Deforma5ons in the Macular Profile Serous re5nal detachment (RD) Serous re5nal pigment epithelial detachment (PED) Hemorrhagic pigment epithelial detachment
Serous Re5nal Pigment Epithelial Detachment (PED)
Intra- Re5nal Anomalies in the Macular Profile Choroidal neovascular membrane Diffuse intra- re5nal edema Cystoid macular edema Drusen Hard exudates Scar 5ssue Atrophic degenera5on Sub- re5nal fibrosis RPE tear
Choroidal Neovascular Membrane
Cystoid Macular Edema Caused by Diabe5c Maculopathy
Sub- Re5nal Fibrosis
OCT and Fluorescein Angiography in Re5nal Diagnosis FAs provide excellent characteriza5on of re5nal blood flow over 5me, as well as size and extent informa5on on the x and y axis (north- south, east- west) The OCT gives us informa5on in the z (depth) axis, telling us what layers of the re5na are affected
OCT and Fluorescein Angiography in Re5nal Diagnosis
OCT and Fluorescein Angiography in Re5nal Diagnosis
OCT Scans for Qualita5ve Analysis of the Re5na The Fast Macular Thickness Scan (FMTS, FMTM, or FMT scan) The Line Scan The Cross Hair Scan (3mm and 6mm)
The Fast Macular Thickness Scan The Fast Macular Thickness Scan consists of 6 radial line scans in a spoke pagern. It is a low resolu5on scan that was designed for quan5ta5ve analysis (thickness and volume)
The Fast Macular Thickness Scan The FMT scan is placed over the area of interest, which is usually the macula. When scanning the macula, the pa5ent simply looks at the fixa5on target. The center of the FMT scan lines up with the fixa5on target by default A scan is saved and then reviewed with any of the re5na analysis tools
The Line Scan The line scan is par5cularly useful because of it's flexibility. The length of the line can be changed, the angle of the line can be changed, and the line can be dragged with the mouse to any posi5on or angle on the video screen
The Cross Hair Scan Cross Hair Scan performs a high resolu5on horizontal line scan and then automa5cally flips to a ver5cal line scan without having to exit the protocol This is a common technique used in B- scan ultrasonography
Serial FMT Scans Over Time One of the most useful func5ons of the OCT is the ability to take volume measurement over 5me For example, a FMT scan before treatment for AMD, and FMT scans at various intervals a_er treatment Successful treatment should be followed by a decrease in re5nal thickness and volume
Op5c Nerve Head Scans When evalua#ng the glaucoma suspect or the glaucoma pa#ent, two parameters that the ophthalmologist is interested in are the characteris#cs of the op#c nerve cup and the thickness of the nerve fiber layer surrounding the op#c nerve head The Fast Op#c Disc scan The Fast RNFL Thickness scan
The Fast Op5c Disc Scan The op5c cup profile can be evaluated by capturing a "Fast Op5c Disc" scan The pa5ent fixes on the target, which is automa5cally placed at the edge of the scan window so that the op5c nerve is viewed toward the center of the video window The operator then moves the scan so that the star pagern is centered on the op5c nerve head
The Fast Op5c Disc Scan
The Op5c Nerve Scan can be Analyzed with the Op5c Nerve Head Analysis" Protocol
The Fast RNFL Thickness Scan Nerve fiber layer thickness can be evaluated with the "Fast RNFL Thickness" scan This is a circular scan that requires the operator to place the circle so that the center of the circle is centered on the op5c nerve head
The analysis so_ware places lines on the top and bogom of the nerve fiber layer and the distance between the two lines is interpreted to be the thickness of the nerve fiber layer
Care must be take to make sure that the image is captured with the circle centered on the op5c nerve The placement of the circle can make a big difference in the analysis of the nerve fiber layer thickness
These two scans (OD) are of a normal eye. The scan in the first analysis is well centered and the RNFL thickness falls within the normal range. The scan in the second analysis is of the same eye (OD), but the scan is not well centered. The analysis is abnormal (black arrows)
OCT A good quality OCT scan has good reflec5vity from edge to edge The "hoger" colors (orange, red, white, yellow) are maximized Generally, the re5na should be in the lower por5on of the scan window so that the vitreous can be images as well
OCT
Scanning Tips Communicate with the doctor regarding the size and loca5on 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 pa5ent 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 pa5ent ver5cally. The outer canthus should be even with the line
Scanning Tips Use the two bugons near the joys5ck for freezing and saving scans. This saves you from having to juggle the joys5ck and the mouse Minimize pa5ent fa5gue by keeping scan 5me to a minimum Never scan an eye for more than 10 minutes Keep the cornea lubricated. Use ar5ficial tears and have the pa5ent blink when you are not saving a scan pass Move the instrument on the x and y axis (using the joys5ck) to work around opaci5es
Scanning Tips Alignment and focus are used to maximize the quality of the scan Alignment begins with centering and zooming in on the "football" shaped reflex in the video image The ini5al lens- to- subject distance is achieved when the re5nal image fills the video screen This is similar to the image you see when doing re5na photography. At this point, your agen5on should shi_ to the scan window