Advances in OCT Murray Fingeret, OD

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1 Disclosures Advances in OCT Murray Fingeret, OD Consultant Alcon, Allergan, Bausch & Lomb, Carl Zeiss Meditec, Diopsys, Heidelberg Engineering, Reichert, Topcon Currently Approved OCT Devices OCT Devices FDA Approved in US Full approval including NDB Optovue RTVue, Avanti and ivue Carl Zeiss Meditec Cirrus and Cirrus Photo Heidelberg Spectralis RNFL only Only instrument, No Normative Database Topcon 3D-2000 Nidek RS-3000 Advance Optos OCT SLO Bioptigen OCT Imaging Fovea To Disc Angle (FOD) Fovea to Disc angle measurement varies among healthy individuals and the foveal position in relation to the optic nerve head might cause asymmetry in the distribution of the RNFL On average in healthy individuals, the fovea is located 6.3 ±3.0 vertically below the optic disc disc Heidelberg is the only company that currently compensates for this Other companies did not find it a factor No evidence that compensating for the foveal position relative to the OD will improve variability or ability to detect glaucoma Improves variability in one sector but makes it worse in another Position of Retinal Blood Vessels - evaluate 1

2 OCT Imaging OCT Imaging The circumpapillary retinal nerve fiber layer (RNFL) thickness profile shows a double hump pattern, with its peak in the superior and inferior quadrants Glaucoma is characterized by a loss of retinal ganglion cells and their axons and consequently by a reduction of circumpapillary RNFL thickness RNFL thickness measurements support the diagnosis of glaucoma by comparing the resulting RNFL thickness profiles with normative values derived from a healthy population However, considerable variation in RNFL thickness profiles exists in the normal population Known factors determining RNFL distribution are retinal blood vessel position, age, ethnicity, sex, axial length, optic disc (OD) area and refractive error Retinal blood vessel distribution (RVD) may also influence on the RNFL thickness profile and responsible for inter-subject variability Currently OCT s are not able to take into account blood vessels in the RNFL measurements Blood vessels are included in RNFL measurement no matter where they are located In future, it is important to assess RVD as an important anatomical factor responsible for inter-subject variability in circumpapillary RNFL measurements One possibility is to remove BV from RNFL before measurement is taken Advantages of Flipping the RNFL Use All the Parts of the Printout to Evaluate the RNFL RNFL Analysis is the Most Important Part of the OCT Printout TSNIT was an arbitrary designation 25 years ago Temporal region is most important part of curve and with NITSN, region is not broken up and loss more obvious Easier to recognize structure-function correlation RNFL loss correlates easily with field loss Easier to understand if macula area may be involved and central field loss present Is there a reduction in RNFL within the central 8 0 RNFL - Two Methods for Display 2

3 There is a Benefit to See Where the Measurement Falls with the Normative Range Optic Disc Analysis How is the rim tissue identified? What is the disc margin? Optic Disc Analysis How Does An Instrument Decide on Optic Disc Size? Use Bruch s Membrane Opening (BMO) Use BMO with New parameter- Minimal Rim Width (MRW) Both Cirrus and Spectralis use this metric Line drawn perpendicular from BMO to Rim 3

4 A new method for documentation of optic nerve & peripapillary anatomical structure Burgoyne, Chauhan, & colleagues reminded us all that 3-D is better than 2-D The clinically perceived disc margin is most likely not the innermost edge of Bruch s membrane detected by SD-OCT. (Ophthalmology APR2012) Minimal Rim Width New Metric to Assess Optic Disc BMO-MRW (minimum rim width based upon BM opening) quantifies the neuroretinal rim from a true anatomical outer border... (IOVS APR2012) Macula Testing in Glaucoma Imaging to detect glaucoma damage has concentrated around RNFL and optic nerve evaluation Complicating the assessment of the optic nerve when evaluating for glaucoma damage is: High variability of the ONH size and shape Even among healthy individuals Wide range of optic cup shapes and sizes Variable size and configuration of blood vessels Variable angle of penetration into the eyeball of the optic nerve (tilted disc) Parapapillary changes such as atrophy These are the reasons why it is difficult to detect early glaucomatous damage Macula Testing in Glaucoma Imaging allows measurement of features that are not possible otherwise Imaging can detect changes in the macular region The eye has about 1 million retinal ganglion cells, and their numbers are densest in the macula about six cells deep About 50% of ganglion cells are in the central 4.5 mm of the retina an area that represents only 7% of the total retinal area This area is not well covered in most visual field testing Measuring the ganglion cell complex directly (ILM IPL) Inner retinal layers and provides complete Ganglion cell assessment: Nerve fiber layer (g-cell axons) Ganglion cell layer (g-cell body) Inner plexiform layer (g-cell dendrites) What is EDI? Enhanced Depth Imaging For spectral domain, sensitivity is highest at top of window (vitreous) and declines with depth With EDI, sensitivity in window is flipped and now sensitivity is higher on bottom (lamina or choroid) Loss of sensitivity at top (vitreous) Advantage of swept source is less drop off in sensitivity with depth of imaging Valuable to examine lamina cribosa visibility All OCTs have ability to shift sensitivity with depth Images courtesy of Dr. Ou Tan, USC 4

5 Blood Flow Measurements using Spectral Domain OCT OCT Angiography Measuring Blood Flow Ocular blood flow and optic nerve injury have been linked The question still not answered is which comes first Can a device be developed that provides reproducible, quantitative, objective assessment of retinal and optic nerve blood flow Both global and local Does not require expert operator Measurement should correlate with structure and function Measuring Blood Flow There have been numerous devices to measure blood flow over the years Varying degrees of invasiveness, accuracy and precision From injectable dyes to ultrasonography to laser Poorly reproducible or variations in acquisition of data Optical Coherence Tomography Angiography Used to map retinal and superficial optic nerve vasculature and blood flow Not clear if there is a floor effect Is technique useful from early to advanced disease? SDOCT measurements are highly reproducible. 2-4 Steps in Range We can measure multiple steps of statistically significant change while a glaucoma suspect still is in the green normal range. Normal significance Limits for Average RNFLT 95th percentile = 107 microns 50th percentile = 89 microns 5 th percentile = 75 microns 1 st percentile = 67 microns Leung et al. Ophthalmology 2009;116:1257 Roh et al. Ophthalmology 2013;120:969 Wong et al. Optom Vis Sci 2014;92 Matlatch et al, IOVS Sep Risk of Disability <50 microns Values shown are for a 69 year old normal. 5

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