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**Chapter 10**

**Provisional chapter**

**OCT in Glaucoma Diagnosis, Detection and Screening**

Glaucoma is a chronic and progressive optic neuropathy in which increased intraocular pressure is the most important risk factor in the etiopathogenesis. The basic pathology is the progressive loss of retinal ganglion cells (RGCs) especially the death of the axons of ganglion cells initially (apoptosis), followed by peripapillary retinal nerve fiber layer (RNFL) defects. Since optical coherence tomography (OCT)'s first demonstration in 1991 by Huang et al. and introduction commercially in 1996, it began gaining popularity in 2000s for retinal evaluation and the detection, diagnosis, and follow-up of glaucoma. Previously available OCT instruments used a technique referred to as time-domain (TD-) OCT, followed by spectral-domain (SD-) OCT, which has an increased scan acquisition rate, allowing for a more detailed sampling of the area of interest. Recently, swept-source OCT (SS-OCT), a newer generation of OCT, has been introduced. Clinical assessment using multiple parameters, including peripapillary RNFL, ganglion cells, optic nerve head, and macular parameters, has proven useful for managing and diagnosing glaucoma as well as for evaluating risk in glaucoma suspects. In this chapter, we aim to evaluate the use of OCT and its modalities in diagnosis, screening, and progression of

**Keywords:** OCT, glaucoma, retinal nerve fiber layer, ganglion cell, optic nerve

Glaucoma is a progressive optic neuropathy where intraocular pressure is considered to be the most significant risk factor in its etiopathogenesis. The fundamental pathology of the disease is the progressive loss of the ganglion cells. Glaucoma predominantly affects the inner macular retinal layers: the macular RNFL (mRNFL), ganglion cell layer (GCL) and

**OCT in Glaucoma Diagnosis, Detection and Screening**

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.78683

Aydin Yildiz

Aydin Yildiz

**Abstract**

glaucoma.

**1. Introduction**

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.78683

#### **OCT in Glaucoma Diagnosis, Detection and Screening OCT in Glaucoma Diagnosis, Detection and Screening**

DOI: 10.5772/intechopen.78683

#### Aydin Yildiz Aydin Yildiz

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.78683

#### **Abstract**

Glaucoma is a chronic and progressive optic neuropathy in which increased intraocular pressure is the most important risk factor in the etiopathogenesis. The basic pathology is the progressive loss of retinal ganglion cells (RGCs) especially the death of the axons of ganglion cells initially (apoptosis), followed by peripapillary retinal nerve fiber layer (RNFL) defects. Since optical coherence tomography (OCT)'s first demonstration in 1991 by Huang et al. and introduction commercially in 1996, it began gaining popularity in 2000s for retinal evaluation and the detection, diagnosis, and follow-up of glaucoma. Previously available OCT instruments used a technique referred to as time-domain (TD-) OCT, followed by spectral-domain (SD-) OCT, which has an increased scan acquisition rate, allowing for a more detailed sampling of the area of interest. Recently, swept-source OCT (SS-OCT), a newer generation of OCT, has been introduced. Clinical assessment using multiple parameters, including peripapillary RNFL, ganglion cells, optic nerve head, and macular parameters, has proven useful for managing and diagnosing glaucoma as well as for evaluating risk in glaucoma suspects. In this chapter, we aim to evaluate the use of OCT and its modalities in diagnosis, screening, and progression of glaucoma.

**Keywords:** OCT, glaucoma, retinal nerve fiber layer, ganglion cell, optic nerve

#### **1. Introduction**

Glaucoma is a progressive optic neuropathy where intraocular pressure is considered to be the most significant risk factor in its etiopathogenesis. The fundamental pathology of the disease is the progressive loss of the ganglion cells. Glaucoma predominantly affects the inner macular retinal layers: the macular RNFL (mRNFL), ganglion cell layer (GCL) and

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

inner plexiform layer (IPL) where ganglion cell complex (GCC) consists of RNFL, GCL and IPL thickness [1]. The ganglion cell damage occurs at the lamina cribrosa level in the optic disc; first, the axons get damaged, then the ganglion cells which these axons are connected to disappear through a programmed cell death called apoptosis. This loss of axons and ganglion cells cannot be identified with any clinical diagnosis methods before it exceeds a certain critical threshold [2–5]. Research in this area shows that the earliest symptom that can be detected clinically in glaucoma is the loss or thinning of the retinal nerve fiber layer (RNFL). The loss or thinning of the neuroretinal tissue is usually detected later on [6–8].

As also mentioned earlier, the OCT calculates the delay in the reflection of light from different layers of the tissue. Light reflected from the deep layers of the tissue would exhibit a longer period of delay, compared to that of the light reflected from the surface. The distribution of the intensity of the reflected light according to this period of delay is demonstrated as the axial A-mode scan. Many A-mode scans are obtained through scans across the sample, and

OCT in Glaucoma Diagnosis, Detection and Screening http://dx.doi.org/10.5772/intechopen.78683 157

The most critical issue for the formation of the image in OCT systems is the measurement of the time difference of the lights reflecting from different tissues, that is, the reflection delay. A reference mirror which provides the time difference is available in time domain OCTs. This mobile mirror system is a factor that limits the speed of obtaining an image in OCT. In the spectral domain OCT system on the other hand, the mirror is fixed. Thanks to this feature, the

In all OCT systems manufactured since the clinical use of the OCT technology, super luminescent diodes (SLDs) have been used as sources of light. In time domain OCT-3 whose axial resolution in the tissue is the highest, the resolution value is approximately 8–10 microns. Super luminescent diode lasers that could be different from each other but similar to each other in terms of the range of wave light emissions are also used in spectral domain OCT

Thanks to the development of the spectral domain OCT technology, the speed for obtaining images has also increased and risen up to 70,000 A-mode scans per second from 400 A-mode scans (OCT-3) per second. The increase in the scan speed has lowered the amount of the

There are several OCT devices working with similar principles but vary in diagnostic ability, acquisition speed and resolution. In this section, three commonly used SD-OCTs that are the Spectralis (Heidelberg Engineering, Dossenheim, Germany), the Cirrus (Carl Zeiss Meditec, Dublin, CA) and the RTVue (Optovue Inc., Fremont, CA) and their features are discussed. Several studies have addressed the diagnostic accuracy of the SD-OCTs one by one or com-

Since RNFL is, without a doubt one of the most important factors which is also discussed extensively in the literature, a comparison between the protocols through this value will be

However, in recent studies comparing protocols on the capability of OCT in the diagnosis of

Cirrus TM High Definition (HD)-OCT Spectral Domain (Carl Zeiss Meditec, Dublin; CA) used

glaucoma, no significant differences were observed between the protocols [14, 31, 32].

devices. Axial resolution in these devices has been lowered up to 3 microns [14].

these are converted into gray or colored scales indicating the signal intensity [29, 30].

mirror movement which limits the speed is avoided [31].

**3. OCT use in glaucoma and some basic protocols**

pared them to time-domain technology [1, 14, 32–42].

**4. A-Cirrus Zeiss glaucoma scanning protocol**

for the analysis of glaucoma.

made and the diagnostic accuracy of this value will be examined [27].

artifact in the image even further [32].

Circumpapillary RNFL (cpRNFL) and GCC thickness measurements are the parameters that have high performance in detecting glaucoma-detecting ability and are comparable to cpRNFL thickness [9–11].

OCT is an imaging method that obtains high-resolution sections of biological tissues, and it is possible to simply define this mechanism as the conversion of the light that is reflected from the tissue to an image [12–14].

Commonly used in the area of ophthalmology especially in the past 20 years, the optical coherence tomography (OCT) has provided significant contributions for the early diagnosis of the glaucoma disease and monitoring and analysis of the glaucoma patients [14–18].
