**10.2 Quantitative assessment using AS-OCT**

An in-built software in most of the AS-OCT helps in quantitative measurement of the anterior chamber angle. Several parameters designated for the quantitative analysis has shown good reproducibility [48–50]. Difficulty in visualizing the scleral spur and the wide natural variation in angle anatomy within the same eye as well as between eyes are limiting factors in the routine use of quantitative measurement for angle assessment.

The various quantitative parameters reported are as follows (**Figure 12a–c**):

#### **Figure 12.**

*Quantitative measurement of (a) angle opening distance using RTVue anterior segment OCT, (b) angle recess area using RTVue anterior segment OCT, and (c) trabeculo-iris space area using RTVue anterior segment OCT.*

**135**

*Role of Optical Coherence Tomography in the Evaluation and Management of Glaucoma*

a.Angle opening distance (AOD in mm): it is the perpendicular distance between a point 500 μm (AOD 500) or 750 μm (AOD750) anterior to the scleral spur

bounded by the AOD 500 or 750, the anterior iris surface, and the inner

bounded by the AOD 500 or 750, the anterior iris surface, the inner corneo-scleral wall, and the perpendicular distance between the scleral spur and the opposing iris.

In clinical glaucoma practice, AS-OCT is used as an adjunct to gonioscopy. It can act as a substitute when gonioscopy is not feasible due to corneal pathology or lack of patient co-operation. Furthermore, it is extremely useful as a patient education tool, to explain the pathophysiology of angle closure to patients before any laser procedures like peripheral iridotomy. Its advantages over gonioscopy lie in the fact that it is a non-contact procedure and can be performed under dark conditions allowing angle assessment during physiological mydriasis. A major limitation however is its inability to visualize the structures behind the iris. This limits its ability in diagnosing the posterior mechanisms of angle closure such as iridociliary lesions and plateau iris. AS-OCT may also be used to visualize trabeculectomy blebs and anterior segment implants such as drainage devices and keratoprosthesis—however,

Advances in OCT technology have made it possible to apply OCT in a wide variety of applications. The high depth and transversal resolution in OCT and the ability to decouple depth resolution from transverse resolution make it an important tool in ophthalmic imaging. Few other advantages are high probing depth in scattering media, contact free, and non-invasive operation, and the possibility to create

1.Because OCT utilizes light waves (unlike ultrasound which uses sound waves), media opacities such as vitreous hemorrhage, dense cataract, or corneal opaci-

2.Motion artifacts: eye movements can sometimes diminish the quality of the image. However with the spectral domain shortened acquisition, time often

3.Learning curve: acquiring good quality images are an art and has a learning curve. Although with the advent of newer technologies, such as spectral domain acquisition or the use of eye tracking equipment, the likelihood of

): it is a triangular area (ARA 500 or 750)

): it is the trapezoidal area (TISA 500 or 750)

*DOI: http://dx.doi.org/10.5772/intechopen.84202*

b.Angle recess area (ARA in mm<sup>2</sup>

Trabecular space area (TISA in mm<sup>2</sup>

the clinical value in these situations appears to be limited.

various function-dependent image contrasting methods.

ties can interfere with optimal imaging.

results in fewer motion related artifacts.

such acquisition error has been reduced dramatically.

and the opposing iris.

corneo-scleral wall.

**10.3 Clinical applications**

**11. Conclusion**

**11.1 Limitations**

*Role of Optical Coherence Tomography in the Evaluation and Management of Glaucoma DOI: http://dx.doi.org/10.5772/intechopen.84202*


Trabecular space area (TISA in mm<sup>2</sup> ): it is the trapezoidal area (TISA 500 or 750) bounded by the AOD 500 or 750, the anterior iris surface, the inner corneo-scleral wall, and the perpendicular distance between the scleral spur and the opposing iris.

### **10.3 Clinical applications**

*A Practical Guide to Clinical Application of OCT in Ophthalmology*

**10.2 Quantitative assessment using AS-OCT**

gonioscopy.

ment for angle assessment.

of detecting closure of the anterior chamber angle [46, 47]. The degree of apposition however may not correlate exactly with appositional closure as defined by

An in-built software in most of the AS-OCT helps in quantitative measurement of the anterior chamber angle. Several parameters designated for the quantitative analysis has shown good reproducibility [48–50]. Difficulty in visualizing the scleral spur and the wide natural variation in angle anatomy within the same eye as well as between eyes are limiting factors in the routine use of quantitative measure-

The various quantitative parameters reported are as follows (**Figure 12a–c**):

**134**

**Figure 12.**

*Quantitative measurement of (a) angle opening distance using RTVue anterior segment OCT, (b) angle recess area using RTVue anterior segment OCT, and (c) trabeculo-iris space area using RTVue anterior segment OCT.*

In clinical glaucoma practice, AS-OCT is used as an adjunct to gonioscopy. It can act as a substitute when gonioscopy is not feasible due to corneal pathology or lack of patient co-operation. Furthermore, it is extremely useful as a patient education tool, to explain the pathophysiology of angle closure to patients before any laser procedures like peripheral iridotomy. Its advantages over gonioscopy lie in the fact that it is a non-contact procedure and can be performed under dark conditions allowing angle assessment during physiological mydriasis. A major limitation however is its inability to visualize the structures behind the iris. This limits its ability in diagnosing the posterior mechanisms of angle closure such as iridociliary lesions and plateau iris. AS-OCT may also be used to visualize trabeculectomy blebs and anterior segment implants such as drainage devices and keratoprosthesis—however, the clinical value in these situations appears to be limited.

## **11. Conclusion**

Advances in OCT technology have made it possible to apply OCT in a wide variety of applications. The high depth and transversal resolution in OCT and the ability to decouple depth resolution from transverse resolution make it an important tool in ophthalmic imaging. Few other advantages are high probing depth in scattering media, contact free, and non-invasive operation, and the possibility to create various function-dependent image contrasting methods.

#### **11.1 Limitations**


*A Practical Guide to Clinical Application of OCT in Ophthalmology*
