**2. Anterior lens capsule complex measurement using SD-OCT**

The lens, as a transparent structure, is a very important refractive element of the human eye. It consists of three major components: capsule, epithelium, and lens substance [2]. The lens epithelial cells and fibers keep the balance of molecules moving into and out of the lens. Previous histological studies have demonstrated that the lens capsule thickness varies by location and that the posterior capsule is the thinnest. The lens epithelium, a single layer of cuboidal cells beneath the anterior capsule, extends to the equatorial lens bow. The lens substance consists of densely packed cells with little extracellular space. With the development of time-domain

**Figure 1.** The entire anterior chamber and lens cross-sectional images using OSE-1200 time-domain anterior segment optical coherence tomography (software version 2013.1.1.90; Moptim, Inc., Shenzhen, Guangdong, China). Panel A shows the anterior segment structure: cornea, sclera spur, iris and lens; panel B shows the lens anterior capsule, lens posterior capsule, and lens substance.

OCT, it became possible to image the entire anterior chamber and lens in vivo (**Figure 1**) [3]. Due to the limited resolution (around 15-μm), it was not possible to measure the thickness of the lens capsule or the epithelium.

anterior segment time-domain and spectral-domain OCT applications before and after cata-

• Anterior lens capsule and lens epithelium evaluation in senile cataract and Fuchs' hetero-

• Investigation of clear corneal incision in manual phacoemulsification and femtosecond la-

• IOL power calculation (true net power measurement) in post-myopic excimer laser eyes

The lens, as a transparent structure, is a very important refractive element of the human eye. It consists of three major components: capsule, epithelium, and lens substance [2]. The lens epithelial cells and fibers keep the balance of molecules moving into and out of the lens. Previous histological studies have demonstrated that the lens capsule thickness varies by location and that the posterior capsule is the thinnest. The lens epithelium, a single layer of cuboidal cells beneath the anterior capsule, extends to the equatorial lens bow. The lens substance consists of densely packed cells with little extracellular space. With the development of time-domain

**Figure 1.** The entire anterior chamber and lens cross-sectional images using OSE-1200 time-domain anterior segment optical coherence tomography (software version 2013.1.1.90; Moptim, Inc., Shenzhen, Guangdong, China). Panel A shows the anterior segment structure: cornea, sclera spur, iris and lens; panel B shows the lens anterior capsule, lens

chromic cyclitis using spectral-domain anterior segment OCT (SD-OCT);

• Capsular block syndrome evaluation before and after treatment using SD-OCT;

**2. Anterior lens capsule complex measurement using SD-OCT**

ract surgery. Four aspects will be discussed in this chapter:

ser assisted cataract surgery using SD-OCT;

using SD-OCT.

176 OCT - Applications in Ophthalmology

posterior capsule, and lens substance.

A previous study manually measured and constructed an anterior lens capsule thickness map across the entire field of view using a femtosecond laser OCT system, which has a central wave length of 780 nm with an axial resolution of 2.3 μm [4]. In a study conducted by Szkulmowski et al., it was reported that the anterior lens capsule and epithelium could be clearly imaged using a SD-OCT system with a central wavelength of 820 nm and axial resolution of 4.2 μm with the help of the speckle contrast reduction technique [5]. The commercial Avanti RTVue XR spectral-domain OCT system provides a high-resolution anterior segment scanning protocol with a scan length of 8 mm and an axial resolution of 5 μm. It can show a substantially clearer delineation after the two highly reflective layers, the anterior lens capsule and the subcapsular epithelium, are combined (**Figure 2**).

We defined the combination of anterior lens capsule and the subcapsular epithelium as the anterior lens capsular complex (ALCC) in a previous study [6]. One hundred thirty-four normal eyes (age range: 5–86 years) were investigated using the Avanti RTVue XR OCT system. The results indicated that the manual measurement of ALCC was both reproducible and reliable. The mean thickness of the central ALCC was approximately 33 μm, which is approximately 15 μm thicker than the anterior lens capsule values calculated using time-domain OCT and other imaging modalities [4, 7]. Therefore, we hypothesized that the subcapsular epithelium was approximately 15 μm thick in vivo. Moreover, a positive correlation between age and ALCC was noted in our study. A 10-year increase in age resulted in a 0.74–1.4 μm increase in the ALCC thickness. From a certain point of view, these findings were consistent

**Figure 2.** A horizontal anterior segment scanning image of the central part of the lens and the dilated pupil margin in a 34-year-old female using the Avanti RTVue XR spectral-domain optical coherence tomograph (panel A). Panel B shows a magnification of the selected area in panel A (blue frame). Panel C demonstrates the schematic diagram of the anterior lens capsule (corresponding to the yellow reflective layer in panel B), the subcapsular epithelium (corresponding to the red reflective layer in panel B), and the lens fibers.

with previous findings regarding the positive correlation between age and lens capsule or total lens thickness [8, 9].

**3. Investigation of clear corneal incision using SD-OCT**

advantage of predictable configuration and dimensions.

in the femtosecond laser group.

In most industrialized countries, cataract surgery accounts for the largest proportion of surgical interventions in ophthalmology. The advent of minimal incision, phacoemulsification (introduced by Charles Kelman in the 1970s), and foldable intraocular lens, has made cataract surgery safer and more efficient [14]. Moreover, modern cataract surgery combined with new generation intraocular lens types, which can be designated refractive surgery, aims to provide optimal visual quality and render the visual function better [15]. As a significant part of the cataract surgery, the constructional architecture of proper clear corneal incisions (CCIs) is vital for a perfect outcome of phacoemulsification. Faulty CCI construction can lead to complications, such as wound leak, Descemet's membrane detachment, and excessive surgicallyinduced astigmatism, and is a situation every cataract surgeon attempts to avoid. However, it is not easy to predictably construct perfect manual single-plane, two-plane, or three-plane clear corneal tunnels using steel or diamond blades [16]. With the higher expectations of patients from modern cataract and refractive surgery and the advent of trifocal and accommodating IOLs, femtosecond laser was introduced into cataract surgery by Zoltan Nagy in 2009 [17]. Previous studies demonstrated that a femtosecond laser-assisted cataract surgery technique could provide repeatable, predictable clear corneal incisions, perfect capsulotomies, and safe nuclear fragmentation [18, 19]. Therefore, CCIs created using femtosecond laser have the

OCT Application Before and After Cataract Surgery http://dx.doi.org/10.5772/intechopen.77281 179

Clinical manual CCI parameters (incision location, angle of incision, incision length) and features (posterior wound gape, Descemet's membrane detachment, posterior wound retraction, loss of coaptation along the CCI tunnel) in the early postoperative period (up to 1 month) of standard cataract surgery have been reported [20–23]. Based on the above-mentioned studies, we evaluated the quantitative CCI parameters and features in subjects who underwent femtosecond laser-assisted cataract surgery [24]. Except for no sign of loss of coaptation along the CCI tunnel, all the other three CCI features were found in femtosecond laser CCI (**Figure 4**). As expected, the femtosecond laser lens fragmentation ensures that the phacoemulsification energy (Femto group: 16 ± 13%; manual group: 20 ± 5%) and effective phacoemulsification time (Femto group: 17 ± 9 s; manual group: 32 ± 13 s) were dramatically lower in the Femto group than in the conventional manual group. Moreover, the femtosecond laser group had a lower incidence of Descemet's membrane detachment and posterior wound gape at each follow-up time-point. However, a higher incidence of posterior wound retraction was found

Descemet's membrane detachment may potentially hinder the local endothelium pump mechanism and affect corneal wound healing. The routine procedure for CCI by femtosecond laser is from the anterior chamber (inner cornea) to the epithelium (outer cornea), which makes the Descemet's membrane detachment an unusual complication for this group. However, phacoemulsification probe manipulation through the CCI, the blunt dissection of the tunnel, and incision hydration probably contributed to the occurrence of Descemet's membrane detachment in the femtosecond group. For the difference in posterior wound gape incidence, we are inclined to implicate the difference in tunnel incision geometry between the

With the help of anterior segment SD-OCT, researchers also can obtain more detailed useful information regarding accommodation, presbyopia, Fuchs' heterochromic iridocyclitis (**Figure 3**), posterior capsule opacification, and pseudoexfoliation syndrome [10–13]. Moreover, with the OCT technology development, the respective measurement of anterior capsule, posterior capsule and epithelium layer thickness, even plotting corresponding topography in specific regions will be available in the future.

#### **2.1. Summary**

In summary, anterior segment SD-OCT can be used to visualize anterior and posterior lens capsule, lens epithelium, keratic precipitates, iris stroma atrophy. The use of anterior segment SD-OCT will enable us to better investigate changes in lens structure of patients with Fuchs' heterochromic iridocyclitis or other lens related conditions.

**Figure 3.** Color images and optical coherence tomography cross-sectional images of a 60-year-old female with Fuchs' heterochromic iridocyclitis. The anterior color slit-lamp photos and corresponding anterior segment OCT crosssectional images show atrophy of the iris stroma (panel A, A′), small keratic precipitates scattered over the entire corneal endothelium (panel B, B′), and plaque of posterior subcapsular opacity (panel C, C′).
