9.4 Incision Quality in MICS

9.4 Incision Quality in MICS

Bassam El Kady and Jorge L. Alió

Core Messages

ßMinimization of the incision is a consequence of a natural evolution of the cataract surgery

technique.

ßGood-quality incision is the cornerstone for the success of any type of cataract surgery.

ßMicroincision cataract surgery (BMICS) provides not only a small incision size of 1.5 mm,

but also an incision of good quality with minimal tissue damage.

ßExcellent incision quality in BMICS provides immediate, postoperative, unaided visual reha-

bilitation and early patient satisfaction.

ßOne of the major advantages of BMICS is the reduction of surgical trauma resulting in a reduc-

tion of surgically induced astigmatism (SIA) and corneal high-order aberrations.

ßBy using the optical coherence tomography (OCT), Visante Anterior Segment OCT we are

able to develop a standardized model and protocol to objectively evaluate incision quality in BMICS.

ßThis high-quality incision opened the door for BMICS to be the surgery of choice for refractive

lens exchange.

9.4.1Introduction: History of Incision Size Reduction

Being a cornerstone and one of the major limbs for the success of any type of cataract surgery, the incision performed has been subjected to revolutionary transformations over many years aiming towards its reduction in size.

Consequently, the incision size has been subjected to many waves of development. The history started years ago with a 10 mm, or even larger, incision size for intracapsular and then extracapsular cataract extraction techniques through a corneoscleral incision. The operating incision was approximately 180° around the limbus and this caused considerable damage to the outside layers of the eye with subsequent large numbers of intraoperative and postoperative complications. Owing to surgical advances, the incision size further reduced down to 7–8 mm for the extracapsular era [1].

Then, the method of lens phacoemulsification with the help of ultrasound discovered by Charles Kelman in the late 1960s was a turning point [2] that allowed further reduction of incision size from 3.4 to 2.8 mm, which was the minimum incision performed before the recent era of microincision cataract surgery (BMICS) [1, 3]. Nowadays, BMICS can provide an incision of 1.5 mm or smaller [3–5].

9.4.2The Trends Towards Microincision Cataract Surgery (BMICS)

With the advantages and benefits of innovative technologies, BMICS has become an increasingly utilized phaco technique, and this modality has been investigated by many authors such as Shock and Girard in the 1970s [6–7], Shearing in 1985 [8], Hara in 1989 [9], as well as Amar Agarwal in 1998 [10], and more recently by Jorge Alió in 2001 [1]. The goal is to achieve smaller incisions with excellent quality, less invasive surgical techniques, and more rapid visual rehabilitation [3].

These trends towards minimizing the incision size had driven us to the biaxiality technique, which requires separation of function for irrigation and aspiration using a bare phacoemulsification tip [3]. Two separate microincisions provide minimal operative stress to the cornea, better incision stability, less astigmatism, and corneal aberrations [11–16].

9.4.3Advantages of Minimizing the Incision Size

such a type of incision, being of a tiny size, allows minimal tissue manipulation and functional disturbances, and hence is considered anatomically capable of providing many other advantages. The decrease in incision size has proved to be associated with a significant decrease in postoperative intraocular inflammation and endophthalmitis [17, 18], less incision-related complications, less surgical time, and shorter postoperative rehabilitation [1, 3], in addition to lower incidents of vitreous loss, iris extrusion, better management of intraoperative floppy iris syndrome (IFIS) [19, 20], and less CME [1, 4, 11, 13].

9.4.4Model for the Analysis of Corneal Incision Quality [21]

BMICS, in conjunction with microincision IOLs, new phaco technology and fluidic technology, and microinstruments, represents a major breakthrough in cataract surgery. Using the Visante Anterior Segment OCT, we are able to analyze incision quality [21].

The optical coherence tomography system, the Visante OCT, uses infrared light of a 1,310-nm wavelength [22]. The system is connected to a computer with a software that provides different options for image

capture and measurement. We developed the following model for analysis.

The patient is well positioned and the related data is introduced in the software. After this, the option “High Res Corneal” is chosen in order to obtain accurate scans of the corneal structure. The patient is asked to fixate on an object located on the opposite direction of the corneal incision in order to obtain a complete crosssectional scan. A linear scan is used with the same orientation of the incision. This linear scan is rotated 10° in a clockwise direction and 10° in a counterclockwise direction in order to find the image with the best resolution. After this, the scanning is performed and an image is acquired. All scans have a characteristic appearance with arcuate configuration (Fig. 9.4.26).

After obtaining the image, it is analyzed. The following characteristics are determined:

•Angle of the incision: continuously variable, angle formed between the line joining the epithelial and endothelial edges and the tangent line to the epithelial edge of the incision (Fig. 9.4.27). The distances are measured and the angle is calculated by trigonometry.

•Sealing of the epithelial edge: sealed or not sealed (Fig. 9.4.28).

•Sealing of the endothelial edge: sealed or not sealed (Fig. 9.4.29).

•Thickness of the cornea in the area of the incision and at 1mm at each side of the incision (Fig. 9.4.30).

•Central corneal thickness and mean thickness in an area of 2–5 and 5–7 mm of the cornea (pachymetric map) (Fig. 9.4.31).

•Percentage of the incision length without coaptation (Fig. 9.4.32).

•Detachment of Descemet’s membrane (Fig. 9.4.33).

•Endothelial bulge or bullae (Fig. 9.4.34).

9.4.5Our Protocol for Evaluation of Incision Quality in BMICS [21]

Based on our experience with BMICS [1, 3, 4], and our published data that documents the ability of BMICS incision to neutralize the corneal optics and to reduce aberrations and astigmatism [11], we created our protocol for adequate objective evaluation of BMICS incisions in both short and long-term outcomes, and subsequently its impact on visual outcomes and optical behavior. Our protocol is as follows:

Patients are scheduled for the postoperative followup visits with the clinical examinations and specific measurements are performed at each visit according to the following protocol:

Thirty minutes after surgery: clinical slit-lamp examination with localization of the incision.

One day postoperative: visual acuity, IOP, slit-lamp examination, Seidel’s test to check for incision leakage and analysis of the corneal incision using OCT.

One week postoperative: visual acuity, refraction, IOP, slit-lamp examination and analysis of the corneal incision using OCT.

One month postoperative: visual acuity, refraction, IOP, slit-lamp examination, analysis of the corneal incision using OCT, corneal topography, corneal aberrometry and ocular aberrometry.

The stability of corneal incision is analyzed 30 min after surgery with the slit lamp biomicroscopy and its localization is detected. The sealing of the corneal incision is analyzed using fluorescein Seidel’s test (Colircusi fluotest® 3 mL (2.5 mg fluorescein sodium + 4 mg Oxibuprocaine chloride) Alcon Cusi, BarcelonaSpain). Any epithelial or stromal alteration is recorded and analyzed. After slit lamp biomicroscopic evaluation, the analysis with the Visante OCT is performed.

We can observe that 1 month postoperatively, corneal topography, corneal and total ocular aberrometry are performed in order to evaluate the incision quality.

Twenty-five eyes of 16 patients with nuclear or corticonuclear cataracts underwent MICS surgery through 1.8 mm incision with IOL implantation. For adequate

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B. El Kady and J. L. Alió

Fig. 9.4.32 OCT images of MICS incisions showing an example of a gaped

incision (a) and a completely sealed incision (b)

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b