Clear Corneal Incisions (CCIs) and innovative blade design in C-MICS

Dan Calladine - No financial interestsRichard Packard – Consultant for Core Surgical

Poorly constructed clear corneal incisions in cataract surgery can result in gaping and loss of coaptation which may be risk factors for leaking and endophthalmitis. These two examples show wounds that have been created too short and combined with hypotony in the immediate post operative period show

significant gaping and loss of coaptation.

• Ideal wound architecture…– Not too long– Not too short– ‘Square’ 1 or ‘Nearly Square’ 2

configuration– ‘Curvilinear’ profile 3

1. Ernest PH, et al. J Cataract Refract Surg 1994;20:626-9.

2. Masket S, et al. J Cataract Refract Surg 2007;33(3):383-6

3. Fine IH, et al. J Cataract Refract Surg 2007;33(1):94-7.

– A tapered single-bevel cutting edge to provide a flat base to construct a multi plane wound and direct the blade easily;

– Blade support technology to prevent flexing of the next of the blade;

– An incision length measuring mark which is the base of the surface facet to create consistent a length CCI

A blade to help achieve a consistent and reliable wound architecture was

sought…

The Windsor Knife (Core Surgical, UK) has been specifically designed to designed to create a 3-plane CCI profile (see figure on left). In particular it has:

We believe the correct wound architecture is a 3-plane profile with a nearly square shape, i.e. 2.2 x 1.8 mm (see figure below)

The Windsor Knife is designed to be used with a a 3-Plane incision construction:STEP 1 – The tip of the blade is directed steeply in to the cornea just inside the limbus and burried no more that 1/3 of the corneal thickness;STEP 2 – the blade is then flattened on to the globe and advanced forward almost parallel to the corneal surface curvature until the incision length measuring mark is reached to create a stromal tunnel;STEP 3 – The handle is lifted and the tip is directed towards the centre of the pupil and advanced in to the anterior chamber to complete the incision.

STEP 1

STEP 2 STEP 3

The RASTER (grid) image capture programme was used. This allowed for a high level of

consistency because an incision at the midpoint of the wound could be easily

identified by counting in from one side and extracted for analysis of incision length.

All eyes examined by DC within 2 hours of surgery

using Fourier Domain Anterior Segment Optical Coherence Tomography imaging system (RTVue,

Optovue)

Methods- A consecutive series of 30 cases by the same surgeon (RP)- Coaxial-Micro Incision Cataract Surgery (C-MICS)- 2.2 mm wide Windsor Knife using 3-plane technique

Methods: OCT Raster grid image capture

programme

Results: 97% had 3-planes

Only 1 CCI in the study had a 2-plane profile. This was because the tip of the blade was not buried deep enough during STEP 1 of the construction technique.

The vast majority of the CCIs in the study (29/30) has a 3-plane profile.

Results • Incision length

– Mean = 1.75 ± 0.16 mm – Median = 1.74 mm– Range = 1.51 - 2.08 mm– Mode in the range 1.61 –

1.7 mm– Mean 1st plane = 0.25 mm,

2nd plane = 0.85 mm, 3rd plane = 0.65 mm

• Mean IOP in the immediate post operative period was 18 ± 3.7 mmHg (11 - 24 mm Hg). No cases of hypotony.

• OCT architectural features were similar to previous studies, slightly higher due to better resolution and grid image capture programme

The distribution was skewed to the left

Conclusions• CCI lengths were highly consistent

– This was attributed to the Incision length measuring mark

• The majority of incisions had a 3-plane architectural profile – This was attributed to the good surgical control provided by the

Windsor Knife, which is the result of:– The tapered single-bevel cutting edge

» provides consistent cutting resistance

– Novel blade support technology» Prevents flexing of the neck of the blade which avoids any sudden and uncontrolled

release of stored (flexed) potential energy as the blade enters and passes through the corneaThe FDAS-OCT imaging system we used (RTVue, Optovue) proved

particularly well suited to scanning CCIs because of its: - Rapid scan speed - High resolution - Grid image capture program, which allowed different architectural features to be indentified in different cross sections of the wound. An example is shown in the figure on the right. The top image is from the edge of the wound and the bottom from the midpoint of the same wound showing markedly different amounts of endothelial gaping and loss of coaptation