to perform the epithelial separation. Comparison of the effect of mechanical (Epi-LASIK) and alcohol-assisted excision (LASEK) on the histological ultrastructure of epithelial disks from human corneas showed that EpiLASIK technique is less invasive to epithelial integrity than LASEK [51].

Comparison of PRK, LASEK and epi-LASIK patients showed that epi-LASIK patients had the best day 1 visual acuity and had comparable visual and refractive results to other surface ablation techniques with lower levels of post-operative pain for the first 2 h. However, there was a high rate of flap failure and conversion to PRK [50]. One year results of 234 eyes of 138 patients underwent epi-LASIK for the correction of low to moderate myopia showed good refractive outcomes with only 14% of eyes have clinically insignificant (trace) haze [30]. Further long-term studies will be necessary to compare the effectiveness of EpiLASIK compared to other excimer laser refractive surgery techniques.

5.3.3 Summary

We can see that currently the technology is available for refractive surgeons to achieve the aims of minimal invasive surgery in LASIK, that is, to perform accurate and predictable LASIK while at the same time minimise tissue damage and time required. In our centre, we use the Intralase® FS laser to create the cornea flaps for most of our LASIK patients and we use the Schwind Amaris excimer laser system in order to achieve our goals of minimal invasive surgery in LASIK.

5.4 Intraocular Refractive Surgery

5.4.1 Phakic Intraocular Lens Surgery

Trends in Phakic Intraocular Lens Surgery

1.Minimising incision size

(a)With newer lens design

(b)With newer materials

2.Advances in diagnostic anatomy and PIOL sizing technology

3.Decrease in complication rates

4.Improving outcomes of phakic intraocular lens surgery

5.Ability to treat all types of refractive errors

Phakic intraocular lenses (PIOLs) are an important part of a refractive surgeon’s armamentarium. PIOLs are used in the correction of eyes with high refractive errors, especially if the cornea is thin. PIOLs are also used in cases where the corneal topography is abnormal or suspicious. As in the case of LASIK, refractive surgeons are continuously searching for new methods and technology to perform minimal invasive surgery for PIOL implantation. As implantation of PIOL requires incisions in the eye, the advantages of minimal invasive surgery are clear. A smaller incision will enable a more rapid patient rehabilitation, induce much less astigmatism, especially if no sutures are required, and cause less patient discomfort. In addition, advances in lens designs and diagnostic equipment have led to a reduction in the risk of complications related to PIOLs.

Development of PIOL began in the 1950s. But early lens models were plagued with poor outcomes and complications associated with poor quality lenses and surgical techniques. Jan Worst introduced an innovative lens design whereby the lens is attached to the mid-peripheral iris in 1978. The Baikoff ZB (Domilens, Lyon, France) angle-supported intraocular lens was introduced in 1986. Since then, phakic intraocular lens technology has advanced greatly.

The Baikoff ZB PIOL was made of polymethylmethacrylate with a Z-flex design and an optic diameter of 4.5 mm. This rigid PIOL required a limbal incision of at least 6 mm and the patient required regional anaesthesia for the surgery. With such a large incision, surgically induced astigmatism is unavoidable in many cases. Hence, it may be difficult to predict the final refractive outcome. This is ironic, considering that this is a refractive procedure. Such a large incision is also associated with a higher incidence of pupil ovalisation. Thus, a PIOL which can be implanted with a sutureless incision of 3 mm or less is one of the most important considerations in minimal invasive surgery for PIOLs.

The Baikoff ZB angle-supported intraocular lens has a 25° anterior haptic angle. Vaulting of PIOLs, especially angle-supported PIOLs, has been postulated to be a major cause of endothelial cell loss, a common problem associated with PIOLs. Newer designs of

angle-supported PIOLs, for example the ZB5M (Domilens), have incorporated design changes such as a smaller vaulting angle and thinner optics to reduce the risk of long-term endothelial cell loss. However, longterm endothelial cell loss in eyes with angle-supported PIOLs is observed in some studies.

Newer PIOL designs include different methods of securing the PIOLs in the anterior chamber. Irissupported models include the iris-fixated Artisan PIOL (Ophtec BV, Groningen, The Netherlands; marketed in the USA as Verisyse, Advanced Medical Optics, Santa Ana, CA) and the posterior chamber lens-supported PIOL include the Visian Implantable Collamer Lenses (ICL; Staar Surgical Company, Monrovia, CA). Chief consideration in the design of the iris-supported and posterior-chamber-supported models was to increase the distance between the PIOL and the endothelium, thereby reducing the risk of long-term endothelial cell loss.

The Verisyse/Artisan PIOL incorporates specially designed iris claws in its haptics to secure the PIOL to the iris. With this iris claw, this PIOL should not cause problems like anterior vaulting or instability in the anterior chamber [9]. However, implantation of the Verisyse/Artisan PIOL requires at least a 5.5-mm limbal incision which must be closed by sutures. Studies on a foldable version of the Verisyse/Artisan PIOL, the Artiflex PIOL, are still underway in Europe [14]. This foldable version will require a smaller incision and hopefully, achieve the aims of minimal incision surgery for PIOLs.

The posterior-chamber-supported PIOLs are implanted in the sulcus, between the natural crystalline lens and the iris. Long-term endothelial cell loss is less of a problem in such lenses. However, the close proximity of these lenses to the natural lens increases the risk of cataract formation. One of the more commonly used posterior-chamber-supported PIOLs today is the Visian ICL. The older version of the Visian ICL, the V3 ICLs, which has been discontinued, was associated with a higher incidence of anterior subcapsular cataract formation compared to the newer V4 ICLs [54].

Conventional PIOLs also do not correct astigmatism. However, recently, newer PIOLs with toric designs have been introduced to correct astigmatism at the same time. Hence, more invasive procedures like limbal relaxing incisions or combining PIOL implantation with excimer laser treatment to correct astigmatism are no longer necessary with these new toric PIOLs. Currently, toric models of the Artisan

[21] and Visian ICL are available. However, as discussed above, the Artisan PIOL requires a larger incision which may result in a surgically induced astigmatism.

5.4.1.1 Advances in Diagnostic Equipment

Choosing the appropriate model and size of PIOLs is essential to avoid potential complications. Inserting an oversized angle-supported PIOL in an eye with an anterior chamber depth of less than 3 mm will result in a high risk of long-term endothelial cell loss. Traditionally, the sizing of PIOLs was based on measurements of the white-to-white distance of the cornea. However, it is well known that the white-to-white distance is a poor indicator of the internal dimensions of the anterior or posterior chamber and does not accurately measure the distance between the irido-corneal angles [28]. Anterior segment anatomy also differs significantly from myopes to hyperopes and this will affect the choice of PIOL. Specialised surgical devices such as intraocular calipers are still inaccurate and have not been able to solve the problem of precise PIOL sizing. The advent of the Visante anterior segment optical coherence tomography (AS-OCT; Carl Zeiss Meditec Inc, Dublin, CA) has revolutionised the way refractive surgeons evaluate the anterior segment and perform PIOL sizing. The Visante AS-OCT uses a 1,320 nm wavelength to obtain images of the anterior chamber similar to A and B scanning (Fig. 5.11). Of importance to the refractive surgeon are the measurements for anterior chamber depth, angle-to-angle measurements and calculations of the anterior chamber angle. These values will assist the refractive surgeon in deciding the choice of PIOL and to size the appropriate PIOL for the patient.

Fig. 5.11 OCT image of a phakic intraocular lens in the eye