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Chapter 2: Overview and importance of refractive surgery techniques
Refractive surgery is a set of surgical techniques whose objective is to correct refractive errors of the eye such as near-sightedness (myopia), far-sightedness (hyperopia), astigmatism or presbyopia, in order to improve a patient’s vision.
The purpose of this chapter is to describe the key historic milestones in the development of this field of ophthalmology, to classify the different techniques and to address the socio-economic importance of laser-assisted techniques.
History and development of laser-assisted refractive surgery
History of refractive surgery
In 2001, about 30 km south of Cairo, archaeologists discovered the tomb of Skar, the chief physician of one of Egypt’s fifth dynasty of pharaohs. The tomb included on its walls drawings of ophthalmic surgery and about 30 bronze surgical tools. This tomb was dated bac c. 4,000 years which confirms the high surgical skill level achieved by old Egyptian which were performing the “couching operation” for dislodging the cataract away from the pupil.
This procedure was very simple. The physicians were using a lancet to push the clouded lens backward into the vitreous body (Huerva & Ascaso, 2013).
Figure 26 Wall painting in a tomb in Thebes dated about 1,200 BC (Huerva & Ascaso, 2013)
This technique which the ancestor of modern cataract surgery has been performed until 1748, when the French doctor Daviel performed the first known modern cataract surgery (SNOF, s.d.).
While refractive surgery dates to the pharaonic ages, laser-assisted refractive surgery has only emerged as an established clinical discipline in the late 1980s. However, some of the principles behind current techniques were already known back in the 19th century. We will describe below the key steps of development of these techniques until the emergence of the Laser-Assisted In-Situ Keratomileusis (LASIK) technique.
The origins: Leendert January Lans (19th Century)
In 1850, Prussian ophthalmologist Albrecht von Graefe (1828 – 1870) developed a new cataract surgery based on a wide ab externo limbic incision. This new technique was the source of a very high incidence of post-operatively induced high astigmatisms (SNOF, s.d.). In 1898, Dutch ophthalmologist Leendert January Lans (1869 – 1941), published his PhD thesis which title was « Experimental studies of the treatment of astigmatism with non-perforating corneal incisions » (SNOF, s.d.). This thesis can be considered as the first scientific publication on refractive surgery. It described Lans’ findings about the effect of non-perforating incision parallel to the limbus performed on rabbits in a laboratory i.e. that the flattening of the central cornea is increased by the depth of the corneal incisions and increases during healing.
The above is the basic principles of what will be known as the radial keratotomy (RK), the first refractive surgical methods to correct myopia, that were developed in 20th century.
The beginnings in Japan and the Soviet Union (1930s – 1970s)
More than 80 years after the works of Lans, Japanese ophthalmologist Tsutomu Sato (1902 – 1960) observed empirically the corneal flattening caused by acute keratoconus, which was the starting point for him to develop the first radial keratotomy technique to treat keratoconus and astigmatism. Sato was performing posterior corneal incisions using a knife blade. He treated more than 200 patients between the late 1930s and early 1940s.
In 1940s, Sato and his team added anterior corneal incisions to their technique and started during the 1950s to use the same principle to correct myopia performing an average of 40 incisions. Sato’s technique resulted in multiple complications (bullous keratopathy) which were reported more than 10 years after the surgical procedures were performed to correct myopia and helped to understand the role in the endothelium for corneal transparency (SNOF, s.d.).
While Sato’s technique was never used outside Japan, radial keratotomy reappeared in 1969 when Soviet military ophthalmologist Yenaliev adapted Sato technique by removing posterior incisions and maintaining only the anterior corneal’s incisions. He operated 426 myopic eyes (myopia less than 12 dioptres) between 1969 and 1977, and used several incisions ranging between 4 and 24. He obtained an average correction of 3 to 4 dioptres (SNOF, s.d.).
In the 1970s, Soviet ophthalmologists Svyatoslav Fyodorov (1927 – 2000) and his team demonstrated the variation of the correction with the length of the incisions, as well as the peripheral curvature of the cornea to compensate the central flattening of the cornea. They defined the minimum optical zone diameter consistent with the absence of functional gene to 3 mm, then described the role of the ocular pressure, the keratometry, the depth of the incisions, and their ideal number (sixteen).
The emergence as an established clinical discipline in the Soviet Union, the US and Europe (1980s – 1990s)
Fyodorov established a considerable number of specialized surgical centres in the USSR treating a high number of patients. His technique was imported to the US and Europe during the late 1970s and the 1980s. The first RK was performed in the US by Leo Bores in Detroit in 1978.
Many clinical studies such as Deitz (Deitz & Sanders, 1985) – (Deitz, Sanders, & Marks, Radial keratotomy: An overview of the Kansas City study, 1984) – (Deitz, Sanders, & Raanan, Progressive hyperopia in radial keratotomy. Long-term follow-up of diamond-knife and metal-blade series, 1986) and Sawelson (Sawelson & Marks, 1987), helped to better understand the limits of efficiency of the technique and improve its limits in particular functional complications (irregular astigmatism), daytime refractive instability and progressive hypermetropisation.
Instrumentation evolved from steel to diamond blades which had a better precision of cutting, the maximum refractive correction limit was reduced from -4 to -12 dioptres, and the centripetal incisions were replaced by centrifugal incisions while the number of incisions was reduced from 16 to 4. The RK technique disappeared gradually in the mid-1990s with the emergence of the excimer laser-assisted techniques.
Development of laser-assisted refractive surgery techniques
In the 1960s, Catalan ophthalmologist Jose I. Barraquer has set most of the theoretical ground for the emergence of current laser-assisted refractive surgery techniques.
He worked on the development of the microkeratome, a surgical instrument able to achieve a regular keratectomy i.e. a superficial lamellar cut of the cornea with a controlled diameter and depth. The principles developed by Barraquer for the microkeratome are the basis of the femtosecond laser keratectomy which is the first phase a LASIK surgery.
Besides, Barraquer has also tried to develop secondary cutters in the microkeratome able to execute ablations in the posterior stromal bed which is the second phase of a Laser-Assisted In-Situ Keratomileusis (LASIK) (SNOF, s.d.). Barraquer’s results were disappointing and he abandoned this workstream but the principles of in-situ keratomileusis were established.
In 1988, a new laser – the excimer- used in the industry since the 1970s was introduced in ophthalmology starting the age of photorefractive keratectomy (PRK). The excimer laser is a pulsed laser which emits in the far ultraviolet (193 nm). The high energy of the laser allows to break the intermolecular bonds without significant thermal effect. After various tests on blind eyes, Marguerite McDonald performed the first PRK on a seeing eye in 1988. While showing its effectiveness, the PRK results on visual quality and refractive performance were limited by centring and cornea healing issues due to the alteration of the anterior layers of the cornea.
To avoid the alteration of the anterior layers of the cornea due to the PRK, Pallikaris and Buratto developed in 1990-1991 a keratomileusis based on a photoablation in the corneal stroma using an excimer laser to treat high degree myopia. The improvement of the performance of lamellar keratectomy using an automated microkeratome (ACS) developed by Ruiz will help spreading Pallikaris’ and Buratto’s technique starting the age of Laser-Assisted In-Situ Keratomileusis (LASIK).
The further improvement of microkeratomes and optimisation of the issuance and control of laser beams, allowed for the use of LASIK to correct astigmatism, hyperopia and low degree myopia.
Classification of refractive surgery techniques
Interaction between laser and cornea
There are four types of possible interactions between a laser beam and the cornea: absorption, transmission, reflection and dispersion. The proportion of the different effects observed depends on the respective characteristics of the laser and tissue, and more precisely of the energy absorbed by the molecules of the tissue.
The cornea transmits wavelengths between 300 and 1,300 nanometres. The phenomenon of dispersion of energy is especially observed when large surfaces are treated as thermal effects are strongest in the vicinity of the laser impact. The reflection of the laser beam at the anterior and posterior surfaces of the cornea is very small. The most important laser-cornea interaction is the absorption of the laser’s energy by the cornea.
The absorption of the laser pulse energy within the cornea depends on the wavelength and pulse duration. For wavelengths lower than 300 nm, absorption is due to the macromolecules of the cornea while for wavelengths of 600 nm or more, it is mainly due to the water.
Table of contents :
Introduction
Chapter 1: Optics of the human eye
1.1 Overview of the human eye
1.1.1 Anatomy of the human eye
1.1.2 The cornea
1.1.3 The pupil
1.1.4 The axis of the eye
1.1.5 The retina
1.2 The light
1.3 Optical phenomena influencing the formation of the image
1.3.1 Specular reflection
1.3.2 Absorption
1.3.3 Diffraction
1.3.4 Light scattering
1.3.5 Optical aberrations
1.3.6 Resolution limit of the retina
1.3.7 Stiles-Crawford effect
1.4 Assessment of the quality of vision
1.4.1 Visual Acuity (“VA”)
1.4.2 Contrast Sensitivity (“CS”)
1.4.3 Depth of Field (“DOF”)
1.4.4 Root Mean Square (“RMS”)
1.4.5 Optical Transfer Function (“OTF”)
Chapter 2: Overview and importance of refractive surgery techniques
2.1 History and development of laser-assisted refractive surgery
2.1.1 History of refractive surgery
2.1.2 Development of laser-assisted refractive surgery techniques
2.1 Classification of refractive surgery techniques
2.1.1 Interaction between laser and cornea
2.1.2 Classification
2.2 Socio-economic weight and perspectives of laser-assisted refractive surgery
Chapter 3: Materials and methods
3.1 General methodology
3.2 Materials
3.2.1 Measurement instruments
3.2.2 Surgical instruments
Chapter 4: Pupil dynamics in refractive surgery
4.1 Assessing repeatability of pupillometric measurements in the eyes of refractive surgery candidates using infrared pupillometer
4.1.1 Abstract
4.1.2 Introduction
4.1.3 Patients and Methods
4.1.4 Results
4.1.5 Discussion
4.2 Measurement of pupil centre shift in refractive surgery candidates Caucasian eyes using infrared pupillometry
4.2.1 Abstract
4.2.2 Introduction
4.2.3 Patients and Methods
4.2.4 Results
4.2.5 Discussion
4.3 Assessment of pupil dynamics and biometry in eyes undergoing cataract surgery
4.3.1 Abstract
4.3.2 Introduction
4.3.3 Patients and methods
4.3.4 Results
4.3.5 Discussion
Chapter 5: Importance of the corneal epithelium in refractive surgery
5.1 Topography of the corneal epithelium and the bowman layer in low to moderately myopic eyes
5.1.1 Abstract
5.1.2 Introduction
5.1.3 Patients and methods
5.1.4 Results
5.1.5 Discussion
5.2 Investigating the topographic effect of epithelium in myopic eyes with and without topographic preoperative abnormalities
5.2.1 Abstract
5.2.2 Introduction
5.2.3 Patients and Methods
5.2.4 Results
5.2.5 Discussion
Chapter 6: Anatomical and visual outcomes after a LASIK performed in moderately to high myopic eyes with the WaveLight® Refractive Suite (Alcon® Laboratories Inc., USA)
6.1 Abstract
6.2 Introduction
6.3 Patients and methods
6.4 Results
6.5 Discussion
Conclusions and perspectives
Bibliography
