Pioneering laser eye surgery is proving to be a successful treatment for corneal disorders, offering lower costs and quicker recovery compared to transplants
Romesh angunawela
MD, MRCOphth
Corneal Fellow,
Moorfi elds Eye Hospital
London, UK
Ali Mearza
FRCOphth
Consultant ophthalmic surgeon
Charing Cross Hospital
Imperial College
Healthcare NHs Trust
London, UK
The eyes may be the window to the soul, but the cornea is the window to the eye. This unique structure serves two important
functions: protection and optical refraction of light into the eye. The cornea is optically transparent because of a highly evolved arrangement of collagen fibres, which allows light to pass into the eye without reflection, and provides most of the focusing ability – the lens does the fine tuning.
Disease processes that affect the cornea
A number of disease processes compromise the transparency – and hence clarity of vision – and protective function of the cornea. These broadly fall into five categories (see Table 1).
The treatment of these broad groups is guided by disease mechanism, severity, effect on visual acuity and the presence of pain and discomfort. Medical management is used with success in some cases but, as this article focuses on the surgical treatment of corneal disease, we shall not dwell on this. Where conservative measures have failed, we must perform surgery to remove scars and deposits from the cornea and to encourage surface stability of the epithelium. Superficial deposits and epithelium can be manually scraped off to clear the optical axis and allow a new surface to grow. Deeper aberrations in the cornea, however, require surgical removal of tissue and transplantation of corneal tissue from a donor.
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Corneal transplantation is the beginning of a process that can take up to three years to optimise vision gradually. During this period, patients must continue to administer eye drops to reduce the risk of transplant rejection and the patient will attend hospital 10-15 times.[1] This is a considerable inconvenience, particularly for those in employment. Since 1995, laser surgery has become a successful, precise and quick method for treating corneal pathology in the superficial layers of the cornea without the need for manual surgery, thereby avoiding or delaying transplantation and its inherent risks.
The laser eye surgery revolution
In 1980, a scientist working for IBM described the use of the excimer laser for photo-etching polymers with submicron precision. It was later recognised that the excimer laser could be used at a wavelength of 193nm to shape corneal tissue accurately with a precision of 0.25 microns (a micron is 1/1000 of a millimetre) and, importantly, without collateral damage to adjacent tissue.[2]
The extreme precision of this laser is a result of a phenomenon known as photo-decomposition, in which the energy of the laser is capable of disrupting molecular bonds at the atomic level and thereby decomposing tissue to its atomic constituents, mainly carbon and water. In 1983, this technology was described as a method for correcting refractive errors and has since spawned a multi-billion-dollar industry.[2] Laser correction of refractive errors such as myopia is now common practice and many of the problems encountered during the early stages of development have been understood and overcome, making it a very safe form of surgery. In 1988, the excimer laser was investigated for removal of pathological tissue from the cornea. The potential of this device as a therapeutic surgical instrument for treating corneal disease has since been refi ned and developed into a technique known as phototherapeutic keratectomy (PTK). PTK was approved by the US Food and Drug Administration (FDA) in 1995 for the treatment of anterior (superfi cial) corneal disorders.[3]
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Phototherapeutic keratectomy
PTK is a laser surgical technique in which the laser is used to remove layers of corneal tissue, starting from the most superficial and moving backwards into the stroma and deeper layers.[4]
This allows for defects in the superficial layers of the cornea to be precisely removed, and is ideal for the accurate removal of a scar or deposits from the cornea. It can also be used to remove the epithelium very precisely and just a few microns of its
anchoring membrane (Bowman’s membrane), which allows a new layer of healing epithelium to anchor into Bowman’s membrane more securely. This has proved more effective than manual surgery in the treatment of conditions such as
recurrent erosion syndrome – a common indication for PTK, where the epithelial layer is unstable and intermittently breaks down causing considerable pain, discomfort and reduction of
vision.[5] In practical terms, PTK is usually performed as a day-case procedure under local anaesthesia and takes around ten minutes. The patient has to wear a protective contact lens over the cornea for 3-4 days while the surface heals and is
required to apply a combination of antibiotic and steroid drops for a few weeks. The use of PTK to treat superficial corneal
disorders effectively, conditions where the corneal surface is unstable and the ability to delay or postpone the need for corneal transplantation are very important achievements. Advantages and disadvantages of PTK are listed in Table 2.
PtK in the UK National Health service (NHS)
Although PTK as a treatment option for pathological conditions of the cornea has been recognised for some time, its use in the NHS is limited to a few specialist centres in the UK. The reasons for this are the costs of the laser equipment required (upwards of £300,000) and the level of clinical expertise required to carry out such treatments. With the advent of mobile laser units and liaison with private clinics, the large capital expense in purchasing an excimer laser is bypassed. As such, treatments can now be performed for as little as £550 per eye, inclusive of all disposables, nursing staff and medication. This then makes
the option of laser treatment a lot more palatable to NHS trusts.
Mr Ali Mearza is a consultant ophthalmic surgeon who is one of only a handful of specialists in the UK who is trained to fellowship level in both diseases of the cornea as well as laser refractive surgery. He led the bid to incorporate laser as a
treatment option for eligible patients at Imperial College Healthcare NHS Trust, London. The increased cost-effectiveness compared to alternative treatments such as corneal transplant surgery were clearly evident and the Trust quickly approved the treatment. Specifically, the laser technique takes less
than ten minutes and offers very good clinical outcomes and quicker recovery. The alternative, a corneal transplant, takes more than an hour and has a very long visual recovery time with several potential problems. There is the risk of rejection,
infection, suture complications and glaucoma. In addition, corneal transplant surgery is dependent on the availability of donor tissue of which there is a shortage in the UK.
Furthermore, after the laser procedure, the vision recovers in a matter of days to weeks as opposed to months to years for a corneal transplant. As such, Imperial College Healthcare NHS
Trust is one of only a few centres in the UK that provides a truly comprehensive corneal service with the ability to offer its patients the most up-to-date treatment options.
Case study 1
A 58-year-old patient had a rare inherited eye disorder that led to scarring in both corneas. She had already undergone two corneal transplant procedures in the right eye and the condition of her left eye was deteriorating, for which previously, she would have been listed for a corneal transplant. Instead, she was one of the first patients to be treated with laser eye surgery at Imperial College Healthcare NHS Trust. According to the patient, the results were “amazing”. “Within a week, I was back at work and my vision had improved dramatically. With the transplants, I was in a lot of pain and had months off work. After a couple of years, both transplants were being rejected.” She added that the laser treatment offered real hope for her daughter who has inherited the same condition.
Case study 2
A 62-year-old patient presented to the Trust with scarring in both her corneas after a severe bout of conjunctivitis. She had been on numerous eye drops, but to no avail, and had significant reduction of her eyesight. Before the availability
of laser eye surgery, the only treatment option would have been a corneal transplant. Instead, the patient underwent laser eye surgery (PTK) and the scars were reduced significantly. The
patient commented that, following the surgery, she could read a newspaper and use the computer without glasses – something she hadn’t been able to do for years.
Conclusion
Laser eye surgery is well known for correcting vision in people who wear glasses and contact lenses. It is the most common type of surgery that patients choose to have, with over 30 million procedures performed worldwide. Only recently has the same technology been used in the NHS to treat pathological conditions of the eye, offering patients a cost-effective solution with faster visual recovery. As the technology required to
perform the procedure becomes more affordable, and with increasing numbers of surgeons trained in these specific techniques, patients will see these treatments offered routinely in more centres both in the UK and across Europe.
References
1 .Roussy JP et al. Can J Ophthalmol. 2009;44(1):36-41.
2. Trokel SL et al. Am J Ophthalmol. 1983;96(6):710-5.
3. Stasi K et al. Curr Opin Ophthalmol. 2009;20(4):272-5. Review.
4. Fagerholm P. Acta Ophthalmol Scand. 2003;81(1):19-32.
5. Das S et al. Surv Ophthalmol 2008;53:3-15.
