What is Keratoconus?
Keratoconus is an inherited corneal dystrophy. You are born with it, although it tends not to manifest until the beginnings of puberty and can sometimes be subclinical and not noticed until an evaluation is performed for intervention such as laser vision correction.
Keratoconus is an inherent weakness of the collagen that the cornea is made up of. With time it allows the cornea to bulge and stretch forward. This distortion in the corneal shape blurs vision and as it progresses glasses become ineffective.
Excellent visual quality can be achieved in the setting of Keratoconus with a rigid gas permeable (hard) contact lens. It will not stop progression and not everybody can tolerate them.
When Keratoconus is identified, it is critical to evaluate progression. If demonstrated, it can be arrested by performing a procedure called Collagen Cross-linking.
Collagen Cross-Linking procedure is an in-rooms intervention that takes approximately one hour and it involves disruption of the surface layer of the cornea, which allows a riboflavin (vitamin B2) drop to penetrate into the substance of the cornea. When the cornea is soaked in riboflavin, the eye is then exposed to an ultraviolet light of a known energy level for a period of 30 minutes that allows the collagen fibres of the cornea to connect with one another and stiffen up.
Collagen Crosslinking stops the natural progressive steepening of Keratoconus and can prevent more significant intervention if it continued to get worse, such as a corneal transplant. If a refractive correction to achieve independence from glasses is being considered in the setting of Keratoconus, stabilisation with Collagen Cross-linking is considered critical.
If the best-corrected vision with glasses cannot be significantly improved due to the abnormal corneal shape, one can improve visual quality by either reshaping the cornea or replacing it. Reshaping the cornea involves either the use of an excimer laser or an intracorneal ring segment.
Reshaping the cornea
If the magnitude of visual correction is small, the cornea can be reshaped following Collagen Cross-linking by using a surface-based laser (ASLA/PRK) with a topographic-linked algorithm. This maps the abnormal shape of the cornea and the laser then optimises the surface to improve generalised visual quality with the aim of hopefully achieving independence from glasses.
If ASLA/PRK is deemed inappropriate, the cornea can be reshaped with an intracorneal ring segment (Keraring) insertion. The procedure is a quick 15-minute in-room procedure. Initially, a 1 mm channel at 70% depth of the cornea is created using a femtosecond laser. The ring segment is then implanted into this channel and improves corneal symmetry to optimise vision with glasses. It is a pain-free procedure with rapid recovery.
Intra Collamer Lens (ICL)
If the corrected vision is adequate with glasses; however, the magnitude of the correction is significant, the patient can still achieve complete independence from glasses by utilising an implanted Intraocular Collamer lens (ICL). This lens is constructed to the exact visual requirements of the individual’s eye, including significant degrees of astigmatism and short-sightedness. Implantation is done in an operating theatre under general anaesthetic and takes only 15 minutes. It is a pain-free recovery with good vision achievable the next day.
The ICL is implanted through a peripheral 3 mm incision that does not require stitches and is positioned behind the iris inside the eye without touching the patient’s own natural lens. By retaining the patient’s natural lens, an entire spectrum of vision at all distances is achievable with the best possible visual quality.
Keratoconus can often be quite advanced on initial presentation and more minimal intervention such as Kerarings, ICLs or PRK may be completely inappropriate. If Keratoconus is advanced, the most appropriate procedure assuming contact lenses are intolerable is a corneal transplant.
Corneal transplantation for Keratoconus has evolved enormously over the last decade or so and the optimal treatment of choice is a Deep Anterior Lamellar Keratoplasty (DALK). By replacing the cornea, one can achieve optimal vision by eliminating the asymmetric corneal shape. In a DALK transplant, the natural inner lining of the patient’s own cornea is maintained. The advantage of this is the complete absence of corneal graft rejection in the future and a stronger eye tectonically.
DALK transplants do take a significant length of time to stabilise. The sutures holding the cornea in position need to remain in position for at least nine months, although they cannot be felt or seen.
When the sutures are removed, the new normal central cornea can then be modified according to the residual glasses prescription with techniques such as surface-based laser (ASLA/PRK).
Obviously, careful evaluation of the individual’s status with regard to the severity of Keratoconus is essential for developing a step-wise appropriate and effective treatment plan.
Dr James Genge is a sub-specialist in the treatment of Keratoconus and very experienced in all modalities of treatment. Following evaluation, he will personally discuss with you the most appropriate approach to achieve the best possible vision for you. Contact us on 02 9981 1771.