Ophthalmologists, specifically refractive surgeons, along with their patients, have enjoyed huge success with ablative (corneal tissue removal) procedures over the 30 years since Dr Marguerite McDonald performed the first PRK on a sighted eye in New Orleans on 25 March 1988
How things have developed since then, with the advent of LASIK, LASEK, TE-PRK, FemtoLASIK and SMILE-a plethora of tools that allow the refractive surgeon to select the most appropriate procedure for each patient. All these procedures modify the corneal shape by removing corneal tissue, thereby correcting the refractive error. LASIK has become the most studied and most successful elective procedure, with the highest patient satisfaction rating of any elective procedure.
So why are we looking for even more options? There are several reasons, most of them related to shortcomings of the ablative procedures. All procedures that remove corneal tissue reduce the corneal biomechanical strength to some extent.
At one extreme is a thick-flap microkeratome LASIK and at the other are PRK and SMILE, which maintain more biomechanical strength.
Dry eyes are less of an issue today thanks to heightened awareness and the tools that we have at our disposal to treat dry eye prior to surgery.
There are some refractive errors that simply don’t do particularly well with ablative techniques; for example, high hyperopia and conditions like keratoconus. Presbyopia remains the last refractive challenge, and potentially represents the biggest market. Besides monovision/blended vision, there are no widely adopted corneal ablative refractive procedures to treat presbyopia.
Also, market research indicates that some people steer away from the ablative techniques as they feel they are too permanent and non-reversible. Some might think a permanent outcome would be a bonus but not all patients agree.
Corneal tissue addition
Step up Allotex, the corneal tissue addition and permanent biological contact lens company. Instead of removing tissue to change the corneal shape, Allotex adds tissue to achieve the same result.
The human corneal tissue can be added intrastromally under a flap (an inlay) or as an onlay, on top of Bowman’s membrane but under the epithelium. Addition as an onlay is reversible, addressing some patient concerns. An onlay should have very minimal dry eye side effects and no biomechanical side effects.
An inlay, under a thin LASIK flap, would also have fewer dry eye effects as there is no excimer ablation of corneal nerves and no further removal of corneal tissue from the stromal bed.
For example, consider a 32-year-old high hyperope (+6.00 D) with a flat cornea (40 D) and insufficient anterior chamber depth to consider
a phakic IOL. This patient would be deemed untreatable by most surgeons, being too young for refractive lens exchange, having no space for an iris claw lens and being too hyperopic for most surgeons to consider LASIK.
With Allotex, a +6.00 lenticule- fashioned by the excimer laser to have appropriate characteristics for the particular eye-placed under
a flap may provide an excellent outcome. And if it doesn’t work out as intended, the lenticule can simply be removed and you’re back where you started.
Synthetic materials must be placed deeply to avoid the immunologically active part of the anterior cornea, but this is not the case with allografts. Given that no immunologic response is anticipated, the effect of the lenticule can therefore be varied by changing not only its shape and thickness but also the depth at which it is placed. The more anterior the lenticule, the more effect it will have.
Furthermore, the lenticule can be customised to meet the exact refractive needs, including higher order aberration needs. Imagine the application for keratoconus. Placing the exact shape required to regularise the cornea and improve the vision, while thickening the cornea. For presbyopia, instead of having a one-size-fits-all approach like the Raindrop inlay, there are more options.
Allotex have brought further innovation to the allograft space with improved storage techniques including a much longer shelf life (2 years). This is a new era for refractive surgery.
Monitoring visual behaviour
A second technology that greatly excites is the Vivior vision behaviour monitor (VBM), a wearable device that attaches to a pair of spectacles and seamlessly gathers visual behaviour information about the patient.
It’s not a camera but it records working distances, ambient lighting conditions and the head positions used while performing different tasks, allowing you to “sit on the shoulder” of your patient and observe their every move for a few days. Of course, you don’t really accompany them at home and work! But you could have just as well.
This is the first time that patients and I have had the opportunity to discuss their visual needs and the best solution using their own personal, objective data. The conversation is elevated to a different level, as understanding increases on both sides. The whole issue of compromise is better understood.
Prior to surgery many patients have a dream of great, natural distance vision and don’t truly understand the impact of losing near vision (if they were myopic and presbyopic). After wearing the VBM, the limitations of perfect distance vision are very easily understood. They now comprehend that perfect distance vision is going to translate to a light reading add for the computer and reading glasses for near, and they know what percentage of each day they spend looking at the PC and how much time they spend doing close work.
I have seen a significant upsurge in the number of patients requesting multifocal, trifocal and EDOF IOLs, depending on where their greatest needs are. Any early side effects from these IOLs are more readily tolerated because the patient is more aware of the problems that the selected IOL is solving.
Dr Cummings is based at Wellington Eye Clinic, Dublin, Ireland. He is an investigator for Allotex but has no nancial interest in the company, and is on the Medical Advisory Board of Vivior.