Technique has great potential but further development is required
First application of femtosecond laser in presbyopia
"An initial application of a femtosecond laser in presbyopia surgery would be situated in the cornea," said Dr Gerten. "This is the INTRACOR technique and involves cutting five concentric rings into the corneal stroma in the very centre of the cornea."
However, Dr Gerten explained that there are consequences to this option as in destabilization of the cornea as a result of a deeper flap. "Also, we are not cutting parallel to the surface but perpendicularly and we are cutting all cornea lamellae five times, which destabilizes the cornea a lot and could be an ongoing effect," he said.
New and exciting application
Many current therapies in ophthalmology do not focus on the cause or reasons of presbyopia, noted Dr Gerten but can be simply viewed as 'crutch' treatments. It is known that presbyopia is caused by a stiffening of the lens so he questioned why we do not look to treat this.
"Perhaps, we could create separate planes with the femtosecond laser to make the lens more flexible again, which is a new therapy concept," Dr Gerten added. To understand if this new option is viable Dr Gerten examined four main areas of concern.
Is it possible to treat parts of the lens with femtosecond laser?
"The answer to this is yes," he asserted. "We put in a lot of effort with our presbyopia study group to figure out a suitable numerical aperture and energy levels to treat the inner part of the lens."
Can cataracts be avoided when cutting the lens?
To answer this question, Dr Gerten and colleagues performed an animal study with chinchilla white rabbits (Laserzentrum, Hanover, Germany). They treated one eye and used the contralateral eye as the control. "Directly postop bubbles were visible and it was possible to see the femtosecond laser pattern in the lens and a lot of straylight was visible in the Scheimpflug picture," he added. "However, the cuts were executed in a very fine line, and after a month the pattern faded away and the straylight remarkably reduced. We had no cataract in this study," affirmed Dr Gerten.
But, how does this translate to humans? Dr Gerten explained that the human lens has three repair mechanisms in principle. "The first two apply to the chronic hazards and the third one is interesting for direct injuries," he said.
As an example, Dr Gerten described a past experience of a graft in a young male patient, who had granular dystrophy. "While doing the graft I perforated the anterior capsule with a parenthesis knife," he continued. "But you see after 10 years that it is still localized opacity. It did not spread into the whole lens."
In looking at cataracts more carefully he noted that there are cloudy wedges, sharply distinguished from the clear zone right beside them. Dr Gerten questioned how the lens does this, to which he answered, "Well, the lens closes down intercellular metabolic channels between layers and even between single cells, so it isolates these areas." Therefore, if the trauma to the lens can be localized and not include all the adjacent cells he explained it is plausible to assume cataracts will not develop.
"But there is still the question of straylight," he warned. "If you look at the lens there is natural straylight already. If you compare that to the straylight caused by lentotomy you can see it is at least in the same order of magnitude. So, maybe the patient can tolerate that."