Making laser eye surgery even more personal
For a surgeon planning laser eye surgery, identifying the optimal treatment for astigmatism has always been a challenge.
It is the shape of the cornea, the transparent window at the front of the eye, that causes astigmatism, and a person’s glasses that correct it.
However, in many cases, these two parameters differ in magnitude and direction.
Aiming to correct astigmatism in the glasses will come at the expense of the cornea, leaving the eye with an avoidable amount of uncorrected astigmatism.
Finding a balance is not easy, but a new method for calculating astigmatic treatments – developed by Professor Noel Alpins AM to extend his decades of work on vector planning for astigmatism with laser eye surgery – has the potential to bring patients closer to their ideal vision than was previously possible.
Refractive errors, such as nearsightedness and farsightedness, are caused by long or short eye length, too steep or flat corneal shape, respectively, or a combination of both.
An oval-shaped cornea, which focuses light onto two focal points on the retina, causes astigmatism.
Astigmatism causes visual symptoms ranging from blurred or double vision at all distances to glare and halos from lights at night.
Astigmatism can also be classified into regular and irregular types.
In regular astigmatism, the typical shape of the cornea as shown on topographic maps is that of a bow tie, where the two halves of the cornea are symmetrical and orthogonal (in a straight line, Fig. 1).
With irregular astigmatism, the two halves of the cornea are asymmetrical, non-orthogonal, or both (Fig. 2).
Laser surgery can correct astigmatism by reshaping the cornea symmetrically to focus light to the correct point.
However, astigmatism can be further personalized based on a person’s unique circumstances, especially in eyes with irregular astigmatism.
“It is very common to be nearsighted or farsighted with astigmatism,” explains Professor Noel Alpines OAlong-time supporter of CERA and Honorary Clinical Professor at the University of Melbourne.
“This can be corrected along with regular astigmatism, or irregular where the bow tie is irregular or crooked.”
Professor Alpins says that if astigmatism did not exist, refractive surgery to correct nearsightedness or nearsightedness would be relatively simple.
“The practitioner would only have to flatten or accentuate the corneal curvature to the appropriate amount to produce a focused image on the patient’s retina.”
However, with astigmatism it is much more difficult.
Professor Alpins’ new method for planning laser eye surgery to correct astigmatism builds on his decades of experience in the field.
The Alpins method, first introduced nearly 30 years ago and now an international standard in the treatment and analysis of astigmatism, incorporates the vector planning method used to find the best possible visual outcome for a patient astigmatic.
Vector Planning reshapes the cornea in a way that balances astigmatism measured in glasses and that of the cornea.
By aiming to optimally reduce astigmatism on the cornea, patients may end up with better vision than treatment based on glasses alone.
The new Regular and Irregular Astigmatism Treatment update takes this customization even further.
As described in his recently published article Hemidivisional Vector Planning to reduce and regularize irregular astigmatism by laser treatmentRecently published in Graefe’s Archive for Clinical and Experimental Ophthalmology, the new method conceptually divides the cornea in half, with vector planning applied independently to each half of the cornea to minimize total astigmatism.
Since astigmatism can now be measured for each half of the cornea, this added layer of computation provides even greater precision in reducing and regularizing corneal astigmatism.
“Since you can do this calculation on the entire cornea, we wondered why we couldn’t consider treating the cornea in two parts, getting the measurements for each half and personalizing the treatment even more? said Professor Alpines.
This method not only provides maximum reduction in astigmatism, but also regularizes any remaining corneal astigmatism resulting in a symmetrical orthogonal cornea which has the potential to improve a patient’s best corrected visual acuity and reduce remaining aberrations.
It is important to note that the reduction and regularization of corneal astigmatism is beneficial to all treatments whether the astigmatism is regular or irregular.
This result potentially translates into a better quality of vision without glasses or contact lenses.
“We ask ourselves: What is the optimal shape of the cornea? This is the shape that leaves people without glasses with the best quality of vision,” says Professor Alpins.
“This form of hemidivisional vector planning involves trying to give someone the eyes they should have had at birth without the distortions of irregular or avoidable astigmatism remaining.”
Although the new method is not yet implemented in current laser surgery devices, the Designer Cornea calculator is already available free online for experimental use by ophthalmologists to guide treatments in collaboration with manufacturers of refractive excimer or femtosecond laser devices.
The full paper: Hemivisional vector planning to reduce and regularize irregular astigmatism by laser treatment is also available online.
A problem solver at heart, Professor Noel Alpins AM, ophthalmologist, discovered a passion for science and helping people when he was a medical student at the University of Melbourne.
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