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Let´s continue with this topic, Dr. Carlos Lisa is going to talk about
the relation between coma and astigmatism following this classificatory scheme.
He has a degree in Medicine and surgery at Universidad de Navarra, and he has done several
postgraduate investigation courses and
at present he works in the unit of refractive surgery, anterior segment
and cataracts, at Instituto Oftalmológico Fernandez-Vega together with
Dr. Jose Alfonso, one of the most qualified doctors and surgeons in the treatment of keratoconus.
He specialises in segment implantation and corneal transplantation
using femtosecond laser.
Good afternoon everyone, and thank you to Imex
for their invitation and to Doctor Rafael Barraquer.
We are going to talk about the first results with SAANA classification for keratoconus.
There are four basic rules in the study of keratoconus and they are going to help us
identify what segments to implant in each case and to know what
type of keratoconus we have in each case.
One of them consists on the assumption that the thinness part is always located in the temporal inferior quadrant.
Also, that the keratoconus can be classified depending on where
the thinnest spot is and the distancies between this spot and the centre of the pupil.
Therefore, it will be central if the distance is under a millimetre, paracentral between one and two milimetres and pericentral
if it´s bigger than two milimeters. The flatter medium topographic axis
in the right eye is at 45 degrees in the right eye and 135 degrees in the left eye.
And the comatic aberration doen´t always coincide with the topographic axis.
Therefore we can have three different groups: when the difference
between both is less than 30 degrees, when there is between 30 and 75 degrees
and when this difference is bigger than 75 degrees.
Taking into consideration all this data, we have 9 different possible combinations.
If we also take into account the asphericity
this can help us identifying cases where we are in doubt.
This is what Dr. Ferrara does.
There are different types of segments with different arc lengths and different optical diameters:
5 mm optical zone, triangular cross section and 600 microns base,
and 6 mm optical zone, triangular section and 800 microns base.
There are different implant possibilities as Dr. Lamarca
has explained. If we implant one or two different arc length segments in the
topographic axis this will be asymmetric and axial.
When we implant one or two different segments these
can be asymmetric and not axial if we dont implant them in the topographic axis.
It can be symmetric and axial when we implant two identical segments in the topographic axis.
It will be symmetric and not axial when we implant two identical segments
but in the topographic axis that is not the flatter one.
This is the classification that the previous speaker
has explained. As a general approach to this surgery
we can implant the segments outside the ectasia and in the flatter
topographic axis.
I am goint to show the results of the paracentral ectasias which cover 80%
of all the ectasias. By controlling all the paracentral ectasias
we can control a big part of the keratoconus problem.
In those cases where the topographic axis and the coma coincide,
if the coma is diverted less than 30%, we will be looking at
a croissant, which is a paracentral ectasia.
As I have previously explained, it has an inverted astigmatism
or oblique and the coma coincides as we have
previously explained with a topographic astigmatism.
In these cases, by inserting a 150 degree segment we can
correct both things, the astigmatism and the comatic aberration.
If we have more astigmatism, a moderate astigmatism, we will work with a segment
with a lower arc length that will better correct the astigmatism.
And if we have a higher astigmatism we will work with a superior segment
to correct a higher astigmatism.
And depending on these parameters we have developed this nomogram based on the astigmatism
and the corneal thickness.
We have carried out research on this cases
on 56 eyes. The tunel has been done with a femtosecond laser
and we have implanted one or two segments at a 70% depth.
The results show that there is an improvement in comparison to the preoperatory, noticeable by looking at the
refractive and keratometric cylinder, at around 3 diopters.
The visual acuity improves with and without correction
and the predictability is high.
Up to 78% of patients have +/- 1 diopters of astigmatism.
With regard to the vector analysis during postoperatory most of patients
are around a 0 value of low astigmatism.
And in terms of security 60% of patients
earn at least a line of sight.
What happens with those other cases where
astigmatism and coma don´t coincide, and where there is a difference between 30 and 75 degrees?
As you see, topographic astigmatism is commonly
oriented towards 20 degrees and there is a 53% chance
of this happening, a bit more frequent that the croissants.
This would be the "duck" type as we see in the Obscan, a paracentral ectasia
as we have explained before. The thinnest point is located between 1 or 2 mm
distance from the centre, this is a direct or oblique astigmatism
unlike the other one that was inverse and oblique
and the coma doesn´t coincide. It doesn´t coincide with the
topographic astigmatism. In these cases, if we have a low and moderate astigmatism
we will have to work on the bottom part with 150 degrees segments
because it will prevent from astigmatism and coma.
If we worked with 120 degrees segments we would miss one or the other.
Therefore we will always work with 150 degrees segments.
And if we have a higher astigmatism we can increase the thickness of the inferior segment and add
a superior segment. And taking all this into account we have done
a nomogram as it can be seen here, always working with 150 degrees segments
and 90 degrees superior segments if the astigmatism is high.
We have taken as a sample 3 eyes from 3 patients.
The tunnel is done with intralase and we have implanted one or two segments at
a 70% depth. And we can see that in these cases the astigmatism
was a bit better than in the croissants, but we can
now see a clear improvement in the refractive and keratometric astigmatism
in the postoperatory.
Also, when the visual acuity has had an improvement with or without correction.
In terms of predictability, it is similar to croissants, in a 79% of cases
we have +/- 1 diopter left.
The vector analysis also shows and improvement during the postoperatory.
And as regards security 44% of patients
earn at least 1 line of sight.
We have seen the different phenotypes
of keratoconus and what I have now explained covers 80%
of the cases that exist, which are:
paracentral location, with coincident topographic axis, without coincident topographic axis,
the "duck" type, and with asymmetric and axial segment implantation
with one or two segments at a 6 mm optical zone.
In future meeting during the coming months we will try
to present the results with different phenotypes.
To sum up, take into consideration that the procedure
can be standardised in more that 90% of cases
and also the option of correcting the asphericity
in those cases where we are in doubt.
Thank you, very much.