Efficacy of LASIK In Treating Corneal vs.

Lenticular Astigmatism

•If not, does today’s wavefront-based treatment (I.e., correcting BOTH corneal and lenticular features ALL at cornea), really make sense?

•Does a corneal procedure such as LASIK perform equally well in correcting abnormalities on cornea vs. lens?

Question?

Let’s Look At Correcting One Type of Abnormality: Astigmatism

• Question: Does a cornea-based procedure such as LASIK perform equally well in correcting corneal vs. lenticular astigmatism?

• I.e., does “where on the Z axis the astigmatism is located (corneal vs. lens)” make any difference when the location of treatment is restricted ONLY on one point along the Z axis (cornea)?

The Study• 61 eyes of 61 consecutive

patients who had primary myopic LASIK;

• Refractive range: -1.75D to -15.00D;

• VISX S3 and Moria LSK ONE;• Single surgeon.

Study Design• Preop: cylinder R, corneal

astigmatism K (Orbscan), and percentage of non-corneal (lenticular) astigmatism (R-K)/R;

• Low lenticular astigmatism group [low (R-K)/R value];

• High lenticular astigmatism group [high (R-K)/R value].

• Postop: analyze percentage of residual untreated cylinder R’/R.

Testable Hypothesis

• Astigmatic correction by a cornea-based procedure such as LASIK performs BETTER for correcting corneal astigmatism (leaving smaller residual untreated cylinder), than for lenticular astigmatism.

Analysis: Double Angle plot

Result: Residual uncorrected astigmatism is twice as high in high lenticular astigmatism group.

Pre-Operative Percentage of non-Corneal Astigmatism (R-K/R) vs. Fraction of Post-Operative Residual Astigmatism (R'/R)

0

0.1

0.2

0.3

0.4

0.5

0.6

low high

Percentage of non-Corneal Astigmatism (R-K/R)

Frac

tion

of P

ost-

Ope

rativ

e R

esid

ual

Ast

igm

atis

m (R

'/R)

0.239

0.502

Figure 3

P < 0.05.

Comparison of Other Variables Group I [(R-K)/R < 1.000] Group II [(R-K) > 1.000] P-values

Age 43.71 45.867 0.29Pre-operative Spherical Equivalent -5.419 -5.775 0.66Pre-operative Cylinder (R) 1.355 0.742 0.0001

Table 2

Averages Group I [(R-K)/R < 1.000] Group II [(R-K)/R > 1.000] P-valuesFraction of Residual Cylinder (R'/R) 0.239 0.502 0.036

For Text: 95% Confidence Interval

Group I [(R-K)/R < 1.000] Group II [(R-K)/R > 1.000]Age 40.473 to 46.947 43.628 to 48.106Pre-operative Spherical Equivalent -4.157 to -6.681 -4.839 to -6.705Pre-operative Cylinder (R) 1.115 to 1.595 .585 to .899

Age, SE comparable, though magnitude of total preop astigmatism is higher in the low lenticular astigmatism group.

Diagrammatic Summary of Result

End result:End result: a nice circular a nice circular image on retina, minimal image on retina, minimal residual uncorrected cylinder.residual uncorrected cylinder.

Circular incoming light.

1)LASIK treating cornealcorneal astigmatism

Good result!Good result!

Diagrammatic Summary of Result

End result:End result: a bizarre imperfect a bizarre imperfect image on retina, higher amount image on retina, higher amount of residual of residual uncorrecteduncorrected cylinder. cylinder.

Circular incoming light.

2)LASIK treating lenticularlenticular astigmatism

Not so good result!Not so good result!

ConclusionCornea based procedure such as

LASIK performs better in correcting corneal vs. lenticular astigmatism.

Correcting lenticular astigmatism by creating “reverse astigmatism” on cornea does not work as well.

Discussion• It is better to correct the problem “at its

source” (i.e., correct corneal problem at the cornea);

• The result suggests that the current wavefront approach (I.e., correcting everything on the cornea) may not make sense.

• Particularly such as correcting iatrogenic post-corneal procedure irregular astigmatism, should we base our correction on corneal topography, rather than on wavefront information?

And Also, The Lens “walks off” With Time….

• Even for virgin eyes, does it really make sense to apply once-in–a-lifetime “DC” (stationary) treatment (LASIK) based on information that contains an “AC” (changing) component (the lens)?

• Does today’s wavefront-based treatment approach really make sense, i.e., creating “reverse aberration patterns” on the time-stationary cornea, when the age-changing lens can just “escape” later and “walk” off, leaving a generation of patients with iatrogenically created irregular cornea and poor vision permanently (and get even worse after CE)?

Take-home messageThe most clinically needed improvement in today’s

refractive surgery is more accurate corneal topographic system upon which ALL corneal treatment such as LASIK should be based.

Patients today should not cling to the unrealistic promise of 20/10 wavefront vision, but a clinically useful improvement on our current practices (I.e., reducing post-LASIK visual quality problems by being more vigilant of intraop irregularizing of the cornea, or correcting post-LASIK problems based on incorrect information that was previously acquired – the cornea).

Do you really want to be 20/10 for just two years,

or 20/25 for 20 years?