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Ming Wang, M.D., Ph.D.
Director of Refractive Surgery, Aier Eye Hospitals, PR China
And
Former Panel Member, US FDA Ophthalmic Device Panel
Harvard & MIT (MD)
Clinical Associate Professor of Ophthalmology for the University of Tennessee
Attending Surgeon of Saint Thomas Hospital, and Director of Wang Vision Institute
20 years have passed since the excimer laser was first used to create refractive corneal shape in 1986. The past two decades have been a period of explosive technological and business development in excimer laser keratorefractive surgery. It has not only permanently changed the way we see things, but also dramatically increased our understanding of the optics and physiology (and pathology) of the human eye.
The various stages of development of excimer laser keratorefractive surgery in the past 20 years have been marked with various “Ks”, as they are all keratorefractive surgical approaches. First there was PRK, then came LASIK, then LASEK and now Epi-LASIK. We have solved the problem of various refractive errors, from mild to mid-range myopia to moderate astigmatism and hyperopia. From the standpoint of the anatomical location of laser ablation, we started on the top (surface PRK), then went under the flap (LASIK), and now it appears we have come back to the top (LASEK, Epi-LASIK). As for information used to plan the treatment, it began with spherocylindrical refraction, then went to wavefront aberration, and now appears to be going in the direction of a combined corneal topography and wavefront approach. In regards to the laser delivery system, we began with broad-beam large energy ablation, then we moved to a flying spot customized treatment. From the standpoint of the clinical optimal range of indication, we began with a broad range of refractive error (myopia up to -12 D or even higher, and hyperopia up to +6D), but over time, the intrinsic limitation and resistance of the cornea to the alteration of its shape, and the availability of various intraocular lens approaches (phakic or pseudophakic) finally settled the optimal range of refractive error by excimer keratorefractive laser treatment to a lower and more conservative range (up to -8 D for myopia and up to +3 D for hyperopia). The explosive technological development not only created unprecedented quality of vision in our patients, but also a new dimension of understanding of the structure and function of the human eye.
A hallmark of modern medicine is the increasingly significant role played by business and economical considerations. Never before in human history have we had the availability of such safe and effective surgical correction for refractive error (RK is no match), so excimer laser keratorefractive surgery has enjoyed the unprecedented benefit of an accumulated pool of untapped population which is eligible for refractive surgery, resulting in the explosive growth of LASIK in the mid to late 1990s. In the US, the shear magnitude of the size of this annual $5 billion industry and the exciting sense of freedom from dependence on optical correction has captured the consumer’s attention and has attracted creative talent from all walks of human society, from financing to marketing, from bench research to large-scale clinical patient trial, from ethics to consumer psychology, from business management to legal infrastructure, from traditional medical practice mode (private practices and academic centers) to brand new business conglomerate structures such as TLC, LVC and LCA Vision. These companies, like the almighty Wal-mart, threaten to crush the traditional small private practices (mom and pop shops which became extinct after the invasion and dominance of the Wal-marts of the world). In one word, the advent of excimer laser keratorefractive surgery has forever changed the way we practice ophthalmology. It has not only solved many of our (vision) problems and increased our understanding of our vision system, but has also created an entire new way of practicing ophthalmology and eyecare delivery.
The state-of-the-art status of excimer laser keratorefractive surgery is characterized by the following:
1. New development in laser ablation technologies:
a. New laser ablation pattern and algorithm;
b. Ideal excimer laser: spot size, energy and ablation depth per pulse, frequence, latency, treatment duration, tracking;
c. Broad-beam vs. scanning flying spot approaches;
d. Beam integrator module;
e. Cosine energy compensation;
f. Thermal loading avoidance and laser frequency;
g. The issue of effective increasing frequency with decreasing diameter of treatment: plum and thermal effect and increased random error with high myopic treatment;
h. New technique: high frequency (1 kHz) evaporative lamellar transplantation (CLAT);
2. New technologies in ablation platform: input data and treatment strategies:
a. Wavefront customized treatment profile;
b. Biological wound-healing responses: Biological Planck’s Constant;
c. Zernike vs. Fourier: which is better?
d. Cylinder treatment: cross-cylinder approach;
e. Wavefront optimized Q-value consideration to minimize spherical aberration and main prolate corneal shape;
f. New understanding of the transitional zone: width vs. slope;
g. Optimal treatment axis considerations: pupillary axis vs. corneal morphological axis, which is the functional visual axis?
h. Vertical and horizontal decentration clinical tolerance;
i. Pupil center shift due to asymmetric pupil dilation;
j. Pitfalls in horizontal X-Y tracking;
k. The importance of vertical alignment: no tracking available;
l. Cyclotorsional tracking (iris registration): does it really matter?
m. Limitation of wavefront-sensing- and refraction-based treatment: constant lenticule approach;
n. Topography-driven treatment and indications;
o. The role of posterior corneal shape: how do we incorporate it into our surgical planning;
p. Preoperative considerations to prevent ectasia;
q. Modern excimer laser treatment nomogram;
r. The unsolvable question of lack of objective verification of fixation;
s. New technologies in multi-focal corneal ablations for presbyopia;
t. Excimer laser wavefront ablation of contact lens: preop simulation and beyond;
u. New combined topography and wavefront-based treatment;
3. Ablation location and corneal architectural considerations:
a. Surface treatment vs. under-the-flap treatment: pros and cons;
b. Mechanical vs. laser flap;
4. Clinical indications and limitations of excimer laser keratorefractive surgery:
a. Ideal excimer laser keratorefractive surgery range;
b. Bioptics: phakic and pseudophakic;
c. Combining excimer keratorefractive procedure with pseudophaic multifocal/accommodative IOL (Rezoom, Restore, CrystalLens);
d. Surface treatment for FFKC;
e. Treating a problem at its source: the fundamental question about whether the axial location of an aberration does matter; how to treat lenticular astigmatism? Does it make sense to make the cornea bear the burden of correcting the entire visual axis aberration?
5. Emerging technologies in treating post-refractive surgery complex eyes:
a. New technologies in treating decentered ablation and small optical zones;
b. Emerging technologies in treatment of irregular astigmatism;
c. Management of ectasia;
d. New philosophy – “The shape of the glass door”: abandoning the traditional constant lenticule approach (which ignore the shape of the glass door (cornea), ideal corneal shape, ideal wavefront, ideal vision.
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