The LASIK industry & the FDA have conspired since LASIK's inception to purposely withhold information vital to the public in making a truly informed LASIK decision. With Lasikdecision.com, The hope is to show you what the industry and FDA would not and did not even think of doing until LASIK casualties started speaking out, and yet, they still did NOTHING.
Corneal Studies & Articles PDF Print E-mail

Wound healing in the cornea: a review of refractive surgery complications and new prospects for therapy - The corneal wound healing response is of particular relevance for refractive surgical procedures since it is a major determinant of efficacy and safety. The purpose of this review is to provide an overview of the healing response in refractive surgery procedures.

Long-term corneal keratoctye deficits after photorefractive keratectomy and LASIK - To measure changes in keratocyte density up to 5 years after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).

Estimation of true corneal power after keratorefractive surgery in eyes requiring cataract surgery: BESSt formula - To describe a new formula, BESSt, to estimate true corneal power after keratorefractive surgery in eyes requiring cataract surgery.

Considerations of glaucoma in patients undergoing corneal refractive surgery - Corneal thickness, which is modified during corneal refractive surgery, plays an important role in monitoring glaucoma patients because of its effect on the measured intraocular pressure.

Corneal Keratocyte Deficits After PRK and LASIK - To measure changes in keratocyte density up to 5 years after PRK and LASIK.

Effective corneal refractive diameter as a function of the object tangent angle in visual space - To determine whether the currently accepted method of selecting a minimum optical zone diameter for laser refractive surgery that is equal to or slightly greater than the dark-adapted pupil diameter provides a sufficient diameter of corneal surface to focus light arising from objects in the paracentral and peripheral visual field.

Evaluation of Corneal Sensitivity to Mechanical and Chemical Stimuli After LASIK: A Pilot Study - To evaluate the effect of laser in situ keratomileusis (LASIK) on corneal sensitivity, nerve morphology, and tear film characteristics.

Changes in corneal thickness and curvature after different excimer laser photorefractive procedures and their impact on intraocular pressure measurements - To analyze the changes in central corneal thickness (CCT) and curvature before and after different excimer laser photorefractive procedures and their possible impact on intraocular pressure (IOP) estimations with Goldmann applanation tonometry.

Effect of Corneal Curvature and Corneal Thickness on the Assessment of Intraocular Pressure Using Noncontact Tonometry in Patients After Myopic LASIK Surgery - To evaluate the effect of corneal curvature and corneal thickness on the assessment of intraocular pressure (IOP) using noncontact tonometry (NCT) in patients after myopic LASIK surgery.

Failed LASIK Depleting Supply Of Donor Corneas - Optometrist specializing in post-refractive surgery disaster claims that FAILED LASIK EYE SURGERY IS DEPLETING SUPPLY OF DONOR CORNEAS.

Epidemic of Corneal Weakening After Refractive Surgery - Here is an excerpt and link to a comment posted by Optometrist Dr. Greg Gemoules who specializes in the treatment of patients damaged by refractive surgery by fitting them with rigid gas permeable contact lenses.

Effect of Corneal Curvature and Corneal Thickness on the Assessment of Intraocular Pressure Using Noncontact Tonometry in Patients After Myopic LASIK Surgery -  Even if a residual corneal bed of 300 microm or thicker is preserved, anterior bulging of the cornea after LASIK can occur.

Structural Analysis of the Cornea Using Scanning-Slit Corneal Topography in Eyes Undergoing Excimer Laser Refractive Surgery - Myopic PRK and LASIK induce significant forward shifts of the cornea, which are not true corneal ectasia.

Permanent Disease Changes Present in all Post-LASIK Corneas! - Permanent pathologic changes were present in all post-LASIK corneas. These changes were most prevalent in the lamellar interface wound. These changes along with other pathologic alterations in post-LASIK corneas may change the functionality of the cornea after LASIK.

Corneal Nerve Damage Continues to Increase years 2-3 after LASIK - Both subbasal and stromal corneal nerves in LASIK flaps recover slowly and do not return to preoperative densities by 3 years after LASIK.

Critical thoughts on current laser surgery of the cornea (1995) - If we look at refractive surgery, especially laser photoablation, in the context of the needs for ophthalmic care of the whole world, then this type of surgery is out of proportion.

Theoretical Elastic Response of the Cornea to Refractive Surgery: Risk Factors for Keratectasia - "In particular, a forward shift and an increase in power of the posterior surface was predicted for myopic LASIK, in agreement with previous experimental findings." 

Cohesive tensile strength of human LASIK wounds with histologic, ultrastructural, and clinical correlations - The human corneal stroma typically heals after LASIK in a limited and incomplete fashion; this results in a weak, central and paracentral hypocellular primitive stromal scar that averages 2.4% as strong as normal coeneal stroma.

Pathologic findings in postmortem corneas after successful LASIK - Permanent pathologic changes were present in all post-LASIK corneas. These changes were most prevalent in the lamellar interface wound. These changes along with other pathologic alterations in post-LASIK corneas may change the functionality of the cornea after LASIK.

Ex vivo confocal microscopy of human LASIK corneas with histologic and ultrastructural correlation - Confocal microscopy, along with histologic and ultrastructural correlations, demonstrated that the most prevalent alterations in the centers of LASIK corneas were a slightly thickened epithelium caused by focal basal epithelial cell hypertrophic modifications, random undulations in Bowman's layer over the flap surface, and a variably thick hypocellular primitive stromal interface scar.

Corneal reinnervation after LASIK: prospective 3-year longitudinal study - Both subbasal and stromal corneal nerves in LASIK flaps recover slowly and do not return to preoperative densities by 3 years after LASIK.

Progression to end-stage glaucoma after LASIK - 2 patients, one a glaucoma suspect because of family history and the other with juvenile glaucoma.

Steroid-induced glaucoma after LASIK associated with interface fluid - To report the ocular manifestations and clinical course of eyes developing interface fluid after LASIK.

Biomechanical modeling of refractive corneal surgery - A biomechanical study before surgery is therefore very convenient to assess quantitatively the effect of each parameter on the optical outcome.

Confocal Microscopy of Corneal Flap Microfolds After LASIK - To describe the morphological characteristics of microfolds that appear at the corneal flap after LASIK, as seen under confocal microscopy.

Objective method to measure corneal clarity before and after LASIK - To develop, evaluate, and use an objective method to determine the effect of LASIK on corneal clarity.

Histopathology of corneal melting associated with diclofenac use after refractive surgery - To describe the histopathology of the cornea in 3 cases of corneal melting associated with diclofenac therapy after refractive surgery procedures.

Central corneal iron deposition after myopic LASIK - To describe central corneal iron deposition after myopic LASIK.

Corneal ectasia after LASIK in patients without apparent preoperative risk factors - To evaluate patients who developed ectasia with no apparent preoperative risk factors.

Interface Corneal Edema Secondary to Steroid-induced Elevation of Intraocular Pressure Simulating DLK - To describe interface corneal edema secondary to steroid-induced elevation of intraocular pressure (IOP) following LASIK.

Delayed Ectasia Following LASIK With No Risk Factors: Is a 300-µm Stromal Bed Enough? - To report a case of ectasia occurring >4 years following LASIK with no risk factors and a residual stromal bed >300 µm.

Steroid glaucoma after laser in situ keratomileusis - A steroid-induced glaucoma may develop after bilateral laser in situ keratomileusis (LASIK)  with normal intraocular pressure in applanation tonometry.

Keratocytes' Density Remains Low After Refractive Surgery  - According to a paper presented this month at the 6th International Congress on Advanced Surface Ablation and SBK, keratocytes' density decreases substantially in the anterior stroma of  refractive surgery patients during the first postoperative year and remains low for several years.

Risk Assessment for Ectasia after Corneal Refractive Surgery - To analyze the epidemiologic features of ectasia after excimer laser corneal refractive surgery, to identify risk factors for its development, and to devise a screening strategy to minimize its occurrence.

More on the cornea...

Biomechanics of Corneal Refractive Surgery

JOURNAL OF REFRACTIVE SURGERY

Vol. 22 No. 3 March 2006  

Dan Z. Reinstein, MD, MA(Cantab), FRCSC; Cynthia Roberts, PhD  

Excerpt: "Some of the evidence pointing to the impact of corneal biomechanical properties on surgical outcomes lies in the measurement of intraocular pressure (IOP), both before and after refractive surgery. It is well known that measured IOP is reduced, on average, following a refractive procedure. It has been assumed that this is the result of reduced curvature and thickness in myopic procedures. However, Chang and Stulting performed a retrospective review of over 8000 myopic LASIK patients, and determined that although measured pressure was reduced on average by approximately 2 mmHg, the range of change was approximately +10 to -15 mmHg. Every patient in this population had reduced thickness and curvature, and yet almost half of them had an increase in measured IOP.  

Clearly, the artifact in IOP measurement cannot be explained by thickness alone, and “correction” of measured IOP postoperatively using a linear correction factor based on thickness is problematic. This leads to the conclusion that refractive surgery likely alters the fundamental biomechanical properties of the cornea.

Biomechanical modeling of refractive corneal surgery

J. Biomech Eng. 2006 Feb;128(1):150-60.

Alastrue V, Calvo B, Pena E, Doblare M.

Group of Structural Mechanics and Material Modelling, Aragon Institute of Engineering Research (13A), University of Zaragoza, Spain.

The aim of refractive corneal surgery is to modify the curvature of the cornea to improve its dioptric properties. With that goal, the surgeon has to define the appropriate values of the surgical parameters in order to get the best clinical results, i.e., laser and geometric parameters such as depth and location of the incision, for each specific patient. A biomechanical study before surgery is therefore very convenient to assess quantitatively the effect of each parameter on the optical outcome. A mechanical model of the human cornea is here proposed and implemented under a finite element context to simulate the effects of some usual surgical procedures, such as photorefractive keratectomy (PRK), and limbal relaxing incisions (LRI). This model considers a nonlinear anisotropic hyperelastic behavior of the cornea that strongly depends on the physiological collagen fibril distribution. We evaluate the effect of the incision variables on the change of curvature of the cornea to correct myopia and astigmatism. The obtained results provided reasonable and useful information in the procedures analyzed. We can conclude from those results that this model reasonably approximates the corneal response to increasing pressure. We also show that tonometry measures of the IOP underpredicts its actual value after PRK or LASIK surgery.

Considerations of glaucoma in patients undergoing corneal refractive surgery

Comment in: Surv Ophthalmol. 2005 Nov-Dec;50(6):611-2; author reply 612.

Bashford KP, Shafranov G, Tauber S, Shields MB.  Department of Ophthalmology and Visual Sciences, Yale University School of Medicine, New Haven, Connecticut; and Glaucoma Consultants of Colorado, P.C., Littleton, Colorado, USA.

Glaucoma patients present a unique set of challenges to physicians performing corneal refractive surgery. Corneal thickness, which is modified during corneal refractive surgery, plays an important role in monitoring glaucoma patients because of its effect on the measured intraocular pressure.

Patients undergo a transient but significant rise in intraocular pressure during the laser-assisted in situ keratomileusis (LASIK) procedure with risk of further optic nerve damage or retinal vein occlusion. Glaucoma patients with filtering blebs are also at risk of damage to the bleb by the suction ring.

Steroids, typically used after refractive surgery, can increase intraocular pressure in steroid responders, which is more prevalent among glaucoma patients.

Flap interface fluid after LASIK, causing an artificially low pressure reading and masking an elevated pressure has been reported. The refractive surgeon's awareness of these potential complications and challenges will better prepare them for proper management of glaucoma patients who request corneal refractive surgery.

Evaluation of Corneal Sensitivity to Mechanical and Chemical Stimuli After LASIK: A Pilot Study

Eye Contact Lens. 2006 Mar;32(2):88-93.

Stapleton F, Hayward KB, Bachand N, Trong PH, Teh DW, Deng KM, Yang EI, Kelly SL, Lette M, Robinson D.  From the Cornea and Contact Lens Research Unit (F.S., K.B.H., N.B., P.H.T., D.W.H.T., K.M.Y.D., E.I.H.Y.), School of Optometry and Vision Science and Vision Cooperative Research Centre, University of New South Wales, Sydney, Australia; and Sydney Laser and Vision Centre (S.L.K., M.L., D.R.), Bondi Junction, Australia.]

PURPOSE: To evaluate the effect of laser in situ keratomileusis (LASIK) on corneal sensitivity, nerve morphology, and tear film characteristics.

METHODS: A cross-sectional study design was used. Eighteen patients (eight men and 10 women with a mean age of 36.9 +/- 11.2 years) who had undergone bilateral LASIK for low myopia within 18 months of the study and 28 control subjects (16 men and 12 women with a mean age of 27.2 +/- 7.7 years) were enrolled. Central and inferior corneal thresholds to mechanical (air) and chemical (air plus carbon dioxide) stimuli were determined by using a staircase technique. Stimuli of a 1-second duration at 34 degrees C were delivered with a CRCERT-Belmonte aesthesiometer. Images of subbasal nerves in the central cornea were captured with confocal microscopy. Nerve morphology was classified as no nerves, short nerves (<175 mum), or long nerves (>175 mum), with or without interconnections. Noninvasive tear break up time was measured. The phenol red thread test was used to indicate basal tear secretion. Differences between groups were evaluated with analysis of variance, and associations between variables were evaluated with parametric or nonparametric correlation, when appropriate.

RESULTS: Central corneal mechanical sensitivity was significantly reduced in the post-LASIK group compared with the control subjects (P<0.001). Nerve morphology was associated with mechanical threshold. Nerve morphology, mechanical sensitivity, and tear breakup time improved during the first 1 to 3 months after surgery, with little change thereafter. Chemical sensitivity was associated with tear secretion (P<0.05).

CONCLUSIONS: Central corneal mechanical sensitivity is reduced in patients after LASIK, with partial recovery seen 3 months after surgery. A similar recovery trend is seen for nerve morphology.

Cross-linking therapy a promising treatment for keratectasia

SOURCE

TOP STORIES 2/28/2006

SAO PAULO, Brazil — A therapy that uses ultraviolet light and riboflavin to create cross-linking of corneal collagen may be a promising treatment for keratectasia, a preliminary study has shown.

At the World Ophthalmology Congress, Maria Regina Chalita, MD, reported results from a prospective analysis of the treatment in seven patients who had developed corneal ectasia following LASIK surgery. Prior to the treatment, each patient had progression of ectasia documented by at least two corneal topography maps, she said.

Dr. Chalita said the procedure begins with proparacaine topical anesthesia, followed by mechanical epithelial debridement, and then instillation of a riboflavin solution 5 minutes before UV light irradiation using UV-emitting goggles. Patients then wear a bandage contact lens for 4 days after the treatment.

At the 3-month follow-up point, uncorrected visual acuity had improved in the seven patients and best corrected visual acuity remained the same, Dr. Chalita said.

“Most patients reported better [visual] quality than before surgery,” she said.

“We expected to see a lot of change in corneal topography, but we didn’t,” she continued. “There were no reported adverse affects and no patients lost lines [of visual acuity]. No regression was observed at the 3-month follow up.”

Dr. Chalita concluded that corneal cross-linking with riboflavin and UV light seems to be a safe procedure, but longer-term follow up with a larger patient cohort is needed.

Ultrastructure of the lamellar corneal wound after LASIK in human eye

J Cataract Refract Surg. 2001 Aug;27(8):1323-7.

Rumelt S, Cohen I, Skandarani P, Delarea Y, Ben Shaul Y, Rehany U.  Department of Ophthalmology, Western Galilee-Nahariya Medical Center, Israel.

A 30-year-old patient with keratoconus, a stable refraction, and normal central corneal thickness had laser in situ keratomileusis (LASIK). Six months later, she had uneventful penetrating keratoplasty for keratectasia. The lamellar LASIK interface could not be clearly identified by light microscopy. The corneal wound site did not stain for methyl metalloproteinase 1 or 2. Both the corneal flap undersurface and the stromal bed were devoid of interconnections and cells. Throughout the lamellar incision, including the laser-ablated zone, the surface was smooth on scanning electron microscopy. The collagen fibrils on both sides of the incision remained well aligned with one another, indicating good flap apposition. Under higher magnification transmission electron microscopy, some collagen fragments were found in the interface, especially adjacent to the hinge. The diameter of the collagen fibrils along the lamellar wound were identical to those farther from the incision. The absence of bridging collagen fibrils and cells between the flap undersurface and the stromal bed confirms the clinically known lack of wound repair at the interface and explains the easy separation of the flap from the stromal bed months after LASIK and the possible formation of an interface fluid pocket.

Close-up microkeratome blades reveal variation

May 28, 2002

Eurotimes May 2002

A close-up look at a number of different disposable microkeratome blades using electron microscopy revealed considerable variation in size and cutting edge between both different manufacturers and among blades made by the same manufacturer. Researchers examined ten different microkeratome blade types, comparing five blades of each type. They studied scanning electron microscopic images up to a magnification of 700x the original size and measured blade length, width, and cutting edge. The researchers also examined the blades for any irregularities. The researchers looked at blades manufactured by Bausch & Lomb, Nidek, Moria, Allergan, Oasis, Schwind, Beaver, Alcon, and Asclepion-Meditec. They found variations between the ten different blade groups and among the five blades within each microkeratome blade group. The differences noted included length, width and cutting edge. They expressed concern about the diversity of size and cutting edge seen in blades created by different manufacturers for the same microkeratome, which could potentially compromise the procedure's precision. The blades studied also revealed different degrees of impurities and surface smoothness. These were readily visible at a magnification of 175x. Some blades were coated with impurities or showed deposits. The cutting edge of a particular blade was left relatively unsharpened by some manufacturers. Other blades revealed an additional cutting edge, while the same blade made by another manufacturer lacked it. They noted that some blades were fine, revealing no irregularities along the length of the cutting edge, no impurities or deposits on the blade surface and no variations in size. Such smoothness and consistentency were particularly evident with Amadeus (Allergan) microkeratome blades.

This was published in 2002, and they were doing lasik for years before that. Why they would subject patients to this. Wouldn't they at least look at the blades before rolling lasik out to millions of people? This doesn't make sense.

Healing process at the flap edge in its influence in the development of corneal ectasia after LASIK

Curr Eye Res. 2006 Nov;31(11):903-8.

Abdelkader A, Esquenazi S, Shihadeh W, Bazan HE, He J, Gill S, Kaufman HE.

Department of Ophthalmology, LSU Eye and Neuroscience Center, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.

Quote:

Corneal ectasia may be related to the clinically observed lack of corneal wound-healing at the edge of the flap that allows the cornea to bulge.

Refractive power of the cornea

Compr Ophthalmol Update. 2006 Sep-Oct;7(5):243-51.Ayres BD, Rapuano CJ.Cornea Service, Wills Eye Institute, Thomas Jefferson University, Philadelphia, PA.Corneal refractive surgeries, such as laser in situ keratomileusis and photorefractive keratectomy, have become some of the most commonly performed elective surgical procedures today. Many of the patients undergoing these surgeries are beginning to show signs of cataract formation and are in need of surgical correction. A common problem in the postrefractive patient is accurate prediction of the corneal power for use in intraocular lens calculation. The purpose of this article is to review the literature and to discuss why it is difficult to determine the power of the postkeratorefractive cornea, and to describe the multiple techniques used to assist in calculation of the power of the cornea. We will also examine some of the current technological advances that may aid in power calculation. With proper patient history, examination, and careful calculation(s), it is possible to closely estimate the refractive power of the postkeratorefractive cornea.