Recent advances in prophylaxis and management of corneal ectasia afterLaser In Situ Keratomileusis
John KeddisShehata;
Abstract
LASIK is currently gaining acceptance as an effective surgical procedure for the correction of refractive errors. But it weakens the cornea from the mechanical aspect because of the inherent tissue ablation and the lamellar keratectomy involved in the procedure. This weakening can precipitate progressive anterior shift of the cornea - ectasia of the cornea
Several theories have been proposed to explain the development of this condition and to explain the biomechanical changes that occur due to corneal thinning by ablation. It was proposed that this biomechanical remodeling involves not only the mechanical aspects of the load-bearing collagen fibrils but also the hydration response of the stroma which is also affected by wound-healing response of the stromal cells.
Another theory was put forward and noting that the elastic deformation starts in the posterior surface and depends on inherent corneal factors, the intraocular pressure (IOP), and the ablation profile. And it was concluded that these changes rise proportionally with the degree of the attempted correction, and are greater for thinner preoperative corneas, higher IOP, and thicker flaps.
The incidence remains undetermined, and reported estimates have ranged greatly from 0.04% to 0.6%. Approximately 50% of cases present within the first 12 months, but late onset can also occur. These cases present with myopic shift and decreased visual acuity, due to central steepening and thinning.
Risk factors for development of post-LASIK keratectasia include thin corneas, high myopia (greater than 10 diopters), low residual stromal bed (RSB) thickness, and abnormal corneal topography in form of forme fruste keratoconus, inferior steepening and asymmetrical bowtie. Thin RSB can result from excessive ablation or thick flap creation, and the minimal RSB recommended ranges from 250µm to 300µm. But still keratectasia can also occur in patients without currently recognized risk factors.
Randleman and coauthors presented a quantitative assessment system and taking in account the preoperative topography, residual stromal bed thickness, age, preoperative corneal thickness degree of myopia. And categorized the patients in to low risk, moderate risk and high risk patients, and when this quantitative system applied to ectasia cases and controls it was highly sensitive and specific.
The best treatment for postoperative ectasia is to avoid its occurrence. By good examination of both eyes, careful investigating the three corneal parameters: corneal topography, thickness and corneal biomechanics and applying ectasia scoring system
Newer treatment modalities have been developed to tackle this rare, yet devastating complication of refractive surgery. These modalities include:
All patients with any evidence of early postoperative ectasia should be strongly cautioned to completely avoid eye rubbing, as this may exacerbate the process.
Several theories have been proposed to explain the development of this condition and to explain the biomechanical changes that occur due to corneal thinning by ablation. It was proposed that this biomechanical remodeling involves not only the mechanical aspects of the load-bearing collagen fibrils but also the hydration response of the stroma which is also affected by wound-healing response of the stromal cells.
Another theory was put forward and noting that the elastic deformation starts in the posterior surface and depends on inherent corneal factors, the intraocular pressure (IOP), and the ablation profile. And it was concluded that these changes rise proportionally with the degree of the attempted correction, and are greater for thinner preoperative corneas, higher IOP, and thicker flaps.
The incidence remains undetermined, and reported estimates have ranged greatly from 0.04% to 0.6%. Approximately 50% of cases present within the first 12 months, but late onset can also occur. These cases present with myopic shift and decreased visual acuity, due to central steepening and thinning.
Risk factors for development of post-LASIK keratectasia include thin corneas, high myopia (greater than 10 diopters), low residual stromal bed (RSB) thickness, and abnormal corneal topography in form of forme fruste keratoconus, inferior steepening and asymmetrical bowtie. Thin RSB can result from excessive ablation or thick flap creation, and the minimal RSB recommended ranges from 250µm to 300µm. But still keratectasia can also occur in patients without currently recognized risk factors.
Randleman and coauthors presented a quantitative assessment system and taking in account the preoperative topography, residual stromal bed thickness, age, preoperative corneal thickness degree of myopia. And categorized the patients in to low risk, moderate risk and high risk patients, and when this quantitative system applied to ectasia cases and controls it was highly sensitive and specific.
The best treatment for postoperative ectasia is to avoid its occurrence. By good examination of both eyes, careful investigating the three corneal parameters: corneal topography, thickness and corneal biomechanics and applying ectasia scoring system
Newer treatment modalities have been developed to tackle this rare, yet devastating complication of refractive surgery. These modalities include:
All patients with any evidence of early postoperative ectasia should be strongly cautioned to completely avoid eye rubbing, as this may exacerbate the process.
Other data
| Title | Recent advances in prophylaxis and management of corneal ectasia afterLaser In Situ Keratomileusis | Other Titles | التطورات الحديثة في وقاية وعلاج تمدد القرنية التابع لعملية الليزك | Authors | John KeddisShehata | Issue Date | 2014 |
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