Studies presented at this years Association for Research in Vision and Ophthalmology (ARVO) meeting revealed two possible causes of LASIK-induced dry eye and showed how phototherapeutic keratectomy (PTK) may be an effective treatment for recurrent corneal erosion syndrome (RCES). This years meeting also yielded myriad findings about intraocular lenses, including aspheric IOLS and IOLS for patients who have ruptured capsular bags from previous cataract procedures.
LASIK and Dry Eye
Researchers in Spain and Minnesota may have proven two previously theorized causes for post-LASIK dry eye.273
The researchers in Spain found that post-LASIK dry eye may be due to a decrease in goblet cells caused by the suction rings of both bladeless and mechanical microkeratome surgery. They studied 50 eyes of patients between the ages of 22 and 48 who had normal ocular surfaces prior to myopic LASIK. Half the eyes underwent the mechanical microkeratome procedure, and the other half underwent the bladeless procedureboth performed by the same surgeon.
Conjunctival impression cytology and epithelial cell morphology showed an enormous decrease in goblet cell populations in both groups, although the reduction was greater in those who underwent the bladeless procedure. The bladeless suction ring was applied for a mean period of 108 seconds, while the mechanical microkeratome laser suction ring was applied for 22 seconds. The researchers concluded that the greater decrease in goblet cell populations seen in those who underwent the bladeless procedure was due to the longer length of time the suction ring was applied to patients ocular surfaces. Still, goblet cell recovery was seen in all patients at six months post-op.
Meanwhile, researchers in Min-nesota discovered that post-LASIK dry eye may be due to a reduction in sub-basal nerve density resulting from both bladeless and microkeratome LASIK.516 The researchers studied 20 patients who underwent LASIK for astigmatism or myopia, randomizing one eye of each patient to undergo flap creation via microkeratome and the other to undergo bladeless flap creation.
Using confocal microscopy, esthesiometry and signed rank tests, the researchers found that nerve density was decreased at one, three and six months after both treatments vs. preoperatively. They also found no difference in the reduction in nerve density or corneal sensitivity between either procedure at any time. Anatomical loss of sub-basal nerves did not correspond with changes in mechanical corneal sensitivity.
We have always thought that Laser Assisted Epithelial Keratomileusis (LASEK) provides better vision and less haze than photorefractive keratectomy (PRK) because it is a more complex and labor-intensive procedure and because alcohol is used to break the bond of the epithelium. PRK is not quite as complex, and the epithelium is scraped.
But, researchers in Texas found the opposite to be true.531 They studied 50 eyes that underwent PRK and 50 that underwent LASEK for moderate myopia (-4.00D to -8.00D). Results showed that both surgeries provided patients with uncorrected visual acuity (UCVA) of 20/40 or better at six months. No statistically significant difference in UCVA was seen between the two groups at one, three and six months postoperatively, and there was no significant difference in postoperative pain.531
One difference, however: The PRK group had less haze and faster visual recovery times than the LASEK group.
Although LASEK is a successful refractive procedure, we should not consider it superior to standard PRK for treating moderate myopes, the researchers concluded.
Researchers in Italy found that PRK was effective for up to 13 years.538 They studied 47 eyes (30 patients) that underwent myopic PRK. They found that the PRK-induced refractive status was accomplished at three months and stayed that way for up to 13 years without any evidence of late regression. There was a reduction in corneal haze over time, and patients had a complete recovery of best-corrected visual acuity (BCVA). The researchers noted no complications during this study.
This prospective study had the longest follow-up available of myopic PRK and confirmed the findings of shorter studies, according to the researchers. Still, these findings do not mean that we should recommend PRK to all our refractive surgery candidates. The only reason we have a 13-year study on PRK is because PRK has been around much longer than LASIK. I would expect the same results in a study done on the long-term effects of LASIK, and Im sure we can expect such a study soon.
Riboflavin/ultraviolet (UVA)-induced collagen cross-linking may stabilize post-LASIK progressive ectasia by increasing corneal rigidity, say researchers in Greece.536 The researchers examined seven eyes of five patients who had moderate to advanced post-LASIK ectasia. Central epithelium was removed, and photosensitizing riboflavin drops were instilled. The eyes were then exposed to UVA (370nm, 3m/Wcm2) at a distance of 2cm for 30 minutes.
Postoperative evaluations at six-month intervals showed improvement of the ectasia in all seven eyes. Six eyes had decreased maximal keratometry readings (mean of 3.01D) and decreased refractive error (2.14D). Corneal and lens transparency, endothelial cell count density and intraocular lens pressure (IOP) were unchanged. Corneal elasticity measurements were altered from an average of 15.75m/sec preoperatively to 32.25m/sec postoperatively. Finally, both best spectacle-corrected visual acuity (BSCVA) (20/50 to 20/25) and UCVA (20/100 to 20/60) significantly improved in all eyes.
Some of these same researchers showed that excimer refractive surgery correction for keratoconus after previous riboflavin/UVA-induced collagen cross-linking may be safe and effective.557 They examined seven eyes of five patients who had moderate to advanced post-LASIK ectasia. Three months after pre-treatment with UVA collagen cross-linking, six eyes underwent topography-guided PRK to aid in visual rehabilitation.
Results showed that UCVA (20/100 to 20/30) and BSCVA (20/50 to 20/22) were improved in all eyes that underwent PRK. Still, the researchers maintain that long-term results are needed to assess the duration of the stiffening effect and long-term side effects, if any.
However, researchers in Mexico revealed that post-PRK ectasia is also possible.1313 They examined a 35-year-old healthy man, who underwent bilateral PRK three months prior and presented with post-PRK ectasia, even though he had no prior risk factors. After reviewing this patients family history, however, the researchers found he had a sister who had clinical and topographic keratoconus.
So, before referring a patient for PRK, be sure to obtain an accurate history of the patients family, as another family member may have ametropic errors.
GP Lenses and LASIK
Prior gas permeable contact lens wear is the greatest risk factor for LASIK retreatment, say researchers in California.560
I believe these findings reveal that a GP lens changes the corneas shape. After undergoing LASIK, these patients no longer wear these lenses, so their eye slowly goes back to its original shape. We must educate GP lens-wearing patients of this finding, so that they will not be surprised if they undergo LASIK and then require a retreatment.
PTK for Erosions
RCES patients treated with PTK did not have recurrences, and side effects as a result of the procedure were minimal, say researchers in Canada.541
If youve exhausted all your RCES treatment options, consider PTK, as this study shows it is very effective long-term.
The Verisyse Intraocular lens (Advanced Medical Optics) may offer hope to patients who experience traumatic cataract, in which the capsular bag has ruptured, say researchers in France.604
Some IOLs may be contraindicated in certain patients, say researchers in Mexico.318 These researchers examined 44 patients (with a mean age of 29) who had high myopia and less than -3.00D of astigmatism and were implanted with the Artisan lens (Ophtec)21 cases were bilateralto determine the lens efficacy and safety.
Results showed that all patients had an average UCVA gain of six or more lines, a BCVA gain of one line, no significant statistical difference in IOP and a decrease in spherical equivalent from -15.00D to -1.50D at one-year follow-up. Also, mean anterior chamber depth was 3.13mm prior to surgery and 3.0mm after surgery. Prior to surgery, endothelial cell density was an average of 2,640. This decreased to 2,471 at six months post-op and to 2,227 at one-year post-op.
While the Artisan lens is an effective method of correcting high myopia, be sure to evaluate your cataract patients endothelium prior to recommending this lens, as endothelial cell density decreased significantly after this lens was implanted.
Imagine this: A 60-year-old male presents with a cataract in his left eye. He is an avid golfer, and his occupation requires him to drive at night. A conventional spherical IOL will provide him with good vision, but you also want to ensure that he has no contrast sensitivity or problems with halos and night vision. What should you recommend? An aspheric IOL, according to researchers in France.322
The researchers studied 20 patients randomized into two equal groups. One group received a prolate aspheric lens, and the second group received a spherical lens. The aspheric IOL with a prolate anterior surface resulted in a decrease of spherical aberration and improved contrast sensitivity under mesoptic conditionsreinforcing the findings of previous studies.
Dr. Karpecki is director of research at Moyes Eye Center in Kansas City, Mo., and he is a paid consultant to Bausch & Lomb. He is clinical and education conference advisor for Review of Optometry and writes Reviews Research Review column.
273. Rodriguez AE, Alio JL, Rodriguez-Prats JL. Decrease in goblet cell density following LASIK as a cause of dry eye post surgery.
312. Nguyen C, Titz, P, Bornet C, et al. Long term results with the STAAR Implantable Contact Lens (ICL) for moderate to high myopia. Relation of vaulting and lens opacities.
318. Villanueva G, Velasco R, Baca O, et al. Efficacy and safety of Artisan lens in high myopia.
322. Denoyer A, Majzoub S, Halfon J, et al. Improving quality of vision after cataract surgery with the Tecnis Z9000 IOL: contrast sensitivity, wavefront aberration analysis and daily vision quality.
516. Erie JC, Patel SV, McLauren JW, et al. Corneal nerve morphology and function after bladeless and microkeratome LASIK. A randomized-controlled study.
531. Lazos VP, Dudenhoefer EJ. PRK vs. LASEK: A comparison of corneal haze, postopera-tive pain and visual recovery in 100 eyes with moderate myopia (-4.00D to -8.00D).
536. Barbarino SC, Papakostas AD, Sperber L. Post-LASIK ectasia: stabilization and effective management with riboflavin/ultraviolet A-induced collagen cross-lining.
538. Bricola G, Scotto R, Mete M, et al. Long-term results of photorefractive keratectomy: a 13-year prospective study.
539. Parikh M, Mashouf J. Wavefront-guided spectacle lenses for post-LASIK patients with sub-optimal results.
541. Baryla J, Pan I, Hodge, W. The long-term efficacy of phototherapeutic keratectomy (PTK) on recurrent corneal erosion syndrome (RCES).
557. Wong JJ, Papakostas AD, Kanellopoulos AJ, Sperber LT. Post-LASIK ectasia: PRK following previous stabilization and effective management with riboflavin/ultraviolet A-induced collagen cross-linking.
560. Halfpenny CP, Hwang DG. Rigid gas permeable contact lens use as a risk factor for LASIK retreatment.
565. Pitault G, Sultan G, Leroux les Jardine S, et al. Accuracy of Orbscan II maps in determining the corneal refractive power after myopic laser in situ keratomileusis.
604. Gicquel JJ, Khoa Nguyen JJ, Ellies P, Dighiero PL. Optical quality of the eye with the Verisyse intraocular lens for the correction of aphakia.
1313. Fermon S, Navas A, Navaez A, et al. Ectasia post-photorefractive keratectomy (PRK). Case report.