eMedicine Specialties > Ophthalmology > Refractive Disorders

Astigmatism, PRK: Follow-up

Author: Manolette R Roque, MD, MBA, President and CEO, Service Chief of Ocular Immunology and Uveitis, Refractive Surgery, EYE REPUBLIC Ophthalmology Clinic; General Manager, Ophthalmic Consultants Philippines; Section Chief of Ocular Immunology and Uveitis, Department of Ophthalmology, Asian Hospital and Medical Center; Section Chief of Ocular Immunology and Uveitis, Department of Ophthalmology, St. Luke's Medical Center Global City; Senior Eye Surgeon, The LASIK Surgery Clinic
Coauthor(s): Ruben Limbonsiong, MD, Chief of Service, Refractive Surgery Service and Vision Laser Center, St. Luke's Medical Center; Program Director, Clinical Assistant Professor, Department of Ophthalmology, University of the Philippines at Manila; Barbara L Roque, MD, Full Partner, Ophthalmic Consultants Philippines Co, Chief of Service, Pediatric Ophthalmology and Strabismus, Consulting Staff, Orbit and Eye Plastics, Eye Republic Ophthalmology Clinic; Roberto Pineda II, MD,, Scholar, The Academy at Harvard Medical School; Director, Refractive Surgery Service, Massachusetts Eye and Ear Infirmary; Assistant Professor of Ophthalmology, Harvard Medical School
Contributor Information and Disclosures

Updated: Sep 30, 2009

Outcome and Prognosis

PARK in the context of application under a LASIK flap and as a solitary procedure under an epithelial LASEK flap is gaining popularity among keratorefractive surgeons.50 Numerous studies have been performed to determine the efficacy and safety of PARK.51,52,53 Results show that the reduction in total cylinder is 15-95%. Uncorrected visual acuity of greater than or equal to 20/40 is 55-90%. Two or more lines of best-corrected visual acuity were lost in 0-28% of eyes. Postoperative results and uncorrected visual acuity of PARK versus PRK are similar.

Kremer observed 28 eyes (mild astigmatism) for 12 months and noted that the preoperative cylinder of –0.84 +/-0.22 D decreased to a postoperative cylinder of –0.40 +/-0.33 D. Uncorrected visual acuity of greater than 20/40 occurred in 89% of eyes. In 44 eyes (moderate astigmatism), the preoperative cylinder of –1.77 +/-0.42 D decreased to a postoperative cylinder of –0.54 +/-0.48 D. Visual acuity of greater than 20/40 was evident in 82% of eyes. In 20 eyes (high astigmatism), the preoperative cylinder of –3.54 +/-0.64 D decreased to a postoperative cylinder of –0.69 +/-0.32 D. Uncorrected visual acuity of greater than 20/40 occurred in 90% of eyes.54

Using a whole-field technique, they found PARK to be less effective in reducing the preoperative astigmatism in individuals with low levels (<1 D) of cylinder (48%) in comparison with individuals with moderate levels (1.25 to 2.50 D) of cylinder (68%) and high levels (2.75 to 5 D) of cylinder (81%). They postulated that the effect of treating lower levels of astigmatism might be lost in the overall healing process of the spherical part of the ablation. The efficacy of PARK could vary according to the amount of preoperative astigmatism, and, as such, the dictum of "greater the amount of preoperative astigmatism, the greater the percentage of correction" was coined.

Kremer and associates also found that the residual refractive cylindrical axis after PARK did not change significantly from the cylindrical axis preoperatively, with a range of 5-15°.

Alio observed 46 eyes for 12 months with a preoperative cylinder of –2.50 +/-0.70 D and a postoperative cylinder of –0.50 +/-0.20 D. No patient lost 2 lines of best-corrected visual acuity.41

For 6 months, Kim observed 168 eyes with a preoperative cylinder of 1.51 +/-0.81 D and a postoperative cylinder of 0.67 +/-0.60 D. Uncorrected visual acuity of greater than 20/40 was evident in 91% of eyes.55

Lazzaro conducted a 12-month follow-up study of 7 eyes with a preoperative cylinder of 5.32 D and a postoperative cylinder of 2.79 D.56 Despite results of decreasing the cylinder to nearly half, 2 lines of best-corrected visual acuity were lost in 28% of eyes. They discovered that when PARK was used to correct residual astigmatism present after penetrating keratoplasty using a whole-field technique, an average reduction in the refractive astigmatism of 38% and 48% was achieved. Differences in corneal wound healing in a grafted eye compared with a nongrafted eye were believed to have resulted in the reduced efficacy of PARK in these cases.

Gallinaro presented a 6-month follow-up study of 72 eyes with a preoperative cylinder of –2.14 +/-1.99 D and a postoperative cylinder of –1.75 +/-1.32 D. Uncorrected visual acuity of greater than 20/40 occurred in 65% of eyes. Two lines of best-corrected visual acuity were lost in 12.5% of patients.57

Taylor also presented a 6-month follow-up study of 65 eyes, with 72% of them achieving an uncorrected visual acuity of greater than 20/40 and 12.5% of them losing 2 lines of best-corrected visual acuity.58,8

Hamberg-Nystrom and coworkers presented a 12-month follow-up study of 113 eyes. They used a whole-field technique and found a smaller reduction in the preoperative astigmatism in individuals with low levels (<2 D) of astigmatism (44%) in comparison with individuals with higher levels (>2 D) of astigmatism (72%).59 Similar to Kremer's results, the efficacy of PARK could vary according to the amount of preoperative astigmatism.

Gomez de Liano also presented a 12-month follow-up study of 53 eyes, with a preoperative cylinder of –2.28 +/-1.25 D and a postoperative cylinder of –1.40 +/-0.78 D; of these, 58% of eyes achieved visual acuity of greater than 20/40.60

For 3 months, Cherry observed 34 eyes with a preoperative cylinder of 2.35 D and a postoperative cylinder of 1.22 D.61,62

Also, for 3 months, Hersh observed 10 eyes with a preoperative cylinder of 1.48 D and a postoperative cylinder of 0.86 D, with 74% of them having uncorrected visual acuity of greater than 20/40 and 10% of them losing 2 lines of best-corrected visual acuity. Hersh used an erodible mask and found undercorrection present in the spherical correction after PARK, with no eyes achieving an overcorrection using a mask. Using the erodible mask, the postoperative axis did not rotate more than 10°.63,64

Brancato presented a 6-month follow-up study of 21 eyes with a preoperative cylinder of -2.46 D and a postoperative cylinder of –1.56 D; 60% of eyes achieved an uncorrected visual acuity of greater than 20/40.65

Niles presented a 6-month follow-up study of 25 eyes with a preoperative cylinder of 2.31 D and a postoperative cylinder of 0.69 D, with 76% of eyes achieving uncorrected visual acuity of greater than 20/40 and 8% of them losing 2 lines of best-corrected vision. Niles and associates used an erodible mask and found a greater overcorrection of the spherical component when performing PARK in comparison with PRK. The observed overcorrection presumably arose from increased corneal dehydration as a consequence of longer surgical times for PARK. More difficulty was noted in maintaining patient eye fixation while using the erodible mask.66

Kaskaloglu conducted a 6-month follow-up study of 28 eyes with a preoperative cylinder of –2.53 +/-1.49 D and a postoperative cylinder of –0.16 +/-0.99 D, with 55% of eyes achieving uncorrected visual acuity of greater than 20/40 and 7.1% of them losing 2 lines of best-corrected visual acuity.67

Dausch presented an 18-month follow-up study of 17 eyes with a preoperative cylinder of –2.53 +/-1.32 D and a postoperative cylinder of –0.44 +/-0.67 D; 93% of eyes achieved uncorrected visual acuity of greater than 20/40. The high astigmatism group had a preoperative cylinder of –4.75 +/-1.17 D and a postoperative cylinder of –0.89 +/-0.60 D, with 82% of them achieving uncorrected visual acuity of greater than 20/40. They investigated the use of PARK on patients with mixed and irregular astigmatism by designing a custom asymmetric mask, which was based on computerized video keratography, to perform the asymmetric ablation. Of the 3 patients who were treated, the preoperative cylinders of 5.50 D, 1.25 D, and 7 D were reduced postoperatively to 0 D, 0.50 D, and 1.50 D, respectively.68,69

Future and Controversies

Refractive laser surgery is becoming extremely popular. More and more procedures are performed by keratorefractive specialists and by PRK/LASIK-certified general ophthalmologists. The response of the general population to this procedure is overwhelming yet expected. The relative freedom from the use of glasses and contact lenses is a tempting and irresistible offer.

As a subspecialty in ophthalmology, keratorefractive surgery is one of the more exciting and fastest-growing disciplines in recent years. Being relatively, if not totally, dependent on the precision offered by the technology associated with it, continuous advancements will occur. This marriage of surgical application and technology-driven hardware brings a new frontier in patient care. Aggressive keratorefractive surgeons and newer upgrades of excimer lasers will continue to push the envelope of refractive treatment possibilities and applications.

This advent of cutting-edge research in newer machines and newer technology promises a bright future. Smoother and more precise ablations are to be expected. Real-time topography and wavefront-guided lasers will allow surgeons to perform customized ablations. Many reports are already available on the early generations of wavefront-guided excimer lasers.

In the laboratory and pharmaceutical world, studies are underway to develop a means to control the wound-healing properties of the cornea. Hopefully, the complications that are being observed today will decrease. Newer forms of complications with the latest "tech-savvy" machines are possible. Until the time that a perfect refractive laser surgery procedure is performed consistently, innovations in medical and surgical refractive treatments will continue.

 


More on Astigmatism, PRK

Overview: Astigmatism, PRK
Workup: Astigmatism, PRK
Treatment: Astigmatism, PRK
Follow-up: Astigmatism, PRK
Multimedia: Astigmatism, PRK
References
Further Reading
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Keywords

astigmatism, photorefractive keratectomy, PRK, photoastigmatic refractive keratectomy, PARK, LASEK, laser epithelium keratomileusis, laser subepithelial keratomileusis

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Contributor Information and Disclosures

Author

Manolette R Roque, MD, MBA, President and CEO, Service Chief of Ocular Immunology and Uveitis, Refractive Surgery, EYE REPUBLIC Ophthalmology Clinic; General Manager, Ophthalmic Consultants Philippines; Section Chief of Ocular Immunology and Uveitis, Department of Ophthalmology, Asian Hospital and Medical Center; Section Chief of Ocular Immunology and Uveitis, Department of Ophthalmology, St. Luke's Medical Center Global City; Senior Eye Surgeon, The LASIK Surgery Clinic
Manolette R Roque, MD, MBA is a member of the following medical societies: American Academy of Ophthalmic Executives, American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, American Society of Ophthalmic Administrators, American Uveitis Society, International Ocular Inflammation Society, Philippine Medical Association, Philippine Ocular Inflammation Society, and Philippine Society of Cataract and Refractive Surgery
Disclosure: Nothing to disclose.

Coauthor(s)

Ruben Limbonsiong, MD, Chief of Service, Refractive Surgery Service and Vision Laser Center, St. Luke's Medical Center; Program Director, Clinical Assistant Professor, Department of Ophthalmology, University of the Philippines at Manila
Ruben Limbonsiong, MD is a member of the following medical societies: American Academy of Ophthalmology and American Society of Cataract and Refractive Surgery
Disclosure: Nothing to disclose.

Barbara L Roque, MD, Full Partner, Ophthalmic Consultants Philippines Co, Chief of Service, Pediatric Ophthalmology and Strabismus, Consulting Staff, Orbit and Eye Plastics, Eye Republic Ophthalmology Clinic
Disclosure: Nothing to disclose.

Roberto Pineda II, MD,, Scholar, The Academy at Harvard Medical School; Director, Refractive Surgery Service, Massachusetts Eye and Ear Infirmary; Assistant Professor of Ophthalmology, Harvard Medical School
Roberto Pineda II, MD, is a member of the following medical societies: American Academy of Ophthalmology and American Society of Cataract and Refractive Surgery
Disclosure: Nothing to disclose.

Medical Editor

Daniel S Durrie, MD, Director, Department of Ophthalmology, Division of Refractive Surgery, University of Kansas Medical Center
Daniel S Durrie, MD is a member of the following medical societies: American Academy of Ophthalmology and Association for Research in Vision and Ophthalmology
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Louis E Probst, MD, Medical Director of Refractive Surgery, Chicago, Madison, Milwaukee, and Windsor Centers, TLC the Laser Eye Centers
Louis E Probst, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Cataract and Refractive Surgery, and International Society of Refractive Surgery
Disclosure: Nothing to disclose.

CME Editor

Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri
Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences
Hampton Roy Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, and Pan-American Association of Ophthalmology
Disclosure: Nothing to disclose.

 
 
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