eMedicine Specialties > Ophthalmology > Refractive Disorders

Astigmatism, PRK: Workup

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

Workup

Imaging Studies

  • Corneal topography
    • Corneal topography provides surgeons with effortlessly understood color-coded maps of corneal curvature in addition to quantitative indexes of irregular astigmatism that correlate with potential visual acuity.35,36
    • Modern instrumentation produces a video keratograph, which generally is in the form of a color-coded contour map.
    • Different manufacturers use different methods (eg, Placido, 40 scanned slits, combination Placido and 40 scanned slits, phase modified laser holography, raster stereography).
    • The use of video keratography in preoperative and postoperative evaluations of all refractive surgery patients is valuable.
  • Pachymetry
    • The pachymeter (optical, ultrasonic) is used to measure corneal thickness.
    • Accurate determination of corneal thickness preoperatively allows the surgeon to set the depth of incision to two thirds of the measured result.
    • Orbscan II by Orbtek uses both 40 scan slits and Placido methods to provide anterior and posterior corneal curvature in addition to data on corneal thickness.

Other Tests

  • Wavefront aberrometry
  • Keratometry
  • Placido ring reflections
  • Refraction
    • Manifest
    • Automated
    • Cycloplegic

Histologic Findings

Several authors have performed and reported histologic analysis of treated tissue. The excimer laser ablation of the cornea results in a very smooth ablated surface, no damage to adjacent tissue, and an abrupt transition to the untreated tissue.32 An estimated 0.25 µm of corneal tissue is removed with each pulse of the laser. Furthermore, with electron microscopy, an extremely narrow zone of damage may be demonstrated next to the treated area.

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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References

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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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