Very high-frequency ultrasound corneal analysis identifies anatomic correlates of optical complications of lamellar refractive surgery: Anatomic diagnosis in lamellar surgery1, 2☆
Presented in part as a poster at the American Academy of Ophthalmology annual meeting, San Francisco, California, October 1997.
Received 4 March 1998; accepted 29 September 1998.
Abstract
Objective
To examine the utility of very high-frequency (VHF) ultrasound scanning in determining the anatomic changes and correlates of optical complications in lamellar refractive surgery.
Study Design
Case series.
Participants
Cases analyzed included marked asymmetric astigmatism postautomated lamellar keratoplasty (ALK), image ghosting despite normal videokeratography post-ALK, uncomplicated myopic laser in situ keratomileusis (LASIK), and hyperopic LASIK with regression.
Methods
A prototype VHF ultrasound scanner (50 MHz) was used to obtain sequences of parallel B-scans of the cornea. Digital signal processing techniques were used to measure epithelial, stromal, and flap thickness values in a grid encompassing the central 4 to 5 mm of the cornea, enabling pachymetric mapping of each layer with 2-micron precision.
Main outcome measure
The appearance of the corneas in VHF ultrasound images and thickness values of individual corneal layers determined from VHF ultrasound data.
Results
VHF ultrasound resolved the epithelial, stromal cap, or flap and residual stromal layers 1 year after lamellar surgery. Asymmetric stromal tissue removal was differentiated from stromal cap irregularity. Epithelium acted to compensate for asymmetry of the stromal surface about the visual axis and for localized surface irregularities. Irregularities in the epithelial-stromal interface accounted for image ghosting present despite apparently normal videokeratography. Epithelial thickening was shown after uncomplicated myopic LASIK. Hyperopic LASIK demonstrated relative epithelial thickening localized to the region of ablation accounting for refractive regression.
Conclusions
VHF ultrasound shows promise as a sensitive method of determining the anatomic correlates of optical complications in lamellar refractive surgery.
Manuscript no. 98114.
1Department of Ophthalmology, Weill College of Medicine of Cornell University, New York, New York, USA
2Department of Ophthalmology, University of British Columbia, Vancouver, British Columbia, Canada
3Department of Ophthalmology, Mount Sinai School of Medicine, New York, New York, USA
Address correspondence to Dan Z. Reinstein, MD, MA(Cantab), FRCS(C), Department of Ophthalmology, Weill College of Medicine of Cornell University, 1300 York Ave., Room A851, New York, NY 10021 USA
☆ Supported in part by NIH grant EY01212, the Dyson Foundation, the St. Giles Foundation, and Research to Prevent Blindness, Inc.
1 This work was prepared in partial fulfillment of the requirements for the doctoral thesis, University of Cambridge, for Dr. Reinstein.
2 Certain aspects of the ultrasound technology described in this report are protected by U.S. patents. Patents are administered by the Cornell Research Foundation, Ithaca, New York.
ABSTRACT