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At least 91 records · Page 5Linked to original sources
PubMed2003

Successful implementation of a protocol for photorefractive keratectomy in children requiring anesthesia.

PURPOSE: To describe a protocol for treating children with photorefractive keratectomy (PRK) under general anesthesia and to review intraoperative and postoperative complications. SETTING: Institutional academic practice. METHODS: Nine patients between 3 years and 9 years of age were treated with PRK under general anesthesia for anisometropia with unilateral high myopia or high hyperopia and amblyopia of the affected eye. Induction of anesthesia and the surgical procedure were carried out in separate rooms. The laser beam was centered on the entrance pupil, and eye position was monitored throughout the procedure. Specific precautions were taken before and during the procedure to prevent unwanted effects of inhalational anesthetic agents on laser performance. RESULTS: All children did well, with no anesthesia-related or treatment-related complications. CONCLUSIONS: Our protocol for PRK under general anesthesia was effective and efficient in children who were unable to cooperate for the procedure using local anesthesia. It can be adapted for laser in situ keratomileusis and other refractive surgical procedures in children and uncooperative adults.

Amblyopia↗
PubMedDate not supplied

Repeatability and validity of astigmatism measurements.

BACKGROUND: As more patients inquire about refractive surgical procedures, the measurement of astigmatism prior to surgery becomes more important in assessing refractive outcome. Knowledge of the repeatability of the astigmatism measurement allows one to distinguish a true change in cylinder power from measurement error. METHODS: Forty adults with structurally normal eyes and refractive errors were evaluated for the repeatability of astigmatic refractive error measures. Noncycloplegic and cycloplegic measurements of refractive astigmatism were made by retinoscopy, subjective refraction, and autorefraction. All measures were made at 2 visits within 2 weeks by the same examiner. Difference versus mean plots and the 95% limits of agreement of each technique determined the repeatability of a measurement and the agreement between the methods of measurement. RESULTS: The most reliable measure of astigmatic refractive error was cycloplegic autorefraction, with 95% limits of agreement of +/- 0.28 D, followed by noncycloplegic autorefraction (+/- 0.35 D) and cycloplegic subjective refraction (+/- 0.44 D). Noncycloplegic retinoscopy was the least reliable astigmatic refractive error measure, with interoccasion 95% limits of agreement of +/- 1.02 D. The most repeatable measurement of cylinder axis was cycloplegic autorefraction; none of the measurements differed by 10 degrees or more. The least repeatable measurement was noncycloplegic retinoscopy; 40% of the measurements differed by 10 degrees or more. CONCLUSION: For studies seeking to measure changes in astigmatism in normal eyes, cycloplegic autorefraction is the method of choice.

Adult↗
PubMed2001

Wavefront technology in ophthalmology.

Wavefront sensing is an emerging technology that can measure irregular astigmatism as a higher-order wavefront aberration. The application of wavefront sensing in ophthalmology might enable the non-invasive observation of living retinal cone cells; the measurement of detailed visual function of the central nervous system by eliminating higher-order aberrations during examinations by adaptive optics; the correction of irregular astigmatism; and the prevention of iatrogenic irregular astigmatism induced by conventional refractive surgical procedures. In addition, it will be theoretically possible to obtain supernormal vision by wavefront-guided refractive surgery.

Astigmatism↗
PubMedDate not supplied

Comparison of two microkeratome systems.

BACKGROUND: Microkeratomes are currently used for keratomiluesis in situ (automated lamellar keratoplasty) for myopia and hyperopia and for laser in situ keratomileusis (LASIK). Visual and refractive complications have been reported with these refractive surgical procedures. We compared two microkeratomes in their ability to resect corneal lamellae to gain insight into possible mechanism(s) of refractive and visual complications following lamellar refractive procedures. METHODS: Using an eyebank eye model, we performed automated lamellar keratoplasty to theoretically correct 10.00 diopters (D) of myopia using the Automated Corneal Shaper, manufactured by Chiron, Inc. and the MicroPrecision microkeratome, manufactured by Eye Technology, Inc. Diameters before (wet) and after fixation, thicknesses of excised tissue, and scanning electron microscopy were measured in a masked evaluation to compare instruments. Ultrasonic corneal pachymetry and a mechanical tissue compression gauge were also used to assess thickness of excised tissue. RESULTS: The Chiron automated corneal shaper created blade chatter marks at the edges of all excisions, smaller than anticipated excision diameters, and a wide range of tissue thicknesses. In contrast, the MicroPrecision microkeratome created smoother resections of all tissues without creating blade marks; tissue diameters and thicknesses were closer to the intended dimensions compared to the Chiron automated corneal shaper. CONCLUSION: Different microkeratomes create different morphologic features as they excise corneal tissue. Differences in instrument design, mechanics of the tissue excision and blade oscillation, and instrument traverse combined with surgical skill influence the configuration of lamellar keratotomies.

Aged↗
PubMed2003

Intrastromal refractive surgery with ultrashort laser pulses: in vivo study on the rabbit eye.

BACKGROUND: Femtosecond (fs) laser pulses may offer new possibilities in the field of refractive surgery, especially when using the laser as a microkeratome. By induction of nonlinear absorption processes the laser can be used to perform intrastromal cuts. The conventional microkeratome, associated with numerous potential side effects, can possibly be replaced. Furthermore, refractive lenticules can be prepared within the stroma and removed in a single-step operation. METHODS: In 10 rabbits, cuts were made to create both a lamellar flap and an intrastromal refractive lenticule. The flap was lifted, the lenticule was extracted and, finally, the flap was repositioned (intrastromal laser keratomileusis, ILK). The corneal samples were collected up to 120 days after treatment and processed for histopathological analysis. RESULTS: All flaps could be opened and prepared lenticules could be extracted in one piece by the surgeon. The treated corneas developed a mild wound healing reaction, comparable to that known from excimer laser in situ keratomileusis (LASIK) studies. The wound healing was restricted to the flap-stroma interface, most pronounced at the periphery of the flaps. CONCLUSIONS: The use of the fs-laser offers new possibilities in preparation of corneal flaps, possibly providing advantages over conventional microkeratomes. Furthermore, the fs-laser has the potential to create intrastromal refractive lenticules for complete refractive procedures (ILK).

Animals↗
PubMed1997

Anatomically accurate, finite model eye for optical modeling.

There is a need for a schematic eye that models vision accurately under various conditions such as refractive surgical procedures, contact lens and spectacle wear, and near vision. Here we propose a new model eye close to anatomical, biometric, and optical realities. This is a finite model with four aspheric refracting surfaces and a gradient-index lens. It has an equivalent power of 60.35 D and an axial length of 23.95 mm. The new model eye provides spherical aberration values within the limits of empirical results and predicts chromatic aberration for wavelengths between 380 and 750 nm. It provides a model for calculating optical transfer functions and predicting optical performance of the eye.

Biometry↗
PubMed1984

Refractive keratoplasty. Keratophakia in a nonhuman primate.

We performed 11 keratophakia procedures in a baboon (Papio cynocephalus) model using the same instruments and techniques that are presently clinically employed. We requested 10 diopters of correction in nine cases and 14 D in two cases. We were able to achieve a mean (+/- SD) keratometric steepening correction of 5.8 +/- 1.5 D using fresh and 9.3 +/- 5.0 D using prefrozen donor corneas. The overall change was 8.0 +/- 4.3 D. Morphologic results and corneal clarity were consistent with the excellent clinical results. The keratophakia lenticles were sparsely repopulated with keratocytes up to six months following surgery, but at 12 months, partial keratocyte repopulation of one lenticle did occur. We recommend that the baboon model be used for evaluation of all lamellar refractive surgical procedures.

Animals↗
PubMedDate not supplied

Excimer laser photorefractive keratectomy for hyperopia.

BACKGROUND: Excimer laser photorefractive keratectomy has generated considerable interest as a technique for correcting myopia. In this study, the excimer laser was used to correct hyperopia. METHODS: A prospective clinical study based on the results of photorefractive keratectomy in 23 consecutive hyperopic eyes (one eye per patient) is presented. The excimer laser used in this study was a MEL 60 (Aesculap-Meditec); this laser emits 193-nanometer laser light. A 1-year follow-up study of two groups of eyes was performed. All patients were followed for 12 months. The first group comprised 15 hyperopic eyes with preoperative refraction between +2.0 and +7.5 diopters (mean spherical equivalent +4.7 +/- 1.6 D). The second group comprised eight aphakic eyes with preoperative refraction between +11.0 and +16.0 D (mean spherical equivalent +13.1 +/- 2.0 D). RESULTS: In group 1, 12 eyes (80%) were within +/- 1.0 D of the intended correction (baseline, +2.0 to +7.5 D) after 1 year. In group II, only three of the eight aphakic eyes (37%) were within +/- 1.0 D of the intended final refraction (baseline, +11.0 to +16.0 D). The stability of refraction in group I was better than in group II. At 12 months, best corrected visual acuity was unchanged in 14 eyes of group I. One eye had lost two lines. In group II, best corrected visual acuity was unchanged in six eyes after 12 months. In two eyes, best spectacle-corrected visual acuity was lower than the preoperative value, because of decentration of the ablation zone. After 1 year, 80% of the eyes in group I and 25% of those in group II had a visual acuity of 20/40 or better. CONCLUSION: Photorefractive keratectomy is an efficient and relatively safe procedure for correcting hyperopia up to +7.5 D. The predictability is good. Results of photorefractive keratectomy to correct highly hyperopic (aphakic) eyes are not as encouraging. Three patients in this study lost one to three lines of best spectacle-corrected visual acuity due to decentration of the clear zone. Two of the patients belonged to group II. Therefore, we do not recommend photorefractive keratectomy in highly hyperopic eyes, especially if they are aphakic, because even slight decentration may lead to loss of best corrected visual acuity. As in other refractive surgical procedures, great care must be taken to improve the centration of the clear zone.

Adult↗
PubMed1994

Screening for corneal topographic abnormalities before refractive surgery.

PURPOSE: The purpose of this prospective study is to evaluate the corneal topography of patients who sought an opinion regarding refractive surgery for the correction of myopia. METHODS: Both eyes of 53 patients were evaluated with a topographic modeling system. Forty-two patients wore contact lenses (84 eyes: 36 rigid contact lenses and 48 soft contact lenses). Ten patients (20 eyes) wore glasses alone and one patient (2 eyes) wore neither glasses nor contact lenses for correction of myopia. RESULTS: Thirty-five (33%) of 106 eyes were found to have abnormal corneal topography. Of the 42 patients (84 eyes) who wore contact lenses, 32 eyes (38%) had irregular astigmatism, loss of radial symmetry, or absence of the normal progressive flattening from the center to the periphery of the cornea, consistent with contact lens-induced corneal warpage. Alterations were more frequent and severe in rigid contact lens wearers. Three patients (5.7%) received a diagnosis of definite keratoconus, a higher incidence than has been reported in the general population. Topographic abnormalities in most, if not all, of the eyes would not have been detected by visual inspection of the photokeratoscopic images alone. CONCLUSIONS: Appropriate preoperative detection and management of corneal topographic abnormalities are essential steps in every refractive surgical procedure. The overall efficacy and safety of procedures such as radial keratotomy and photorefractive keratectomy likely will be improved once the unpredictable variables of contact lens-induced warpage and occult ectatic disease are eliminated by topographic screening before surgery. Patients with keratoconus may be over-represented in the refractive surgery population due to self-selection.

Contact Lenses↗
PubMed1988

Prospective evaluation of radial keratotomy. Photokeratoscope corneal topography.

Preoperative and postoperative corneascope photographs of 368 myopic patients undergoing radial keratotomy in the Prospective Evaluation of Radial Keratotomy (PERK) study were optically scanned and digitized. A high-resolution scanning system was developed in order to quantify the preoperative and postoperative corneal shape accurately. Careful analysis of the 72 data points in the nine representative rings demonstrated that corneal topography is best represented by radius of curvature from the center to the periphery. The normal myopic cornea flattens approximately +0.28 mm from the center to the periphery, demonstrating the cornea's aspheric nature. More highly myopic patients in the PERK population (-4.50 to -8.00 diopters [D]) demonstrated corneas that are 0.08 to 0.10 mm steeper than the less myopic population (-2.00 to -3.12 D). Optical zone, patient age, and gender are all correlated to changes in corneal topography after radial keratotomy. In more myopic populations, men have corneas which are flatter than those of women by 0.09 to 0.11 mm in all rings represented on corneoscopy. Highly myopic males also experience more corneal flattening after 3.0-mm optical zone radial keratotomy. Regardless of the optical zone used in radial keratotomy, the resulting corneal topography flattens in all rings. However, the ratio of millimeters of radius of curvature change to diopters of correction is consistent for each ring. The dioptric change observed after radial keratotomy corresponds closely with the millimeters of flattening at the respective rings being examined. The central rings flatten 0.166-mm radius of curvature per diopter of refractive alteration obtained. The largest degree of corneal flattening occurs centrally, 0.72 mm, in the more highly myopic patients who underwent 3-mm optical zone radial keratotomy. The use of smaller optical zones in radial keratotomy produces larger changes in the radius of curvature and, consequently, in the amount of refraction than when larger optical zones are used. When compared with younger patients, older patients with 3.0, 3.5, and 4.0 optical zone radial keratotomies experience more central and peripheral corneal flattening. This study of the corneal topography of the myopic population demonstrates that the refractive change resulting from radial keratotomy is related to alterations in corneal topography. The use of similar modifications of the corneal surface may be effective for newer refractive surgical procedures.

Adult↗
PubMed2005

The effect of laser refractive surgery on the on-field performance of professional baseball players.

BACKGROUND: The aim of this study was to determine the effect of laser refractive surgery on the offensive performance of professional baseball players. METHODS: Extensive search of the public media was conducted to determine which major league baseball players had undergone laser refractive surgery and when the procedure was performed. Baseball performance data were then used to determine presurgery and postsurgery baseball performance averages. A total of 17 position players were identified; however, 5 of these players were not considered in the analysis owing to insufficient playing experience either before or after the laser procedure. RESULTS: No statistically significant or practically significant difference was found between the presurgery and postsurgery means on either on-base percentage (P = 0.31), batting average (P = 0.39), slugging percentage (P = 0.66) or on-base plus slugging (OPS; P = 0.997) of major league baseball players. CONCLUSIONS: These preliminary findings suggest that professional baseball players should not expect a laser refractive surgical procedure to significantly improve their offensive baseball performance, despite the elimination of glasses or contact lens wear.

Baseball↗
PubMed2004

The effects of LASIK on the ocular surface.

Laser in situ keratomileusis (LASIK) can affect corneal sensation, aqueous tear production, wound healing, and the incidence of corneal erosions. Virtually all patients experience dry eye at least transiently after LASIK. Because intact corneal sensation drives tear production, denervation associated with the LASIK procedure is the most significant cause of post-LASIK dry eye. To prevent symptomatic postoperative dry eye, it is crucial to identify and treat pre-existing dry eye before surgery. This review addresses the pathophysiology and management of dry eye, as well as the relationship between LASIK and corneal erosions, and suggests intra- and post-operative management techniques to minimize complications and maximize the stability of the ocular surface. Contraindications to LASIK and alternative refractive surgical procedures are discussed.

Journal Article↗
PubMed2000

[Current status of refractive surgery].

RATIONALE: An attempt is made to review the different surgical procedures for the treatment of the ocular refraction defects and their organs. Special emphasis is placed on the advantages and disadvantages of them, their principal indications and present situation in the surgeon's strategy when solving the problems which, in practice, are caused by these defects, as well as the possibilities that are being tested to solve the problems that presently have not satisfactory response. METHODOLOGY: In addition to analyzing the bibliography, the procedures used by the author and his or her opinion on them, an attempt is made to group them based on the objective on which the intervention is centered to obtain the result desired. COMMENTARY: Both the accuracy of the procedures as well as the complications that are presently derived from this surgery are discussed. Reasonable limits of each procedures, the reasons that make it obligatory to discontinue some of them and the problems that must be solved in the future to up-date each one of the techniques presently in use are commented on.

Humans↗
PubMed1994

Management of astigmatic keratotomy overcorrections by corneal sutures.

Astigmatic overcorrection is a significant possible complication of refractive surgical procedures such as radial keratotomy, astigmatic keratotomy, and combined radial and astigmatic keratotomy. We present the results of a study in which astigmatic overcorrection was reversed by suturing the astigmatic incisions. Videokeratoscopic studies of 15 patients showed that this technique induced a wide range of central corneal steepness, thus correcting variable amounts of astigmatic overcorrection. Mean preoperative uncorrected visual acuity was 20/100 while the mean postoperative uncorrected visual acuity was 20/40. One year after surgery, 13 patients had gained two or more Snellen lines of uncorrected vision; the remaining two had no improvement. Refraction was stable in all cases. No significant complications were observed at one year postoperatively. Corneal sutures may be used safely to manage overcorrections after astigmatic keratotomy or combined radial and astigmatic keratotomy with satisfactory results, even though the predictive value of the technique is limited.

Adult↗
PubMedDate not supplied

Energy fluctuations in an excimer laser during photorefractive keratectomy.

We performed an experiment with the MEL 60 excimer laser (Aesculap Meditec Technology) to demonstrate the variations of energy of the laser beam that could happen during a refractive surgical procedure. In order to quantify such variations, we measured the whitening of a photographic paper after a series of exposures to the laser beam with the X rite 400 B/W reflection densitometer. The energy fluctuations noted between two series of pulses averaged 11.02% (minimum 0; maximum 46). These fluctuations tended to decrease progressively during the procedure. The energy of the laser beam decreased with time. At the end of the experiment, the total loss of energy was 45.16%. These results suggest that clinically meaningful energy variations could happen during the photorefractive keratectomy and reduce refractive predictability.

Cornea↗
PubMedDate not supplied

Complications of radial and transverse keratotomy.

Radial keratotomy for myopia and transverse keratotomy for astigmatism are the most commonly performed refractive surgical procedures. A decade of experience with modern techniques has produced considerable literature on the complications of keratotomy. Vision-threatening complications (bacterial keratitis, traumatic rupture of the globe through weakened keratotomy scars, endophthalmitis, cataract formation from surgical trauma to the lens) are quite rare, occurring in less than 1% of eyes in published series. The most common side effects affect most patients in the first few months after surgery: pain for 24 to 48 hours, transient glare and light sensitivity, and fluctuating visual acuity. The most common persistent complications are overcorrection and undercorrection. Persistent irregular astigmatism occurs in almost all cases in the region of the incision scars, but it is rarely severe enough to reduce spectacle acuity. Most individuals have mild glare, but this is rarely disabling. Diurnal variation of refraction in visual acuity occurs commonly, but the magnitude of the fluctuation is seldom enough to require multiple pairs of spectacles. Longterm refractive stability occurs in approximately half of eyes by six months, but approximately one in four eyes will experience continued change over six months to four years. Complications, such as scarring from intersecting keratotomy incisions, irregular astigmatism resulting from multiple reoperations, and overcorrections with the attendant early onset of symptomatic presbyopia are becoming much less frequent.

Contact Lenses↗
PubMed1997

[Biomechanical study of corneal stability after photorefractive keratectomy].

BACKGROUND: Photorefraktive keratectomy (PRK) is the most frequent refractive surgical procedure worldwide. The central corneal thickness is reduced due to removal of the anterior stroma, including Bowman's layer, with a laser beam. This procedure results in considerable alterations of the corneal structure. What does this mean for the mechanical properties of the cornea? METHODS: Intraocular pressure was increased via a 180 degrees tilt. Before and during this procedure, corneal topography was measured by photokeratoscopy. We examined 26 patients after PRK and 25 controls who had not undergone any surgical procedure. RESULTS: The corneal center flattened by 0.038 +/- 0.05 dpt (P > 0.05) in the PRK patients and by 0.187 +/- 0.045 dpt (P < 0.05) in the control group. PRK patients within 1 year after operation showed a minimal central corneal steepening, whereas PRK patients after more than 1 year showed a reaction similar to that in normal corneas (P < 0.05). CONCLUSION: Corneal stability is altered after PRK. After 1 year corneal stability seems to normalize due to stromal remodelling.

Adult↗