Automated superficial lamellar keratectomy augmented by excimer laser masked PTK in the management of severe superficial corneal opacities.
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AIM: To assess superficial lamellar keratectomy augmented by excimer laser smoothening with sodium hyaluronate 0.25%, for the management of superficial corneal opacities. METHODS: Consecutive procedure performed in 14 eyes (13 patients) with an automated microkeratome and excimer laser phototherapeutic keratectomy (PTK) smoothening using sodium hyaluronate 0.25%. MAIN OUTCOME MEASURES: UCVA, BCVA, pachymetry, degree of haze, ray tracing analysis, and complications. Mean follow up was 12 (SD 1.6) months. RESULTS: Mean preoperative haze from previous corneal refractive surgeries was 3.5 (SD 0.5) (11/14 cases). In one case, opacity was caused by ocular trauma and in two by infectious keratitis. The mean preoperative UCVA was 0.7 logMAR (0.2 (SD 0.13) decimal value). BCVA was 0.4 logMAR (0.4 (SD 0.17) decimal value). Mean preoperative corneal pachymetry was 508 (SD 62.5) micro m and mean opacity depth measured by corneal confocal microscopy was 115.2 (SD 49.4) micro m. At 6 months, 71.4% of the eyes with previous corneal refractive surgery showed grade I haze or less. Mean postoperative corneal pachymetry at 6 months was 352.36 (SD 49.05) micro m. CONCLUSIONS: Automated superficial lamellar keratectomy combined with excimer laser PTK smoothening assisted by sodium hyaluronate 0.25% induces a significant improvement of corneal transparency and visual acuity in cases of corneal opacity caused by previous refractive surgery, ocular trauma, and keratitis. (+info)
Compensation for experimentally induced hyperopic anisometropia in adolescent monkeys.
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PURPOSE: Early in life, the optical demand associated with the eye's effective refractive state regulates emmetropization in many species, including primates. However, the potential role of optical demand and/or defocus in the genesis of common refractive errors, like myopia, that normally develop much later in life is not known. The purpose of this study was to determine whether chronic optical defocus alters refractive development in monkeys at ages corresponding to when myopia typically develops in children. METHODS: A hyperopic anisometropia was produced in seven adolescent rhesus monkeys by photorefractive keratectomy (PRK) with an excimer laser. Standard treatment algorithms for correcting myopia in humans were used to selectively flatten the central cornea of one eye thereby producing relative hyperopic refractive errors in the treated eyes. The laser ablation zones were 5.0 mm in diameter and centered on the monkeys' pupils. The laser procedures were performed when the monkeys were 2 to 2.5 years old, which corresponded to onset ages between approximately 8 and 10 human years. The ocular effects of the induced anisometropia were assessed by corneal topography, retinoscopy, and A-scan ultrasonography. RESULTS: By approximately 30 days after PRK, the experimentally induced refractive errors had stabilized and the treated eyes were between +0.75 and +2.25 D more hyperopic than their fellow eyes. Subsequently, over the next 300 to 400 days, six of the seven monkeys showed systematic reductions in the degree of anisometropia. Although some regression in corneal power occurred, the compensating refractive changes were primarily due to relative interocular differences in vitreous chamber growth. CONCLUSIONS: Vision-dependent mechanisms that are sensitive to refractive error are still active in adolescent primates and probably play a role in maintaining stable refractive errors in the two eyes. Consequently, conditions that result in consistent hyperopic defocus could potentially contribute to the development of juvenile onset myopia in children. (+info)
Effects of photorefractive keratectomy-induced defocus on emmetropization of infant rhesus monkeys.
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PURPOSE: To investigate whether photorefractive keratectomy (PRK) performed in infant primates can modify emmetropization and therefore could be used to study mechanisms of refractive error development. METHODS: Six healthy rhesus monkeys ranging in age from 2 to 3 months were randomly divided into two groups (n = 3 each). Anisometropia was induced in each animal by performing PRK on one eye. Hyperopic anisometropia was induced in group A monkeys by flattening the cornea of the right eye, whereas myopic anisometropia was produced in group B monkeys by steepening the cornea of the right eye. Corneal morphology and topography, refractive status, and axial growth were evaluated over a 5-month observation period. RESULTS: All the PRK-treated corneas were re-epithelialized and transparent within 3 days after surgery. Subsequently, all the surgically treated eyes exhibited interocular alterations in axial growth rate that were appropriate to compensate for the PRK-induced anisometropia. Specifically, vitreous chamber elongation rates were faster in the eyes with induced hyperopias than in their fellow eyes (0.63 +/- 0.05 mm vs. 0.40 +/- 0.09 mm), but slower in the eyes with induced myopia than in their fellow eyes (0.58 +/- 0.13 mm vs. 0.73 +/-0.10 mm). In some animals, the recovery from the induced anisometropia was facilitated by interocular differences in the rate of corneal flattening. However, the rates of corneal flattening in the treated eyes and their fellow eyes were not significantly different. CONCLUSIONS: PRK-induced defocus predictably alters axial growth rate and the normal course of emmetropization in developing eyes. Thus, PRK is a useful alternative to current methods used to impose experimental refractive errors in laboratory animals. These results also indicate that refractive surgery performed in childhood may affect normal growth of the eye, resulting in decreased predictability of future refractive status. (+info)
Corneal aberrations before and after small-incision cataract surgery.
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PURPOSE: To study the effect of small-incision cataract surgery on the optical aberrations of the cornea. METHODS: Corneal topography was measured before and after cataract surgery on 70 eyes of 70 patients. Monofocal foldable IOLs were implanted after phacoemulsification through a clear-cornea, 3.5-mm incision without suture. Corneal aberrations, up to the fifth order and 6-mm pupil, were calculated by ray-tracing from the corneal topography. Pre- and postoperative aberrations were compared in each patient and the optical changes induced by surgery investigated. RESULTS: The root mean square of the wave aberration slightly increased on average after surgery (pre, 0.65 +/- 0.46 microm; post, 0.85 +/- 0.63 microm). Most aberration terms were similar, averaged across the 70 patients, before and after surgery (spherical aberration: pre, 0.32 +/- 0.12 microm, and post, 0.34 +/- 0.19 microm; astigmatism: pre, 0.9 +/- 0.8 D, and post, 1.1 +/- 1.0 D; coma: pre, 0.27 +/- 0.18 microm, and post, 0.32 +/- 0.33 microm). However, in each patient, there were changes after surgery in the magnitude (either increasing or decreasing) and/or orientation of aberrations. The mean induced astigmatism was -1.0 +/- 0.9 D at the orientation of the surgical meridian. Induced trefoil also showed a predominant pattern at this direction. Patients with nasal incisions experienced larger changes. CONCLUSIONS: Small-incision surgery does not systematically degrade the optical quality of the anterior corneal surface. However, it introduces changes in some aberrations, especially in nonrotationally symmetric terms such as astigmatism, coma, and trefoil. The incision site plays a main role in the corneal changes after surgery. (+info)
Adaptive optics simulation of intraocular lenses with modified spherical aberration.
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PURPOSE: Adaptive optics systems can be used to investigate the potential visual benefit associated with correcting ocular wave-front aberration. In this study, adaptive optics techniques were used to evaluate the potential advantages and disadvantages associated with intraocular lenses (IOLs) with modified spherical aberration profiles. METHODS: An adaptive optics vision simulator was constructed that allows psychophysical tests to be performed while viewing targets through any desired ocular wave-front profile. With this simulator, the subjective visual performance of four subjects was assessed by letter acuity and contrast sensitivity (at 3, 6, and 15 cyc/deg) for two different values of induced spherical aberration. The values of spherical aberration were chosen to reproduce two conditions: the average amount measured in pseudophakic patients with implanted IOLs having spherical surfaces and the complete correction of the individual's spherical aberration. Visual performance was assessed in both white and green light, at best focus and for defocus of +/-0.5 and +/-1.0 D. RESULTS: There was an average improvement in visual acuity associated with the correction of spherical aberration of 10% and 38% measured in white and green light, respectively. Similarly, average contrast sensitivity measurements improved 32% and 57% in white and green light. When spherical aberration was corrected, visual performance was as good as or better than for the normal spherical aberration case for defocus as large as +/-1 D. CONCLUSIONS: Correcting ocular spherical aberration improves spatial vision in the best-focus position without compromising the subjective tolerance to defocus. (+info)
VSX1 mutational analysis in a series of Italian patients affected by keratoconus: detection of a novel mutation.
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PURPOSE: Keratoconus is a noninflammatory corneal disorder that is clinically and genetically heterogeneous. Mutations in the VSX1 (visual system homeobox 1) gene have been identified for two distinct, inherited corneal dystrophies: posterior polymorphous corneal dystrophy and keratoconus. To evaluate the possible role of the VSX1 gene in a series of Italian patients, 80 keratoconus-affected subjects were screened for mutations. METHODS: The diagnosis of keratoconus was made on the basis of clinical examination and corneal topography. The whole coding region and the exon-intron junctions of the VSX1 gene were analyzed by direct sequencing. RESULTS: Three already-described changes, D144E, G160D, and P247R, and a novel L17P mutation were found in 7 of 80 unrelated patients (8.7%). Two undescribed intronic polymorphisms are also reported. CONCLUSIONS: Mutational analysis of the VSX1 gene in a series of Italian patients revealed one novel mutation and confirmed an important role played by this gene in a significant proportion of patients affected by keratoconus, when it is inherited as an autosomal dominant trait with variable expressivity and incomplete penetrance. (+info)
Near work induced wavefront aberrations in myopia.
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We undertook a detailed analysis of the wavefront aberrations of the eyes of 20 young progressing myopes (mean age=22 years; mean spherical equivalent=-3.84 D, range -1.00 to -7.5 D) and twenty young age matched emmetropes (mean age=23 years; mean spherical equivalent=-0.00 D, range +0.25 to -0.25 D). A wavefront sensor was used to measure the ocular wavefront and a videokeratoscope was used to measure corneal topography. The corneal wavefront was subsequently calculated and the difference between the corneal and ocular wavefront was derived to give the internal wavefront component of the eye. Ocular and corneal wavefronts were measured before and after a 2-h reading task. At the baseline measurements, the myopes showed greater levels of some high order ocular wavefronts than the emmetropes. These differences between the groups became larger following 2 h of reading. Ocular higher order wavefront RMS was (baseline RMS: myopes=0.21 microm, emmetropes=0.16 microm, difference p=0.05 and after 2 h reading was RMS: myopes=0.27 microm, emmetropes=0.17 microm, difference p=0.02). The differences between the groups are primarily due to changes in the corneal wavefront associated with a narrower lid aperture during reading for the myopes. These differences are enhanced by longer periods spent reading, larger pupils and consequently low light levels. We suggest lid induced corneal changes caused by reading in downgaze provides a theoretical framework that could explain the known features of myopia development. The inherited characteristics of facial and lid anatomy would provide a mechanism for a genetic component in the genesis of myopia. (+info)
Dynamic changes in the tear film in dry eyes.
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PURPOSE: To examine the dynamics of the tear film in patients with dry eye by measuring the wavefront aberrations of the anterior surface of the film. METHODS: Anterior surface aberrations for a 7-mm pupil were determined in 13 patients with dry eye at 1-second time intervals, for 15 seconds after a blink. The aberrations were calculated from the elevations provided by corneal topography. All data were decomposed using Zernike polynomials. Total, spherical, and comalike aberrations terms were studied separately. Results were compared with those in normal eyes. Outcome measures included comparison with clinical tear breakup time measurements. RESULTS: The total root mean square (RMS) wavefront aberration in patients with dry eye passed through in a minimum of 2.9 +/- 0.4 seconds after a blink in comparison to the minimum at 6.1 +/- 0.5 seconds in normal patients. In both groups, the minimum in total aberration appeared to be associated with similar changes in comalike aberrations, rather than in spherical aberrations, which increased monotonically with time. The time at which minimum RMS aberration occurred correlated reasonably well with the measured tear breakup times. CONCLUSIONS: Measurements of the dynamic changes in the optical aberrations introduced by the anterior tear film surface give valuable insights into tear film changes and may provide a convenient objective method for the diagnosis of dry eye. (+info)