Tear Film Function and Corneal Sensation After LASEK for the Correction of Myopia
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Objective To observe the influences of tear film interrupting on corneal surface aberration and ocular aberration.Methods Sixty eyes of thirty patients in myopia were selected by randomly.Tear film interrupt-ing was performed by 0.5% tetracaine hydrochloride in dilated pupil.corneal surface height were acquired to cal-culated corneal surface aberration by ORBSCANIIz system and ocular aberration were examined by Zywave sys-tem.Rusults(1)corneal anterior surface aberration increased(P=0.023);(2) Of ocular aberration,defocus increased(P=0.020),spherical aberration increased(P=0.000),foil-like aberration increased(P=0.000),astigmatism increased(P=0.361) and coma reduce(P=0.267).Conclusion Tear film interrupting destroyed stability and uniform of tear film,leads to corneal surface aberration and ocular aberrations up and to quality of vision down.
Coma (optics)
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Comparative Study of Two Silicone Hydrogel Contact Lenses Used as Bandage Contact Lenses after LASEK
To evaluate two silicone hydrogel contact lens materials as continuous-wear bandage contact lenses after laser-assisted subepithelial keratomileusis (LASEK).The inclusion criteria were myopia of -6.00 diopters (D) or less, astigmatism lower than -1.5 D, bilateral best-corrected visual acuity of 20/20 or better, and candidates for bilateral LASEK. The patients were randomized to be fitted with a Balafilcon A (PureVision) lens in one eye and Galyfilcon A (Acuvue Advance) in the fellow eye. Uncorrected visual acuity, corneal epithelial status, conjunctival and limbal hyperemia, lens movement, contact lens debris, and the responses to a subjective-comfort questionnaire were assessed postoperatively. The parameters were evaluated before and 1 and 5 days after the procedure. A paired Student's t-test and chi-square tests were used when appropriate.We analyzed 44 eyes of 22 consecutive patients who underwent LASEK to correct low-to-moderate myopia. The mean spherical equivalent was -3.25 +/- 2.36 D. There was no difference in conjunctival or limbal hyperemia, lens movement, uncorrected visual acuity, or epithelial healing between the two lenses at any visit. A significant difference was found in lens deposition and discomfort, which were greater with the PureVision lens 5 days postoperatively (p = 0.01 for both comparisons).PureVision and Acuvue Advance contact lenses seem to be useful as continuous wear bandage contact lenses. There is no major clinical difference between the lenses, although patients report greater comfort with Acuvue Advance.
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Objective To investigate the alteration of tear film after LASIK with optical coherence tomography （OCT） and the effect of the operation on tear film and whether OCT can measure the tear film. Methods Tear film were measured in both eyes of 56 patients （112 eyes） before LASIK and at 1 week, 1 month, 3 months after LASIK with several ways including OCT. Results The information given by OCT indicated that tear meniscus height （TMH）, tear meniscus depth （TMD） and tear meniscus area （TMA） had significant differences at 1 week after LASIK （P 〈0.05）. In SchirmerI test, tear secretion was mostly limited at 1 week after LASIK. Fluorescein showed that corneal epithelial defect was the most significant, and the break-up time indicated that tear film stability was the worst at 1 week postoperatively. Conclusions With excellent non-invasiveness and repeatability for measuring the tear film, OCT has the function of determining quantity and would become a clinical measurement method.
Key words:
Optical coherence tomography; Laser in situ keratomileusis; Tear film
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Schirmer test
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Objective: To evaluate the correlation factors for the posterior corneal curvature after myopic LASIK. Methods: The retrospective study of 92 eyes which underwent myopic LASIK was conducted. All LASIK procedures were done using Hansatome® Microkeratome and Tecnolas® 217 excimer laser (B&L, USA). Pre- and post-operative data were collected including refraction, corneal thickness, anterior and posterior corneal curvature measured by Orbscan® Corneal Topography. Statistical analysis was done to evaluate the posterior corneal curvature related to other factors. Results: The posterior corneal curvature after myopic LASIK showed no correlation to anterior corneal curvature (R2 = 0.0036). It also showed low to moderate correlation to amount of myopia treated (R2 = 0.286) and corneal thickness (R2 = 0.37 for measured corneal thickness and R2 0.40 for calculated corneal thickness which is calculated by subtract ablation depth from pre-operative thickness) (all p value < 0.05). Conclusion: The posterior corneal curvature after myopic LASIK can be partially correlated with corneal thickness, anterior corneal curvature and amount of myopia treated.
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[Objective] To discuss the correlation among refractive error, central corneal thickness (CCT), intraocular pressure and corneal curvature. [Methods] Corneal topography, non-contact torrometry, central, corneal thickness and retinophotoscopy were performed on 1250 eyes of 665 patients. We divided 665 patients into three groups according to spherical equivalent refraction, and then statistically analyzd the relationship among refractive error, central corneal thickness, intraocular pressure and corneal curvature. [Results] There was significant difference between high myopia and medium myopia, low myopia in central corneal thickness. There was no significant difference among three groups in intraocular pressure and corneal curvature K1. There was significant difference between high myopia and low myopia in corneal curvature K2. [Conclusion] The central corneal thickness decreases as refractive error increases. There is no correlation between intraoucular pressure and refractive error. Astigmatism is one of the main factors for myopia accelaration.
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The cornea of the human eye is not only refracts the light, but also acts as a convex mirror, which reflects the surroundings. In ophthalmology, an image reflected by its anterior surface is known as the 1st Purkinje image. Characteristics of this image are determined by the properties of the light source and the state of corneal surface. At the present time, there are many methods in ophthalmology to study various properties of the cornea, but most of them either require expensive equipment or are qualitative and not informative. Meanwhile, a “shining” characteristic of the cornea in general is assessed subjectively and is not properly addressed in the ophthalmic literature. Our work was conducted to study the possibility of applying the method of measuring the reflective ability of the cornea to measure the state of its anterior surface. Our study involved men and women aged 18–45 years after laser-assisted in situ keratomilesis (LASIK). With our new method of measuring the corneal reflectance, we investigated patients before surgery, day 1 post-op and after 1 week. Each study case included a measurement of the reflectivity of the cornea after blinking, and after 15 sec. We found that on the day 1 after surgery corneal reflectivity increases, at the same time, 15 sec after blinking it is reduced to normal. This suggests a reduction of the tear film stability and that the patients had some symptoms of corneal syndrome, and as a consequence, increased tear production. One week after surgery, we observed a different picture: the reflective power of the cornea decreased. We consider this to be a sign of corneal nerves damage and decreased tear production.
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Refractive Surgery
Anterior surface
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