Home About us Contact
|
Home About us Contact | ||
|
|
||
Refractive Surgery (refractive + surgery)
Selected AbstractsRefractive surgery: lessons to be learnedCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 2 2005Sanjay Mantry FRCS(Ed) No abstract is available for this article. [source] The prospects for super-acuity: limits to visual performance after correction of monochromatic ocular aberrationOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2003W. N. Charman Abstract It has recently been suggested that correction of the monochromatic aberration of the eye could lead to substantial improvements in visual acuity and contrast sensitivity function. After consideration of the best-corrected visual acuity of normal eyes, the optical and neural limits to visual performance are reviewed. It is concluded that, even if current problems with the accuracy of the suggested techniques of aberration correction, through corneal excimer laser ablation or customised contact lenses, can be overcome, changes in monochromatic ocular aberration over time, the continuing presence of chromatic aberration, errors of focus associated with lags and leads in accommodation, and other factors, are likely to result in only minor improvements in the high-contrast acuity performance of most normal eyes being produced by attempted aberration control. Significant gains in contrast sensitivity might, however, be achievable, particularly under mesopic and scotopic conditions when the pupil is large, provided that correct focus can be maintained. In the immediate future, reduction of the high levels of aberration that are currently found in eyes that have undergone refractive surgery and in some abnormal eyes should bring useful benefits. [source] A statistical model of the aberration structure of normal, well-corrected eyesOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2002Larry N. Thibos Abstract A statistical model of the wavefront aberration function of the normal, well-corrected eye was constructed based on normative data from 200 eyes which show that, apart from spherical aberration, the higher-order aberrations of the human eye tend to be randomly distributed about a mean value of zero. The vector of Zernike aberration coefficients describing the aberration function for any individual eye was modelled as a multivariate, Gaussian, random variable with known mean, variance and covariance. The model was verified by analysing the statistical properties of 1000 virtual eyes generated by the model. Potential applications of the model include computer simulation of individual variation in aberration structure, retinal image quality, visual performance, benefit of novel designs of ophthalmic lenses, or outcome of refractive surgery. [source] Some possible longer-term ocular changes following excimer laser refractive surgeryOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 4 2002Laura Oliveira-Soto While the short- and medium-term refractive and acuity results of excimer laser refractive surgery may now be generally satisfactory, the relatively brief history of the procedures involved (around 10 years or less) means that those concerned with eye care must remain vigilant to the possibility of longer-term problems. This paper reviews some relevant studies of potential post-surgical effects, including imperfect corneal healing and recovery of innervation, reduced corneal sensitivity and dry eye problems, changes in corneal rigidity leading to slow refractive change, possibly misleading reductions in measured intraocular pressure, and retinal and vitreous pathology. [source] Visual function of police officers who have undergone refractive surgeryAMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 11 2006Jeffery K. Hovis OD Abstract Introduction The visual acuity and contrast sensitivity of police recruits and officers was evaluated in both normal and dim illumination conditions to determine whether officers who have had refractive surgery have compromised night vision. Methods The control group consisted of 76 officers and recruits who have not had refractive surgery and the refractive surgery group consisted of 22 officers and recruits who had refractive surgery. Visual acuity and contrast sensitivity were measured under both room illumination and dim illumination. The room illumination test series included high contrast acuity, low contrast acuity and Pelli-Robson contrast sensitivity. The dim illumination test series included high contrast acuity, low contrast acuity, Pelli-Robson contrast sensitivity, license plate number acuity (with and without glare) and the Mesotest. Results The general findings were that the refractive surgery group had lower acuity scores on low contrast targets in both room and dim light levels along with a reduction in the Mesotest scores with a glare source compared to the control group. Conclusions Although refractive surgery police recruits and officers had reduced performance on some vision tests, these reductions were small and it is unlikely that their performance on vision related tasks would be compromised, on average. The major concern is the small number of refractive surgery candidates whose results were well outside the range of the non-surgical candidates. Their vision may be unacceptable for policing. Am. J. Ind. Med. 49:885,894, 2006. © 2006 Wiley-Liss, Inc. [source] 3223: Dry eye syndrome and omega-3 fatty acidsACTA OPHTHALMOLOGICA, Issue 2010T KAERCHER Purpose Dry eye disease is characterized by an inflammatory component of the ocular surface. Pathways to modulate inflammation include corticoids and cyclosporine. Omega-3 fatty acids like eicosapentaenoic acid and docosahexaenoic acid represent an alternate pharmacologic way to influence the inflammatory cascade. Methods Clinical studies. Results An epidemiologic study in 32.470 healthy women showed that those with a higher intake of omega-3 fatty acids had a 68% decreased prevalence of dry eye syndrome. Hyposecretory dry eye was tested after intake of omega-3 fatty acids for 45 days. Symptoms, signs and inflammatory markers like HLA-DR improved. Hyperevaporative dry eye improved after a long-term supplementation with omega-3 fatty acids with respect to symptoms, break-up time and meibom score. Patients with refractive surgery (PRK) improved after omega-3 fatty acids intake; this was derived from the OSDI-score, Schirmer I test and tear clearance. In 102 contact-lens wearers the symptoms and signs of dry eye improved after 12 weeks therapy with omega-3 fatty acids. Conclusion Nutricionals with omega-3 fatty acids show evidence-based effects on the inflammatory component of ocular surface disease and tear film disorder. Their beneficial effect was tested for hypovolemic and hyperevaporative dry eye. Patients after refractive surgery and contact lens wearers improved after supplementation, too. In contrast to the available anti-inflammatory therapy the supplementation is apt for a long-term application. [source] 4434: Wavefront guided and custom wavefront refractive surgeryACTA OPHTHALMOLOGICA, Issue 2010B COCHENER [source] 3233: Effectiveness of a new lubricant for dry eye after photoablation using an osmolarity measurementACTA OPHTHALMOLOGICA, Issue 2010B COCHENER Purpose LASIK has been shown to lead to corneal hypoesthesia, which can trigger a decrease in the reflex arc regulating tears secretion. The goal of this study was to evaluate the benefits of a new lubricant after LASIK compared to a classical treatment by measuring tear osmolarity. Methods Twenty patients scheduled to undergo LASIK were enrolled in the study and randomized into two groups. A baseline osmolarity measurement was taken (TearLab Osmolarity System, TearLab Corp) and then randomized into one of two groups. Patients in the first group received two artificial tears (Refresh and Celluvisc, Allergan) following surgery while the 2nd group received a PEG 400 and hylauronic acid (HA) artificial tear (Blink, Abbott Medical Optics) following treatment. These patients were assessed at 1 month postoperative for changes in osmolarity. Results Normal values of osmolarity with Tear Lab range between 275 and 308 mOsm/L; above this, we consider that the eye is dry. The single tear treatment had the same efficiency as our standard two-drop therapy. No side effects were noted in any patients. Most patients found it easier to have only one kind of lubricant instead of a combination of two, which lead to a better observance. The use of the tear osmolarity system provided a quick, reliable test for detecting patient with a risk of postoperative dry eye and for assessing the effectiveness of the therapy. Conclusion The new lubricant, Blink, is another choice in the therapeutic panel for treatment of dry eye disease. It is well tolerated and as efficient as the combination of Refresh and Celluvisc. New osmolarity measurement is an easy, fast and non-invasive well tolerated test for detecting infraclinical dryness especially before refractive surgery. [source] 4134: Central corneal thickness in North AfricaACTA OPHTHALMOLOGICA, Issue 2010S LAZREG Purpose Central corneal thickness (CCT) measure is a critical point before refractive surgery. It is well known that surgery can not be performed under a thickness of 500 microns. Methods Pentacam pachymetry was performed in refractive surgery centers in Algeria , Tunisia and Morroco on 1615 eyes of patients originating from North Africa. Results Most of the patients (70%) were aged from 20 to 35 years old. Thirty eight percent(38%) had a CCT between 450 and 500 microns,40% between 500 and 550 microns. Patients with Keratoconus were excluded from this study Conclusion Publications on this subject being very poor, a study on a larger number of patients has to be conducted in order to confirm the relationship between CCT and ethnic origin. [source] 2354: The range of waveform score of Ocular Response AnalyzerTM (ORA) in healthy subjects: interim analysisACTA OPHTHALMOLOGICA, Issue 2010M VANTOMME Purpose To assess the range of waveform score in IOP measurements with ocular response analyzer (ORA, Reichert) in healthy subjects. Methods Prospective study including both eyes of healthy subjects with no ocular pathology or previous refractive surgery. The IOP measurements with ORA from both eyes were performed. The inclusion criteria of the measurements were solely based on good waveforms by an experienced clinician. The waveform score of three measurements were included for statistical analysis. Other parameters including age, central corneal thickness (CCT) and axis length were also analysed to evaluate possible correlations. Spearman correlation coefficient was used to assess the correlation. Results To date, both eyes of 42 healthy subjects are included (Mean age: 46.6 ± 14.3 yrs, Axial length: 23.7 ± 1.1, CCT: 554 ± 34 µm). The mean waveform scores from the first IOP measurement were 4.2±2.3 and for the 2de and 3th respectively 4.2±1.9 and 4.2±2.1 (not significantly different). The mean waveform score of 252 signals (both eyes and 3 measurements) was 4.2±2.1 and ranged from 0.3 to 9.6. Considering the best signal value per patient, the mean of all best signal values was 5.5±2.0 and it ranged from 1.9 to 9.5. The lowest 10% of all the best signal value was<3. Conclusion The waveform score is a new parameter indicating the reliability of each measurement signal. The best signal value indicates the best measurements of each session (Not the mean of the measurements). To date, our results show that the lower 10% percentile is <3. This could suggest that all the measurements with waveform score lower than 3 should be discarded. [source] Refraction and refractive surgeryACTA OPHTHALMOLOGICA, Issue 2009B COCHENER [source] Corneal hysteresis using the Reichert ocular response analyser: findings pre- and post-LASIK and LASEKACTA OPHTHALMOLOGICA, Issue 2 2008Caitriona Kirwan Abstract. Purpose:, To evaluate and compare corneal hysteresis in patients prior to and following laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK) using the Reichert ocular response analyser (ORA). Methods:, Corneal hysteresis was recorded prior to and 3 months after corneal laser refractive surgery for myopia. Preoperative corneal hysteresis was correlated with age and preoperative central corneal thickness (CCT). Postoperative corneal hysteresis was correlated with postoperative CCT in both the LASIK and LASEK treatment groups. The correlations between postoperative change in hysteresis and stromal ablation depth, percentage of tissue ablated, optical zone and patient age were also examined. Results:, A total of 84 eyes of 84 patients were involved in the study. LASIK was performed in 63 eyes and LASEK in 21. Mean preoperative corneal hysteresis of all eyes was 10.8 ± 1.5 mmHg. Mean age, preoperative CCT, corneal hysteresis and ablation profile were similar in both groups. A statistically significant decrease in hysteresis occurred following LASIK (p < 0.01) and LASEK (p < 0.01) with similar decrements observed in both treatment groups. A moderate correlation was found between postoperative hysteresis and postoperative CCT in LASIK (r = 0.7) and LASEK (r = 0.7) treated eyes. A weak correlation was found between postoperative decrease in hysteresis and the parameters examined. Conclusion:, Corneal hysteresis decreased following LASIK and LASEK. Similar reductions occurred following both procedures, indicating that LASIK involving a thin 120-,m flap did not induce additional biomechanical change. Postoperative reduction in hysteresis did not correlate with the amount or percentage of corneal tissue removed, nor with optical zone or patient age. [source] AER lecture: Some reflections on corneal thicknessACTA OPHTHALMOLOGICA, Issue 2007N EHLERS The corneal thickness as an object for studies was recognized in the renaissance. A value of 1 mm, representing the maximally swollen human cornea, was reported. Optical in vivo measurements were done by Blix in 1880 reporting a thickness of about 0.5 mm, the value that we today know is correct. Blix lived in "the golden age of physiologic optics". His interest was the contribution of the cornea to the optical refraction of the eye, and was thus the distance between the anterior and the posterior surface rather than the thickness of the cornea as such. A biomechanical interest in corneal thickness was initiated by the studies of tonometry, in particular Hans Goldmann's development of applanation tonometry. He predicted correctly that corneal thickness would influence the estimated pressure reading. Another physiological aspect of the cornea is its transparency. Earlier explanations by equal refractive index was revolutionized by the interference theory by David Maurice. Optical transparency required a regular fiber pattern, and thus a stabilized thickness and stromal hydration. This led to extensive interest in the permeability of the limiting layers, in particular the transport of fluid across the endothelium. The physiological concepts required a regulated or stabilized thickness. The thickness as such became interesting. The human cornea is thinner in the center than more peripherally and the central, presumably regulated central thickness (CCT) became a biometric and clinical study object. The exact individual value became of interest. Several optical and later ultrasonic principles were presented. Questions addressed were: Is CCT a life-long, age independent characteristics. Is CCT diagnostic for certain disease conditions (e.g. Macular dystrophy of Groenouw). Is CCT a useful clinical parameter to follow disease processes (e.g. progression in keratoconus or acute changes in graft rejections). Today refractive surgery has revived the interest in biomechanical and optical properties of the cornea. Modern computer technology allows for a description of the "thickness profile" of the entire cornea. This gives us access to an overwhelming amount of data, and reopen many issues of the past. We must realize, however, that what we see is the pendulum swinging back to the problems of the last century. The machinery is smarter but many of the basic questions remain to be solved. [source] | ||||||||||