Laser Corneal Refractive Surgery Research Articles

Intraocular lens calculation adjustment after laser refractive surgery using Scheimpflug imaging

To test a new method of intraocular lens (IOL) calculation after corneal refractive surgery using Scheimpflug imaging (Pentacam HR) and partial coherence interferometry (PCI) (IOLMaster) that does not require historical data; that is, the Schuster/Schanzlin-Thomas-Purcell (SToP) IOL calculator. Shiley Eye Center, San Diego, California, and Walter Reed National Military Medical Center, Bethesda, Maryland, USA. Retrospective data analysis and validation study. Data were retrospectively collected from patient charts including data from Scheimpflug imaging and refractive history. Target refraction was calculated using PCI and the Holladay 1 and SRK/T formulas. Regression analysis was performed to explain the deviation of the target refraction, taking into account the following influencing factors: ratio of posterior-to-anterior corneal radius, axial length (AL), and anterior corneal radius. The regression analysis study included 61 eyes (39 patients) that had laser in situ keratomileusis (57 eyes) or photorefractive keratectomy (4 eyes) and subsequent cataract. Two factors were found that explained the deviation of the target refraction using the Holladay 1 formula; that is, the ratio of the corneal radii and the AL and the ratio of corneal radii for the SRK/T formula. A new IOL adjustment calculator was derived and validated at a second center using 14 eyes (10 patients). The error in IOL calculation for normal eyes after laser refractive treatment was related to the ratio of posterior-to-anterior corneal radius. A formula requiring Scheimpflug data and suggested IOL power only yielded an improved postoperative result for patients with previous corneal laser refractive surgery having cataract surgery. No author has a financial or proprietary interest in any material or method mentioned.

Prevalence of laser vision correction in ophthalmologists who perform refractive surgery

To determine the prevalence of laser corneal refractive surgery (laser vision correction [LVC]) among ophthalmologists who perform these procedures and to assess the willingness of these ophthalmologists to recommend LVC to immediate family members. Online survey with results analyzed at Surgivision Consultants, Inc., Scottsdale, Arizona, USA. Prospective randomized questionnaire study. The 22-question Global Survey on Refractive Surgery in Refractive Surgeons was sent by e-mail to 250 ophthalmologists randomly selected from a database of 2441 ophthalmologists known to have performed LVC at some point in the past decade. Responses were solicited by e-mail, with subsequent telephone reminders to nonresponders. Responses were received from 248 (99.2%) of 250 queried individuals, of which 232 (92.8%) met the protocol criteria of currently working as refractive surgeons. Of the 232 subjects, 161 (69.4%) reported that they had refractive errors potentially amenable to treatment with LVC, not including presbyopia. Of the 161 ophthalmologists with treatable refractive errors, 54 (33.5%) reported they were not candidates for LVC for a variety of reasons and 107 (66.5%) reported they were candidates for LVC. Of the LVC candidates, 62.6% reported that they had an LVC procedure in their own eyes. Of the overall 232 subjects, more than 90% recommend LVC for adult members of their immediate family. Ophthalmologists who perform LVC were significantly more likely than the general population to have LVC in their own eyes. The prevalence of refractive errors was significantly higher among ophthalmologists performing refractive surgery than in the general population. No author has a financial or proprietary interest in any material or method mentioned.

Where are we in laser corneal refractive surgery

Where are we in laser corneal refractive surgery

Measurement of pupil center shift in refractive surgery candidates with caucasian eyes using infrared pupillometry.

To evaluate the effectiveness of the pupil center shift with changes in the state of pupil size and with other ocular variables. Dynamic pupillometry with the Topolyzer Vario (Alcon Laboratories, Inc., Fort Worth, TX) was performed in 248 eyes of 124 patients scheduled for corneal laser refractive surgery. High-resolution images were obtained using the infrared-sensitive camera (incorporated in the videokeratoscope) under mesopic and photopic conditions. Measurements of pupil diameters, distance between the pupil center and keratoscopic axis, and spatial shift of the pupil center were obtained after analysis. The mean distance between the pupil center and the corneal vertex in mesopic and photopic conditions of illumination in myopic eyes was 0.27 ± 0.14 (range: 0.02 to 0.70 mm) and 0.24 ± 0.12 mm (range: 0.06 to 0.65 mm), respectively, whereas it was 0.36 ± 0.15 (range: 0.03 to 0.70 mm) and 0.31 ± 0.16 mm (range: 0.03 to 0.77 mm) in hyperopic eyes, respectively. The mean spatial pupil center shift was significant: 0.11 ± 0.07 mm (range: 0.02 to 0.57 mm) in myopic eyes and 0.12 ± 0.09 mm (range: 0.02 to 0.47 mm) in hyperopic eyes. The pupil center shifted consistently temporally as the pupil dilated. The pupil center shift was not significantly related to sex, age, eye (right or left), or refractive error. The mean distance between the pupil center and the corneal vertex is greater in hyperopic eyes than in myopic eyes, whereas the spatial shift of this pupil center has a temporal direction as the pupil dilates and is constantly small in all groups. However, pupil center shift can be important in a few patients.

Pediatric photorefractive keratectomy for anisometropic amblyopia: a review

Article type Review article Amblyopia is one of the most important reversible eye disorders in children and different treatments are suggested. Early diagnosis and effective treatment in amblyogenic age are important criteria. These critical periods correspond to the period when the child's developing visual system is sensitive to abnormal input caused by stimulus deprivation, strabismus or significant refractive errors. Traditional treatments such as glass wearing, contact lens used with patch therapy have limitations. Laser corneal refractive surgeries introduce an alternative for the treatment of anisometropic amblyopia. Current indications for refractive surgery include anisometropia, bilateral high myopia and accommodative esotropia. Several reports confirmed that with recent development in keratorefractive surgery, it could be a safe method to be used in children. The goal of the permanent surgical treatment is to reduce refractive errors, treat amblyopia and make better the binocular function. Corneal haze is certainly a major concern in children receiving surface ablation, especially in high myopic treatments. However, controversies still exist on whether it could be done in this population or not. This article reviews the available data about refractive surgery for treating anisometropic amblyopia.

Put into perspective clinical advantages and limitations of all-in-one femtosecond laser corneal refractive surgery

The all-in-one femtosecond laser corneal refractive surgery,especially small incision lenticule extraction (SMILE),has gained more and more attention in clinic,because of its small incision,“no flap” and corneal biomechanical stability advantages.However,like any other kind of corneal refractive surgery,the all-in-one femtosecond laser refractive surgery not only exists its clinical advantages,but also has its limitations.It is very important to put into perspective clinical advantages and limitations of all-in-one femtosecond laser corneal refractive surgery. Key words: Femtosecond laser; Corneal refractive surgery; Advantage; Limitation

Analysis of seasonal changes in residual refraction 1-year after corneal laser refractive surgery: a retrospective study

PurposeTo analyze the effect of seasonal changes in residual refraction 1-year after corneal refractive surgery using the SCHWIND AMARIS laser system. Methods5740 consecutive treatments have been retrospectively reviewed. For all eyes, aspheric treatments were planned with the Custom Ablation Manager software and the ablations were performed with the SCHWIND AMARIS system (SCHWIND eye-tech-solutions). Seasonal outcomes were evaluated in terms of residual refraction stratified per treatment month, as well as stratified per year season. Student's T test comparing stratified values with global ones was used for the statistical analysis. ResultsTreatments performed in April, June, August, September, and October showed relative undercorrections of the spherical equivalent (SE) (−0.09D), whereas treatments performed in January, February, and March showed relative overcorrections of the SE (+0.13D). Similarly, treatments performed in spring and summer showed relative undercorrections of the SE (−0.04D), whereas treatments performed in winter showed relative overcorrections of the SE (+0.10D). ConclusionsSeasonal differences in refractive outcomes were observed among a large scale population. The effect of these environmental variables on refractive outcomes warrants further evaluation.

Influence of stromal refractive index and hydration on corneal laser refractive surgery

To evaluate the influence of the stromal refractive index and hydration on postoperative outcomes in eyes that had corneal laser refractive surgery using the Amaris laser system. Augenzentrum Recklinghausen, Recklinghausen, Germany. Comparative case series. At the 6-month follow-up, right eyes were retrospectively analyzed. The effect of the stromal refractive index and hydration on refractive outcomes was assessed using univariate linear and multilinear correlations. Sixty eyes were analyzed. Univariate linear analyses showed that the stromal refractive index and hydration were correlated with the thickness of the preoperative exposed stroma and was statistically different for laser in situ keratomileusis and laser-assisted subepithelial keratectomy treatments. Univariate multilinear analyses showed that the spherical equivalent (SE) was correlated with the attempted SE and stromal refractive index (or hydration). Analyses suggest overcorrections for higher stromal refractive index values and for lower hydration values. The stromal refractive index and hydration affected postoperative outcomes in a subtle, yet significant manner. An adjustment toward greater attempted correction in highly hydrated corneas and less intended correction in low hydrated corneas might help optimize refractive outcomes. Mr. Magnago and Dr. Arba-Mosquera are employees of and Dr. Diego de Ortueta is a consultant to Schwind eye-tech-solutions GmbH & Co. KG. Mr. Rüden has no financial or proprietary interest in any material or method mentioned.

Diagnosis of open-angle glaucoma after myopic excimer laser corneal refractive surgery

Patients with high myopia are at high risk of glaucoma and are difficult to be discovered at early stage in the case of existing glaucoma. Myopic excimer laser corneal refractive surgery changes the structure of the eye, which makes early glaucoma diagnosis more difficult. Furthermore, refractive surgery may aggravate existing condition of glaucoma. To prevent the exacerbation of glaucoma, it is great important to perform the preoperative glaucoma risk assessment. In this paper, we presented the key diagnostic points of glaucoma assessment before and after excimer laser refractive surgery and discussed the postoperative intraocular pressure measurements and its impact on the diagnosis and treatment of glaucoma including characterization of open angle glaucoma and long-term follow up in patients with high myopia.

Intraocular lens prediction accuracy after corneal refractive surgery using K values from 3 devices

To compare results of intraocular lens (IOL) power calculation methods using different keratometry (K) values after myopic refractive surgery. Seoul St. Mary's Hospital, Seoul, South Korea. Evaluation of diagnostic test or technology. The IOL power of patients who had cataract surgery after refractive surgery was calculated using the SRK/T formula with true net power (TNP) and the equivalent K using the Pentacam Scheimpflug system. The simulated K, 2.0 mm zone of total mean power (TMP 2.0 mm) maps, and 4.0 mm zone of total optical power (TOP 4.0 mm) maps were calculated using the Orbscan II scanning-slit topographer and keratometer of the IOLMaster partial coherence interferometer (PCI). The IOL power was also calculated with the Haigis-L method with the corneal radius using the PCI system. The PCI axial length was used with all methods. The prediction error and absolute prediction error measured with the Haigis-L, TNP, TMP 2.0 mm, and TOP 4.0 mm were significantly lower than the equivalent K, simulated K, and PCI K (P<.05). The percentages of correct refraction predictions within ± 0.50 diopter (D), ± 1.00 D, and ± 2.00 D in the Haigis-L method were the highest (64.5%, 80.6%, and 100%, respectively) of all methods. The Haigis-L using corneal radius with the PCI measurement was the most predictable method for IOL calculation after corneal refractive laser surgery in patients without a clinical history. The TMP 2.0 mm in the scanning-slit topographer and the TNP in the Scheimpflug system may also be relatively predictable keratometric values for IOL calculation.

Influence of topical Iotemax on intraocular pressure following excimer laser corneal refractive surgery

Background Excimer laser corneal refractive surgery is widely used because it reduces the dependency of refractive error eye to glasses.However,the adverse effects of anti-inflammatory drugs is a problem after operation.Lotemax eyedrops is a kind of steroidal anti-inflammatory drug,with a good effect on the operative eye.But its influence on intraocular pressure(IOP) after long-term topical administration is less studied.Objective This study was to investigate the influence of lotemax eyedrops on IOP after long-term topical administration in myopic eyes received excimer laser corneal refractive surgery.Methods An one-month retrospective case serial study was adopted.The case history data of 1552 eyes from 1552 Patients who received excimer laser corneal refractive surgery were collected in Tangshan Eye Hospital from 2011 January to 2012 January,including 321 eyes with laser in situ keratomileusis(LASIK),608 eyes with sub-Bowman keratomileusis (SBK) and 623 eyes with femtosecond laser for flap excimer laser in situ keratomileusis(FS-LASIK).Lotemax eyedrops was topically administered after operation 4 times per day initial and then decreased 1 time weekly for 1 month.IOP was measured in before,1 week,2 weeks,3 weeks,4 weeks after operation with non-contact tonometer.The increasing range of IOP was divided into ＜5 mmHg,5-15 mmHg and ＞ 15 mmHg after operation.Optical head parameters were measured by Heidelberg retina tomography when IOP increasing after operation.Results Within 1 month,elevated IOP was found in 47 of 1552 eyes after administration of lotemax eyedrops,including 3.12％ (10/321) in the LASIK group,3.29％ (20/608) in the SBK group and 2.73％ (17/623) in the FS-LASIK group,without significant difference among them(x2 =1.95,P＞0.05).The IOP elevated 1 week after operation and remained normal after that till drug withdrawal in all eyes.There were no significant differences in the disk area (1.65 ±0.44) mm2 vs.(1.66 ±0.44) mm2,disk volume (0.40 ±0.09)mm3 vs.(0.39±0.08) mm3 and mean nerve fiber layer thickness (0.28 ± 0.08) mm vs.(0.29 ± 0.07) mm in IOP elevation duration compared with 1 month after IOP recovery(t =0.34,0.81,0.48,P＞0.05).Conclusions Topical administration of 0.5％ lotemax eyedrops after excimer laser corneal refractive surgery leads to reversible high IOP.It is very important to monitor the IOP during use of the drug. Key words: Lotemax eyedrops; Excimer laser corneal refractive surgery/ laser in situ keratomileusis, Sub-Bowman keratomileusis, Femtosecond laser for flap excimer laser in situ keratomileusis; Intraocular pressure

Screening for Ectasia Risk: What Are We Screening For and How Should We Screen For It?

ow should we screen our patients for postoperative ectasia risk prior to excimer laser corneal refractive surgery, or laser vision correction, in 2013? This has been debated in the literature1-4 and remains a “hot topic” at most meeting venues. The challenge we face as refractive surgeons in daily practice is to most accurately identify individuals who have increased susceptibility for developing biomechanical failure (progressive ectasia), without excluding candidates who may safely benefi t from laser vision correction procedures. In screening, sensitivity (the ability to detect disease) and specifi city (the ability to confi rm absence of disease) are the most basic aspects to evaluate the effi cacy of diagnostic tests. In studies that aim to evaluate screening ability of a test, it is critical to use the appropriate study populations; this may include individuals who have developed a specifi c complication (ectasia after LASIK) or patients who are at known high risk to develop the complication. The fi rst population is easy to identify but diffi cult to fi nd when studying rare complications; the second population is diffi cult to fi nd because, by defi nition, suboptimal strategies for identifying those individuals exist. A reasonable substitute for the “at-risk” group is a population with subclinical or very mild disease, because these are closest to the individuals we want to identify. Patients with disease that is easily identifi ed by other testing are only helpful to establish a basic “proof of concept” that a new test might be able to identify the target population. Among eyes known to be susceptible for ectasia progression are those with relatively normal corneal topography from patients with clinical keratoconus detected in their fellow eyes. Such cases have been designated as “forme fruste keratoconus” (FFKC) by Klyce5 and others. Other reasonable alternatives are cases with progressive ectasia after laser vision correction with no identifi able agreed-upon risk factors.6 The role of Placido-disk based corneal topography and central corneal thickness in screening have been well recognized,7 but shortcomings exist, necessitating that we move beyond, but not discount, the data topography provide as an isolated screening evaluation. A variety of Placido and tomography units and automated screening systems are available and have been proposed to facilitate this screening.8-11 Yet, peer reviewed data, which should provide the critical basis for these technology comparisons, have lagged behind anecdotal information and suppositions. So, what should we do to appropriately screen our patients? Should the primary testing modality be topography, tomography, some combination, or something else? Two articles in this issue of the Journal of Refractive Surgery highlight some benefi ts and possible shortcomings of each approach, when viewed within the context of what is and is not currently known.

Modified double-K method for intraocular lens power calculation after excimer laser corneal refractive surgery

To propose the new anterior-posterior method (A-P method) that does not require historical data to calculate intraocular lens (IOL) power after laser in situ keratomileusis (LASIK) and to compare the accuracy of the method with other IOL formulas after LASIK. Keio University Hospital, Tokyo, Japan. Case series. Eyes having phacoemulsification and IOL implantation after myopic LASIK were analyzed retrospectively. The A-P method is a modification of the double-K method using the SRK/T formula in which the estimated pre-LASIK keratometry (K) power calculated from the post-LASIK posterior sagittal power in the 6.0 mm zone is used for the preoperative K value in the double-K method and the post-LASIK anterior sagittal power is used for the postoperative K value. The accuracy of the A-P method was compared with that of other formulas that do not require preoperative data and with formulas that require preoperative data. The median values of the arithmetic and absolute prediction errors using the A-P method were 0.16 diopter (D) and 0.54 D, respectively. The prediction errors using the A-P method were within ± 0.50 D in 46.4% of eyes and within ± 1.00 D in 75.0%. The percentage of eyes within ± 1.00 D of the prediction errors with the A-P method was highest with the no-history methods. The A-P method may be a good option for calculating IOL power in eyes having cataract surgery after LASIK when preoperative LASIK data are unavailable.

Influence of patient age on high myopic correction in corneal laser refractive surgery

To evaluate the influence of patient age on the postoperative outcomes in eyes with myopia higher than 5.00 diopters (D) that had laser in situ keratomileusis using the Schwind Amaris laser system. Private practice, Utrecht, The Netherlands. Case series. At the 1-year follow-up, right eyes with preoperative myopia higher than 5.00 D were analyzed. The effect of the patient's age on postoperative status was assessed using univariate linear and multilinear correlations. The study analyzed 612 eyes. Univariate linear analyses showed that residual refraction was correlated with patient age. Univariate multilinear analyses showed that spherical equivalent (SE) was correlated with the attempted SE and patient age, whereas cylinder was correlated with attempted cylinder only. Analyses suggested overcorrections and higher residual astigmatism values for older patients. Patient age affected postoperative outcomes in a subtle, yet significant manner. An age-dependent adjustment toward greater attempted correction in younger patients and less intended correction in older patients may help optimize refractive outcomes. Drs. Ewering and Arba-Mosquera are employees of Schwind eye-tech-solutions GmbH. Dr. Luger has no financial or proprietary interest in any material or method mentioned.

Application and notice of a new generation of non-steroidal eye drops in refractive surgery

The efficacy and safety of excimer laser corneal refractive surgery for refractive error correction have been widely recognized,and effective and appropriate application of perioperative medication also greatly improved patients' satisfaction with surgery.Topical application of glucocorticoid is indispensable for the excimer laser corneal refractive surgery,and it can not be replaced by any other medication for more than 20 years.However,adverse reactions and complications after the application of glucocorticoid are not rare,especially in patients who are long-term users.Therefore,in recent years,non-steroidal anti-inflammatory drugs are becoming more widely used in ophthalmology.Bromfenac sodium,an inhibitor of cyclooxygenase-2,could assume the role as low-concentration glucocorticoids with good medical effects and less adverse effects.But whether it could attain the same therapeutic effects as glucocorticoids in corneal refractive surgery is a subject worth studying. Key words: Excimer laser corneal refractive surgery; Non-steroidal anti-inflammatory drug; Bromfenac sodium ; Prostaglandin

Advances in biomechanical effects of laser corneal refractive surgery

Corneal biomechanical properties will change after laser refractive surgery, which can be evaluated by several biomechanical parameters. The biomechanical stress will decrease remarkably after LASIK, but thin flap is helpful to maintain its stress. Excimer laser surface ablation has biomechanical advantages over LASIK procedure. The femtosecond laser technology can achieve smooth and regular incision and make the angle design. Flap adhesion is stronger when completed by a femtosecond laser. Laser refractive surgery will become safer and achieve more stable outcomes with the emphasis on biomechanical effects.

Corneal power estimation for intraocular lens power calculation after corneal laser refractive surgery in Chinese eyes

To develop and evaluate an algorithm for corneal power estimation in intraocular lens (IOL) power calculation after corneal laser refractive surgery in Chinese eyes. Guangdong Eye Institute, Guangdong Academy of Medical Sciences, Guangzhou, China. Prospective comparative case series. Corneal parameters in Chinese eyes and German eyes were measured using a rotating Scheimpflug camera. Corneal power was simplified as a corrective algorithm: K(C) = 1.114 × K(M) + K(2) (K(M) = measured K reading; K(2) = K(P) - K(A) × K(P) × CT/1.376; K(A) = anterior corneal power; K(P) = posterior corneal power; CCT = central corneal thickness). The variation and change in K(2) induced by refractive surgery were analyzed in Chinese eyes. The corrective algorithm was identified as K(C) = 1.114 × K(M) - 6.20. The method was evaluated in Chinese cataract cases after refractive surgery using the Haigis formula. No difference in anterior corneal radius (R(A)) or CCT between Chinese eyes and German eyes were found; however, the posterior corneal radius (R(P)), R(A)/R(P) ratio, keratometric index, and K(2) were different. The mean K(2) was -6.23 diopters (D) ± 0.24 (SD) in Chinese eyes and -6.12 ± 0.23 D in German eyes (P<.01). The mean change in K(2) induced by refractive surgery was -0.02 ± 0.06 D. The median absolute prediction error in IOL power calculation was 0.43 D (range 0.01 to 1.80 D). The algorithm was a relatively reliable method in IOL power calculation after corneal refractive surgery in Chinese eyes.

The marriage of corneal graft and laser refractive surgery

Department of Ophthalmology and Visual Sciences, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, New York, NY, USA Correspondence to Prabjot Channa, MD, Department of Ophthalmology, Montefiore Medical Center, 111 E 210th Street, Centennial Building, Bronx, NY 10467, USA. Tel: +1 718 920 4428; e-mail: [email protected]e.org

Combining refractive and topographic data in corneal refractive surgery for astigmatism

To provide a theoretical approach for combining refractive and topographic data in the planning of corneal laser refractive surgery for astigmatism. Refractive and topographic data for astigmatism were transformed to the corneal plane. Net astigmatisms were converted to polar values. An optimization process was performed with the use of differential calculus. With this method, the magnitude of the corneal astigmatism is reduced or unaltered, while its orientation is maintained. The method identifies the reduction in corneal astigmatism, which will yield the largest reduction in refractive astigmatic magnitude. The advantage of the optimization method described in this article is a consistent reduction in corneal astigmatism towards sphericity. No new corneal astigmatism is carved on the cornea, and probably less tissue is ablated. The optimization method may also be used to combine refractive and topographic data for higher order aberrations with sinusoidal components. However, compared to the traditional purely refractive driven treatment, more refractive astigmatism will remain in the eye in most cases. A controlled clinical trial is necessary for comparing these two treatment modalities.

In Vivo Measurements of Thermal Load During Ablation in High-speed Laser Corneal Refractive Surgery

To evaluate the thermal load of ablation in high-speed laser corneal refractive surgery with the AMARIS excimer laser (SCHWIND eye-tech-solutions). Thermal load from refractive corrections on human corneas using a 500-Hz laser system with a fluence of 500 mJ/cm(2) and aspheric ablation profiles was recorded with an infrared thermography camera. Each single in vivo measurement was analyzed and temperature values were evaluated. Overall, the maximum temperature change of the ocular surface induced by the refractive ablations was ≤4°C. The increase in the peak temperature of the ocular surface never exceeded 35°C in any case. This low thermal load was independent of the amount of correction the eye achieved. The thermal load of the ablation in high-speed laser corneal refractive surgery was minimized using a computer algorithm to control the peak temperature to avoid corneal collagen denaturation with minimal compromise on treatment duration.