post-LASIK Eyes Research Articles

Effect of Previous Myopic Laser In Situ Keratomileusis on Contrast Sensitivity After Diffractive Multifocal Intraocular Lens Implantations

Objective: To evaluate effects of previous myopic laser in-situ keratomileusis (LASIK) on decrease in contrast sensitivity after implantation of diffractive multifocal intraocular lens (MF-IOL). Methods: Retrospective case series included eyes that were implanted diffractive MF-IOLs after myopic LASIK. Contrast sensitivity was measured 1 month postoperatively and the area under log contrast sensitivity (AULCSF) was calculated. Principle component analysis (PCA) was used for extracting principal factors related with the previous LASIK and MF-IOL implantation. Effects of decrease in postoperative AULCSF and contrast sensitivity at each spatial frequency were evaluated using step-wise multiple regression analysis. Results: Twenty-six eyes of 20 patients were included. The mean postoperative uncorrected distance visual acuity was -0.06 ± 0.13 logMAR (20/17 in Snellen) and all eyes achieved 20/20 or better. The PCA determined central corneal thickness (CCT), distance-corrected near visual acuity, and absolute manifest refraction as principal factors. The multiple regression analysis revealed that the AULCSF showed significant decrease with a thinner CCT (P=0.017), while a particular trend was not found in the analysis results at the spatial frequencies. Conclusion: Degradation in contrast sensitivity after implantation of MF-IOLs in post-LASIK eyes was more affected by the amount of the previous LASIK corrections.

Accuracy of Corneal Power Measurements for Intraocular Lens Power Calculation after Myopic Laser In situ Keratomileusis.

Purpose:To evaluate the accuracy of corneal power measurements for intraocular lens (IOL) power calculation after myopic laser in situ keratomileusis (LASIK).Methods:The study evaluated 45 eyes with a history of myopic LASIK. Corneal power was measured using manual keratometry, automated keratometry, optical biometry, and Scheimflug tomography. Different hypothetical IOL power calculation formulas were performed for each case.Results:The steepest mean K value was measured with manual keratometry (37.48 ± 2.86 D) followed by automated keratometry (37.31 ± 2.83 D) then optical biometry (37.06 ± 2.98 D) followed by Scheimflug tomography (36.55 ± 3.08). None of the K values generated by Scheimflug tomography were steeper than the measurements from the other 3 instruments. Using equivalent K reading (EKR) 4 mm with the Double-K SRK/T formula, the refractive outcome generated 97.8% of cases within ± 2 D, 80.0% of cases within ± 1 D, and 42.2% of cases within ± 0.5 D. The best combination of formulas was “Shammas-PL + Double-K SRK/T formula using EKR 4 mm.”Conclusion:Scheimflug tomography imaging using the Holladay EKR 4 mm improved the accuracy of IOL power calculation in post-LASIK eyes. The best option is a combination of formulas. We recommended the use the combined “Shammas-PL ± Double-K SRK/T formula using EKR 4 mm”h for optical outcomes.

Evaluation of point-of-care test for elevated tear matrix metalloproteinase 9 in post-LASIK dry eyes

AimTo evaluate the performance of a point-of-care test for detection of matrix metalloproteinase 9 (MMP-9) levels in post-laser-assisted in situ keratomileusis (LASIK) dry eyes.MethodsA comparative study between patients with mild...

Accuracy of corneal power measurements for intraocular lens power calculation after myopic laser in-situ keratomileusis

Purpose The aim of the study was to evaluate the accuracy of corneal power measurements for intraocular lens (IOL) power calculation after myopic laser in-situ keratomileusis (LASIK). Setting The study was conducted at the Faculty of Medicine, Alexandria University, Egypt. Patients and methods The study was conducted on 45 eyes that had undergone myopic LASIK previously. Corneal power was measured using manual keratometry, automated keratometry, IOLMaster, and Pentacam. Different hypothetical IOL power calculation formulas were used in each case. Results The steepest mean K value with manual keratometry (37.48 ± 2.86 D) followed by automated keratometry (37.31 ± 2.83 D) and the IOLMaster mean K value (37.06 ± 2.98 D) were steeper than any other mean K value measured by Pentacam. Using 4 mm Holladay equivalent K reading (EKR) with the double-K SRK/T formula, the refractive outcome was good, with 97.8% of cases within ± 2 D, 80.0% of cases within ± 1 D, and 42.2% of cases within ± 0.5 D. The best combination of formulas was 'Shammas-PL+double-K SRK/T using EKR 4 mm'. Conclusion Pentacam Scheimpflug imaging using EKR at 4 mm improved the accuracy of IOL power calculation in post-LASIK eyes. The best option is a combination of formulas. It is recommended to use the mean of the combination of 'Shammas-PL+double-K SRK/T with EKR 4 mm'.

Comparison of different methods for the measurement of central and paracentral corneal thickness in post-LASIK eyes

Background Accurate measurement of corneal thickness is very important during the pre-and post-operative management of corneal surgical procedures,especially laser-assisted in-situ keratomileusis (LASIK),which is the most popular approach to the correction of refractive errors currently.This may be particularly important for the patients who have undergone previous laser refractive surgery with suboptimal outcomes and are being considered for an enhancement procedure.Objective This study was to compare the measuring outcomes of corneal thickness by slit-scanning pachymetry,non-contact specular microscope,anterior segment optical coherence tomography (AS-OCT)and ultrasound pachymetry,with a focus on central and midperipheral (from the central 3.0 mm) region of cornea in post-LASIK eyes.Methods Sixty-four right eyes of 64 patients who received LASIK were collected in Henan Eye Institute,Henan Eye Hospital from March to June 2011 with the equivalent spherical diopter of (-4.75±2.38)D and horizontal corneal diameter of (11.36±0.32)mm.Central corneal thickness was measured on each eye by using non-contact specular microscope (Topcon SP-3000P),slit-scanning pachymetry (Orbscan Ⅱ),AS-OCT and A-type ultrasound pachymetry,respectively,and the paracentral corneal thickness including 12:00,2:00,6:00 and 10:00 meridian was measured using Orbscan Ⅱ,non-contact specular microscope and AS-OCT.The measuring values and the agreement from different instruments were compared and evaluated.Results The mean central corneal thickness was (467.12±31.10)tμm for AS-OCT,(466.67±30.99)μm for ultrasound pachymetry,(441.84 ± 33.65) μm for specular microscopy and (422.51 ± 44.09) μm for Orbsan Ⅱ,respectively,showing a significant difference among the four methods (F =23.730,P =0.000).The central thickness value of the A-type ultrasound pachymetry was significantly higher than that of Orbsan Ⅱ or non-contact specular microscope (q =6.940,6.720,both at P =0.000).Compared with Orbscan Ⅱ,the measuring values of non-contact specular microscope and AS-OCT were significantly higher (q =-5.54,6.940,both at P =0.000),and the measuring value of AS-OCT was significantly higher that of non-contact specular microscope (q =6.800,P =0.000).The lowest difference value (25.3 μm)and the best agreement was found between the ultrasound pachymetry and AS-OCT.The paracentral corneal thickness values in 12:00,2:00,10:00,6:00 meridians were highest for Orbsan Ⅱ and the next for AS-OCT,and non-contact specular microscope had the lowest values,with significantly differences among them (F =5.020,22.950,67.890,18.850,all at P ＜ 0.01).Conclusions The corneal thickness values vary with the different instruments.Orbsan Ⅱ underestimates the central corneal thickness and overestimates the midperipheral corneal thickness,and non-contact specular microscope underestimates both the central and midperipheral corneal thickness.The measuring outcome from AS-OCT has a good agreement with ultrasound pachymetry and therefore they can be used interchangeably. Key words: Corneal thickness; Laser-assisted in-situ keratomileusis; Specular microscope; Anterior segment optical coherence tomography; Orbscan Ⅱ ; Ultrasound pachymetry

Early Corneal Nerve Damage and Recovery Following Small Incision Lenticule Extraction (SMILE) and Laser In Situ Keratomileusis (LASIK)

We compared early corneal nerve changes after small incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK). A total of 12 rabbits underwent LASIK in one eye and SMILE in the fellow eye. Baseline and follow-up evaluations at 1, 2, and 4 weeks postoperatively were performed with in vivo confocal microscopy to evaluate 5 different areas within the treated zone: center, superior, inferior, nasal, and temporal. Cryosections of the corneas and whole mount of the extracted SMILE lenticules were analyzed with immunostaining of βIII-tubulin. One week after SMILE and LASIK, a decrease in nerve length and density was observed in all evaluated areas. A trend toward greater subbasal nerve length and density (SLD), more eyes with subbasal nerves (ESN), more eyes with subbasal nerves longer than 200 μm (SNL), and higher mean number of subbasal nerves by frame (NSN) in SMILE than in LASIK groups was observed at subsequent follow-up time points. Only the SMILE group showed a recovery of SLD, ESN, and NSN by week 4 (P > 0.05). A trend toward more eyes with sprouting subbasal nerves and greater mean number of sprouting nerves was observed in LASIK than in SMILE, indicating that more subbasal nerves were disrupted and undergoing regeneration after LASIK. Immunostaining at postoperative week 4 revealed a faster stromal nerve recovery in post-SMILE eyes compared to post-LASIK eyes. Our findings suggest that SMILE results in less nerve damage and faster nerve recovery than LASIK.

Optical and Visual Simulation of Standard and Modified Spherical Aberration Implantable Collamer Lens Post Myopic LASIK Surgery

To evaluate the visual quality achieved in patients undergoing standard or modified implantable Collamer lens (ICL) to correct residual myopic error after laser-assisted in situ keratomileusis (LASIK) surgery. The adaptive optics visual simulator was used to simulate LASIK surgery of moderate and high myopia with a myopic regression corrected by a standard and modified ICL. Visual acuity (VA) and contrast sensitivity (CS) were measured in 14 subjects at 3- and 4.5-mm pupil. Point spread function and simulated retinal images were calculated. Comparing LASIK plus standard ICL and LASIK plus modified ICL simulations, for moderate myopia, VA improvement was less than 1 line in all VA contrasts and both pupils evaluated. No statistically significant differences were found in CS between the simulations at any spatial frequency evaluated and for 3-mm pupil (p>0.05), but differences were significant at 4.5-mm pupil (p<0.05). For high myopia, the VA improvement was less than 1 line at 3-mm pupil, although it increased 2 or more lines at 4.5-mm pupil. Statistically significant differences were found in CS between the simulations for all spatial frequencies and both pupils evaluated (p<0.05), except for low and medium spatial frequencies at 3-mm pupil (p>0.05). These outcomes suggest that an ICL is a good option to correct the myopic residual error after myopic LASIK. When the ICL's spherical aberration is modified, the post-LASIK eyes of high myopia are the most benefited, as these eyes are more aberrated than after moderate myopic LASIK.

Pressure-Induced Stromal Keratopathy as a Result of Ocular Trauma After Laser In Situ Keratomileusis

Pressure-induced stromal keratopathy is a rare kind of complication of laser in situ keratomileusis (LASIK) that may cause vision loss in affected eyes. Herein, we described the clinical features and treatment of 2 cases of pressure-induced stromal keratopathy due to traumatic hyphema in post-LASIK eyes. Two patients sought treatment for painful vision loss after blunt trauma on post-LASIK eyes. On examination, high intraocular pressure was found in the injured eyes. Hyphema was seen in the anterior chamber. High-resolution slitlamp biomicroscopy demonstrated interface hyperreflection, which resembled interface keratitis. However, an isolated pocket of fluid was clearly demonstrated at the level of the LASIK flap interface in the anterior segment optical coherence tomographic images. After topical corticosteroid and antiglaucoma medication, the hyphema and the hyperreflection in the cornea resolved in several days. The intraocular pressure and visual acuity returned to normal levels. Repeated anterior segment optical coherence tomographic examinations revealed completed resolution of the interface fluid. To our knowledge, this is the first report of pressure-induced stromal keratopathy caused by traumatic hyphema. Anterior segment optical coherence tomography plays a unique role in revealing occult interface fluid in post-LASIK eyes, which may masquerade as interface keratitis during slitlamp examination.

Assessment of Tear Osmolarity and Other Dry Eye Parameters in Post-LASIK Eyes

To assess the tear osmolarity using the TearLab device after laser in situ keratomileusis (LASIK) and to compare the values with those obtained by traditional tear film tests before and after the procedure. Thirty eyes of 15 refractive surgery candidates (5 men and 10 women of mean age: 30.55 ± 11.79 years) were examined. Using a special questionnaire (Ocular Surface Disease Index), subjective dry eye complaints were evaluated, and then, the tear osmolarity was measured with the TearLab system (TearLab Corporation) and conventional dry eye tests were carried out. Examinations were performed preoperatively and at 1, 30, and 60 days after the surgery. The mean value of tear osmolarity was 303.62 ± 12.29 mOsm/L before the surgery and 303.58 ± 20.14 mOsm/L at 60 days after the treatment (P = 0.69). Mean lid parallel conjunctival folds value was 0.68 ± 0.68 before the procedure and 0.58 ± 0.65 subsequent to surgery (P = 0.25). Meibomian gland dysfunction was not detected. No significant deviation was observed in the values of Schirmer test, corneal staining, tear break-up time, and lid parallel conjunctival folds when compared with postoperatively obtained values during the follow-up period (P > 0.05). During LASIK flap creation, intact corneal innervation is damaged, and the ocular surface lacrimal functional unit can be impaired. In our study, no abnormal dry eye test results were observed before or after the procedure. Based on our results, LASIK treatment is safe for dry eye involving the administration of adequate artificial tears for a minimum of 3 months.

Nonarteritic ischemic optic neuropathy secondary to severe ocular hypertension masked by interface fluid in a post-LASIK eye

We report a case of ischemic optic neuropathy arising from elevated intraocular pressure (IOP) masked by interface fluid in a post-laser in situ keratomileusis (LASIK) eye. A 51-year-old man, who had had LASIK 6 years prior to presentation, sustained blunt trauma to the left eye that resulted in a hyphema and ocular hypertension. Elevated IOP resulted in accumulation of fluid in the stromal bed-LASIK flap interface, leading to underestimation of IOP when measured centrally over the flap. After days of unrecognized ocular hypertension, ischemic optic neuropathy developed. To our knowledge, this is the first reported case of ischemic optic neuropathy resulting from underestimated IOP measurements in a post-LASIK patient. It highlights the inaccuracy of IOP measurements in post-LASIK eyes and a vision-threatening potential complication. No author has a financial or proprietary interest in any material or method mentioned.

Evaluation of corneal thickness using a Scheimpflug–Placido disk corneal analyzer and comparison with ultrasound pachymetry in eyes after laser in situ keratomileusis

To evaluate the repeatability and reproducibility of corneal thickness measurements in post-laser in situ keratomileusis (LASIK) eyes using a rotating Scheimpflug camera combined with a Placido disk corneal topographer (Sirius) and compare the results with those of ultrasound (US) pachymetry. Eye Hospital of Wenzhou Medical College, Wenzhou, China. Comparative evaluation of a diagnostic test or technology. Patients were examined 3 times with the Scheimpflug-Placido topographer by 2 examiners. The central pupil corneal thickness (CTpupil), apical corneal thickness (CTapex), and thinnest corneal thickness (CTthinnest) were recorded. After noncontact examinations, US pachymetry was used to obtain the central corneal thickness (CCT). The Scheimpflug-Placido topographer showed high intraoperator repeatability as indicated by a test-retest repeatability of less than 8.5 μm for CTpupil, CTapex, and CTthinnest, The coefficients of variation (CoV) were less than 0.7%, and the intraclass correlation coefficient was higher than 0.99. Excellent results were also obtained for interoperator reproducibility. All CoVs were less than 0.5%. The 95% limits of agreement between the Scheimpflug-Placido measurement and the US pachymetry measurements were narrow (-16.62 to 12.44 μm for CTpupil versus US pachymetry CCT; -17.49 to 12.16 μm for CTapex versus US pachymetry CCT; -18.59 to 10.90 μm for CTthinnest versus US pachymetry CCT). The Scheimpflug-Placido topographer showed excellent intraoperator repeatability and interoperator reproducibility of CTpupil, CTapex, and CTthinnest measurements in post-LASIK eyes. The CCT measurements obtained using the device were in high agreement with those obtained by US pachymetry, suggesting that the 2 devices are interchangeable. No author has a financial or proprietary interest in any material or method mentioned.

Post-LASIK interface fluid syndrome caused by steroid drops

Interface fluid syndrome after laser in situ keratomileusis (LASIK) is a rare but visually threatening postoperative complication. In this case series we present 8 post-LASIK eyes that developed interface fluid syndrome after prolonged steroid use. Patients presented with signs mimicking diffuse lamellar keratitis (DLK) that worsened with steroid treatment. Slit-lamp examination revealed corneal haze and an optically clear fluid-filled space between the flap and stroma. The IOP was high in all cases. Topical steroids were stopped and replaced with topical and systemic anti-glaucoma medications resulting in a dramatic improvement in visual acuity.

Confirmation and refinement of the Diehl-Miller nomogram for intraocular lens power calculation after laser in situ keratomileusis

To validate the Diehl-Miller equation for achieving emmetropia after cataract surgery in post-laser in situ keratomileusis (LASIK) eyes and to present a refined equation. Jules Stein Eye Institute, Los Angeles, California, USA. Cohort study. Preoperative and postoperative refractive and cataract surgery data were collected from the medical records of post-LASIK patients. The IOL power data and postoperative refractive information were used to calculate the true target refractive error that should have been chosen to achieve emmetropia. Regression analysis of the combined data from Diehl-Miller and the current study was used to develop a refined equation. Diehl-Miller relates the manifest refraction spherical equivalent (MRSE) change induced by LASIK to an adjusted target postoperative refractive error to be used in intraocular lens (IOL) power calculations. Twenty-three eyes of 18 patients were evaluated. The target refractive error calculated by Diehl-Miller differed from the true target refractive error by an absolute mean of 0.481 diopter (D) ±0.376 (SD). Regression analysis of the combined data from Diehl-Miller and the current study yielded the following 2nd-order polynomial equation: Target refractive error = -0.0198 (MRSE change)(2) +0.170 (MRSE change)-0.0079. The calculated target refractive error fell within ±0.50 D of the true target in 49% of patients and within ±1.00 D in 93% of patients. This study validated that the Diehl-Miller equation accurately predicts the target refractive error to achieve emmetropia in post-LASIK eyes. The slightly refined Diehl-Date-Miller equation and associated lookup tables can be used to avoid postoperative refractive surprises.

Repeatability and agreement of corneal thickness measurement with Pentacam Scheimpflug photography and Visante optical coherence tomography

To evaluate the repeatability and agreement of central and peripheral corneal thickness (CT) measurements by high resolution Pentacam rotating Scheimpflug photography and Visante optical coherence tomography (OCT) in unoperated myopic eyes and eyes after Laser In Situ Keratomileusis (LASIK). CT at central, thinnest, 1.0 mm and 2.5 mm superior, inferior, nasal and temporal periphery locations, and the location of the corneal thinnest thickness were measured using Pentacam and Visante OCT in 60 myopia patients (60 eyes) and 60 patients (60 eyes) after LASIK. The results were analyzed by paired-t test, Pearson correlation analysis and Bland-Altman method. Both Pentacam and Visante OCT demonstrated high intraobserver repeatability, with all intraclass correlation coefficients and Cronbach's alphas were more than 0.9, and coefficient of variation were less than 0.9%. Significantly higher CoV was measured with Pentacam than by Visante OCT in at central (0.46 ± 0.30), thinnest (0.43 ± 0.28) and 1.0 mm locations in both groups (t = 2.465, 2.226, P < 0.05), but no statistically significant difference were found at 2.5 mm locations in healthy subjects and all locations in post-LASIK eyes (t = -0.518, 1.542, -0.876, 0.756, P > 0.05). The thickness of central corneal with Pentacam was (543.01 ± 22.89) µm, the thinnest point was (540.61 ± 22.84) µm, they were greater than the value of Visante OCT (t = 17.946, 23.071, P < 0.05). The Pearson correlation coefficients were all more than 0.9 (all r > 0.9, P < 0.01). The Bland-Altman plots showed the 95% LoA between both devices were lower than 22 µm at central, thinnest and 1.0 mm locations. However, the 95% LoA were 24 µm to 44 µm at 2.5 mm locations. Pentacam and Visante OCT demonstrate high repeatability for central and peripheral CT measurements in young myopia and post-LASIK eyes. However, both devices can't be used interchangeably for measurements of peripheral CT.

The role of presbyopia-correcting intraocular lenses after laser in situ keratomileusis

There is a growing number of patients who wish to remain spectacle independent after cataract surgery, and this number includes some of the millions of people worldwide who have undergone laser in situ keratomileusis (LASIK). This article reviews the evidence of the use of presbyopia-correcting intraocular lenses (IOLs) in patients who have previously undergone LASIK. Small studies have demonstrated that the use of hybrid refractive-diffractive multifocal IOLs in eyes with previous myopic or hyperopic LASIK can result in good refractive results. However, refractive surprise can be common and may require further intervention, such as laser surgery enhancement, to achieve satisfactory results. The use of these IOLs can also result in lost lines of vision, and visual quality may be poorer under mesopic or glare conditions. No reports were found regarding the use of accommodating IOLs in such patients. There is a surprising paucity of literature on this topic, given the millions that have undergone LASIK. Further and timelier research is needed to assess the use of newer multifocal and accommodating IOLs in post-LASIK eyes, the effect of IOL asphericity on visual quality, and patients' experience, satisfaction and level of spectacle independence after surgery.

Assessments of total corneal power and intraocular lens power in post-LASIK eyes

To compare the different evaluations of corneal power in post-laser-assisted in situ keratomileusis (LASIK) eyes and assess the accuracy and differences of intraocular lens (IOL) power prediction with corneal powers through different calculation methods. For this prospective study, 71 eyes of 39 candidates undergoing LASIK and 3 months later returning for reexamination were included. All subjects were divided into 2 groups according to the axial length: Group A (23.46 - 25.97 mm) 44 eyes, Group B (26.00 - 28.52 mm) 27 eyes. The ranges of spherical equivalents were -1.75 - -9.50 D with an average of (-4.82 ± 1.98) D. Subjective refraction and Pentacam Scheimpflug analyzer were performed at pre-operation and subjective refraction, IOLMaster and Galilei II dual Scheimpflug analyzer at over 3 months post-operation. The following values were obtained: SimK by Galilei II dual Scheimpflug analyzer, Kn calculated with Gaussion thick lens formula, Kray with ray tracing method, Kchm calculated with clinical history method and Km by IOLMaster. Repeated measures analysis of variance analyze the differences between SimK, Kn, Kray, Km and Kchm. Repeated measurement analysis of variance was employed to analyze the differences between SimK, Kn, Kray, Km combining intraocular lens power formula and Kchm combining intraocular lens power formula. Pearson's analysis was performed to analyze the correlations between SimK, Kn, Kray, Km and Kchm. Those combining with formulas for IOL power calculations were also analyzed. P < 0.05 indicated statistical significance. The values of SimK, Kn, Kray, Km and Kchm were (39.02 ± 1.8), (37.8 ± 1.51), (36.8 ± 1.84), (39.18 ± 1.75) and (38.55 ± 1.83) D respectively. The differences between SimK, Kn, Kray, Km and Kchm had statistical significances (P < 0.01). High correlations existed between SimK, Kn, Kray, Km and Kchm (r > 0.9, P < 0.01). In the same IOL formula, Kray had the highest IOL power value, Kn followed, Kchm the third, SimK and Km the smallest. Among the IOL formulas, Haigis-L and Haigis predicted the highest IOL power, HofferQ followed, Holladay the third and SRK/T the smallest. Kn/Kray combining with Haigis formula may be a new and effective method for predicting the IOL power in post-LASIK eyes.

Effect of corneal aberrations on intraocular lens power calculations

To use ray tracing to determine the influence of corneal aberrations on the prediction of the optimum intraocular lens (IOL) power for implantation in normal eyes and eyes with previous laser in situ keratomileusis (LASIK). Hospital Universitario Virgen de la Arrixaca, Murcia, Spain. Case series. The optimum IOL power was calculated by ray tracing using a patient-customized eye model in cataract surgery cases. The calculation can be performed with or without inclusion of the patient's corneal aberrations. Standard predictions were also generated using current state-of-the-art IOL power calculation techniques. The results for all predictions were compared with the optimum IOL power after cataract surgery. For patients without previous LASIK (n = 18), the standard approaches and the ray-tracing procedure gave a similar mean absolute residual error and variance. The incorporation of corneal aberrations did not improve the accuracy of the ray-tracing prediction in these cases. For post-LASIK patients (n = 10), the ray-tracing prediction incorporating corneal aberrations generated the most accurate results. The difference between the prediction with and without considering corneal aberrations correlated with the amount of corneal spherical aberration (r(2) = 0.82), resulting in a difference of up to 3.00 diopters in IOL power in some cases. Ray tracing using patient-customized eye models was a robust procedure for IOL power calculation. The incorporation of corneal aberrations is crucial in post-LASIK eyes, primarily because of the elevated corneal spherical aberration. Mrs. Canovas and Dr. Artal hold a provisional patent application on the ray-tracing procedure. Mrs. Canovas is an employee of Abbott Medical Optics Groningen B.V. No other author has a financial or proprietary interest in any material or method mentioned.

Repeatability and reproducibility of retinal straylight measurement using C-Quant compensation comparison method

Background In an ideal eye there would be no light scattering at all,but the eye media is not optically ideal.Intraocular straylight causes a veil of light and reduction in the contrast of the retinal image and thus decrease the quality of vision. Objective The present study was to investigate the repeatability and reproducibility of C-Quant straylight meter( Oculus,Germany) in measuring retinal straylight of myopia and post-laser in situ keratomileusis(LASIK) corneas. Methods This is a prospective research.The consecutive 35 eyes of 21 myopic patients and 34 eyes of 22 patients who received LASIK were included in this trail.Retinal straylight was measured for 7 times at a period of time and analyzed quantificational to evaluate the repeatability of measurement.Thirty-eight eyes of 19 patients were measured again at 3-7 days for 3 times at a period of time to assess the reproducibility of C-Quant straylight meter.The mean standard difference (SD) and coefficient of variation (CV) were used as the credibility evaluation.This clinical study complied with Helsinki Declaration and the informed consent was obtained prior to the medical procedure. Results The straylight Log(s) of 7 times measurement were all less than 0.95.The mean Log(s) were 0.92±0.12 and 0.93±0.17 respectively in myopia group and post-LASIK group,without statistically significant differences among 7 times measurement( F=0.335,P=0.812;F=1.000,P=0.409).The mean SD for the 7 times measurement was 0.07 Log units.SD and CV increased with the number of measurements.The differences of mean SD and CV between 3 times result and 6 times result were significant different (t =-2.080,P =0.045;t =-2.190,P =0.035 ).No difference was found between different time periods( t =-0.531,P=0.598 ).The difference of the results between two measurements from the same patient was 0.013. ConclusionsC-Quant is a noncontact,noninvade,rapid and convenient method for the measurement of straylight in myopia and post-LASIK eyes due to the high repeatability and reproducibility. Key words: C-Quant; Straylight; Myopia; Laser in situ keratomileusis; Repeatability; Reproducibility

Retinal straylight and light distortion phenomena in normal and post-LASIK eyes

To assess the relationship between measures of light distortion and retinal straylight in normal and post-LASIK subjects. Cross-sectional, non-randomized, masked observational case series Clinica Oftalmologica Novovision, Madrid, Spain. Thirty eyes from 30 healthy subjects (mean age 33.9 ± 8.3years old; mean spherical equivalent (MSE) -2.06 ± 1.40 D) and thirty six eyes from thirty six refractive surgery patients (mean age 36.1 ± 7.7years old; mean preop MSE -3.43 ± 2.23 D) were examined with the Starlights and the C-Quant straylightmeter in a case-control study. The age of both treated and control groups was not statistically different (p > 0.05). Statistically significant differences between controls and post-LASIK eyes were found for luminous distortion index (LDI), but not for retinal straylight. Correlation analysis yielded significant correlation between retinal straylight Log(s) values and BCVA measures (r = 0.379, p = 0.002). Control subjects showed significant correlation between MSE and retinal straylight Log(s) values (r = -0.650, p < 0.001), while post-LASIK eyes showed a significant correlation between LDI and Log(s) values (r = 0.338, p = 0.044) and between Log(s) values and BCVA (r = 0.460, p = 0.005). Correlation between measures obtained by both methods was higher after LASIK than in control eyes, although values were quite scattered in any case. Light distortion phenomena and retinal straylight measures are correlated in both normal and postsurgical eyes. Both parameters are increased in LASIK subjects compared to control non-operated subjects.

Practical method to calculate post-LASIK corneal power: the Actual K(a+p) method.

To evaluate the accuracy of a practical method (the Actual K(a+p) method) of corneal power measurement for post-LASIK eyes undergoing cataract surgery. Ten eyes of 7 patients (4 male, 3 female, average age 50.10±4.01 years, with -11.01±3.55D mean refraction before LASIK), underwent post-LASIK phaco+IOL cataract surgery. We used the posterior corneal curvature as measured by the Pentacam in a method we named Actual K(a+p) to calculate the post-LASIK corneal power for IOL calculation. The refractive outcomes after cataract surgery were evaluated. The Actual K(a+p) was compared with the back- calculated corneal power (BCK), which was thought to be the benchmark of true corneal power. The corneal power estimated by other published methods, including Maloney, Shammas, Koch-Maloney, Savini, and McCulley, together with the true net power and equivalent K reading (EKR) as found by the Pentacam were also compared with the BCK. All eyes achieved satisfied refractive status after cataract surgery. The difference between the postoperative refraction and the target refraction was 0.04±0.40D, range from -0.63D and +0.85D. Among all the methods we studied, although the Bonferroni multiple comparison tests did not detect significant differences between any two of them, the Actual K(a+p) yielded the highest agreement with the BCK, with 80% of the eyes falling within ±0.5D and 100% within ±1.0D from the BCK values. The Actual K(a+p) method can provide encour- aging results in post-LASIK eyes undergoing cataract surgery.