Transepithelial photorefractive keratectomy to treat mild myopia

PURPOSE

To assess the safety and effectiveness of transepithelial photorefractive keratectomy (T-PRK) in patients with mild myopia using the Schwind Amaris 750 s Excimer laser system which take corneal epithelium variability in consideration during ablation.

METHODS

A prospective case series study of patients with mild myopia with or without astigmatism (spherical equivalent ≤ -3 diopters), who underwent T-PRK as a single-step treatment, was carried out at King Abdulaziz University Hospital, Riyadh between May 2017 and January 2018. The main outcomes included postoperative uncorrected distance visual acuity (UDVA), residual refraction (manifest refraction) and complications.

RESULTS

A total of 42 patients (84 eyes) underwent bilateral T-PRK with a preoperative spherical equivalent ranging from - 0.75 to - 3.00 D. Median spherical equivalent before Trans-PRK was - 1.75 (- 1.25to - 1.75). The spherical equivalent six months after Trans-PRK was 0.0 (- 0.25 to 0.5). All patients had a postoperative UDVA of 20/20 or better in the last follow-up. Transient postoperative corneal haze was observed in five eyes (6%).

CONCLUSION

T-PRK appears to be safe and effective in patients who have mild myopia, with or without astigmatism. The normal variation in corneal epithelial thickness seems not to affect the outcomes.

Impact of Refractive Outcomes on Bias in Follow-up and Completion of Patient-Reported Outcome Measures after Laser Vision Correction

PURPOSE

To examine factors contributing to completion of a patient-reported outcome (PRO) measure in patients undergoing laser vision correction.

DESIGN

Retrospective, population-based study.

PARTICIPANTS

All patients who underwent primary laser vision correction with a target of plano from July 1, 2014, to June 30, 2016, at a large refractive surgery center.

METHODS

Patients were asked to complete a PRO measure at the time of their preoperative and months 1 and 3 postoperative visits. Characteristics between patients who attended and did not attend the follow-up visits and completed and did not complete the PRO measure were compared. A logistic regression was performed to identify factors associated with likelihood of follow-up and completion of PRO measure. An inverse probability censoring weighted model was created to account for selective loss to follow-up and used to adjust the PRO satisfaction measure.

MAIN OUTCOME MEASURE

Completion of the PRO measure at 1 and 3 months.

RESULTS

A total of 37 043 patients were identified. Of these, 20 501 completed a 1-month postoperative PRO measure and 10 474 completed a 3-month postoperative PRO measure. Patients completing a PRO measure were more likely to be older, be female, have had photorefractive keratectomy (PRK), have completed a preoperative PRO measure, and have had a preoperative hyperopic correction (P < 0.001 for all comparisons). For every line of postoperative uncorrected acuity worse than 20/16, the odds ratio of completing a PRO measure was 1.33 (95% confidence interval [CI], 1.30-1.36, P < 0.001) at 1 month and 1.29 (95% CI, 1.26-1.33, P < 0.001) at 3 months. At 1 month, there was no difference between the raw and model-adjusted rates of satisfaction with vision, but at 3 months the adjusted rate was significantly higher than the raw rate.

CONCLUSIONS

Patients with worse objective visual outcomes were more likely to complete PRO measures in this population-based study. In a setting with loss to follow-up, PRO measures require methods to address missing data for correct interpretation.

Altered Spontaneous Brain Activity Patterns in Patients After Lasik Surgery Using Amplitude of Low-Frequency Fluctuation: A Resting-State Functional MRI Study

OBJECTIVE

Previous studies demonstrated that myopia could result in alterations of brain activity in specific areas. However, whether the visual function could improve by Lasik surgery, with the brain activity alterations also change, is still unknown. Here, we intended to use the amplitude of low-frequency fluctuation (ALFF) technique to investigate the intrinsic brain activity changes in pre-Lasik (PRL) and post-Lasik (POL) patients.

METHODS

A total of 15 patients with myopia (nine male and six female) were recruited in our study, who were matched according to age, weight, and height. These patients comprised both the PRL and POL groups, which is self-controlled. The patients all underwent resting-state functional magnetic resonance imaging (MRI), and the spontaneous brain activity changes were recorded by the ALFF technique. The data were recorded and arranged in the receiver operating characteristic (ROC) curve, which presented how intrinsic activities altered in different brain regions. Moreover, by Graphpad prism 8, we can analyze the linear correlation between HADS (Hospital Anxiety and Depression Scale) and ALFF values as well.

RESULTS

Differences in ALFF values existed in brain regions between the same patient before and after the Lasik operation. The regions with increased ALFF values after Lasik surgery were the left parahippocampal gyrus, cerebellar vermis, and left posterior cingulate cortex. The regions with decreased ALFF values after Lasik surgery were the left supramarginal gyrus and right trigonometric inferior frontal gyrus.

CONCLUSION

We demonstrated significant fluctuations of ALFF values in specific brain areas between the same patients before and after the Lasik surgery. The altered ALFF values reflected the hyperactivity or hypoactivity of the specific brain areas, which may help predict the recovery level of patients' vision after Lasik surgery. Furthermore, based on the experimental results that presented significant activity alterations in specific brian regions, patients could be speculated equipped with a better visual function.

Intraocular Pressure After Corneal Refractive Surgery

Introduction:

Laser in situ keratomileusis (LASIK), a refractive surgery procedure is being performed in a large number among people with refractive errors. In all the people undergoing the procedure, there is a potential risk to misdiagnose the glaucoma disease due to changes in central corneal thickness (CCT). In subjects who have undergone laser refractive interventions, intraocular tension may be lower and underestimated, and this can lead to later detection of glaucoma.

Aim:

The objective of this study was to analyze the intraocular pressure (IOP) after LASIK in patients with myopia.

Methods:

Thirty-seven patients underwent LASIK intervention to treat myopia. In total, 74 eyes were treated. Before the intervention, all patients underwent complete ophthalmologic examination, including the measurement of central corneal thickness (CCT) and measurement of IOP with non-contact tonometer. The IOP was also measured on days 1, 3 and 30 after the surgery. The mean IOP was taken for statistical analysis.

Results:

Seventy-four eyes of 37 patients (mean age 31.6) underwent LASIK intervention to treat myopia. Mean CCT before the intervention was 551.9 ±31.9µm, while mean postoperative CCT was 469.8 ±45.3µm (p<0.0001). Mean preoperative IOP was 16.4mmHg while mean postoperative IOP was 11.0mmHg (p<0.0001). The average spherical equivalent was -5.9 diopters.

Conclusions:

The reduction of IOP after LASIK refractive surgery is significant. This reduction is about 1mmHg per 1 diopter. This should be taken into account in the future in these patients because, due to the underestimation of the IOP, the glaucoma disease may be overlooked.

Tear Martix Metalloproteinase-9 and Tissue Inhibitor of Metalloproteinase-1 in Post-Lasik Ectasia

PURPOSE

To estimate the concentrations of matrix metalloproteinase-9 (MMP-9) and tissue inhibitors of metalloproteinase-1 (TIMP-1) in the tear film of cases with post-Lasik ectasia (PLE) to spot any role of these mediators.

SETTINGS

Ophthalmology department, Benha University hospitals, Egypt.

METHODS

Twelve eyes of 12 patients with PLE, 30 eyes of 30 patients with KC, 25 eyes of 25 subjects with uncomplicated Lasik and finally 25 eyes of 25 healthy subjects as a control group were studied. Subjects with ocular surface diseases, previous ocular surgeries except for Lasik in PLE group and Lasik group, were excluded. All subjects had full ophthalmic examination and Pentacam imaging. The concentration of tear MMP-9 and TIMP-1 was measured by ELISA.

RESULTS

Our results showed a significant elevation in the level of MMP-9 and a significant reduction in the level of TIMP-1 in tear samples from PLE cases (MMP-9 was 59.17 ± 28.15 ng/ml, and TIMP-1 was 110.3 ± 50.6 ng/ml) and also in KC cases (MMP-9 was 53.12 ± 17.35 ng/ml, and TIMP-1 was 105.8 ± 56.3 ng/ml) when compared to post-Lasik group (MMP-9 was 35.65 ± 17.32 ng/ml, and TIMP-1 was 155.2 ± 39.4 ng/ml) and control group (MMP-9 was 31.92 ± 20.78 ng/ml, and TIMP-1 was 162.5 ± 48.2 ng/ml).

CONCLUSION

The results pointed to potential role of MMP-9 in the pathogenesis of PLE and also referred to a biochemical similarity between PLE and KC. More studies are needed in the future to investigate larger number of tear mediators.

Prediction accuracy of intraocular lens power calculation methods after laser refractive surgery

Background

This study aimed to evaluate the prediction accuracy of postoperative refractions using partial coherence interferometry (IOL-Master) and applanation ultrasound (AL-3000) assisted with corneal topography (TMS-4) in eyes that had undergone myopic laser-assisted in situ keratomileusis (LASIK).

Methods

Haigis-L formula, Koch–Maloney method using Haigis formula, Shammas clinically derived K-value (simulated keratometric value) correction (Shammas c.d.) using Haigis formula, and Shammas post-LASIK (Shammas-PL) formula were used in eyes with myopic LASIK. Constants were derived from the optimized constants in 133 virgin eyes. Refractive outcomes were determined by streak retinoscopy and subjective manifest refraction. Methods and formulas were evaluated by mean error (ME), standard deviation (SD), range of error, mean absolute error (MAE), median absolute error, 95% confidence interval of MAE, and percentage of eyes within ±0.5 diopter (D), ±1.0 D, and ±1.5 D of prediction.

Results

SDs of the Haigis-L, Koch-Maloney method using the Haigis formula, Shammas c.d. using the Haigis formula, and the Shammas-PL formula using IOL-Master were 0.721, 0.695, 0.695, and 0.698; and those using AL-3000 assisted with TMS-4 were 0.782, 0.741, 0.743, and 0.778, respectively.

Conclusions

No-history methods that corrected corneal power with measurements using IOL-Master were promising in myopic post-LASIK eyes, but still a gap in prediction accuracy exists between virgin eyes and post-LASIK eyes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12886-017-0439-x) contains supplementary material, which is available to authorized users.

Correlation between apical protrusion in the Scheimflug imaging and Corneal Hysteresis and Corneal Resistance factor by Ocular Response Analyzer, among refractive non-keratoconic Egyptian patients

Introduction

Apical protrusion in the central 4-mm ring in the Scheimflug imaging (Pentacam), both for the anterior and posterior floats as well as Corneal Hysteresis and Corneal Resistance Factor by Ocular Response Analyzer (ORA), generally are considered important predictors for post-Lasik ectasia. The aim of this work was to find out if there is a statistically significant correlation between these different predictors and their correlation with the central corneal thickness for refractive non-keratoconic Egyptian patients trying to achieve a better decision and avoiding ectasia.

Methods

This case-control study involved 142 eyes (of 77 patients with various refractive errors) arriving at the refractive surgery unit in the Research Institute of Ophthalmology in Giza (Egypt) in 2014–2015 seeking excimer laser ablation. The flattest, steepest keratometry readings, central corneal thickness as well as the apical protrusion in the central 4-mm ring, both for the anterior and posterior floats, in microns were measured by Scheimflug imaging. The Corneal Hysteresis and Corneal Resistance Factor were measured by the ocular response analyzer. Statistical analysis was performed by SPSS, using the Pearson correlation test.

Results

The spherical refractive error ranged from +7.00 to −13.00 diopters (−3.80 ± 2.89). The central pachymetry ranged from 494 to 634 μm (550.35 ± 32.13). For the central 4-mm ring, the apical protrusion ranged from 0 to +15 μ (6.93 ± 2.99) for the anterior float and from −3 to +20 μ (9.33 ± 4.55) for the posterior float. The Corneal Hysterisis (CH) ranged from 7 to 14.8 mmHg (10.18±1.44), while the Corneal Resistance Factor (CRF) ranged from 7.5 to 14.9 mmHg (10.58 ± 1.67). There was a strong positive correlation between the central corneal thickness and both Corneal Hysteresis (CH: r = 0.56, P ≤ 0.01) and Corneal Resistance Factor (r = 0.46, P ≤ 0.01). A significant correlation (P < 0.05, r = 0.15) existed between apical protrusion in the posterior float and the central corneal thickness. Also, significant negative correlation (P < 0.05, r = −0.12) existed between apical protrusion in the anterior float by pentacam and the Corneal Resistance Factor by ocular response analyzer.

Conclusions

Our finding of a strong positive correlation between both Corneal Hysteresis and Corneal Resistance Factor and the Central corneal thickness being important for biomechanical corneal stability. The findings of this study also support using both machines preoperatively to decrease the risk of post-Lasik ectasia.

[Long-term results of lasik refractive error correction after penetrating keratoplasty in patients with keratoconus]

OBJECTIVE

To evaluate the long term results of Lasik for residual refractive errors (RE) after penetrating keratoplasty (PKP) for keratoconus (KC).

DESIGN

Retrospective cohort.

METHOD

Records of 14 consecutive patients (19 eyes) who had Lasik after PKP for KC were retrospectively reviewed. In all eyes with refractive stability and suture removed before Lasik, far distance Visual Acuity with (AVCC) and without correction (AVSC), spherical equivalent (EE), refractive (Ast) and keratometric (dK) astigmatism were analyzed pre- and post-operatively before and after one year of follow up. Data were analyzed using Shapiro-Wilk normality test, Student t test and Mann-Whitney test. A P-value of <0,05 was considered statistically significant.

RESULTS

The mean follow-up time was 3.16 months for the follow-up before one year postoperative and 5.8 years for the follow-up after one year postoperative. The best spectacle corrected visual acuity of 0,11 LogMAR (DE 0,07) before Lasik remained stable throughout the study. The SE decreased from -2.6 (DE 3.53) to -0,36 D (DE 1.33) (P<.05) for the follow-up before one year postoperative and -1.28 D (DE 1.63) (P=.07) for the follow-up after one year postop. The refractive cylinder was reduced from -3.43 (DE 1.35) preoperative to -1.37 D (DE 1.24) (P<.05) and -3.21 D (DE 2.29) (P=.36) in the long term after one year of follow-up.

CONCLUSIONS

Lasik refractive results regress one year after the operation; therefore it is not an effective long-term surgical refractive procedure for residual refractive errors after PKP for KC.

Refractive outcome of wavefront guided laser in situ keratomileusis and wavefront guided photorefractive keratectomy in high pre-existing higher order aberration

PURPOSE

To compare visual outcome and higher order aberrations (HOA) between wavefront-guided LASIK (WF-LASIK) and wavefront guided PRK (WF-PRK) in patients with high preoperative HOA.

METHODS

Randomized prospective interventional study. Conducted at Guru Nanak Eye Centre, Maulana Azad Medical College, Delhi, India. Eighty myopic eyes of forty patients were included.

INCLUSION CRITERIA

age more than 21 years, best corrected visual acuity of 20/20 or better, a stable refraction, to be off soft contact lens for minimum 14 days prior to preoperative examination, preoperative RMS HOA more than 0.35 μ, preoperative central corneal thickness at least 500 μm, estimated residual stromal bed thickness of at least 275 μm in patients undergoing WF-LASIK and 350 μm in patients undergoing WF-PRK. Exclusion criteria were severe dry eye, blepharitis, corneal disease and warpage, uveitis, posterior segment abnormalities involving the macula or optic nerve and systemic diseases. Patients were randomly divided into two groups. They underwent either WF-LASIK (group A) or WF-PRK (group B) over 2 years (40 eyes each). Patients were followed up for 6 months. Main outcome measures were efficacy, safety, stability, predictability and HOA.

RESULTS

At 6 months mean uncorrected visual acuity (logMAR) in group A was -0.01 ± 0.04 and group B was 0.00 ± 0.07 (P = 0.23). HOA RMS (6mm pupil) in group A was 0.61 ± 0.24 μm and group B was 0.55 ± 0.25 μm. The increase was statistically significant in both the groups (P < 0.05). Both the groups showed similar efficacy, predictability and safety.

CONCLUSION

WF-LASIK and WF-PRK have similar efficacy, safety and predictability, though WF-PRK induces less HOA.

[Epithelial basement membrane dystrophy diagnosed following LASIK surgery]

A 48-year-old woman with no significant past history underwent bilateral simultaneous laser in situ keratomileusis for correction of her myopia. On the tenth postoperative day, the patient complained of visual decrease and photophobia. Slit lamp exam showed corneal epithelial irregularities. Confocal microscopy was performed and revealed a characteristic appearance of epithelial basement membrane dystrophy (EBMD). The patient was successfully treated with artificial tears and autologous serum eyedrops. EBMD may be missed before LASIK surgery, even after a careful pre-operative examination. Exacerbation of EBMD after LASIK surgery is rare. It should be considered when unexplained corneal epithelial defects or irregularities occur following LASIK. Confocal microscopy is very useful to confirm the diagnosis.

Intraocular lens power calculation after myopic and hyperopic laser vision correction using optical coherence tomography

PURPOSE

To use optical coherence tomography (OCT) to measure corneal power and calculate intraocular lens (IOL) power in cataract surgeries after myopic and hyperopic laser vision correction (LVC).

METHODS

Patients with previous LVC were enrolled in this prospective study at two centers (Doheny Eye Institute, Los Angeles, CA, USA and Cullen Eye Institute, Houston, TX, USA). Corneal power was measured with a Fourier-domain OCT system. The intravisit repeatability of OCT corneal power measurement was evaluated by the pooled standard deviation of repeat scans. Axial length, anterior chamber depth, and automated keratometry were measured with the IOLMaster. An OCT-based IOL formula was developed. The mean absolute error (MAE) of refractive prediction for OCT-based IOL formula was calculated. The results were compared with the MAE for Haigis-L formula.

RESULTS

A total of 31 eyes of 24 subjects who had uncomplicated cataract surgery with monofocal IOL implantation were enrolled in the two sites. Twenty-two eyes of 16 subjects had previous myopic LVC that ranged from -12.46 D to -0.88 D. Nine eyes of 8 subjects had previous hyperopic LVC that ranged from 0.66 D to 5.52 D. The intravisit repeatability of OCT corneal power measurement was 0.24 D. For the myopic LVC group, the OCT formula had a MAE of 0.57 D compared to an MAE of 0.73 D for the Haigis-L formula (p = 0.19). For the hyperopic LVC group, the MAE for OCT and Haigis-L formula was 0.26 D and 0.54 D, respectively (p > 0.05).

CONCLUSIONS

Corneal power can be precisely measured with OCT. The predictive accuracy of OCT-based IOL power calculation is equal to current standards for post-LVC eyes.