Atomic force microscopy for the evaluation of corneal surface roughness after femtosecond laser flap creation and excimer ablation.

INTRODUCTION: It is well known that the femtosecond laser lamellar cut induces some degree of surface roughness. Nevertheless, as in femtosecond laser-assisted LASIK (FS-LASIK), an excimer LASIK ablation is performed, and the post-ablation stromal bed should show some degree of smoothening. We decided to compare, using atomic force microscopy (AFM), the roughness of the corneal stromal bed, after a femtosecond lasers device flap was created with or without an excimer myopic ablation. METHODS: Using 6 freshly enucleated porcine eyes, we created in every eye a flap using a femtosecond laser. Additionally, in 3 eyes, an excimer laser ablation to correct-3 diopters (D) was made. AFM imaging of the remaining corneal stroma was performed. Ten different square areas of 20 µm x 20 µm at the central area of the stroma of each corneal sample were studied. The roughness parameters used were the root-mean-square deviation from a perfectly flat surface. RESULTS: The RMS deviation was 360 ± 120 nm in femtosecond laser only, and 110 ± 20 nm in those cases where excimer is also involved (p < 0.0001). CONCLUSIONS: Our results show that the roughness of the surface treated with excimer is clearly lower than in the group with no excimer ablation; thus, the application of laser excimer after a flap created by femtosecond laser seems to soften the nano-irregularities created by this technique.

Femtosecond LASIK for the correction of low and high myopic astigmatism.

INTRODUCTION: Higher preoperative myopic astigmatism is associated with a higher probability of retreatment due to patient dissatisfaction as a result of residual cylindrical error. Nonetheless, retreatment is safe and the final clinical results are comparable to those of patients with lower preoperative astigmatism who were satisfied with the primary treatment. Our purpose is to compare the efficacy and safety of femtosecond LASIK (FS-LASIK) for the refractive correction of patients with low (< 1.5 Diopters (D) versus high (≥ 1.5 D) myopic astigmatism. METHODS: Retrospective observational study of 841 eyes of 825 eligible patients treated with FSLASIK for the correction of simple or compound myopic astigmatism. Outcome measures included residual error, best corrected and uncorrected distance visual acuity (BCVA and UCVA), efficacy and safety 3 months after the primary procedure or the retreatment. RESULTS: Of 841 eyes in total, 432 (51.37%) had < 1.5 D (Group 1) and 409 (48.63%) had ≥ 1.5 D (Group 2) preoperative myopic astigmatism. The efficacy index of primary treatment was 0.94 ± 0.18 in Group 1 and 0.89 ± 0.22 in Group 2 (P = 0.001). Of 138 eyes (16.41%) that were retreated due to dis-satisfaction related to residual refractive error, 28 belonged to Group 1 (6.5%) and 110 (26.9%) to Group 2 (P < 0.001). Following retreatment, small but statistically significant differences in the residual mean postoperative cylinder (-0.08 ± 0.24 vs -0.27 ± 0.46 D, P = 0.001) and UCVA (1.11 vs 0.96, P = 0.0001) were detected for Groups 1 and 2, respectively. However, there were no statistically significant differences in the safety and efficacy indices. CONCLUSION: Following FS-LASIK, eyes with myopic astigmatism ≥ 1.5 D have approximately four times more chances of undergoing retreatment due to dis-satisfaction caused by residual refractive error compared to eyes with myopic astigmatism < 1.5 D. However, the clinical results after retreatment are highly satisfactory and comparable in both groups.

Atomic force microscopy comparative analysis of the surface roughness of two posterior chamber phakic intraocular lens models: ICL versus IPCL.

BACKGROUND: To compare the anterior surface roughness of two commercially available posterior chamber phakic intraocular lenses (IOLs) using atomic force microscopy (AFM). METHODS: Four phakic IOLs were used for this prospective, experimental study: two Visian ICL EVO+ V5 lenses and two iPCL 2.0 lenses. All of them were brand new, were not previously implanted in humans, were monofocal and had a dioptric power of - 12 diopters (D). The anterior surface roughness was assessed using a JPK NanoWizard II® atomic force microscope in contact mode immersed in liquid. Olympus OMCL-RC800PSA commercial silicon nitride cantilever tips were used. Anterior surface roughness measurements were made in 7 areas of 10 × 10 µm at 512 × 512 point resolution. The roughness was measured using the root-mean-square (RMS) value within the given regions. RESULTS: The mean of all anterior surface roughness measurements was 6.09 ± 1.33 nm (nm) in the Visian ICL EVO+ V5 and 3.49 ± 0.41 nm in the iPCL 2.0 (p = 0.001). CONCLUSION: In the current study, we found a statistically significant smoother anterior surface in the iPCL 2.0 phakic intraocular lenses compared with the VISIAN ICL EVO+ V5 lenses when studied with atomic force microscopy.

Effect of Laser-assisted Subepithelial Keratectomy with Mitomycin C on Corneal Optical Density Measured with Confocal Microscopy.

SIGNIFICANCE: The development of confocal microscopy allows one to obtain high-resolution corneal images like its optical density. Some studies have evaluated the optical density with Scheimpflug cameras in the early post-operative period after photorefractive keratectomy, but no studies have evaluated the long-term evolution of optical density after surface ablation when mitomycin C is used. PURPOSE: This work aimed to study the changes in corneal optical density measured with confocal microscopy in eyes treated with laser-assisted subepithelial keratectomy (LASEK) and intraoperative mitomycin C (MMC) to correct myopia. METHODS: A study of 24 consecutive myopic eyes that underwent LASEK with 0.02% MMC and a control group of 24 healthy nontreated eyes was performed. Optical density was measured using the images by the confocal microscopy of the Heidelberg Retina Tomograph II with the Rostock Cornea Module. An analysis of confocal microscopy images was performed using the ImageJ software to obtain the optical density, in gray-scale units (GSU). The optical density of the stromal bed was evaluated 3 months, 15 months, and 3 years after surgery and was compared with the optical density at the equivalent depth of the stroma in controls. RESULTS: The mean values of optical density for the LASEK group were 81.7 ± 9.7, 78.6 ± 11.7, and 73.6 ± 18.7 GSU at 3 months, 15 months, and 3 years, respectively, and it was 61.8 ± 8.2 GSU for the control group. A statistically higher optical density 3 and 15 months after LASEK with MMC was found compared with controls (P < .001). No significant difference was found in optical density at 3 years post-operatively. CONCLUSIONS: Our study suggests that, after LASEK with MMC, the anterior corneal stroma has a higher optical density at 3 and 15 months post-operatively, which gradually returns to normal values 3 years after surgery.

Analysis of corneal stromal roughness after iFS 150 kHz and LenSx femtosecond LASIK flap creation in porcine eyes.

PURPOSE: To describe and compare the stromal bed roughness obtained after laser in situ keratomileusis (LASIK) flap creation using a corneal femtosecond laser platform (iFS 150) and a "dual" femtosecond (FS) laser platform (LenSx). METHODS: This ex vivo experimental study was conducted in an animal model using 12 freshly enucleated porcine eyes, six with each femtosecond laser. The standard laser treatment parameters were used for the experiment. After LASIK flap creation, the corneal stromal roughness was assessed using atomic force microscopy (AFM) in contact mode immersed in liquid. In each sample, surface measurements were obtained in 60 regions of six eyes per FS laser in 10 20 × 20-micron areas of the central corneal stroma at 512 × 512-point resolution. The surface roughness was measured and the root-mean-square (RMS) values of the roughness were obtained. RESULTS: The mean RMS ± standard deviation values were 430 ± 150 nm for the corneal femtosecond laser platform and 370 ± 100 nm for the dual FS laser platform (P < 0.011). CONCLUSIONS: In this experimental study with AFM, we found smoother stromal beds after LASIK flap creation with LenSx compared to iFS 150 kHz. Further studies are needed to understand visual implications of the differences found.

Comparison of Two Topical Lubricants on the Corneal Surface Recovery and Patient Discomfort After Photorefractive Keratectomy.

INTRODUCTION: This study aimed to compare the effect of two preservative-free (PF) artificial tears, one containing carboxymethylcellulose (CMC) (control group) vs another containing hyaluronic acid and hydroxypropyl guar (HA + HP-guar) (study group), on the healing of the corneal epithelium and the ocular discomfort after bilateral photorefractive keratectomy (PRK) surgery. METHODS: A total of 68 patients that were scheduled to have PRK to correct myopia were randomized into two groups: 34 patients (68 eyes) in the study group and 34 patients (68 eyes) in the control group. Ocular examinations were performed on postoperative days 1, 4, 7, 30, and 90, evaluating the diameter of the de-epithelized cornea, the fluorescein staining using the Oxford scale, the tear film osmolarity and stability (tear breakup time), and the pain using visual analog scale (VAS). RESULTS: On postoperative day 4, 97% of the study eyes vs 84.4% of the control eyes were completely re-epithelized (p = 0.01). Less ocular pain was observed on postoperative day 3 in the study group (5.0 (3.0-6.0) vs 6.0 (3.5-7.0), p = 0.03). No differences were observed beyond postoperative day 7 in the healing of the corneal epithelium, non-invasive Keratograph breakup time (NIKBUT), and the self-perceived ocular discomfort between the two groups. CONCLUSION: The current study shows faster healing of the corneal epithelium and less ocular pain and discomfort in the first days after PRK with the use of topical lubricants containing HA + HP-guar compared to conventional CMC artificial tears, probably due to the different trophic effect of the aforementioned tears on the corneal epithelial cells. TRIAL REGISTRATION: EudraCT No. 2020-003488-25.

Corneal Confocal Microscopy Findings in Neuro Lyme Disease: A Case Report.

Neuro Lyme disease is caused by several bacteriae of the Borreliaceae family, such as Borrelia Miyamotoi. In late stages of illness, patients with Lyme disease may develop chronic neurologic symptoms such as cognitive disturbances or small fiber peripheral neuropathy. Confocal microscopy is a non-invasive method designed to evaluate the human cornea in vivo. Thus, all the corneal layers, including the cells and the sub-basal nerve plexus, can be easily visualized and analyzed. This is the first report of the morphology of small-fiber peripheral neuropathy analyzed by confocal microscopy in a patient diagnosed of neuro Lyme disease. The decrease in the number of unmyelinated sub-basal nerve fibers with abundant presence of dendritic cells (DC) in comparison with healthy corneas strongly supports the diagnosis of small fiber peripheral neuropathy in a case of neuroborreliosis disease.

Corneal stromal roughness after VisuMax and Intralase femtosecond laser photodisruption: An atomic force microscopy study.

PURPOSE: To compare the induced corneal stromal bed roughness measured with atomic force microscopy (AFM) after LASIK flap creation with the IntraLase 60 kHz and the VisuMax femtosecond laser platforms. METHODS: Three freshly enucleated porcine eyes were operated with each femtosecond laser in this experimental study. Standard LASIK treatment parameters were used for the experiment. After LASIK flap creation, the corneal stromal roughness was assessed using a JPK NanoWizard II® AFM in contact mode immersed in liquid. Olympus OMCL-RC800PSA commercial silicon nitride cantilever tips were used. Surface measurements were made in 10 regions of the central cornea of each sample measuring 20 x 20 microns, at 512 x 512 point resolution. Roughness was measured using the root-mean-square (RMS) value within the given regions. RESULTS: Measurements from 30 regions of the 3 eyes (10 measurements per eye) in the Intralase (FS1) group, and 30 regions of the 3 eyes (10 measurements per eye) in the VisuMax (FS2) group were analyzed. There was a statistically significant difference in mean ± standard deviation RMS values between the FS1 and the FS2 groups (360 ± 120 versus 230 ± 100 nm respectively; P< 0.00001). CONCLUSION: This AFM study indicates that the surface of the stromal bed after LASIK flap creation is smoother in the FS2 group than the FS1 group.

Corneal Ectasia Induced by Prostaglandin Analogues.

Our purpose is to document the first case of unilateral mild corneal ectasia developed in an apparently nonpredisposed cornea after topical latanoprost treatment, and its regression after treatment withdrawal. We describe a 44-year-old man with visual impairment in his left eye (OS) and a past medical history of myopic refraction and ocular hypertension with latanoprost treatment, the rest of ocular examination was normal. A decrease in visual acuity was observed with a refractive change. Corneal tomography showed features of mild corneal ectasia in his OS. Topical prostaglandin analogue therapy was removed and replaced by other antiglaucoma topical treatment. Corneal tomography returned to normal, an improvement in the quality of vision was observed and refractive astigmatism recovered to baseline values. This case illustrates that topical latanoprost does affect the matrix metalloproteinases balance in corneal extracellular matrix, and subsequently may produce a corneal weakening. Corneal biomechanical features and corneal stiffness do probably recover after topical prostaglandin analogues withdrawal.

Long-term corneal subbasal nerve plexus regeneration after laser in situ keratomileusis.

PURPOSE: To analyze the recovery of the subbasal nerve plexus in corneas treated with laser in situ keratomileusis (LASIK) at least 10 years prior compared with nonoperated corneas. SETTING: Clínica Novovisión, Madrid, Spain. DESIGN: Prospective nonrandomized observational study. METHODS: Eyes that had LASIK surgery at least 10 years before (LASIK group) were compared with nonoperated healthy eyes (control group). The subbasal nerve plexus morphology (main nerves density, nerve length, nerve branches density, grade of nerve tortuosity, and reflectivity) and the dendritic cell density from the confocal images obtained with the Heidelberg Retina Tomograph II were analyzed. RESULTS: The study comprised 47 eyes (27 eyes in the LASIK group and 20 eyes in the control group). The values were significantly lower in the LASIK group compared with the control group in main nerves density (9.15 nerves/mm2 ± 3.46 [SD] versus 11.75 ± 2.86 nerves/mm2; P = .009) and nerve branches density (2.96 ± 1.99 nerves/mm2 versus 5.35 ± 3.05 nerves/mm2; P = .002). No significant differences were found in nerve length, grade of nerve tortuosity, dendritic cell density, or subbasal nerve plexus reflectivity between the two groups. CONCLUSIONS: The outcomes suggested that the subbasal corneal nerve plexus did not completely recover its preoperative pattern at least 10 years after LASIK. Both main nerves density and nerve branches density continued to be significantly lower compared with virgin corneas after a mean 13-year follow-up, although other parameters of nerve morphology (nerve length, tortuosity, and reflectivity) returned to normal levels.

Evaluation of clarity characteristics in a new hydrophobic acrylic IOL in comparison to commercially available IOLs.

PURPOSE: To perform in vitro assessments of surface haze and roughness, subsurface nanoglistenings (SSNGs), and glistenings of a new hydrophobic acrylic intraocular lens (IOL) in comparison to commercially available IOLs. SETTING: Universities of Utah and Alcalá, and Alcon Vision, LLC. DESIGN: Experimental study. METHODS: The IOLs used were Clareon CNA0T0, Tecnis ZCB00 and Tecnis OptiBlue ZCB00V, Eternity W-60, enVista MX60, and Vivinex XY1. Surface haze was assessed by the pixel intensity units (PIU) from cross-sectional slitlamp images, and it was correlated to atomic force microscopy roughness. For SSNGs, the IOLs were artificially aged up to 10 years, followed by Scheimpflug densitometry (computer-compatible tape unit [CCTU]) measurements. For glistenings, the IOLs were immersed in a water bath and subjected to temperature changes before analysis. RESULTS: The surface haze (n = 10, PIU) was 4.25 ± 0.87 (SD) (CNA0T0), 9.50 ± 1.66 (ZCB00), 39.48 ± 1.97 (ZCB00V), 46.68 ± 3.16 (W-60), 44.70 ± 4.00 (MX60), and 4.42 ± 0.71 (XY1) (P < .001), which showed a strong correlation with surface roughness measurements (R = 0.94, P = .006). The densitometry (n = 10, CCTU at 10 years) was 7.30 ± 1.36 (CNA0T0), 11.88 ± 3.10 (ZCB00), 38.12 ± 2.24 (ZCB00V), 48.13 ± 9.44 (W-60), 20.20 ± 3.84 (MX60), and 6.75 ± 6.66 (XY1) (P < .001), with no significant differences between CNA0T0 vs. ZCB00 and XY1. The glistenings density (n = 30) was the lowest for the CNA0T0, W-60, and MX60 IOLs. CONCLUSIONS: The new Clareon CNA0T0, which is manufactured from a hydrophobic acrylic material, exhibited among the lowest levels of surface haze and roughness, SSNGs, and glistenings compared with other commercially available hydrophobic acrylic IOLs.

Comparison of visual outcomes and flap morphology using 2 femtosecond-laser platforms.

PURPOSE: To compare the 3-month postoperative refractive results and flap thickness homogeneity after correction of myopia using the Intralase femtosecond platform and the Victus dual femtosecond laser platform. SETTING: Novovision Clinic, Madrid, Spain. DESIGN: Prospective case series. METHODS: Eyes treated with a 60 kHz femtosecond laser (Group 1) and eyes treated with a dual femtosecond laser (Group 2) were included. The refractive results 3 months postoperatively were compared. The differences between the maximum and the minimum thickness point of each flap, the intraflap standard deviation (SD), and the achieved and the targeted central flap thickness were evaluated in each group. RESULTS: The study comprised 31 eyes in Group 1 and 20 eyes in Group 2. Three months postoperatively, the uncorrected distance visual acuity, residual refraction, efficacy, safety, and predictability were significantly better in Group 1. The dual femtosecond laser induced a significantly greater increase in higher-order aberrations than the conventional femtosecond laser. The mean central flap thickness was 123.2 µm ± 9.2 (SD) in Group 1 and 116.3 ± 14.4 µm in Group 2 (P = .005). The mean difference between the maximum and the minimum flap thickness points in each flap was significantly lower in Group 1 than in Group 2 (22 ± 8.3 µm versus 35.7 ± 16.9 µm) (P = .0007). The intraflap SD was significantly lower in Group 1 than in Group 2 (6.1 µm versus 10.8 µm) (P = .0001). CONCLUSION: The conventional femtosecond laser provided better efficacy, safety, predictability, and flap thickness homogeneity than the dual femtosecond laser for the correction of myopia.