Comparison of intra-ocular pressure changes with liquid or flat applanation interfaces in a femtosecond laser platform

Comparative study of FLACS vs conventional phacoemulsification for cataract patients with high myopia

PURPOSE

To compare the short-term changes in cornea, retina, and choroid of femtosecond laser-assisted cataract surgery (FLACS) with conventional phacoemulsification (CPS) in high myopia patients with cataract.

SETTING

Affiliated Hospital of Nantong University, Jiangsu Province, China.

DESIGN

Prospective single-center study.

METHODS

Demographics, ocular clinical features, ultrasound power, absolute phacoemulsification time, and effective phacoemulsification time were recorded for each patient. Endothelial cell density (ECD), central corneal thickness (CCT), corrected distance visual acuity (CDVA), intraocular pressure (IOP), center foveal thickness (CFT), subfoveal choroidal thickness (SFCT), and choroidal vascularity index (CVI) were evaluated preoperatively and at 1 week, 1 month, and 3 months postoperatively. Intraoperative parameters and intraoperative/postoperative complications were recorded.

RESULTS

97 eyes (46 eyes and 51 eyes in the FLACS and CPS groups, respectively) were included and analyzed. Effective phacoemulsification time was lower in the FLACS group compared with the CPS group ( P < .05). The increase in CCT was significantly lower in the FLACS group compared with the CPS group at 1 week and 1 month ( P < .05). CDVA and IOP were similar in both groups at the final visit ( P > .05). The ECD decreased was lower among CPS patients compared with FLACS patients. CFT, SFCT, and CVI increase in both groups but were increased more in the CPS group with high myopia patients. No serious complications occurred in either group.

CONCLUSIONS

FLACS is a more safety and effective in cataract patients with high myopia. It has advantages in effectively reducing EPT and promoting faster recovery of the cornea, macular, and choroidal thickness.

The necessity of pretreatment with 0.1% pranoprofen for femtosecond-assisted cataract surgery: A single-center, randomized controlled trial

Purpose

To explore the effect of the variation of pupil diameter (PD) and intraocular pressure (IOP) induced by femtosecond laser treatment on the subsequent phacoemulsfication and intraocular lens implantation. And whether the application of 0.1% pranoprofen could significantly reduce the miosis and increased IOP caused by femtosecond laser treatment in femtosecond laser-assisted cataract surgery (FLACS).

Methods

In this study, patients were pretreated with (trial group) or without (control group) topical 0.1% pranoprofen. The PD and IOP were measured at different time points within 30 ​min after the completion of the femtosecond laser treatment.

Results

The comparisons of the two groups showed the PD of patients pretreated with 0.1% pranoprofen was significantly larger than that of the control only at 15 ​min after FLACS (P ​= ​0.046), and there was no significant difference in IOP at any time point (P ​> ​0.05). Neither the ratio of significant miosis (PD ​≤ ​5 ​mm) nor intraocular hypertension (IOP ≥30 ​mmHg) was significantly different between the control group (1.72%, 6.67%) and the trial group (1%, 4.17%) (P ​> ​0.05).

Conclusions

The PD and IOP of patients undergoing FLACS showed fluctuations within a small range. The rates of significant miosis and intraocular hypertension are very low, it is safe for surgeons to complete the follow-up procedures within 30 ​min after femtosecond laser treatment. Pretreatment with 0.1% pranoprofen exerted a slight, albeit significant prophylactic effect preventing pupil miosis. However, it provided only a limited benefit in patients undergoing FLACS without other complications.

The Effects of High Energy Capsulotomy on Aqueous Cytokine Profiles and Pupil Size During Femtosecond Laser-Assisted Cataract Surgery

PURPOSE

To assess whether aqueous cytokine profiles and pupil size are altered when high capsulotomy energy is used in eyes undergoing femtosecond laser-assisted cataract surgery (FLACS), and if preoperative use of a topical non-steroidal anti-inflammatory drug (NSAID) has an effect on this.

METHODS

This prospective study recruited 83 eyes (63 patients) that were allocated to four treatment groups: conventional phacoemulsification (n = 20 eyes); FLACS with 90% capsulotomy energy without NSAID pretreatment (n = 20 eyes); FLACS with 90% capsulotomy energy with NSAID pre-treatment (n = 21 eyes); and FLACS with 150% capsulotomy energy with NSAID pretreatment (n = 22 eyes). Aqueous humor was collected before and after phacoemulsification to assess cytokine profiles. Pupil size was measured before and after laser capsulotomy.

RESULTS

FLACS increased aqueous concentrations of pros-taglandin E₂ (PGE₂), interferon γ (IFN-γ), and interleukin 6 (IL-6) compared to conventional phacoemulsification. However, when increasing capsulotomy energy from 90% to 150% (with topical NSAID pretreatment), there was no significant increase in aqueous concentrations of PGE₂ (37.7 ± 21.7 vs 33.6 ± 27.6 pg/mL, P = .99), IFN-γ (3.6 ± 1.1 vs 3.6 ± 0.8 pg/mL, P = .99), or IL-6 (7.1 ± 2.9 vs 6.3 ± 2.4 pg/mL, P = .99). For 90% and 150% capsulotomy energy, there was significant miosis following laser capsulotomy. Increased PGE₂ concentration was significantly correlated with a reduction in pupil area (r = -0.58, P < .001) and pupil diameter (r = -0.57, P < .001). However, when a topical NSAID was given preoperatively, there was no difference in the degree of miosis between the 90% and 150% capsulotomy energy groups.

CONCLUSIONS

Pretreatment with a topical NSAID prevented a rise in PGE₂, IFN-γ, and IL-6 levels and excessive miosis when a higher capsulotomy energy was used. When a topical NSAID is used preoperatively, it is safe to use higher capsulotomy energy settings (with a low pulse energy femtosecond laser system) to achieve a satisfactory capsulotomy. [J Refract Surg. 2022;38(9):587-594.].

Femtosecond laser-assisted corneal transplantation with a low-energy, liquid-interface system

Femtosecond laser-assisted keratoplasty has been proposed as a treatment option for corneal transplantation. In this study, we investigated and compared the outcomes of Ziemer Z8 femtosecond laser (FSL)-assisted penetrating keratoplasty (PK) using a liquid interface versus flat interface. Thirty fresh porcine eyes underwent FSL-assisted PK with the Z8 using different levels of energies (30%, 90% or 150%) and different interfaces (liquid or flat). The real-time intraocular pressure (IOP) changes, incision geometry, corneal endothelial damage, as well as the accuracy of laser cutting and tissue reaction, were performed and compared. We found that the overall average IOP at all laser trephination stages was significantly higher with the flat interface, regardless of the energy used (68.9 ± 15.0 mmHg versus 46.1 ± 16.6 mmHg; P < 0.001). The overall mean laser-cut angle was 86.2º ± 6.5º and 88.2º ± 1.0º, for the liquid and flat platform respectively, indicating minimal deviation from the programmed angle of 90º. When high energy (150%) was used, the endothelial denuded area was significantly greater with the flat interface than with liquid interface (386.1 ± 53.6 mm² versus 139.0 ± 10.4 mm²P = 0.02). The FSL cutting did not cause obvious tissue reaction alongside the laser cut on histological evaluation. The results indicated a liquid interface is the preferable choice in FSL-assisted corneal transplantation.

Association between Ocular Parameters and Intraocular Pressure Elevation during Femtosecond Laser-Assisted Cataract Surgery in Open-Angle Glaucoma and Nonglaucoma Individuals

In this study, we evaluate the association between biometrics and intraocular pressure (IOP) during femtosecond laser-assisted cataract surgery (FLACS) in normal patients and those with open-angle glaucoma (OAG). A retrospective cross-sectional study was conducted. A total of 103 patients who had received elective FLACS were enrolled, and those with OAG who received FLACS were further divided into a subgroup. The perioperative IOP of FLACS was measured before, during, and after the suction procedure. Demographic data and preoperative biometrics were collected from the medical records. The generalized linear model was applied to yield the adjusted odds ratio (aOR) and corresponding 95% confidence interval (CI) of each biometric for the IOP elevation in the whole group and the OAG subgroup. The mean preoperative IOP was 20.96 ± 4.79 mmHg, which rose to 55.37 ± 11.58 mmHg during suction, and decreased to 23.75 ± 6.42 mmHg after suction; the IOP both during and after suction was significantly higher than the presuction IOP (both p < 0.001). The mean IOP elevation was 34.41 ± 9.70 mmHg in the whole study population, and the difference in IOP elevation between OAG and nonglaucoma subgroups was not significant (p = 0.159). In the whole group, the presuction IOP, postdilated pupil size (PPS), and central corneal thickness (CCT) were positively corrected to higher IOP elevation (all p < 0.05), while axial length (AL) was negatively related to IOP elevation (aOR: 0.020, 95% CI: 0.008–0.699, p = 0.042). For the OAG subgroup, the longer AL was more significantly correlated to lower IOP elevation compared to those without glaucoma (aOR: 0.231, 95% CI: 0.106–0.502, p = 0.006). In conclusion, presuction IOP, PPS, and CCT are related to higher IOP during FLAC, while the AL is negatively correlated to the IOP elevation in FLACS, especially for patients with OAG. Reviewing these parameters before FLACS may enable physicians to find patients who are at risk of IOP elevation.

Randomized Controlled Trial Comparing 1-Year Outcomes of Low-Energy Femtosecond Laser-Assisted Cataract Surgery versus Conventional Phacoemulsification

Purpose: To compare 1-year clinical outcomes, phacoemulsification energy, aqueous profiles, and patient-reported outcomes of low-energy femtosecond laser-assisted cataract surgery (FLACS) vs. conventional phacoemulsification.

Methods: The study is a randomized controlled trial (RCT) with paired-eye design. Eighty-five patients were randomized to receive FLACS (Ziemer LDV Z8) in one eye and conventional phacoemulsification in the fellow eye. Clinical data including phacoemulsification energy parameters (cumulative dissipated energy, phacoemulsification power, and phacoemulsification time), uncorrected and corrected distance visual acuities (UCDVA and BCDVA), manifest refraction spherical equivalent (MRSE), central corneal thickness (CCT), endothelial cell count (ECC), anterior chamber flare, and post-operative complications were obtained for 1 year. Aqueous humor was collected for the analysis of prostaglandin (PGE)₂, cytokines and chemokines concentrations. Patients' reported-outcomes on surgical experiences were evaluated using an in-house questionnaire.

Results: Compared to conventional phacoemulsification, the low-energy assisted FLACS group had significantly less ECC reduction at 3 months (1.5 ± 0.3% vs. 7.0 ± 2.4%; P < 0.01) and 1 year (8.2 ± 2.8% vs. 11.2 ± 3.6%; P = 0.03). There were no significant differences in the phacoemulsification energy parameters, UCDVA, BCDVA, MRSE, CCT, occurrence of post-operative complications between the 2 groups throughout post-operative 1 year. Patients' subjective surgical experiences, including the surgical duration and perceived inconvenience, were comparable between the 2 groups. FLACS resulted in significantly higher aqueous PGE₂ (P < 0.01), interleukin (IL)-6 (P = 0.03), IL-8 (P = 0.03), and interferon (IFN)-γ (P = 0.04) concentrations and greater anterior chamber flare at 1 day (P = 0.02).

Conclusions: Our RCT presented 1-year longitudinal clinical and laboratory data. The long-term ECC result was more favorable in low-energy FLACS. The rest of the intraoperative and post-operative outcomes, as well as patient-reported outcomes, were comparable between these two procedures.

Advances in refractive corneal lenticule extraction

Refractive errors are the leading cause of reversible visual impairment worldwide. In addition to the desired spectacle independence, refractive procedures can improve quality of life, working ability, and daily working performance. Refractive corneal lenticule extraction (RCLE) is a relatively new technique, dependent only on a femtosecond laser (FS). This leads to potential benefits over laser-assisted in situ keratomileusis (LASIK) including a quicker recovery of dry eye disease, a larger functional optical zone, and no flap-related complications. SMILE, available with the VisuMax FS (Carl Zeiss Meditec AG, Jena, Germany), is the most established RCLE application, offering visual and refractive outcomes comparable to LASIK. SmartSight (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany) and CLEAR (Ziemer Ophthalmic Systems AG, Port, Switzerland) are two new RCLE applications that received Conformité Européenne (CE) approval in 2020. In this article, we review refractive and visual outcomes, advantages, and disadvantages of RCLE and also report on the latest advances in RCLE systems.

The effects of laser displacement on femtosecond laser-assisted conjunctival autograft preparation for pterygium surgery

AIMS

To evaluate the effects of no-suction femtosecond laser (FSL) stability on conjunctival autograft (CAG) dissection in pterygium surgery.

METHODS

Prospective analysis of 35 eyes from 34 subjects who underwent femtosecond laser-assisted pterygium surgery with the Ziemer Z8 laser (Ophthalmic Systems AG, Switzerland). Intraoperative absolute FSL displacements were measured and correlated with the duration and ease of CAG peel, CAG thickness, measured with intraoperative optical coherence tomography, and deviation from intended graft thickness.

RESULTS

The median absolute FSL displacement was 22 μm (interquartile range [IQR] 14.7 to 60.8), while median vertical FSL displacement was 14.7 μm (IQR 7.3 to 44) and median horizontal FSL displacement was 22.0 μm (IQR 14.7 to 44). 65.7% had a grade 1 peel, 11.4% had grade 2 peel, 14.3% had grade 3 peel and 8.6% had grade 4 peel. The median duration of CAG peel was 5.4 seconds (IQR 3 to 21.4). The median CAG thickness was 69 μm (IQR 60.3 to 78.5), and the median deviation from targeted graft thickness was 9 μm (IQR 1 to 16). Eyes with more difficult peels and longer duration of CAG peels had significantly greater vertical FSL displacements (p = 0.04 and 0.02 respectively), but not horizontal displacement, age, ethnicity, CAG thickness or deviation from original thickness, compared to those with better quality and shorter duration peels. 1 eye (2.9%) had an incomplete CAG peel with a buttonhole and 2 eyes had graft tears (5.7%).

CONCLUSION

Micro-displacements during the suction-free CAG preparation are common but they did not affect the quality of the CAG peel, duration of peel, or CAG thickness. However, vertical globe displacement during FSL-assisted CAG creation was significantly associated with a more difficult and longer CAG peel duration. This highlights the importance of the cornea traction suture fixation to ensure stability of the eye during FSL application.

Evaluation of femtosecond laser-assisted anterior capsulotomy in the presence of ophthalmic viscoelastic devices (OVDs)

The introduction of femtosecond laser-assisted cataract surgery is an alternative approach to conventional cataract surgery. Our study aimed to determine the effectiveness of femtosecond laser-assisted capsulotomy in the presence of different ophthalmic viscoelastic devices (OVDs) in the anterior chamber. Fresh porcine eyes (n = 96) underwent LDV Z8-assisted anterior capsulotomy, either in the presence of an OVD (Viscoat, Provisc, Healon, Healon GV or HPMC) or without, using 90% and 150% energies respectively. Following that, the capsule circularity, tag’s arc-length, tag-length, tag-area and rupture strength (mN) of the residual capsular bag were evaluated. We found that increasing energy from 90 to 150% across the OVD sub-groups improved the studied capsulotomy parameters. Amongst the 90% energy sub-groups, the circularity and tag-parameters were worse with Viscoat and Healon GV, which have higher refractive index and viscosity compared to the aqueous humour. Using 150% energy, Healon GV showed a significantly worse total arc-length (p = 0.01), total tag-length (p = 0.03) and total tag-area (p = 0.05) compared to the control group. We concluded that; an OVD with a refractive index similar to aqueous humour and lower viscosity, such as Healon or Provisc, as well as a higher energy setting, are recommended, to enhance the efficacy of laser capsulotomy.

First Experience in Small Incision Lenticule Extraction with the Femto LDV Z8 and Lenticule Evaluation Using Scanning Electron Microscopy

Purpose

To evaluate the specifications and technique properties of the new Femto LDV Z8 in creating intrastromal refractive lenticules during small incision lenticule extraction (SMILE).

Methods

Six enucleated porcine eyeballs were equally divided into two groups (Femto LDV Z8 or VisuMax) and were randomly assigned to three experienced refractive surgeons who performed SMILE on each group. Five intraoperative time parameters and surgeons' satisfaction on the surgical procedure were compared between two groups. Postoperatively, the roughness of the lenticule surfaces and the irregularity of edges were observed by scanning electron microscopy (SEM) and were also compared between the two groups.

Results

Longer time on suction peak pressure, total laser application, and total surgery were spent in the Femto LDV Z8 group as compared with the VisuMax group. The Femto LDV Z8 group applied OCT scanning and offsetting before performing the laser procedure, which expended more time for these crucial steps. The widest range of surgeons' satisfaction scores was found in the step of lenticule interface identification of the Femto LDV Z8 group. The roughness scores of the anterior and posterior lenticule surfaces were statistically less in the Femto LDV Z8 group than in the VisuMax group (anterior, ×180, p=0.039; anterior, ×250, p=0.337; posterior, ×180, p=0.006; and posterior, ×250, p=0.007).

Conclusions

Femto LDV Z8 showed promising performances as a novel SMILE equipment for the correction of myopia. It has special and unique features for SMILE procedures, which need more learning and researching processes. With its low-energy high-frequency nJ-level laser system, the Femto LDV Z8 provided smoother lenticule surface than VisuMax.

[What will cataract surgery look like in the future? Alternatives in the pipeline]

Phacoemulsification is the most frequently performed surgery in the world. Over the past few years, this surgery seems to have reached a plateau with no further innovative breakthroughs. In this paper, we focus on alternatives techniques, the latest innovations, and the research and development pipeline in this field.

Impact of baseline IOP, vacuum, and different docking mechanisms, and their interaction on IOP rise in femtosecond laser-assisted refractive and cataract surgery

PURPOSE

To study the intraocular pressure (IOP) variation during vacuum and docking of femtosecond laser application.

SETTING

Department for Ophthalmology, Kepler University Hospital, Johannes Kepler University Linz, Austria.

DESIGN

Experimental study.

METHODS

Intracameral intraocular pressure (IOP) was monitored in 30 porcine ex vivo models using a dual femtosecond laser platform (VICTUS). Five different baseline IOP levels (10 to 30 mm Hg) were assessed during fluid-filled (liquid) docking, full-contact (applanating) docking, and vacuum application without docking.

RESULTS

Raising the baseline intracameral IOP from 10 to 30 mm Hg increased the IOP from 27.55 mm Hg ± 5.93 (SD) to 56.85 ± 6.10 mm Hg in the fluid-filled docking group, and from 60.91 ± 8.41 mm Hg to 90.11 ± 6.64 mm Hg in the full-contact docking group. The full-contact docking procedure per se (excluding vacuum effect) increased the IOP by 61.7% (+36.58 ± 5.84 mm Hg). In contrast, fluid-filled docking (excluding vacuum effect) raised the IOP by only 3.1% (+0.72 ± 2.71 mm Hg). Each 5 mm Hg reduction of baseline IOP resulted in a mean IOP reduction of 7.33 ± 3.05 mm Hg in the fluid-filled group, and 7.30 ± 6.88 mm Hg in the full-contact docking group (P < .001). Decreasing baseline intracameral IOP from 15 to 10 mm Hg resulted in the highest IOP reduction between all subgroups (P < .01).

CONCLUSIONS

Baseline IOP, docking procedures, and vacuum influenced IOP during femtosecond laser application in a synergistic manner. Lowering the baseline intracameral IOP resulted in a significantly lower IOP during fluid-filled docking for cataract surgery and full-contact docking for refractive surgery. Full-contact (applanating) docking resulted in a significantly higher IOP elevation compared with similar IOP values found during fluid-filled (liquid) docking and the application of the suction ring alone without docking.

Impact of Patient Interface Diameter and Vacuum Level on Suction Stability Using a Flat Applanating Interface for Femtosecond Laser-Assisted LASIK

PURPOSE

To investigate the impact of different patient interface (PI) diameters and different vacuum levels on the suction stability during vacuum application for femtosecond laser-assisted LASIK.

METHODS

Break-away forces as a marker for suction stability were measured by an automated test bench set-up. The test bench was based on a customized stamp connected to a digital load cell. Three flat applanating PI with different diameters (8.5, 9.5 and 10.0 mm) and four different vacuum levels (500, 600, 700 and 800 mbar) were investigated using the FEMTO LDV Z8 (Ziemer Ophthalmic Systems AG, Switzerland).

RESULTS

Mean break-away force was 5.23N (±0.99N) using the 8.5 mm PI and 500 mbar vacuum, 8.18N (±1.39N) using the 8.5 mm PI and 800 mbar, 3.37N (±0.56N) using the 10.0 mm PI and 500 mbar, and 6.14N (±0.68N) using the 10.0 mm PI and 800 mbar vacuum (p < .001; CI95%). Increasing the PI diameter from 8.5 to 10.0 mm resulted in a 28.89% (+1.97 ± 1.02N) lower break-away force (p < .001) when using default vacuum settings (700 mbar) compared to increasing vacuum from 500 to 800 mbar, which resulted in a 60.37% (+1.95 ± 1.40N) higher mean break away force (p < .001).

CONCLUSION

The vacuum level and the diameter of the PI showed significant impact on suction stability measured as break-away force during flat applanating docking for corneal and refractive surgery. Break-away forces were inversely related to the PI diameter and directly to the vacuum level. Increasing the PI diameter by one step or reducing vacuum by 100 mbar resulted in a comparable decrease of break-away forces. Therefore, the surgeon could potentially maintain stabile suction by increasing vacuum when choosing a larger PI diameter to obtain a larger treatment zone. Furthermore, reduction of the PI diameter and/or increasing vacuum could help improving suction stability in situations of poor suction and in situations with increased risk of suction loss during LASIK.

Preoperative intraocular pressure as a strong predictive factor for intraocular pressure rise during vacuum application in femtosecond laser-assisted cataract surgery

PURPOSE

To evaluate the effect of preoperative intraocular pressure (IOP) and the vacuum level on IOP during femtosecond laser-assisted cataract surgery.

METHODS

Intraocular pressure was measured in 40 enucleated porcine eyes by intracameral manometry prior, during and after vacuum application using the VICTUS femtosecond laser platform (Bausch&Lomb, Technolas Perfect Vision GmbH, Germany). Twenty combinations of different preoperative IOP levels (12, 16, 20 and 24 mmHg) and different vacuum levels (350-550 mbar) were investigated.

RESULTS

Multivariate regression analysis indicated that both the vacuum level (beta = 0.138; p < 0.001) but much stronger the preoperative IOP (beta = 0.861; p < 0.001) were predictive factors for IOP rise during vacuum application. Mean IOP was 28.23 ± 3.86, 34.23 ± 3.92, 40.35 ± 4.41 and 46.82 ± 4.11 mmHg in groups with baseline IOP of 12, 16, 20 and 24 mmHg, respectively. In the 350, 450 and 550 mbar group, and mean IOP was 35.85 ± 7.85, 37.33 ± 7.90 and 39.00 ± 8.04 mmHg, respectively. Lowering the preoperative IOP by 2 mmHg and reducing the vacuum from maximum to minimum resulted in a similar reduction in IOP during vacuum application (-3.10 ± 0.79 mmHg versus -3.15 ± 0.88 mmHg; p = 0.015). Furthermore, decreasing the baseline IOP from 20 to 12 mmHg resulted in a 30.0% reduction in intraoperative IOP.

CONCLUSION

Preoperative IOP was a stronger predictive factor for intraoperative IOP rise than the applied vacuum level. Measurements and critical interpretation of preoperative IOP in a preliminary examination could help estimating the individual risk of significant IOP rise during femtosecond laser-assisted cataract surgery and could help taking early countermeasures in selected cases. Due to the porcine ex vivo model, further studies are needed to verify these findings.

Changes in Pupil Area during Low-energy Femtosecond Laser-assisted Cataract Surgery

Purpose

To study the potential changes in pupil area within low-energy femtosecond-laser assisted cataract surgery (FLACS).

Methods

A retrospective assessment of the pupil size was performed in the eyes undergoing FLACS using the Ziemer LDV Z8. We measured the pupil diameters as part of the images taken preoperatively and at the completion of laser pretreatment (after releasing the suction). We calculated the pupil area in 40 eyes of 40 patients (14 right and 26 left eyes). The mean ± standard deviation (SD) of age of the patients was 74 ± 7.4 years (range: 51-87). Paired t-test was used for statistical analyses. Subgroups were built with reference to age and preoperative pupil area (smaller than or equal to the median versus larger than the median).

Results

The mean ± SD axial length, anterior chamber depth, white-to-white distance and lens thickness were 24.01 ± 1.47, 3.23 ± 0.4, 11.97 ± 0.49, and 4.59 ± 0.41 mm, respectively. The mean ± SD pupil area was 39.33 ± 7.1 mm 2 preoperatively and 39.3 ± 6.75 mm 2 after laser pretreatment. The mean ± SD change in pupil area was -0.03 ± 2.12 mm 2 . There were no statistically significant changes between preoperative and post-laser pupil areas (P = 0.93, 95% CI: -0.71 to 0.65). Comparisons within subgroups also did not detect pupil area reduction.

Conclusion

This study did not detect statistically significant changes in pupil area after laser pretreatment using low-energy FLACS. This observation is in contrast to previous studies using other laser platforms.

Effect of femtosecond laser-assisted lens surgery on the optic nerve head and the macula

AIM

To evaluate the effect of femtosecond laser-assisted lens surgery (FLALS; cataract surgery or refractive lens exchange) on the structure of the optic nerve head and the macula.

METHODS

This prospective longitudinal study included healthy eyes undergoing FLALS. Eyes with glaucoma or any other ocular disease that could alter optical coherence tomography results were excluded. Retinal nerve fiber layer (RNFL), Bruch's membrane opening-minimum rim width (BMO-MRW) and macular thickness (MT) were measured preoperatively, 1 and 6mo after surgery using spectral-domain optical coherence tomography (SD-OCT). Changes between preoperative and postoperative values were evaluated.

RESULTS

A total of 87 eyes of 46 patients were included in this study. Preoperative RNFL, BMO-MRW and MT in microns (µm) were 100.77±10.39, 330.31±49.99 and 276.30±33.39, respectively. Postoperative RNFL, BMO-MRW and MT were 104.74±11.55, 348.32±54.05 and 279.83±22.65 1mo after surgery and 102.93±11.17, 343.11±53.4 and 278.90±22.19 6mo after surgery, respectively; which equals an increase of 3.93%, 5.45% and 1.27%, respectively, 1mo after surgery, and 2.14%, 3.87% and 0.94% 6mo after surgery. The differences between the preoperative and the postoperative RNFL and BMO-MRW values were statistically significant (P<0.001). Regarding MT values, there were not statistically significant differences (P=0.26).

CONCLUSION

Our study suggests that FLALS does not have a negative impact on the structural status of the optic nerve head in healthy eyes, assessed by SD-OCT. There is a slight increase in the values of RNFL, BMO-MRW and MT 1mo and 6mo after surgery.

Intraoperative Optical Coherence Tomography-Guided Femtosecond Laser-Assisted Deep Anterior Lamellar Keratoplasty

PURPOSE

To describe the feasibility and outcomes of intraoperative optical coherence tomography (OCT)-guided, femtosecond laser-assisted deep anterior lamellar keratoplasty in which the lamellar and tunnel cuts were completed by laser.

METHODS

The Ziemer Z8 system was used to scan the corneas intraoperatively and guide the stromal lamellar and tunnel cuts created by the laser. Thirty porcine eyes and 3 human cadaver globes were used to evaluate the accuracy of laser-created intrastromal tunnels and the feasibility of achieving big-bubble pneumatic dissection. The tunnel distance above the Descemet membrane (Dt-dm) was set at 100 and 130 μm, and the accuracy of laser cut was assessed by anterior segment OCT and histological sections. Fourteen patients with keratoconus or corneal scars were then included to evaluate the clinical outcomes.

RESULTS

The deviation from the targeted Dt-dm was 5.5% to 8.6% and 0.7% to 9.8% for the 100 and 130 μm groups, respectively. The achieved thickness had a significantly and positively strong correlation with the targeted thickness (r = 0.86; P < 0.001). In all cases, the anterior stromal lamella was removed without difficulty, except in the patients with corneal scars in whom some remaining stromal fiber attachments were observed. A type 1 big bubble was successfully achieved in all patients.

CONCLUSIONS

We present the accuracy and clinical outcomes of femtosecond laser-assisted, intraoperative OCT-guided deep anterior lamellar keratoplasty, in which controlled lamellar and tunnel cuts at desired depths were performed by laser in one step, and a successful big bubble was achieved.

Retinal nerve fiber layer thickness after laser-assisted subepithelial keratomileusis and femtosecond LASIK: a prospective observational cohort study

Purpose

Based on the assumption that high levels of intraocular pressure (IOP) during femtosecond laser-assisted in situ keratomileusis (FS-LASIK) may compromise the retinal nerve fiber layer (RNFL), newer femtosecond platforms that operate without causing significant IOP elevation have been developed in recent years. However, this assumption has not been adequately tested. The aim of the current study was to evaluate possible changes in RFNL thickness in nonglaucomatous myopic patients undergoing FS-LASIK using the 60 KHz IntraLase^® device that significantly elevates the IOP for an appreciable period of time vs an advanced surface ablation technique (laser-assisted subepithelial keratomileusis, LASEK) that does not induce any IOP elevation.

Methods

This was a prospective, observational, controlled cohort study. One randomly selected eye of 114 consecutive eligible patients was analyzed. Inclusion criteria were myopia up to -6.00 diopters and astigmatism up to -2.00 diopters. As clinically indicated, 50 patients underwent LASEK and 64 underwent FS-LASIK. The RNFL thickness was determined with a spectral-domain optical coherence tomography device preoperatively and 3 months postoperatively by the same masked observer.

Results

There was no significant difference in preoperative refractive error, age, or sex between the groups. Preoperatively, central corneal thickness was significantly lower in the LASEK group (529.1±36.1 vs 562.4±31.6 µm, P=0.001). For the LASEK group, there was no significant difference between preoperative and postoperative RNFL thickness in the studied sectors (superior-temporal, temporal, inferior-temporal, average). For the FS-LASIK group, compared to preoperative RNFL measures, statistically significant thicker postoperative values were found for the average RNFL (mean difference: 0.67 µm, 0.7% increase, P=0.008) and the inferior-temporal sector (mean difference: 0.92 µm, 0.6% increase, P=0.02).

Conclusion

LASIK with a femtosecond platform that induces high intraoperative IOP did not cause RNFL thinning. The observed differences between preoperative and postoperative values are below the axial resolution limit of optical coherence tomography devices.

Temperature- and wavelength-insensitive parametric amplification enabled by noncollinear achromatic phase-matching

Optical parametric chirped-pulse amplification (OPCPA) has been demonstrated to be a promising approach for pushing femtosecond pulses towards ultra-high peak powers. However, the future success of OPCPA strongly relies on the ability to manipulate its phase-matching (PM) configuration. When a high average power pump laser is involved, the thermal effects in nonlinear crystals induce phase-mismatch distortions that pose an inherent limitation on the conversion efficiency. Here, we demonstrate that the noncollinear configuration previously adopted for wavelength-insensitive PM can be employed for temperature-insensitive PM when the noncollinear angle is properly reset. Simultaneous temperature- and wavelength-insensitive PM is realized for the first time by imposing such a temperature-insensitive noncollinear configuration with an angularly dispersed seed signal. Based on the lithium triborate crystal, the proposed noncollinear achromatic PM has a thermal acceptance 6 times larger than that of the conventional wavelength-insensitive noncollinear PM and has a sufficient spectral acceptance to support pulse durations of ~20 fs at 800 nm. These achievements open new possibilities for generating ultra-high peak power lasers with high average power.

The effects of a low-energy, high frequency liquid optic interface femtosecond laser system on lens capsulotomy

The introduction of femtosecond laser assisted cataract surgery (FLACS) is a paradigm changing approach in cataract surgery, the most commonly performed surgical procedure. FLACS has the potential to optimize the creation of an anterior lens capsulotomy, a critical step in accessing the cataractous lens. The merits of using a laser instead of a manual approach include a potentially more circular, consistent, and stronger aperture. In this study we demonstrated for the first time in both a porcine and human experimental setting that with a low energy, high repetition FLACS system, that a circular, smooth and strong capsulotomy was achievable. While there was no demonstrable difference in the resistance to rupture before or after the removal of the nucleus, larger capsulotomies had an increase in tensile strength. The LDV Z8 system appeared to create circular, rupture-resistant and smooth capsulotomies in both porcine and more importantly human globes.