Comparison of Intraocular Pressure During Corneal Flap Preparation Between a Femtosecond Laser and a Mechanical Microkeratome in Porcine Eyes

Changes in Retinal Vessel Flow after Small Incision Lenticule Extraction

Objective

In order to analyze changes in retinal vessel flow after small incision lenticule extraction (SMILE).

Methods

A total of 32 patients (62 eyes) who underwent SMILE were enrolled in this prospective study. Optical parameters, including vessel density (VD), and perfusion density (PD) of foveal, parafoveal, and perifoveal regions, respectively, were measured before surgery and at 1 day, 1 week, 1 month, and 3 months postoperation. Preoperative parameters and surgical parameters were recorded.

Results

Significant decreases in VD and PD on postoperative day 1 were detected in all quadrants, both in 3 mm and in 6 mm regions (P < 0.001). One month after surgery, VD returned to preoperative levels. None of the preoperative and surgical parameters were significantly correlated with the VD and PD fluctuations (all P > 0.05). Conclusion. VD may decrease significantly with regional disparity 1 day after SMILE while recovering at 1 month. Elevation of intraocular pressure due to suction may account for such changes.

Evaluation of peripapillary - macular microvascularity and choroidal vascularity index after refractive surgery

BACKGROUND

To evaluate the microvascularity and choroidal vascularity index (CVI) using optical coherence tomography angiography (OCTA) and OCT following femtosecond laser-assisted in-situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures.

METHODS

Patients with myopia (<-6.0D sphere) or myopic astigmatism (<-4.0D astigmatism) were enroled. The percentage of vessel density and foveal avascular zone (FAZ) size, optic disc flux index and perfusion were noted and the CVI was calculated before and after surgery.

RESULTS

Twenty-nine eyes of 16 patients in the FS-LASIK group and 30 eyes of 16 patients in the SMILE group were enroled. Macular vessel density, FAZ size, and optic disc flux index were significantly higher on postoperative 1st day compared to preoperative day (p = 0.001, p = 0.007, and p < 0.001, respectively). There was no significant difference in terms of macular and peripapillary CVI between postoperative 1st day and preoperative day (p > 0.05). All microvascular parameters were similar on postoperative 7th day and preoperative day (p > 0.05).

CONCLUSIONS

It was detected that there is a transient alteration in macular and peripapillary microvascularity after FS-LASIK/SMILE, whereas choroidal circularity is not significantly affected by these refractive surgeries.

Evaluation of the change in retinal thickness after femtosecond laser-assisted laser in situ keratomileusis and photorefractive keratectomy

PURPOSE OF THE STUDY

To investigate the change in individual retinal layer thickness by spectral-domain optical coherence tomography (SD-OCT) in eyes underwent femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and photorefractive keratectomy (PRK).

METHODS

In patients who underwent PRK and FS-LASIK, changes in the thickness of all retinal layers in the foveal, parafoveal, and perifoveal regions were evaluated by SD-OCT automated segmentation analysis at pre-operatively and different time points post-operatively.

RESULTS

Seventy-one eyes of 71 patients (38 patients in PRK, 33 patients in LASIK) were included. In the pre-operative period, mean spherical equivalent (SE), mean keratometry, axial length, and segmentation values of the retinal layers were similar (P> .05). In the PRK group, the pre-operative measurements of individual retinal layers did not show a statistically significant difference compared to the post-operative measurements on the 1st day, 1st week, and 1st month. In the FS-LASIK group, the mean inner nuclear layer (INL) thickness one day after the surgery was significantly higher than that before surgery in the foveal (21.22 ± 4.66 µm vs 19.03 ± 4.50 µm, P= .013) and parafoveal regions (41.98 ± 3.70 µm vs 40.56 ± 3.49 µm, P= .044).

CONCLUSIONS

The findings of our study suggest that the increase of INL thickness may be due to temporary structural and circulatory changes of the retina that may occur in the suction phase in the FS-LASIK procedure.

Acquired Optic Pits Associated with Laser-assisted In Situ Keratomileusis: A Case Series

Purpose

To present an association between acquired pits of the optic nerve (APON) and prior laser-assisted in situ keratomileusis (LASIK).

Materials and methods

A retrospective case series of patients with an optic disc pit on clinical exam and a history of LASIK. Spectralis Optical Coherence Tomography images and Humphrey Visual Fields were reviewed from prior visits. Extended-depth optical coherence tomography was performed of the optic nerve head at subsequent visits after patients were identified.

Results

Seven patients, aged 45-73 years, were identified each with unilateral optic disc pits. Optic disc pits were located inferior in six patients and centrally in one patient. All demonstrated thinning on optical coherence tomography and six patients had corresponding visual field defects. Four patients identified these defects after their LASIK procedure while two patients were unaware of their reproducible visual field defects. All patients were treated with drops initially. One patient underwent laser trabeculoplasty, and three underwent a trabeculectomy after demonstrating progression on maximum tolerated medical therapy.

Conclusion

This series describes a possible association between LASIK and APON. Given the similarity and severity of vision loss associated with the optic nerve pits in these patients after LASIK, increased awareness and caution is suggested while considering LASIK in susceptible individuals.

How to cite this article

Smith AK, Bussel I, Ling J, et al. Acquired Optic Pits Associated with Laser-assisted In Situ Keratomileusis: A Case Series. J Curr Glaucoma Pract 2020;14(3):106-108.

Transient effect of suction on the retinal neurovasculature in myopic patients after small-incision lenticule extraction

PURPOSE

To characterize retinal neurovasculature changes after small-incision lenticule extraction (SMILE) in myopic patients.

SETTING

Ophthalmic Center, the Second Affiliated Hospital of Guangzhou Medical University, China.

DESIGN

Prospective interventional study.

METHODS

The corrected distance visual acuity/uncorrected distance visual acuity, corrected intraocular pressure (CIOP), and corneal tomography were evaluated at baseline (PRE), postoperative day (POD) 1, and POD 7. Ganglion cell-inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were measured. The vessel area densities (VADs, %), vessel skeleton densities (VSDs, %), vessel diameter index (VDI), and fractal dimensions (Dbox) of the superficial vascular plexus (SVP) and deep vascular plexus (DVP) were measured in a circular area (ϕ 2.5 mm) centered on the fovea.

RESULTS

A total of 38 myopic patients were recruited. The GCIPL thickness was increased after SMILE at POD 1 and POD 7 (P < .01) but no significant changes in the pRNFL thickness. The VAD, VSD, and Dbox of the SVP were decreased at POD 1 (P < .01), but not at POD 7. The VDI in small vessels of the SVP and DVP was decreased at POD 1 (P < .05) and increased at POD 7 (P < .05). Changes in CIOP were positively correlated with changes in the GCIPL thickness. Changes in CIOP were negatively correlated with changes in the VAD of small vessels and the Dbox of total vessels in the DVP. Changes in CIOP were negatively correlated with the VSD and VDI of small vessels in the DVP and changes in the VDI of big vessels in the SVP.

CONCLUSIONS

The transient fluctuations in the retinal neurovasculature after SMILE may represent a characteristic homeostasis pattern in patients after refractive surgery.

Effects of SMILE Surgery on Intraocular Pressure, Central Corneal Thickness, Axial Length, Peripapillary Retinal Nerve Fiber Layer, and Macular Ganglion Cell Complex Thickness

Purpose. To evaluate the change in intraocular pressure (IOP), central corneal thickness (CCT), axial length, peripapillary retinal nerve fiber layer (RNFL) thickness, and macular ganglion cell complex (GCC) thickness after small incision lenticule extraction (SMILE) surgery. Methods. This prospective observational study was conducted in Espace Nouvelle Vision, Ophthalmological Clinic, Paris, France. Fifty eyes of 25 patients were enrolled in this study and underwent SMILE surgeries. IOP, central corneal thickness (CCT), axial length (AL), peripapillary RNFL thickness, and macular GCC thickness were measured before and at 3 months after SMILE. Results. The mean preoperative spherical equivalent was −3.15 ± 1.50 diopters (D), and the mean postoperative value was 0.15 ± 0.28 D. After SMILE surgery, IOP decreased from 15.03 ± 2.79 mmHg to 11.02 ± 2.73 mmHg and 10.02 ± 2.21 mmHg at 1 and 3 months, respectively ( $P<0.01$ for both comparisons). The mean decrease in measured IOP as a function of ablation depth was 0.065 ± 0.031 mmHg/μm. CCT decreased from 545.98 ± 26.61 μm to 478.40 ± 30.26 μm after SMILE surgery ( $P<0.01$ ). AL decreased from 24.80 ± 0.84 mm to 24.70 ± 0.83 mm ( $P<0.01$ ). There was no statistically significant change in mean peripapillary RNFL or mean GCC thickness after SMILE surgery. Conclusions. SMILE surgery modified IOP measurement, CCT, and AL but did not change peripapillary RNFL and macular GCC thicknesses. The postoperative drop in measured IOP might be explained by the decreased CCT. An accurate re-evaluation of AL should be performed before cataract surgery among post-SMILE patients.

Microvascular changes in macula and optic nerve head after femtosecond laser-assisted LASIK: an optical coherence tomography angiography study

Background

To measure the microcirculation change of macula and optic nerve head before and after femtosecond laser assisted laser in situ keratomileusis.

Methods

In total 45 eyes from 45 subjects, who underwent FS-LASIK during June 2017 to December 2017 in Guangdong Provincial People’s Hospital, were recruited in this study. Vessel density in macula and optic nerve head were measured by optical coherence tomography angiography before and after transient elevation in intraocular pressure caused by application of suction ring during surgery.

Results

Vessel density (VD) at superficial (SCP) plexus of macular region did not differ after surgery (F(3,132) = 1.41, P = 0.24), while the deep (DCP) plexus of macular region significantly decreased 1 day after surgery (P = 0.001) but returned to its baseline value 1 month postoperatively (P = 0.1). Vessel density of optic nerve head region had no significant changes after surgery (F(2.51,95.18) = 0.6, P = 0.59).

Conclusions

A short-term temporary decrease of vessel density at deep layer of macular region was observed in eyes undergoing FS-LASIK. However, the retinal capillary density went back to preoperative level 1 month after surgery. Therefore, transient IOP spike during FS-LASIK did not cause long-term decline of retinal microcirculation.

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.

[Scanning electron microscopic investigations of cutting edge quality in lamellar keratotomy using the Wavelight femtosecond laser (FS-200) : What influence do spot distance and an additional tunnel have?]

BACKGROUND

Femtosecond lasers (fs-lasers) are established cutting instruments for the creation of LASIK flaps. Previous studies often showed even rougher surfaces after application of fs-laser systems compared to lamellar keratotomy with mechanical microkeratomes. When cutting the cornea with fs-lasers, an intrastromal gas development occurs, which has a potentially negative influence on the cutting quality if the gas cannot be dissipated; therefore, manufacturers have chosen the way of gas assimilation in so-called pockets. The investigated system creates a tunnel which opens under the conjunctiva. The aim of this study was to investigate the effects of a tunnel as well as the influence of different spot distances on the quality of cut surfaces and edges.

MATERIAL AND METHODS

In this experimental study on freshly enucleated porcine eyes (n = 15), the following cuts were carried out with the FS-200 (Wavelight, Erlangen, Germany): 1. standard setting (spot and line separation 8 µm), 2. with tunnel for gas drainage, 3. without gas-conducting tunnel, 4. with increased spot spacing (spot and line separation 9 μm instead of 8 μm) and 5. with reduced spot spacing (spot and line separation 7 μm instead of 8 μm). Subsequently, scanning electron microscopy (FEI Quanta 650, Hillsboro, OR) of the cut edges and surfaces as well as the gas drain tunnel were performed. The evaluation was based on an established score.

RESULTS

The current fs-laser system (200 Hz) is able to create smooth cutting surfaces and sharp edges. The changed density of laser pulses compared to the standard settings with a reduced or increased distance between the pulses, did not achieve any further improvement in the surface quality. The gas-conducting tunnel could be detected by scanning electron microscope. In the case of cutting without a tunnel, roughened surfaces and irregularities on the cutting edges were found.

CONCLUSION

When the FS-200 fs-laser is used, LASIK cuts with very smooth cut surfaces and sharp cutting edges are achieved. This is only valid as long as an additional tunnel with the fs-laser is placed under the conjunctiva. It can be assumed that the resulting gas is effectively drained through this tunnel. The installation of the tunnel represents a new possibility to replace previous techniques of gas assimilation in deeper lying cutting areas.

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

Cataract surgery is the most common surgical procedure and femtosecond laser assisted cataract surgery (FLACS) has gained increased popularity. FLACS requires the application of a suction device to stabilize the laser head and focus the laser beam accurately. This may cause a significant escalation in intra-ocular pressure (IOP), which poses potential risks for patients undergoing cataract surgery. In this study we aimed to assess the effect of the Ziemer LDV Z8 femtosecond cataract machine on IOP. We demonstrated through a porcine model that IOP was significantly higher with a flat interface but could be abrogated by reducing surgical compression and vacuum. Pressure was lower with a liquid interface, and further altering angulation of the laser arm could reduce the IOP to 36 mmHg. A pilot series in patients showed comparable pressure rises with the porcine model (30 mmHg). These strategies may improve the safety profile in patients vulnerable to high pressure when employing FLACS with the Ziemer LDV Z8.

Bilateral Iris Atrophy after the Femtosecond Assisted Laser In Situ Keratomileusis Surgery

Purpose. To report an unknown complication of laser in situ keratomileusis (LASIK) surgery. Case Presentation. A 28-year-old female presented with photophobia and glare to our eye service. She stated in her medical history that she had undergone femtosecond assisted LASIK surgery in both eyes 15 months ago and her symptoms started just after this surgery. On admission, her best-corrected visual acuity was 10/10 in both eyes. She had mydriatic pupils with no direct light reflex. Examination of the anterior segment revealed bilateral iris atrophy projecting within the LASIK ablation zone and a transillumination defect was remarkable on the slit lamp examination. Conclusion. We hypothesized that this condition may have been caused by the abnormally increased IOP that resulted in ischemia in the iris vascular plexus during the suction process of surgery.

Laser in situ keratomileusis in 2012: a review

Laser in situ keratomileusis (LASIK) is a safe and effective treatment for refractive error. A combination of technological advances and increasing surgeon experience has served to further refine refractive outcomes and reduce complication rates. In this article, we review LASIK as it stands in late 2012: the procedure, indications, technology, complications and refractive outcomes.

Application of the femtosecond laser LASIK microkeratome in eye banking

PURPOSE OF REVIEW

To review the literature for recent advancements in the femtosecond laser technology with regard to its applications in corneal transplantation and eye banking.

RECENT FINDINGS

Advancements in corneal surgery have encouraged the use of disease-specific corneal subcomponents, utilized in procedures such as anterior-lamellar keratoplasty and endothelial keratoplasty, instead of traditional transplant procedures to minimize adverse effects of penetrating keratoplasty. Femtosecond laser microkeratomes can precisely create flaps for such transplant procedures, achieve better wound stability, and promote healing by shaped wound configurations. Laser microkeratomes have been compared to traditional mechanical microkeratomes for keratoplasty procedures from various aspects and are superior in some aspects and offer unique capabilities.

SUMMARY

Femtosecond laser applications in eye banking include preparation of donor and recipient corneas for use in penetrating keratoplasty, anterior-lamellar keratoplasty, and endothelial keratoplasty. Advantages of femtosecond laser microkeratomes include higher precision of the cut, ability to achieve thinner flaps, and wound configurations that allow greater wound stability, shorter recovery time, and less postoperative pain. However, cost and availability at the eye-bank level may hinder widespread and immediate application.

Femtosecond lasers for LASIK flap creation: a report by the American Academy of Ophthalmology

OBJECTIVE

To review the published literature to assess the safety, efficacy, and predictability of femtosecond lasers for the creation of corneal flaps for LASIK; to assess the reported outcomes of LASIK when femtosecond lasers are used to create corneal flaps; and to compare the differences in outcomes between femtosecond lasers and mechanical microkeratomes.

METHODS

Literature searches of the PubMed and Cochrane Library databases were last conducted on October 12, 2011, without language or date limitations. The searches retrieved a total of 636 references. Of these, panel members selected 58 articles that they considered to be of high or medium clinical relevance, and the panel methodologist rated each article according to the strength of evidence. Four studies were rated as level I evidence, 14 studies were rated as level II evidence, and the remaining studies were rated as level III evidence.

RESULTS

The majority of published studies evaluated a single laser platform. Flap reproducibility varied by device and the generation of the device. Standard deviations in flap thicknesses ranged from 4 to 18.4 μm. Visual acuities and complications reported with LASIK flaps created using femtosecond lasers are within Food and Drug Administration safety and efficacy limits. Of all complications, diffuse lamellar keratitis is the most common after surgery but is generally mild and self-limited. Corneal sensation was reported to normalize by 1 year after surgery. Unique complications of femtosecond lasers included transient light-sensitivity syndrome, rainbow glare, opaque bubble layer, epithelial breakthrough of gas bubbles, and gas bubbles within the anterior chamber.

CONCLUSIONS

Available evidence (levels I and II) indicates that femtosecond lasers are efficacious devices for creating LASIK flaps, with accompanying good visual results. Overall, femtosecond lasers were found to be as good as or better than mechanical microkeratomes for creating LASIK flaps. There are unique complications that can occur with femtosecond lasers, and long-term follow-up is needed to evaluate the technology fully.

Laser refractive surgery in diabetic patients: a review of the literature

BACKGROUND

The purpose of this study was to evaluate the current recommendations regarding laser refractive surgery in patients with diabetes mellitus and to assess whether these patients make appropriate candidates for laser vision correction.

METHODS

A literature search was conducted to identify current research on the ocular complications of diabetes and original publications on laser refractive surgery in diabetic patients.

RESULTS

Diabetes was associated with several ocular complications. Initially the US Food and Drug Administration listed these complications as justification to advise against refractive surgery in patients with diabetes. However, recent studies on laser in situ keratomileusis in diabetic patients indicate that this procedure may be safe in diabetic patients with very well controlled systemic disease and no ocular manifestations.

CONCLUSION

Laser refractive surgery may be performed safely in a very selected group of patients with diabetes.