Intrastromal Pockets Research Articles

Femtosecond laser applications in corneal surgery

Abstract Femtosecond laser (FSL) applications in corneal surgery have increased since its inception. Corneal surgery has undergone a tremendous transformation thanks to the introduction of FSL technology. This laser makes precise, three-dimensional incisions while causing minimal damage to surrounding tissue. This review updates and summarizes current and upcoming FSL applications in corneal surgery, current commercially available FSL, and its respective applications. Refractive surgery applications include laser in-situ keratomileusis flaps, refractive corneal lenticule extraction such as small incision lenticule extraction, astigmatic keratotomy, intracorneal ring segments tunnels for keratoconus including corneal allogenic intrastromal ring segments, and presbyopia treatments with intrastromal pockets for corneal inlays and intrastromal incisions (INTRACOR). Keratoplasty applications include penetrating keratoplasty trephination; superficial and deep anterior lamellar keratoplasty trephination, lamellar dissection, and tunnel creation; posterior lamellar keratoplasty donor and recipient preparation; Bowman layer transplantation donor, and recipient preparation; and stromal keratophakia. Other applications include conjunctival graft preparation in pterygium surgery, and keratopigmentation (corneal tattooing). FSL is a surgical instrument widely used in corneal surgery because it improves reproducibility and safety in many procedures.

Mechanism of fluid leak in non-traumatic corneal perforations: an anterior segment optical coherence tomography study

AimNon-traumatic corneal perforations (CPerfs) may present with shallow/flat or formed anterior chamber (AC). This study uses anterior segment optical coherence tomography (ASOCT) to ascertain these differences.MethodThe study included 14 eyes...

Confocal and Histological Features After Poly(Ethylene Glycol) Diacrylate Corneal Inlay Implantation.

PurposeTo evaluate the in vivo biocompatibility of photopolymerized poly(ethylene glycol) diacrylate (PEGDA) intrastromal inlays in rabbit corneas.MethodsSixty-three eyes of 42 New Zealand rabbits were included. Manual intrastromal pockets were dissected in 42 eyes. PEGDA inlays were obtained using a specifically designed photomask and were inserted in the intrastromal pocket of 21 eyes (inlay group); the remaining 21 right eyes did not receive any implant (pocket-only group). Twenty-one eyes with no intervention were used as controls. In vivo confocal microscopy (IVCM) was performed at every visit. After 2 months, rabbits were sacrificed and corneas removed for histological analysis.ResultsCorneas remained clear in all but two animals, and five cases of corneal neovascularization were seen (P = 0.2). Inlays remained stable without evidence of lateral or anterior migration, and no other complications were observed. No changes in anterior and posterior keratocyte density (P = 0.3 and P = 0.1, respectively) or endothelial cell density (P = 0.23) were observed between groups during the study time by IVCM. On pathology samples, thinning of the epithelium over the inlay area and epithelial hyperplasia over the edges were observed. A polygonal empty space with no evidence of PEGDA hydrogel within the midstroma was seen in the inlay group. Keratocytes were normal in shape and number in the vicinity of the PEGDA implant area.ConclusionsPhotopolymerized PEGDA intrastromal inlays have shown relatively good safety and stability in rabbit corneas. Inlays were biostable in the corneal environment and remained transparent during follow up.Translational RelevanceThe investigated PEGDA is promising for the development of biocompatible intrastromal implants.

Correction of hyperopia by intrastromal cutting and liquid filler injection.

.Correction of hyperopia requires an increase of the refractive power by steepening of the corneal surface. Present refractive surgical techniques based on corneal ablation (LASIK) or intrastromal lenticule extraction (SMILE) are problematic due to epithelial regrowth. Recently, it was shown that correction of low hyperopia can be achieved by implanting intracorneal inlays or allogeneic lenticules. We demonstrate a steepening of the anterior corneal surface after injection of a transparent, liquid filler material into a laser-dissected intrastromal pocket. We performed the study on ex-vivo porcine eyes. The increase of the refractive power was evaluated by optical coherence tomography (OCT). For a circular pocket, injection of filler material increased the refractive power by diopters. An astigmatism correction is possible when ellipsoidal intrastromal pockets are created. Injection of filler material into an ellipsoidal pocket increased the refractive power by on the short and on the long axis. OCT will enable to monitor the refractive change during filler injection and is thus a promising technique for real-time dosimetry.

Прочностные характеристики роговицы кролика после интрастромальной имплантации различных имплантов с применением фемтосекундного лазера

Purpose. Comparative experimental study of the effect of the implantation of various intrastromal implants using a femtosecond laser (FSL)on the strength properties of the rabbit cornea. Material and methods . The experimental work was performed on 24 corneas of isolated eyes of 12 rabbits enucleated 1 month after the slaughter. All eyes were divided into 4 groups, depending on the method of operation. Formation of intra-stromal pockets (IP) and tunnels (IT) was performed using the FSL Femto Visum. The eyes of rabbits with intact corneas were included into the first control group. In the group 2, the intrastromal segment 350° was implanted into the IT. In the group 3,the MyoRing was implanted into the IP. In the group 4, the intrastromal closing ring with a «lock» was implanted into the IT. Results. After the implantation of intrastromal implants in comparison with the control group it was noted that the strength of the examined cornea of rabbits was increased to break. The greatest increase in the strength properties of the rabbit cornea was observed after the implantation of the intrastromal closing ring with a «lock» in comparison with the implantation of the intrastromal segment of 350° and the MyoRing. Conclusions. Implantation of intrastromal rings and segments leads to an increase in the strength properties of the cornea. Implantation of an intrastromal closing ring with a «lock» leads to the greatest increase in the strength properties of the cornea compared with the implantation of the intrastromal segment of 350° and the MyoRing.

Strength properties of rabbit cornea after femtosecond laser keratoplasty with and without different intracorneal implants

to conduct a comparative experimental study of the effect of the use of intracorneal implants during femtosecond laser-assisted intrastromal pocket (IP) and intrastromal tunnel (IT) formation on the strength properties of the cornea. The experimental study was performed on 24 corneas of 12 rabbit eyes enucleated 1 month after slaughtering. All eyes were divided into 6 groups according to the method of operation. IP and IT were created with IntraLase FS 60 kHz femtolaser. Group 1 (control group) consisted of rabbit eyes with intact corneas. In group 2 corneas, intrastromal tunnels were formed, in group 3 - intrastromal pockets, and in group 4 - intrastromal tunnels with 2 intracorneal segments (ICS). In groups 5 and 6, intrastromal pockets, each supplemented with an intrastromal ring, were created at the depth of 62-72% and 80% of pachymetry readings from the 5.0-mm optical zone, respectively. Higher voltage had to be applied to stretch the samples from group 2 as compared to those from groups 3 and 6. Distribution of the Young's modulus of the test corneas agreed with voltage distribution in the study groups. IP was associated with greater reduction in corneal biomechanical stability as compared with IT. Ring implantation into an IP yielded a more pronounced increase in the strength properties of the cornea than ICS implantation into an IT. The result was also more favorable at greater depths of intrastromal ring implantation.

Effects of femtosecond and excimer lasers on implanted KAMRA corneal inlay in animal models

To evaluate the effect of femtosecond laser and excimer laser on an intracorneal inlay (KAMRA®) implanted in animal models. Femtosecond laser was used to create corneal intrastromal pockets at 250μm depth in five porcine eyes. Four intact KAMRA inlays, examined by slit-lamp biomicroscopy and light microscopy, were implanted in the pocket of four eyes. A standard LASIK flap was created above each implanted inlay in the four eyes using a femtosecond laser with flap thicknesses of 150μm, 130μm, 110μm and 90μm. In the fifth porcine eye, a LASIK flap was created using femtosecond laser at 110μm depth, and a fifth inlay was then implanted in the 250μm pocket. Excimer laser ablation was performed under the flap targeting a -3.00 refraction. The inlay was then explanted, examined and reimplanted in the same pocket followed by a second similar excimer laser ablation. Significant burn, shrinkage and distortion of microholes were noted in all the first four inlays following the femtosecond laser flap creation at all the various flap thicknesses. The damage was noted to be more prominent as the distance between the flap and inlay decreased. No apparent effect was noted on the fifth inlay following repeated excimer laser ablations. Unlike excimer laser, femtosecond laser appears to be hazardous and damaging to the intracorneal KAMRA inlay when applied above it.

Femtosecond Laser-assisted Endokeratophakia Using Allogeneic Corneal Lenticule in a Rabbit Model.

To investigate the feasibility of allogeneic corneal lenticule implantation using the femtosecond laser as a method for cornea remodeling. Small incision lenticule extraction was performed on the right eyes of 15 New Zealand white rabbits. Corneal intrastromal pockets were created with a femtosecond laser on the left eyes. Allogeneic corneal lenticule implantation was performed on the left eye immediately after the lenticule was extracted from the right eye. All animals had preoperative and postoperative slit-lamp photography, ultrasonic pachymetry, corneal endothelial cell count, anterior segment optical coherence tomography, in vivo confocal microscopy, and retinoscopy refraction during the observation period of 8 weeks. The rabbits were killed 8 weeks after surgery. Corneal wound healing response was analyzed by transmission electron microscopy, hematoxylin-eosin staining, TUNEL assay, and immunofluorescent staining. Mild corneal edema and decreased clarity were noted the first few days after implantation, improving to normal 8 weeks after surgery. The corneal thickness and retinoscopy refraction were stable during the observation period. Viable keratocytes could be detected within the lenticule lamellae by ultrastructural analysis 8 weeks after surgery. The anterior and posterior border of the lenticule showed acellular layers with highly irregular collagen arrangement on transmission electron microscope images. Proliferating Ki-67 positive cells were present only in the epithelium layer. Femtosecond laser-assisted endokeratophakia using allogeneic corneal lenticule may be feasible for reshaping cornea, providing a new possibility in refractive surgery and keratoconus treatment.

Flow-manipulated, crosslinked collagen gels for use as corneal equivalents

Our aim was to construct a mechanically stable and optically transparent collagen gel from an acidified atelocollagen solution which is suitable for use as a corneal stromal equivalent. Light transmission and mechanical testing were conducted on variously crosslinked constructs at different pH levels. Ultrastructural analysis was performed to assess directionality of the molecular arrangement produced by flow manipulation, as well as the amount of collagen fibrillogenesis which resulted from different pH and/or crosslinking conditions. Clinical and histological integration of the gels with living tissue was examined following implantation into rabbit corneal intra-stromal pockets. Transmission electron microscopy revealed the importance of the fine control of pH levels during gel formation and indicated that the stage at which collagen fibrillogenesis is halted within the constructs was critically dependent on the pH of the collagen solution. Transparency testing disclosed that high levels of collagen fibrillogenesis, as well as high levels of crosslinker concentration, detrimentally affected the transparency of the construct. As a result, a dual titration was required to achieve good light transmission through the gels. It was also evident that the amount of crosslinking required to gelate the collagen solution was reduced as the level of fibrillogenesis progressed. Thus, it was necessary to establish a balance between the solution pH and crosslinker concentration. Implantation of the collagen constructs into partial depth intra-stromal pockets in rabbits was followed up for 6 months, and demonstrated favourable biocompatibility. This showed that gels which had lower levels of both fibrillogenesis and crosslinking were degraded more readily by the host tissue. The collagen gels described here are mass-production friendly, and have promise as potential functional stromal equivalents for use in stromal grafting, or in constructing full thickness artificial corneas.

The Effect of Lyophilization on Graft Acceptance in Experimental Xenotransplantation Using Porcine Cornea

The immunogenicity of lyophilized porcine cornea is unknown. The purpose of this study was to examine the possibility of using lyophilized porcine cornea as a substrate for ocular surface reconstruction. A porcine cornea stromal button was freeze-dried and vacuum-packed. Lyophilized and fresh porcine corneas were examined histologically, and then implanted into intrastromal pockets in live rat corneas. Cytokine concentrations in plasma and protein extracts from the corneal buttons of rats were measured using the fluorokine multianalyte profiling assay, and histologic examination was performed. Immunoreactivity to the alpha-gal epitope was not found in lyophilized porcine corneas, whereas it was found in several keratocytes in fresh porcine corneas. The median survival time of rat corneas receiving lyophilized porcine transplants was 28.0 days, significantly longer than the 14.0-day survival of rat corneas that received fresh porcine transplants (P < 0.05). CD45RO(+) and CD68(+) cells were observed in rejected corneas, and interleukin-2 and interferon-gamma were elevated in rat plasma and corneal tissue. The lyophilized porcine corneal stroma, which is devoid of alpha-gal epitope, is less antigenic, and may be a useful biomaterial for ocular surface reconstruction and corneal collagen supplementation.

Infectious crystalline keratopathy

A 57-year-old white female was noted to have unusual intrastromal crystalline-like opacities in her failing right corneal graft five months after transplant surgery. Cultures grew Streptococcus viridans; since the graft was failing it was replaced and sent for pathologic examination. H&E stains revealed intrastromal pockets of basophilic material between the lamellae; there was a notable absence of inflammatory cells. Gram's stain showed the basophilic material to be gram positive and transmission electron microscopy confirmed the presence of intrastromal pockets of bacteria. The term “infectious crystalline keratopathy” was coined by Meisler for this entity, which occurs following longterm topical steroid usage. The quiet clinical appearance may make its infectious etiology unapparent. Management consists of discontinuation of the steroids and the administration of antibiotics; continued infection, corneal scars, or graft failure may occur and transplantation is then required.

Alloplastic Implants for the Correction of Refractive Errors

Convex-shaped, hydrophilic lenticles of various water content were implanted into microkeratome-dissected corneal pockets in a baboon model. Freshly trephined, cryolathed, and factory-lathed hydrogels were evaluated for periods exceeding 15 months, documenting clinical response, corneal curvature shifts, and morphologic features. Previously implanted hydrogels were subsequently removed, documenting the reversibility of the procedure while allowing the corneas to return to their preoperative condition. Various alloplastic materials were then reimplanted into the same intrastromal pockets. Medium and high water content lenses produced good results without affecting the recipient cornea, whereas thick or low water content materials extruded or produced severe anterior segment inflammation. The use of medium and high water content, convex-shaped lenticles for the correction of aphakia is possible using current techniques.

Alloplastic Epikeratophakia for the Correction of Aphakia

SUMMARY Plastic implants were combined with epikeratophakia grafts on the primate cornea. Implants in intrastromal pockets survived but did not substantially increase refractive powers. When implants were placed simultaneously with lyophilized epikeratophakia grafts, necrosis and loss of the graft ensued. Alloplastic implants survived on the cornea only if the overlying tissue contained living keratocytes, i.e., fresh donor tissue grafted over the implant or established lyophilized grafts in which the peripheral scar was opened slightly and the implant slipped between the graft and the cornea. Advantages of easily replaced implants include the ability to accommodate changing refractive needs, as for infants with monocular aphakia.