Stromal Bed Research Articles

Optical coherence tomography evaluation of the corneal cap and stromal bed features after laser in situ keratomileusis for high myopia and astigmatism

ObjectiveTo study the corneal microstructure by optical coherence tomography (OCT) after laser in situ keratomileusis (LASIK) for high myopia with and without astigmatism. DesignNonrandomized self-controlled comparative trial. ParticipantsSixty-three consecutive LASIK eyes with spherical equivalent refraction between −6.0 and −17.0 diopters (D) and astigmatism between 0.0 and −5.0 D were prospectively recruited for examination. InterventionLASIK was performed with the Chiron Hansatome microkeratome (160-μm fixed plate) and Summit Apex Plus excimer laser using a 5.5/6.0/6.5-mm multizone pattern. Proper preoperative calculations were performed to ensure stromal beds thicker than 250 μm. Main outcome measuresOCT imaging and measurement of corneal thickness was performed preoperatively. In addition, corneal cap and stromal bed thickness measurements were performed 1 day, 1 month, and 3 months postoperatively. ResultsThe average central corneal pachymetry was 538.9 ± 26.2 μm preoperatively. Mean corneal cap thickness measured 124.8 ± 18.5 μm 1-day postoperatively. Mean stromal bed thickness was 295.2 ± 37.1 μm on the first postoperative day. Compared with the 1-day postoperative examination, the average stromal bed thickness increased significantly by 5.9 μm (P = 0.001) and 7.2 μm (P = 0.001) at the 1-month and 3-month postoperative examinations, respectively. Mean difference between actual (118.7 ± 27.8 μm) and predicted (104.1 ± 20.8 μm) central ablation depths was 14.6 ± 16.7 μm (P = 0.0001). A weak but statistically significant positive association was found between preoperative refraction and the difference between expected and real ablation depth values (R = 0.26; P = 0.042). Posterior stromal beds were more than 250-μm thick in 58 eyes (89.9%) 1 day postoperatively. This safety requirement improved at the 1-month postoperative examination, when the partial regression accounted for slightly thicker stromal beds and only two cases (3.2%) exhibited posterior stromal tissue thinner than 250 μm. These two cases were seen only for corrections exceeding 12 D (P = 0.04). ConclusionsOCT appears to be a useful tool for the evaluation of both the qualitative and quantitative anatomic outcome of LASIK. Corrections of higher degrees of ametropia run a higher risk of producing a thinner than expected central cornea. Particularly, corrections greater than 12 D may lead eventually to stromal beds thinner than 250 μm, despite proper preoperative calculations. Because corneal flaps are usually thinner than expected with the microkeratome used herein, adequate posterior corneal stroma is preserved in most instances.

Elevated expression of hormone-regulated rat hepatocyte functions in a new serum-free hepatocyte-stromal cell coculture model.

The specific performance of the adult hepatic parenchymal cell is maintained and controlled by factors deriving from the stromal bed; the chemical nature of these factors is unknown. This study aimed to develop a serum-free hierarchical hepatocyte-nonparenchymal (stromal) cell coculture system. Hepatic stromal cells proliferated on crosslinked collagen in serum-free medium with epidermal growth factor, basic fibroblast growth factor, and hepatocyte-conditioned medium; cell type composition changed during the 2-wk culture period. During the first wk, the culture consisted of proliferating sinusoidal endothelial cells with well-preserved sieve plates, proliferating hepatic stellate cells, and partially activated Kupffer cells. The number of endothelial cells declined thereafter; stellate cells and Kupffer cells became the prominent cell types after 8 d. Hepatocytes were seeded onto stromal cells precultured for 4-14 d; they adhered to stellate and Kupffer cells, but spared the islands of endothelial cells. Stellate cells spread out on top of the hepatocytes; Kupffer cell extensions established multiple contacts to hepatocytes and stellate cells. Hepatocyte viability was maintained by coculture; the positive influence of stromal cell signals on hepatocyte differentiation became evident after 48 h; a strong improvement of cell responsiveness toward hormones could be observed in cocultured hepatocytes. Hierarchial hepatocyte coculture enhanced the glucagon-dependent increases in phosphoenolpyruvate carboxykinase activity and messenger ribonucleic acid (mRNA) content three- and twofold, respectively; glucagon-activated urea production was elevated twofold. Coculturing also stimulated glycogen deposition; basal synthesis was increased by 30% and the responsiveness toward insulin and glucose was elevated by 100 and 55%, respectively. The insulin-dependent rise in the glucokinase mRNA content was increased twofold in cocultured hepatocytes. It can be concluded that long-term signals from stromal cells maintain hepatocyte differentiation. This coculture model should, therefore, provide the technical basis for the investigation of stroma-derived differentiation factors.

Experimental evaluation of two current-generation automated microkeratomes: the Hansatome and the Supratome

PURPOSE: To compare flap dimensions, cut quality, and blade deterioration after reuse in an experimental setting using two current-generation microkeratomes for laser-assisted in situ keratomileusis. METHODS: Two pivoting-head principle microkeratomes, the Hansatome and the Supratome, were used to perform a corneal flap in 50 freshly enucleated pig cadaver eyes, with an intended thickness of 160 μm. Provided stainless steel blades were used from one to five times. Flap diameter was measured by planimetry and thickness calculated using ultrasonic pachymetry at three different locations. Scanning electron microscopy of stromal beds and blades’ cutting edges were performed to assess the cut and blade deterioration after repeated use. RESULTS: Mean flap central thickness (Hansatome/Supratome) was 151 μm (SD 18)/192 μm (SD 32). Progressive thinning/thickening of the flap was observed in the direction toward the hinge ( P = .003/ P = .021). Mean vertical flap diameters of 8.9 mm (SD 0.3)/8.0 mm (SD 0.4) differed significantly ( P = .001). No correlation was found between thickness and diameter (r = 0.03, P = .935/r = 0.12, P = .603). At scanning electron microscopy, smooth cuts were observed with both keratomes using a new blade. Periodical chatter lines at keratectomy edge were present and were more pronounced after blade reuse. Cut quality, blade deterioration, and small tissue remnants on the blade surface were noted with repeated blade use, especially using the Supratome. CONCLUSIONS: Local flap thickness and flap diameter variations are inherent to the instrument used. Comparable cut-surface quality can be obtained with new blades. Although cut and blade deterioration appears to be minor after two reuses, the presence of tissue remnants on the blade surface still limits its reuse.

Management of severe flap wrinkling or dislodgment after laser in situ keratomileusis

PurposeTo review the management and results of cases with severe flap wrinkling or dislodgment after laser in situ keratomileusis (LASIK). SettingUniversity Eye Center, Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, The Chinese University of Hong Kong. MethodsFour patients with severe flap wrinkling or dislodgment after LASIK are described. Surgical repositioning of the flap was performed in all cases. Flap status, refractive changes, and final uncorrected and best corrected visual acuities were used to evaluate the outcome of flap repositioning. ResultsFlap repositioning required suturing in 2 patients, 1 of whom developed severe epithelial ingrowth with melting of the corneal flap and stromal bed and eventually required flap removal. The stromal inflammation resolved, and the corneal surface re-epithelialized after flap excision. In 2 other patients, wedge-shaped tissue excision (1.0 × 1.5 mm) from the superior portion of the corneal flap was necessary to allow better flap realignment. In 1 of these patients, the corneal flap was eventually converted to a free cap to correct residual wrinkling. At a mean follow-up of 15 months, the postoperative uncorrected visual acuity ranged from 20/20 to 20/60, and the best spectacle-corrected visual acuity (BSCVA) was 20/30 or better in all patients. In 1 patient, BSCVA decreased by 1 line. ConclusionsFlap dislodgment and wrinkling are serious postoperative complications of LASIK. Early recognition of these complications and prompt surgical management are crucial to achieve a successful surgical and visual outcome.

Discussion

To evaluate corneal flap thickness in laser in situ keratomileusis (LASIK) and to measure variables correlated with corneal flap thickness.Kangnam St. Mary’s Hospital, Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, Korea.This prospective study comprised 69 eyes of 66 patients having LASIK with the VISX Star laser and SCMD manual microkeratome. Corneal thickness, keratometry, and refractive error were measured preoperatively, the time taken to complete the corneal flap and its thickness were recorded intraoperatively, and visual outcome was followed postoperatively. Corneal flap thickness was calculated as the thickness of the corneal stromal bed subtracted from the total corneal thickness.Mean corneal flap thickness was 137.18 μm ± 33.66 (SD). The thickness in 32 eyes (46.4%) was less than 135 μm, in 17 eyes (24.6%) from 135 to 165 μm, and in 20 eyes (29.0%) greater than 165 μm. There was no relationship between corneal flap thickness and degree of myopia, steepening of cornea, or time taken to complete the flap. However, the thickness of the corneal flap increased with the thickness of the cornea. Visual outcome was slightly better in the group with thick corneal flaps than in the one with thin corneal flaps, although the difference was not statistically significant.Corneal flap thickness was variable in LASIK using the SCMD microkeratome. There was a correlation between corneal flap thickness and preoperative corneal thickness.

LASIK for post penetrating keratoplasty astigmatism and myopia

AIMSTo report the results of a series of patients who were treated with LASIK to correct post penetrating keratoplasty ametropia.METHODS26 eyes of 24 patients underwent LASIK to correct astigmatism and...

Corneal perforation during laser in situ keratomileusis

Two cases of corneal perforation that occurred during laser ablation but not during flap formation in laser in situ keratomileusis (LASIK) are reported. In the first case, no problem in flap formation occurred, and stromal bed thickness was assumed to be about 239 μm after laser application. However, a stromal bed perforation was found when 608 pulses were applied (theoretical ablation depth was 140 μm). Excessive dehydration due to prolonged exposure to the operating microscope light may change the ablation rate and cause corneal perforation. In the second case, LASIK retreatment was performed using the original flap for correction of regressed myopia (−4.0 diopters). Although the stromal bed thickness was assumed to be about 175 μm after the laser application, a stromal bed perforation was found when 151 pulses were applied (theoretical ablation depth was 37 μm). Unexpected corneal ectasia after the first LASIK treatment may cause a corneal perforation in LASIK retreatment. In conclusion, excessive dehydration of the cornea should be avoided, and careful examination of the corneal shape is necessary to prevent corneal perforation during laser ablation in LASIK.

Corneal flap thickness in laser in situ keratomileusis using an SCMD manual microkeratome

Purpose To evaluate corneal flap thickness in laser in situ keratomileusis (LASIK) and to measure variables correlated with corneal flap thickness. Setting Kangnam St. Mary’s Hospital, Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, Korea. Methods This prospective study comprised 69 eyes of 66 patients having LASIK with the VISX Star laser and SCMD manual microkeratome. Corneal thickness, keratometry, and refractive error were measured preoperatively, the time taken to complete the corneal flap and its thickness were recorded intraoperatively, and visual outcome was followed postoperatively. Corneal flap thickness was calculated as the thickness of the corneal stromal bed subtracted from the total corneal thickness. Results Mean corneal flap thickness was 137.18 μm ± 33.66 (SD). The thickness in 32 eyes (46.4%) was less than 135 μm, in 17 eyes (24.6%) from 135 to 165 μm, and in 20 eyes (29.0%) greater than 165 μm. There was no relationship between corneal flap thickness and degree of myopia, steepening of cornea, or time taken to complete the flap. However, the thickness of the corneal flap increased with the thickness of the cornea. Visual outcome was slightly better in the group with thick corneal flaps than in the one with thin corneal flaps, although the difference was not statistically significant. Conclusion Corneal flap thickness was variable in LASIK using the SCMD microkeratome. There was a correlation between corneal flap thickness and preoperative corneal thickness.

Comparison of wound healing after photorefractive keratectomy and laser in situ keratomileusis in rabbits

Purpose To evaluate and compare the corneal wound-healing process after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Setting Kangnam St. Mary’s Hospital, Seoul, Korea. Methods Two surgical procedures, PRK with the VISX Star excimer laser and LASIK with a MicroTech microkeratome, were performed in 24 rabbit eyes. In the PRK group (n=12 eyes), the rabbit cornea was treated with a 20 μm ablation. In the LASIK group (n=12 eyes), a 20 μm laser ablation was performed after a 150 μm thick hinged corneal flap had been made. During both procedures, dichlorotriazinyl aminofluorescien (DTAF) dye was applied to the ablated stromal bed; in the LASIK group, the stromal side of the corneal flap was also stained with DTAF to differentiate regenerated collagen from normal stromal tissue. Corneal wound healing was evaluated postoperatively at 1, 4, 8, and 12 weeks using light, electron, and fluorescence microscopy. The amount of regenerated stromal tissue and the number of keratocytes were analyzed by an image-analysis system. Results In the PRK group, epithelial migration and regeneration were observed in the ablated area without any stromal regeneration 1 week postoperatively. However, newly regenerated, irregularly arranged stromal collagen, with epithelial hyperplasia in the ablated area, was observed 4 to 12 weeks postoperatively by light and fluorescence microscopy. The number of keratocytes in the surgical area was also increased. In ultrastructural observation using an electron microscope, the shape of keratocytes in the ablated area was changed, and the number of rough and smooth endoplasmic reticuli, ribosomes, mitochondria, and electron-dense vesicles in the cytoplasm were increased, suggesting that the cells were activated. In the LASIK group, there was no observed regenerated collagen between the corneal flap and the ablated stromal bed except in the wound margin. Lamellated, parallel collagen fibers in the cornealstroma were not disturbed. However, in the wound margin, corneal epithelial ingrowth between the flap and the stromal bed was observed, as was some regenerated stromal tissue. The amount of regenerated stromal tissue and the number of keratocytes in the wound area were statistically smaller than those in the PRK group ( P < .05). Observation by electron microscopy showed no activated keratocytes, unlike in the PRK group. The collagen fibers in the wound area were parallel. Conclusion Stromal wound healing in the LASIK group was minimal compared with that in the PRK group, except in the wound margin. These results may support the clinical findings of less corneal haze in the human cornea after LASIK.

Retreatment after laser in situ keratomileusis

Objective To evaluate the effectiveness, predictability, and safety of laser in situ keratomileusis (LASIK) retreatment for correcting residual myopia. Design Retrospective noncomparative case series. Participants and intervention Fifty-nine consecutive eyes (43 patients) underwent LASIK retreatment at 3 or 6 months after the primary LASIK procedure. Lifting the corneal flap and reablating the stromal bed with a VISX 20/20 excimer laser was the procedure used for LASIK enhancement. Main outcome measures The following parameters were studied before and after retreatment: visual acuity, refraction, videokeratography, applanation tonometry, and corneal thickness. Complications after LASIK enhancement also were evaluated. Follow-up was 12 months. Results Before retreatment, only 3.38% of eyes (2 of 59) had an uncorrected visual acuity of 0.5 (20/40) or better, and after retreatment, this percentage increased to 60% (30 of 50) at 6 months and 61.8% (34 of 55) at 12 months. After reoperation, mean best-corrected visual acuity improved by half a line over the values before retreatment. The preretreatment refraction of −2.92 ± 1.22 diopters (D) (mean ± standard deviation) decreased significantly to −0.44 ± 0.80 D at 6 months and to −0.61 ± 0.82 D at 12 months ( P < 0.001). In 82% of eyes (41 of 50) at 6 months and 81.8% (45 of 55) at 12 months, the spherical equivalent was within 1.00 D of emmetropia. There was a significant regression of effect (0.38 D) between 3 and 12 months ( P < 0.01). Postretreatment refraction was related to the original refraction before the primary LASIK, the preretreatment refraction, and the ablation diameter used. Although no vision-threatening complications were found, epithelial ingrowth and flap melting were more common after than before LASIK retreatment, with 31% of eyes at 12 months with epithelial ingrowth and 10.9% with flap melting. However, LASIK enhancement improved decentration and night-vision problems. Conclusions LASIK retreatment was an effective and predictable procedure for correcting residual myopia. Epithelial ingrowth and flap melting were more frequent after than before LASIK retreatment, whereas decentration and night-vision symptoms improved.

Expression and Distribution of Extracellular Matrices during Corneal Wound Healing after Keratomileusis in Rabbits

We compared the corneal wound healing responses of keratomileusis and keratectomy in rabbits. A single pass of thin lamellar keratectomy was performed with a microkeratome in rabbits. The lenticule was repositioned with a hinge in one group and discarded in the other. With immunofluorescence techniques, we studied the appearance and distribution of fibronectin, fibrinogen and type III collagen at follow-up intervals from 1 h to 3 months. Fibronectin and fibrinogen began to deposit on the periphery of the denuded stroma 3 h after induced injury and diminished once reepithelialization had completed in both groups. In the corneas with attached lenticules, type III collagen was detected 7 days after surgery and lasted for at least 3 months. Type III collagen was detected only in the periphery of the interface and not in its center. These findings suggest that fibronectin and fibrinogen may play roles in epithelial healing after in situ keratomileusis in rabbits. Stromal healing of colla- gen seems to take place 7 days after keratomileusis and to last for several months. No deposits of new collagens in the center of the interface between lenticule and stromal bed may explain the optical clarity in the keratomileusis.

Factors affecting corneal strip stroma-to-stroma adhesion.

Successful laser in situ keratomileusis depends on strong adhesion between the dissected anterior corneal flap and the underlying stromal bed, without suturing. This study attempts to generate new information about the mechanism of this adhesion. Strips of fresh bovine corneal stroma were dissected and split apart. The split strips were then made to adhere to each other with varying amounts of combined heat and drying. A relationship was developed between heat applied and hydration of strips. After each heat and drying treatment, the strips were pulled apart and the force needed to accomplish this task was measured. There was a tight linear correlation between increase in temperature and decrease in water content (R2 = 0.7414) and between decrease in water content and increase in the adhesive force (R2 = 0.3355). This model suggests that drying increases stromal-stromal adhesion. We speculate this is due to the increased concentration of surface molecules, which have high ionic charge densities and ionic bonding. A higher concentration of these molecules produces stroma-to-stroma adhesion via ionic bonding.

Recovery of Corneal Nerve Morphology Following Laser in situ Keratomileusis

Morphological changes in the corneal nerves after laser in situ keratomileusis (LASIK) were investigated and the changes were compared with those observed after creation of the keratectomy flap without subsequent photoablation. After creating the hinged flap, a multizone excimer laser photoablation (myopic correction from 6.00 to 6.66 D; diameter 6 mm) was performed on 27 rabbit corneas. Seven of these 27 rabbits received an automated keratectomy without laser photoablation on the fellow eye. A histochemical acetylcholinesterase reaction was used to demonstrate the changes in the morphology of the corneal nerves 3 days, 2.5 and 5 months after the operations. In all specimens the deepest stromal nerve bundles showed normal morphology. Cut nerve trunks were found at the wound margins and at the level of the flap interphase in the stromal bed. At 3 days, both epithelial and basal epithelial/subepithelial nerves were found at the hinge of the flap but the rest of the flap showed a major loss of epithelial, basal epithelial/subepithelial and superficial stromal nerves. A few new regenerating thin nerve fibers were found to emerge from the cut stromal nerve trunks. They appeared to pass the wound margin into the flap area below the epithelium. At 2.5 and 5 months an increasing number of regenerating nerve leashes were observed to emerge from the cut stromal nerve trunks. They appeared to send anastomosing fibers among the neighboring stromal nerves. By this time the epithelial, basal epithelial/subepithelial and anterior stromal innervation had gained an almost normal nerve density and architecture. In the corneas with the flap only, the epithelial innervation was slightly better spared in the center of the flap, and the stromal changes were somewhat less prominent compared with the LASIK corneas.

Laser in situ keratomileusis for myopia and astigmatism: 6 month results

Purpose: To evaluate the visual and refractive results of laser in situ keratomileusis (LASIK) for mild to moderate myopia with or without astigmatism.Setting: Barnet-Dulaney Eye Center, Phoenix, Arizona, USA.Methods: Data were prospectively collected on 124 consecutive eyes having LASIK over 12 weeks. Eyes with a preoperative spherical equivalent (SE) from −1.35 to -10.00 diopters (D) (mean −4.81 ± 2.21 [SD]) and cylinder from 0 to 5.00 D (mean 1.12 ± 1.12 D) were entered in the study. Thirty-one eyes had spherical corrections. Ninety-three eyes had spherocylinder corrections; preoperative astigmatism in these eyes ranged from 0.50 to 5.00 D (mean 1.47 ± 1.09 D). Surgery included creation of a corneal flap using an automated microkeratome with a 160 jam plate followed by photoablation on the exposed stromal bed. Photoablation was performed using five zones varying from 5.0 to 6.6 mm in eyes with 6.25 D of myopia or less and with five passes at a 5.0 mm zone in eyes with 6.50 D of myopia or more. Astigmatism was corrected using a single-pass ablation through a 6.0 mm slit of varying diameter.Results: Six month follow-up was obtained in 89 eyes (72%). All eyes were completely re-epithelialized by the first postoperative day. Uncorrected visual acuity was 20/40 or better in 81% of eyes at 1 day and in 91% at 6 months. At 6 months, the mean SE was −0.35 ± 0.77 D; 83% were within ± 1.00 D of plano. Postoperative astigmatism in the 93 eyes having cylinder correction ranged from 0 to 1.22 D (mean 0.38 ± 0.42 D). No eye lost more than two lines of best spectacle-corrected visual acuity. Three eyes (2%) required surgical intervention for cap problems. Visually significant corneal haze was not observed.Conclusion: In eyes with myopia with or without astigmatism, LASIK provided rapid visual recovery with satisfactory visual and refractive outcomes. The effect of LASIK on visual function (night glare, contrast sensitivity) awaits further study.

Removal of flap striae following laser in situ keratomileusis

While laser in situ keratomileusis (LASIK) offers advantages over photorefractive keratectomy (PRK), creation of the corneal flap has been associated with postoperative flap striae. These result from misalignment of the corneal flap after flap replacement, movement of the corneal flap during the first postoperative day, or the “tenting effect” of the corneal flap over the ablated stromal bed. Flap striae become more difficult to remove as the postoperative course progresses; therefore, identifying the striae on the first postoperative day is imperative. We describe techniques of flap hydration, refloating, stretching, and smoothing that we use to remove visually significant flap striae.

A simple method for the removal of epithelium grown beneath the hinge after LASIK.

The purpose of this study is to demonstrate a method of how to remove epithelium grown beneath the hinge area after laser in situ keratomileusis (LASIK) without affecting the refractive part of the lenticule. In three cases, an incision was made at the base of the hinge by RK diamond knife to free the lenticule from the stroma. The lenticule was lifted from the nasal edge. The epithelium grown along the interface beneath the hinge area was removed with a Bard-Parker No. 15 knife. The lenticular flap was repositioned with interrupted sutures using 10-0 nylon. No further epithelial ingrowth was observed. The central cornea remained clear leaving a peripheral ring-shaped opacity without affecting the preoperative naked visual acuity. In conclusion, epithelial ingrowth along the interface after LASIK can be removed safely without affecting the refractive part by the incision of the hinge area with a RK diamond knife, removal of the epithelium, and suturing of the lenticule to the stromal bed.

Indications, techniques, results, limits, and complications of laser in situ keratomileusis.

In this article we describe the state of the art of laser in situ keratomileusis (LASIK) through a presentation of the principles, the advantages, the disadvantages, the indications, the techniques, and the main complications. LASIK, as it is known today, involves the creation of a corneal flap using a keratome; this is followed by the in situ photoablation of the exposed stromal bed with an excimer laser. The flap thickness is about 160 mm with a circumference of about 300 degrees, the idea being to leave a portion of tissue attached, thus creating a corneal hinge. The in situ stromal bed exposed by the lamellar cut is then photoablated and the flap is repositioned without sutures. Functional recovery and anatomical healing are rapid. The operation is painless, and it is performed under topical anesthesia in an outpatient environment.

Sutureless homoplastic lamellar keratoplasty.

Previously, penetrating keratoplasty has been used to treat corneal cap complications related to keratomileusis. We sought to develop a technique to avoid the unnecessary use of penetrating procedures for lamellar problems, that would be technically easier than standard lamellar keratoplasty--sutureless homoplastic lamellar keratoplasty. Five eyes with complications from automated lamellar keratoplasty underwent sutureless homoplastic lamellar keratoplasty utilizing an automated microkeratome and topical anesthesia. Three of the five eyes had improved vision; two eyes with final visual acuities of 20/20 and 20/30. The two remaining eyes had poor host stromal beds and required penetrating keratoplasty. The mean follow-up time was 13 months (range 3 to 36 months). All lamellar grafts were clear and well-seated at the last postoperative examination. Sutureless homoplastic lamellar keratoplasty is an alternative to penetrating keratoplasty in some eyes that have cap-related problems.

Potential sites of prostaglandin actions in the periimplantation mouse uterus: differential expression and regulation of prostaglandin receptor genes.

Prostaglandins (PGs), especially PGE2 and PGF2alpha, are considered important for blastocyst spacing, implantation, and decidualization in the rodent uterus. However, information regarding uterine sites of PG actions in these processes is lacking. PGE2 or PGF2alpha interacts with specific G protein-coupled membrane receptors. PGE2 receptors are classified into four subtypes, EP1, EP2, EP3, and EP4. While EP1 is coupled to Ca2+ mobilization, activation of EP2 and EP4 triggers stimulation of adenylyl cyclase. In contrast, activation of EP3 inhibits adenylyl cyclase. PGF2alpha receptor (FP) is coupled to stimulation of phospholipase C-inositol trisphosphate (IP3) pathway and Ca2+ mobilization. This investigation demonstrates that PGE2 and PGF2alpha receptor genes are expressed in a temporal and cell-specific manner in the periimplantation mouse uterus. In the mouse, the attachment reaction occurs in the evening (2200-2300 h) of Day 4 of pregnancy and is preceded by embryo spacing, uterine edema, and luminal closure resulting in an intimate apposition of the blastocyst with the uterine luminal epithelium. Expression of EP3 and FP primarily in the circular muscle of the myometrium on Days 3-5 of pregnancy suggests that the circular muscle, not the longitudinal muscle, is the primary target for PG-mediated uterine contractions required for embryo transport, spacing, and/or accommodation in the uterus. In contrast, expression of EP3 in a subpopulation of cells in the stromal bed at the mesometrial side, and of EP4 in the epithelium and stroma on these days, suggests that PGE2 effects on uterine preparation for implantation (such as epithelial cell differentiation, stromal cell proliferation, uterine edema, luminal closure, and increased localized endometrial vascular permeability at the sites of blastocyst attachment) are mediated by these receptor subtypes. Similar expression patterns of EP3 and EP4 in the Day 4 pseudopregnant mouse uterus or in the ovariectomized uterus under combined treatment with estrogen and progesterone suggest that these genes are regulated by ovarian steroids rather than by the embryo during the preimplantation period (Days 1-4). In contrast, the expression of these genes during the postimplantation period (Days 5-8) is associated with the onset of decidualization.

Laser in situ keratomileusis to treat myopia: Early experience

Purpose: To present our early experience in methodology and results of laser in situ keratomileusis (LASIK) in treating moderate and high myopia.Setting: Vardinoyannion Eye Institute of Crete and the Cornea and Refractive Surgery Service, Department of Ophthalmology, Heraklion University Hospital, Crete, Greece.Methods: Forty-three moderately to highly myopic eyes had LASIK. Follow-up was between 12 and 24 months. The Draeger's rotor microkeratome was used to create a 150 wm thick 8.5 × 9.5 mm corneal flap, and the stromal bed was ablated for the myopic correction using the Munnerlynn photorefractive keratectomy algorithm. The preoperative spherical equivalent ranged from −8.50 to −25.87 diopters (D). Attempted correction ranged from 8.00 to 16.00 D. Four eyes developed complications (i.e., anterior chamber perforation and keratoconus, intrastromal epithelial cells, macular lacquer cracks, and transient endothelial decompensation) and were excluded from the study. The remaining 39 eyes were retrospectively divided into two groups-A (21 eyes) and B (18 eyes)-according to the preoperative spherical equivalent (higher or lower than −14.00 D, respectively).Results: Refraction and corneal topography stabilized between 4 and 12 weeks postoperatively. Best spectacle-corrected visual acuity was within one Snellen line in all eyes. At 24 months, 19 eyes (79.2%) were within 2.00 D of intended correction. Attempted correction (12.20 D ± 2.30 [SD]) was very close to mean achieved correction at 12 and 24 months (11.60 ± 2.65 D). Mean postoperative astigmatism at 24 months (1.41 ± 0.87 D; range 0 to 3.50 D) was close to the mean preoperative value (1.52 ± 1.08 D; range 0 to 4.00 D). An average 2.43% endothelial cell loss was observed at 24.months.Conclusion: With limitations, LASIK could be considered as a treatment for moderate and high myopia.