Haze Development Research Articles

Plasminogen activator inhibitor in human tears after laser refractive surgery

To observe levels of plasminogen activator inhibitor (PAI) in human tears after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). University medical center eye clinic. Tear samples were collected from 46 eyes having PRK and 13 eyes having LASIK immediately before and after surgery and on the first (LASIK), third (PRK), and fifth (PRK) postoperative days. Analyses used enzyme-linked immunoassay, yielding 61 PRK PAI-1 determinations and 146 PRK and 35 LASIK PAI-2 determinations. All determinations of PRK PAI-1 were below the detection limit of 1 ng/mL of the original tear sample. In the PRK eyes, the mean PAI-2 concentration was 19.8 ng/mL +/- 23.4 (SD) in preoperative tears, 112.7 +/- 60.5 ng/mL immediately postoperatively, 12.1 +/- 19.5 ng/mL after 3 days, and 15.5 +/- 20.4 ng/mL after 5 days. In the LASIK eyes, the mean PAI-2 concentration was 19.0 +/- 33.1 ng/mL preoperatively, 111.5 +/- 69.2 ng/mL immediately postoperatively, and 15.7 +/- 18.8 ng/mL after 1 day. The similarity in the general time pattern of PAI-2 after PRK and LASIK suggests commonality in the enzymatic control response to corneal surgical wounding. Taken in the context of previous work, the observed levels of PAI-2 concentration in eyes with and without opacification suggest that in the postsurgical period, PAI-2 is not the controlling mechanism for the later development of corneal opacification and haze.

Corneal response to femtosecond laser photodisruption in the rabbit

In this report we evaluated the effect of femtosecond laser energy on the development of corneal haze and keratocyte activation in rabbits following intra-stromal photodisruption to create LASIK flaps using a modified commercial femtosecond surgical laser. Three groups of flap parameters were studied: 1.5μJ/pulse with 10μm spot separation and complete side cut (Group 1); 3.5μJ/pulse with 14μm spot separation and complete side cut (Group 2); 3.5μJ/pulse with 14μm spot separation and partial (50μm) side cut (Group 3). All flaps were left attached without lifting to avoid epithelial contamination. Rabbits were then evaluated pre- and post-operatively by quantitative in vivo and ex vivo confocal microscopy. The achieved flap thickness 1week after surgery averaged 88.9±12.8, 90.8±6.9 and 86.5±6.8μm for Groups 1–3 respectively (p=NS). Interface thickness was significantly greater (p<0.05) in the higher energy groups averaging 40.0±11.2 and 37.7±5.7μm for Groups 2–3 compared to 28.6±4.5μm for Group 1. Corneal haze was barely detectible and not significantly different between groups, although haze was detected in the region of the side-cuts in Groups 1 and 2. No clinically significant changes in stromal or epithelial thickness were noted. Laser confocal microscopy showed the presence of small diameter cells within the flap interface that resided within disrupted regions of the corneal collagen lamellae. Keratocyte activation was only detected in regions of the 100% side cut and not over the flap interface. In conclusion, the results of this study indicate that photodisruption of the corneal stroma alone without flap elevation regardless of laser energy does not induce significant corneal haze in the rabbit. However, a thicker stromal interface was seen with the higher energy suggesting greater stromal damage.

C-Jun NH2 terminal kinase (JNK) is an essential mediator of Toll-like receptor 2-induced corneal inflammation

TLRs play an important role in the host inflammatory response to bacteria and bacterial products by activating a cascade of intracellular events leading to production of proinflammatory and chemotactic cytokines. To determine the role of MAPKs in TLR- induced corneal inflammation, we stimulated human corneal epithelial (HCE) cells with TLR2 ligands, tripalmitoyl-S-glycero-Cys-(Lys)4 (Pam3Cys) or inactivated Staphylococcus aureus, and examined the time course of expression of MAPKs and the effect of MAPK inhibition on IkBalpha degradation and CXC chemokine production. We found that S. aureus and Pam3Cys stimulate phosphorylation of JNK, p38 MAPK, and ERK within 4 h and that blockade of JNK, but not p38 or ERK phosphorylation, had an inhibitory effect on IkBalpha degradation and CXC chemokine production. To determine if JNK is also important in TLR2-induced corneal inflammation in vivo, we examined JNK1(-/-) mice and pharmacological inhibitors in a murine model of TLR2-induced corneal inflammation which is characterized by neutrophil recruitment to the corneal stroma and development of corneal haze. We found that corneal inflammation was significantly impaired in JNK1(-/-) mice compared with control mice, and in mice treated with the JNK inhibitor compared with vehicle control. Taken together with results from HCE cells, these findings demonstrate that JNK has an essential role in TLR2-induced corneal inflammation.

Photorefractive Keratectomy Retreatment After LASIK

To study the results of late photorefractive keratectomy (PRK) in corneas originally subjected to LASIK. Seven eyes of seven patients who had LASIK for myopia were retreated with PRK at least 2 years after LASIK. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), refraction, and haze were evaluated before and after LASIK and after retreatment by PRK. Photorefractive keratectomy retreatment improved BSCVA in six (86%) of seven eyes, and one (14%) eye showed no changes. None of the eyes lost lines of BSCVA. Five of seven eyes developed mild haze, which disappeared before the last postoperative follow-up. Photorefractive keratectomy retreatment performed at least 2 years after LASIK can improve visual acuity. We hypothesize that LASIK-induced corneal nerve damage disturbs corneal wound healing by increasing the tendency for development of haze.

Toll-like receptor 2 regulates CXC chemokine production and neutrophil recruitment to the cornea in Onchocerca volvulus/Wolbachia-induced keratitis.

The filarial nematode Onchocerca volvulus is the causative organism of river blindness. Our previous studies demonstrated an essential role for endosymbiotic Wolbachia bacteria in corneal disease, which is characterized by neutrophil infiltration into the corneal stroma and the development of corneal haze. To determine the role of Toll-like receptors (TLRs) in neutrophil recruitment and activation, we injected a soluble extract of O. volvulus containing Wolbachia bacteria into the corneal stromata of C57BL/6, TLR2-/-, TLR4-/-, TLR2/4-/-, and TLR9-/- mice. We found an essential role for TLR2, but not TLR4 or TLR9, in neutrophil recruitment to the cornea and development of corneal haze. Furthermore, chimeric mouse bone marrow studies showed that resident bone marrow-derived cells in the cornea can initiate this response. TLR2 expression was also essential for CXC chemokine production by resident cells in the cornea, including corneal fibroblasts, and for neutrophil activation. Taken together, these findings indicate that Wolbachia activates TLR2 on resident bone marrow-derived cells in the corneal stroma to produce CXC chemokines, leading to neutrophil recruitment to the corneal stroma, and that TLR2 mediates O. volvulus/Wolbachia-induced neutrophil activation and development of corneal haze.

Protease-Assisted Clarification of Black Currant Juice: Synergy with Other Clarifying Agents and Effects on the Phenol Content

Conventional clarification with gelatin and silica sol removes a considerable amount of antioxidant phenolics from berry juices. This study examined the clarification and haze-diminishing effects of alternative clarification strategies on black currant juice including centrifugation and addition of acidic protease and pectinolytic enzyme preparations and gallic acid. Centrifugation of freshly pressed juice (10,000 g for 15 min) resulted in a approximately 95% reduction of immediate turbidity and had a decreasing effect on haze development in the juice during cold storage without significantly compromising the total phenols levels. The extent of clarification and haze diminishment varied after individual treatments with five different acidic proteases, but one of the protease preparations, Enzeco, derived from Aspergillus niger, consistently tended to perform best. The individual and interactive effects on juice turbidity, total phenols, and total anthocyanin contents of clarification treatments involving the use of two selected acid proteases (Enzeco and Novozyme 89L), a pectinase (Pectinex BE 3-L), and gallic acid were evaluated in a full factorial 2(4) experimental design. Haze development during cold storage decreased when gallic acid or any of the enzyme preparations were employed individually, but negative interaction effects resulted when the pectinase was employed in combination with any of the proteases. After 28 storage days at 2 degrees C, the lowest levels of haze formation were achieved when the Enzeco protease preparation, added at 0.025 g/L, was added with 0.050 g/L of gallic acid and allowed to react in the juice for 90 min at 50 degrees C. The corresponding anthocyanin reduction was approximately 12% (compared to approximately 30% with gelatin silica sol treatment). The data support the hypothesis that phenol-protein interactions are involved in juice turbidity development during cold storage of berry juices and demonstrate that precentrifugation and protease-assisted clarification show promise as an alternative, phenolics-retaining clarification strategy in black currant juice processing.

PRK and Mitomycin-C

Mitomycin-C is a potent agent that prevents corneal haze. It has been used for the treatment of existing corneal haze and the prophylaxis of haze development and the management of severe LASIK complications. In this presentation, the background of Mitomycin-C therapy in refractive surgery and clinical applications and recent research works will be presented.

Haze formation in beverages

The most frequent cause of hazes in beverages is due to protein–polyphenol interaction. Proteins that bind polyphenols contain proline, and the more proline, the greater the haze-forming activity. Polyphenols that cause haze have at least two sites that can bind to proteins; this enables them to cross-link proteins together and results in insoluble particles that scatter light. Protein–polyphenol interaction is non-covalent and, at least initially, reversible. The size of haze particles and the haze intensity are both affected by the ratio of haze-active (HA) polyphenol to HA protein. Alcohol content and pH also exert strong influences. Particle size in a model system does not vary smoothly as conditions change; rather shifts in the proportions of particles of a few discrete sizes are seen. Haze development occurs over time in packaged products. In clear beverages a treatment (fining, adsorption or ultrafiltration) is normally applied to reduce the concentration of either HA protein or HA polyphenol in order to delay the onset of haze formation beyond the intended product shelf life. A nephelometer observation gives a good indication of the amount of haze people can perceive.

Study of Colloidal Instability of Millet Wine

Millet wine, xiao-mi-jiu, is a traditional fermented beverage consumed in some regions of eastern Asia. This study presents information on post-bottling instability of millet wine during a 20-week storage at 4°C. The pH and ethanol contents of millet wine were stable, but the color turned from brown to darker brown during 20 weeks of storage. Development of haze and sediment were observed. The levels of nitrogen, proteins, polyphenols, and carbohydrates in solution in the millet wine exhibited quantitative changes. Decreases in the amounts of polyphenols and proteins presumably resulted from polyphenol-protein association, which plays a key role in haze formation. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern of millet wine proteins showed that there were polypeptides with molecular mass ranges of 10 to 18 and 25 to 60 kDa. The 14- and 18-kDa millet wine proteins gradually decreased during storage. These proteins were proline-rich (16–17% of total amino acids), prolamin-derived proteins that produced haze with the addition of tannic acid. The 14- or 18-kDa millet wine proteins could be useful indicators for judging the colloidal stability state of millet wines.

Transplantation of Tissue-Engineered Epithelial Cell Sheets after Excimer Laser Photoablation Reduces Postoperative Corneal Haze

To apply tissue-engineered cell sheet transplantation after excimer laser keratectomy as a novel approach for the reduction of postoperative corneal haze. Limbal biopsy specimens were obtained, and epithelial cells were cultured on temperature-responsive culture inserts without the use of feeder cells. Laser keratectomy (7.0-mm ablation zone and 160-microm depth) was performed in the contralateral eye, and autologous epithelial cell sheets were transplanted to the ablated corneal stroma. Transplant and control group eyes were assessed by slit lamp biomicroscopy, and corneal haze was scored in a masked fashion, according to the Fantes grading scale. For further examination histologic and immunohistochemical analyses were performed. Tissue-engineered cell sheets produced stable attachment to the laser-ablated sites, resulting in epithelialization, 5 minutes after transplantation. Conversely, control corneas required 3 to 5 days for complete re-epithelialization. At both 1 and 2 months after surgery, corneal haze was significantly inhibited in the transplant group. Histologic analyses showed that the number of keratocytes undergoing apoptosis was decreased in the transplant group at 3 days after surgery. Similarly, the expression of both collagen III and alpha-smooth muscle actin, which may enhance corneal haze, were diminished in the transplant group at 2 months. The transplantation of tissue-engineered epithelial cell sheets can successfully prevent the development of corneal haze after excimer laser keratectomy.

Stromal haze, myofibroblasts, and surface irregularity after PRK

The aim of this study was to investigate the relationship between the level of stromal surface irregularity after photorefractive keratectomy (PRK) and myofibroblast generation along with the development of corneal haze. Variable levels of stromal surface irregularity were generated in rabbit corneas by positioning a fine mesh screen in the path of excimer laser during ablation for a variable percentage of the terminal pulses of the treatment for myopia that does not otherwise generate significant opacity. Ninety-six rabbits were divided into eight groups: Groups/Treatment I II III IV V VI VII VIII PRK ablation −4.5D −4.5D −4.5D −4.5D −4.5D −9.0D −9.0D Unwounded Induced irregularity – 10% 30% 50% 50%+SM – +SM – SM, smoothing PTK Slit lamp analysis and haze grading were performed in all groups. Rabbits were sacrificed at 4 hr or 4 weeks after surgery and histochemical analysis was performed on corneas for apoptosis (TUNEL assay), myofibroblast marker alpha-smooth muscle actin (SMA), and integrin α4 to delineate the epithelial basement membrane. Slit-lamp grading revealed severe haze formation in corneas in groups IV and VI, with significantly less haze in groups II, III, and VII and insignificant haze compared with the unwounded control in groups I and V. Analysis of SMA staining at 4 weeks after surgery, the approximate peak of haze formation in rabbits, revealed low myofibroblast formation in group I (1.2±0.2 cells/400× field) and group V (1.8±0.4), with significantly more in groups II (3.5±1.8), III (6.8±1.6), VII (7.9±3.8), IV (12.4±4.2) and VI (14.6±5.1). The screened groups were significantly different from each other ( p<0.05), with myofibroblast generation increasing with higher surface irregularity in the −4.5 diopter PRK groups. The −9.0 diopter PRK group VI had significantly more myofibroblast generation than the −9.0 diopter PRK with PTK-smoothing group VII ( p<0.01). Areas of basement membrane disruption were demonstrated by staining corneas for integrin α4 and were prominent in corneas with grade I or higher haze. SMA-positive myofibroblasts tended to be present sub-adjacent to basement membrane defects. Late apoptosis was detected at 1 month after surgery within clusters of myofibroblasts in the sub-epithelial stroma. In conclusion, these results demonstrated a relationship between the level of corneal haze formation after PRK and the level of stromal surface irregularity. PTK-smoothing with methylcellulose was an effective method to reduce stromal surface irregularity and decreased both haze and associated myofibroblast density. We hypothesize that stromal surface irregularity after PRK for high myopia results in defective basement membrane regeneration and increased epithelium-derived TGFβ signalling to the stroma that increases myofibroblast generation. Late apoptosis appears to have a role in the disappearance of myofibroblasts and haze over time.

Phototherapeutic LASEK for a Persistent Epithelial Defect and a Recurrent Epithelial Erosion

To present two patients, one with persistent epithelial defect and one with recurrent epithelial erosion, unresponsive to conventional therapy treated with phototherapeutic keratectomy (PTK) with the laser subepithelial keratomileusis (LASEK) technique (phototherapeutic LASEK). The epithelial flap was created following 18% ethanol application for 20 seconds. A 10-microm deep ablation was performed in the central 7.0-mm zone. A contact lens was placed and the patient examined daily until epithelial closure. Upon epithelial closure, the contact lens was removed. A mild topical steroid and artificial tears were applied for 2 weeks. The epithelium healed in 4 days in both patients. Patients reported only mild pain until epithelial closure. The manifest refraction and uncorrected visual acuity remained unchanged in both eyes. No haze was noted. The first patient has remained asymptomatic without any recurrence for 12 months, and the second for 9 months. Phototherapeutic LASEK provides a therapeutic option for refractory recurrent erosions and persistent epithelial defects, with the additional benefit of being less painful and less risky for haze development than conventional PTK.

Subepithelial scarring after laser-assisted subepithelial keratectomy

Reply: The decision of whether to perform bilateral, same-session LASEK or a sequentially staged procedure must be made for each individual patient. In recent surveys,1 most responding refractive surgeons in the United States indicated that they perform bilateral, same-session surface ablations. As Kervick appropriately points out, the risks of bilateral surface ablation include but are not limited to bilateral scarring, infection, and bilateral outliers in refractive outcome. These risks must be weighed against problems with anisometropia, depth perception, and time lost from work inherent in performing staged procedures in patients, many of whom may be contact lens intolerant. Identifiable risk factors specific for an increased risk for developing corneal haze after surface ablations include atopy, uncontrolled collagen vascular disease, postoperative exposure to ultraviolet (UV) light, and ablations greater than 100 μm or than 0.18 of the total corneal thickness. Such patients can be treated prophylactically with intraoperative mitomycin-C or postoperatively with autologous serum in addition to an intensive corticosteroid regimen, oral vitamins C and E,2 and UV-blocking sunglasses.3 In the patient whom we described, the 2 identifiable preoperative risk factors for the development of corneal haze were the ablation depth (104 μm and 108 μm) and the ratio of ablation depth to total cornea thickness (greater than 0.21). Our current LASEK surgical protocol would, therefore, use prophylactic intraoperative treatment with mictomycin-C.4 With this prophylactic regimen, we have not observed the development of diffuse, dense, disciform corneal haze with resulting loss of best spectacle-corrected visual acuity in a 1-year follow-up of more than 500 consecutive LASEK patients. However, 1 LASEK patient with −11.0 D of myopia treated with intraoperative mitomycin-C presented with the sudden onset of dense, reticular subepithelial fibrosis that manifested in only 1 eye 18 months postoperatively. The patient had had an uncorrected visual acuity of 20/20 with no corneal haze at 1 year after LASEK. Waiting 2 or 3 months to perform surgery in the contralateral eye would not have identified this or other patients who may go on to develop late-onset postoperative haze. Jay S. Pepose MD, PhD Mujtaba A. Qazi MD Azim M. Mirza MD St. Louis, Missouri, USA

Activation of Toll-Like Receptor (TLR)2, TLR4, and TLR9 in the Mammalian Cornea Induces MyD88-Dependent Corneal Inflammation

Toll-like receptors (TLRs), which recognize microbial products, have an important role in the host innate immune response. The purpose of the present study was to determine whether activation of these receptors leads to development of keratitis and to assess the role of the common adaptor molecule myeloid differentiation factor-88 (MyD88). Corneal epithelium of C57BL/6, TLR2(-/-), TLR9(-/-), and MyD88(-/-) mice was abraded and treated with Pam(3)Cys, LPS, or CpG DNA, which bind TLR2, -4, and -9, respectively, and neutrophil recruitment to the corneal stroma, development of corneal haze, and chemokine production were measured. Activation of TLR2 and -9 stimulated neutrophil recruitment to the corneal stroma of C57BL/6 mice, but not TLR2(-/-) or -9(-/-) mice, respectively. In marked contrast, neutrophil migration to the corneal stroma of MyD88(-/-) mice challenged with Pam(3)Cys, LPS, or CpG DNA was completely ablated. Activation of TLR2, -4, and -9 also caused a significant increase in corneal thickness and haze, indicative of disruption of corneal clarity; however, this response was ablated in MyD88(-/-) mice, which were not significantly different from untreated corneas. Production of CXC chemokines MIP-2 and KC, which mediate neutrophil recruitment to the corneal stroma, was elevated in the corneal epithelium and stroma of control, but not MyD88(-/-) mice. Together, these findings demonstrate that the corneal epithelium has functional TLR2 and -9, and that TLR2, -4, and -9 signal through MyD88. This pathway is therefore likely to have an important role in the early events leading to microbial keratitis.

LASIK Induces Minimal Regrowth and No Haze Development in Rabbit Corneas

Purpose: To quantify central corneal regrowth and haze development after LASIK in rabbits. Methods: New Zealand White rabbits received an 89 μ m (–8 diopters) myopic LASIK and were evaluated during 4 months using slit-lamp and in vivo confocal microscopy to monitor changes in central corneal morphology, epithelial and stromal thickness, flap and bed thickness, and corneal light backscattering (haze). At various timepoints, corneas were processed for histology. Results: Using in vivo confocal microscopy, LASIK induced no detectable morphological changes besides a slightly elevated light backscattering at the interface. Correspondingly, all corneas remained clear with no haze development by slit-lamp biomicroscopy. Corneal thickness was stable by 8 weeks after an increase of 17 ± 4 μ m that consisted of a 13 ± 3 μ m stromal regrowth and a 4 ± 2 μ m epithelial hyperplasia. At the LASIK interface, less than 4 μ m new extracellular matrix was deposited. Accordingly, all LASIK flaps were easily pulled off by 6 months. Conclusions: LASIK induces a minimal wound healing response in rabbit corneas with no haze development and a regrowth (regression) of only 17 μ m of an 89-μ m photoablation. Three main factors contributed to the observed regrowth: epithelial hyperplasia (∼ 4 μ m), matrix deposition at the LASIK interface (∼ 4 μ m), and stromal growth outside the interface within the flap and wound bed (∼ 9 μ m).

Role of keratocyte loss on corneal wound repair after LASIK.

To investigate whether an initial keratocyte loss intensifies central corneal wound repair after LASIK in rabbits. New Zealand White rabbits received either conventional LASIK (-8 D, 6-mm diameter) or LASIK combined with a 7-mm diameter, epithelial denudation (LASIK-scrape). Animals were examined during 4 months by slit lamp and in vivo confocal microscopy to monitor changes in central corneal morphology, light backscattering (haze), and sublayer thickness. At various time points, corneas were processed for histology and stained for nuclei; F-actin; ED-A fibronectin; alpha-smooth muscle actin; TGF-beta1, -beta2, and -beta receptor II; and connective tissue growth factor (CTGF). In vivo confocal microscopy identified no major acellular zones or changes in cell morphology or reflectivity after conventional LASIK. By contrast, a complete loss of keratocytes was observed in the anterior 77 +/- 25 microm stroma 1 week after LASIK-scrape. Highly reflective, migratory fibroblasts gradually repopulated the acellular zone, and by week 8, quiescent-appearing keratocytes were observed throughout the stroma. Correspondingly, stromal light backscattering peaked at 2 weeks after LASIK-scrape (2200 +/- 620 U) followed by a decline to approximately 60 U from week 8; comparable to the slightly increased reflectivity (approximately 50 U) observed after conventional LASIK (ns). Stromal thickness appeared stable 8 weeks after both LASIK and LASIK-scrape, after a regrowth of 13 +/- 3 and 20 +/- 11 microm, respectively (ns). In addition, both procedures induced a minor and comparable epithelial hyperplasia of 4 +/- 2 and 7 +/- 5 microm, respectively (ns). No myofibroblast transformation or TGF-beta growth factor expression was observed below the flap after either treatment. LASIK-scrape induces an anterior keratocyte loss, leading to development of temporary haze during cell repopulation. However, 8 weeks after both LASIK and LASIK-scrape, only a slightly increased reflectivity is noted at the interface. Corneal thickness is stable by week 8, and stromal regrowth and epithelial hyperplasia are comparable after both treatments. Thus, an initial loss of stromal keratocytes does not appear to intensify corneal wound repair after LASIK.

Proteomic Analysis of the Soluble Fraction from Human Corneal Fibroblasts with Reference to Ocular Transparency

The transparent corneal stroma contains a population of corneal fibroblasts termed keratocytes, which are interspersed between the collagen lamellae. Under normal conditions, the keratocytes are quiescent and transparent. However, after corneal injury the keratocytes become activated and transform into backscattering wound-healing fibroblasts resulting in corneal opacification. At present, the most popular hypothesis suggests that particular abundant water-soluble proteins called enzyme-crystallins are involved in maintaining corneal cellular transparency. Specifically, corneal haze development is thought to be related to low levels of cytoplasmic enzyme-crystallins in reflective corneal fibroblasts. To further investigate this hypothesis, we have used a proteomic approach to identify the most abundant water-soluble proteins in serum-cultured human corneal fibroblasts that represent an in vitro model of the reflective wound-healing keratocyte phenotype. Densitometry of one-dimensional gels revealed that no single protein isoform exceeded 5% of the total water-soluble protein fraction, which is the qualifying property of a corneal enzyme-crystallin according to the current definition. This result indicates that wound-healing corneal fibroblasts do not contain enzyme-crystallins. A total of 254 protein identifications from two-dimensional gels were performed representing 118 distinct proteins. Proteins protecting against oxidative stress and protein misfolding were prominent, suggesting that these processes may participate in the generation of cytoplasmic light-scattering from corneal fibroblasts.

Urokinase-type plasminogen activator to prevent haze after photorefractive keratectomy, and pregnancy as a risk factor for haze in rabbits.

To observe the effect of urokinase-type plasminogen activator (uPA) on the development of subepithelial haze after photorefractive keratectomy (PRK) and to assess pregnancy as a risk factor for haze. In 30 rabbits, both eyes of 27 were subjected to PRK and both eyes of 3 served as the nonsurgical control. In the first part of the experiment, for 7 days after PRK, three rabbits (one was pregnant) received aprotinin in one eye and no aprotinin in the contralateral eye. uPA activity was measured by a spectrophotometric method from tear samples in these eyes. In the second part, for 5 days after PRK, 24 rabbits (8 were pregnant) were treated with uPA in one eye and no uPA in the contralateral eye. Haze grading was performed according to the system of Hanna. In the first experiment, the aprotinin-treated eyes and the aprotinin-untreated eye of the pregnant rabbit showed development of haze. In the second, there were clear corneas in 24 of 24 uPA-treated eyes and in 15 of 24 uPA-untreated eyes. Post-PRK haze formed in 9 of 24 uPA-untreated eyes (7 of the 9 haze observations in pregnant rabbits). Within the uPA-untreated group, haze formed in corneas of 7 of 8 pregnant versus 2 of 16 nonpregnant rabbits. There was a strong association between the uPA treatment and clear corneas (P = 0.003) and between pregnancy and haze (P = 0.002). The present results suggest that pregnancy is a risk factor for post-PRK haze in untreated rabbit eyes and that uPA is effective in preventing the occurrence of haze.

Results of phototherapeutic keratectomy in the management of flap striae after LASIK

Objective To evaluate the efficacy of phototherapeutic keratectomy (PTK) in reducing or resolving visually significant surface irregularities resulting from flap striae after LASIK. Design Retrospective, noncomparative case series. Participants Twenty-three eyes of 22 patients with flap striae after LASIK and reduced best-corrected visual acuity or visual symptoms that resolved with diagnostic contact lens fitting treated between January 2001 and April 2002 with at least 1 month of follow-up. The mean follow-up interval was 134 days (range, 30–354 days). Intervention Transepithelial PTK. Main outcome measures Uncorrected visual acuity (UCVA), resolution or reduction of preoperative symptoms, corneal haze, and best spectacle-corrected visual acuity (BSCVA). Results Mean BSCVA and UCVA improved significantly from 20/32 and 20/48 to 20/22 and 20/33 ( P<0.0001 and P = 0.027), respectively, after PTK. There was a significant mean hyperopic shift of 0.88 diopters (D; P = 0.002, range, −1.38 to +3.88 D). Fourteen eyes (61%) were clinically clear, 6 eyes (23%) had trace haze, and 3 eyes (16%) had 1+ haze at the last follow-up visit. Mean spherical equivalent refractive error before LASIK was −7.23 D (range, −2.88 to −13.55 D). Twenty-two of 23 eyes had significant qualitative resolution or reduction of preoperative visual symptoms. Conclusions In cases of visually significant LASIK flap striae, PTK is effective in improving best-corrected visual acuity and reducing visual symptoms. High myopia may be a risk factor for development of visually significant microstriae. Development of anterior stromal haze did not exceed 1+ density and was not correlated to either the number of laser pulses or the length of the follow-up period.

The Relative Importance of Temperature and Time in the Cold Conditioning of Beer

The impact on the development of turbidity from chilling lager-style beer at constant low temperatures and alternating to low temperatures has been investigated. Irrespective of whether a beer is held isothermally or has received a change in temperature of storage, the magnitude of the haze that develops is determined by the extent of chilling that the beer encounters. Equally, the length of storing a beer at a prior, higher temperature does not influence the extent of haze development when the beer is subsequently brought to a lower temperature. These observations support the contention that in the formation of insoluble material during cold conditioning of beer, a short period at a very low temperature (e.g., −2.5°C) is more efficacious than a prolonged period at a warmer temperature (e.g., 0°C).