Haze development after photorefractive keratectomy: mechanical vs ethanol epithelial removal in rabbits

Clinical Outcomes of Aberration-Free All Surface Laser Ablation (ASLA) vs. Aberration-Free ASLA Assisted by Smart Pulse Technology in High Myopia: A One-Year Follow-Up Study

Purpose

To compare the clinical outcomes of aberration-free all surface laser ablation (ASLA) with and without the use of smart pulse technology (SPT) in high myopia.

Methods

This study retrospectively analyzed 138 eyes (138 patients, only the right eye was selected) treated for high myopia (spherical equivalent ≥−6.00 diopters) using aberration-free ASLA (non-SPT group; 85 eyes) and aberration-free ASLA assisted by SPT (SPT group; 53 eyes). Examinations such as visual acuity, refraction, and haze were performed before the 12-month follow-up. Corneal epithelial healing time was assessed in the first postoperative day. Visual acuity and refraction examination were performed at 7 days and 1, 3, 6, and 12 months postoperatively. Corneal haze was evaluated in 1, 3, 6, and 12 months. Safety, efficacy, and corneal wavefront aberrations were assessed 12 months after the treatment.

Results

At 12 months postoperatively, 60% versus 40% of eyes achieved 20/16 Snellen lines or better, and 92% versus 82% of eyes achieved 20/20 Snellen lines or better visual acuity in the SPT and the non-SPT groups, respectively. The average postoperative epithelial healing time was 3.75 ± 1.00 days in the SPT group and 3.73 ± 1.30 days in the non-SPT group (P ≥ 0.05). The safety and the efficacy index of the SPT group were better than those of the non-SPT group in the follow-ups. The attempted spherical equivalent before the surgery and the achieved spherical equivalent at 12 months were comparable between the two groups. Regarding the aberrations, the results of Coma 90° in the SPT group were better than those in the non-SPT group (P ≤ 0.05), but the increase of RMS HOAs (root mean square higher order aberrations), Coma 0°, and spherical aberration postoperatively had no statistical difference between the two groups (P ≥ 0.05). Conclusions: Both aberration-free ASLA with and without SPT showed favorable safety, effectiveness, and predictability within 12 months for high myopia. And, ASLA using SPT might have potential advantages in the long-term visual quality.

Differential effects of Hsp90 inhibition on corneal cells in vitro and in vivo

The transformation of quiescent keratocytes to activated fibroblasts and myofibroblasts (KFM transformation) largely depends on transforming growth factor beta (TGFβ) signaling. Initiation of the TGFβ signaling cascade results from binding of TGFβ to the labile type I TGFβ receptor (TGFβRI), which is stabilized by the 90 kDa heat shock protein (Hsp90). Since myofibroblast persistence within the corneal stroma can result in stromal haze and corneal fibrosis in patients undergoing keratorefractive therapy, modulation of TGFβ signaling through Hsp90 inhibition would represent a novel approach to prevent myofibroblast persistence. In vitro, rabbit corneal fibroblasts (RCFs) or stratified immortalized human corneal epithelial cells (hTCEpi) were treated with a Hsp90 inhibitor (17AAG) in the presence/absence of TGFβ1. RCFs were cultured either on tissue culture plastic, anisotropically patterned substrates, and hydrogels of varying stiffness. Cellular responses to both cytoactive and variable substrates were assessed by morphologic changes to the cells, and alterations in expression patterns of key keratocyte and myofibroblast proteins using PCR, Western blotting and immunocytochemistry. Transepithelial electrical resistance (TEER) measurements were performed to establish epithelial barrier integrity. In vivo, the corneas of New Zealand White rabbits were wounded by phototherapeutic keratectomy (PTK) and treated with 17AAG (3× or 6× daily) either immediately or 7 days after wounding for 28 days. Rabbits underwent clinical ophthalmic examinations, SPOTS scoring and advanced imaging on days 0, 1, 3, 7, 10, 14, 21 and 28. On day 28, rabbits were euthanized and histopathology/immunohistochemistry was performed. In vitro data demonstrated that 17AAG inhibited KFM transformation with the de-differentiation of spindle shaped myofibroblasts to dendritic keratocyte-like cells accompanied by significant upregulation of corneal crystallins and suppression of myofibroblast markers regardless of TGFβ1 treatment. RCFs cultured on soft hydrogels or patterned substrates exhibited elevated expression of α-smooth muscle actin (αSMA) in the presence of 17AAG. Treatment of hTCEpi cells disrupted zonula occludens 1 (ZO-1) adherens junction formation. In vivo, there were no differences detected in nearly all clinical parameters assessed between treatment groups. However, rabbits treated with 17AAG developed greater stromal haze formation compared with controls, irrespective of frequency of administration. Lastly, there was increased αSMA positive myofibroblasts in the stroma of 17AAG treated animals when compared with controls. Hsp90 inhibition promoted reversion of the myofibroblast to keratocyte phenotype, although this only occurred on rigid substrates. By contrast, in vivo Hsp90 inhibition was detrimental to corneal wound healing likely due to impairment in corneal epithelial closure and barrier function restoration. Collectively, our data demonstrated a strong interplay in vitro between biophysical cues and soluble signaling molecules in determining corneal stromal cell phenotype.

Effect of the combination of basic fibroblast growth factor and cysteine on corneal epithelial healing after photorefractive keratectomy in patients affected by myopia

Background:

This study sought to evaluate the effect of basic fibroblast growth factor eye drops and cysteine oral supplements on corneal healing in patients treated with photorefractive keratectomy (PRK).

Materials and Methods:

One hundred and twenty patients treated bilaterally with PRK for myopia were enrolled at one of two eye centers (Clinica Santa Lucia, Bologna, Italy and Department of Ophthalmology, University of Magna Graecia, Catanzaro, Italy) and were treated at the former center. Sixty patients included in the study group (Group 1) were treated postoperatively with topical basic fibroblast growth factor plus oral L-cysteine supplements, whereas 60 subjects included in the control group (Group 2) received basic fibroblast growth factor eye drops. We recorded the rate of corneal re-epithelialization and patients were followed-up every 30 days for 6 months. Statistical analyses were performed on the collected data.

Results:

The eyes in Group 1 demonstrated complete re-epithelialization at Day 5, whereas the eyes in Group 2 achieved this status on Day 6. No side-effects were reported.

Conclusions:

Patients treated with basic fibroblast growth factor eye drops and L-cysteine oral supplements benefit from more rapid corneal re-epithelialization. In human eyes, this combination treatment appeared to be safe and effective in accelerating corneal surfacing after surgery.

Financial Disclosure:

No author has any financial or proprietary interest in any material or method used in this study.

Trial Registration:

Current Controlled Trials ISRCTN73824458.

Corneal Regeneration After Photorefractive Keratectomy: A Review

Photorefractive keratectomy (PRK) remodels corneal stroma to compensate refractive errors. The removal of epithelium and the ablation of stroma provoke the disruption of corneal nerves and a release of several peptides from tears, epithelium, stroma and nerves. A myriad of cytokines, growth factors, and matrix metalloproteases participate in the process of corneal wound healing. Their balance will determine if reepithelization and stromal remodeling are appropriate. The final aim is to achieve corneal transparency for restoring corneal function, and a proper visual quality. Therefore, wound-healing response is critical for a successful refractive surgery. Our goal is to provide an overview into how corneal wounding develops following PRK. We will also review the influence of intraoperative application of mitomycin C, bandage contact lenses, anti-inflammatory and other drugs in preventing corneal haze and post-PRK pain.

Air assisted lamellar keratectomy for the corneal haze model

To standardize the corneal haze model in the resection depth and size for efficient corneal haze development, air assisted lamellar keratectomy was performed. The ex vivo porcine corneas were categorized into four groups depending on the trephined depth: 250 µm (G1), 375 µm (G2), 500 µm(G3) and 750 µm (G4). The stroma was equally ablated at the five measurement sites in all groups. Significant differences were observed between the trephined corneal depths for resection and ablated corneal thickness in G1 (p < 0.001). No significant differences were observed between the trephined corneal depth for resection and the ablated corneal thickness in G2, G3, and G4. The resection percentage was similar in all groups after microscopic imaging of corneal sections. Air assisted lamellar keratectomy (AK) and conventional keratectomy (CK) method were applied to six beagles, after which development of corneal haze was evaluated weekly until postoperative day 28. The occurrence of corneal haze in the AK group was significantly higher than that in the CK group beginning 14 days after surgery. Alpha-smooth muscle actin expression was significantly higher in the AK group (p < 0.001) than the CK group. Air assisted lamellar keratectomy was used to achieve the desired corneal thickness after resection and produce sufficient corneal haze.

The increasing importance of translational vision research in refractive surgery

Addressing these business and financial components of research, we believe that including a section on translational vision research especially for refractive surgery will be a welcome addition to the readership of the Journal. Although the section "Translational Science" is new, the Journal has published a number of articles in past years that would have been ideal candidates for such a section. The inaugural Translational Science article in this month's issue is fron Santhiago and colleagues on short-term cell death and inflammation after intracorneal inlay implantation in rabbits. Although not all scientists are in agreement with the promotion of this term, the Journal aims to provide different outlooks and modern usage of translational research in this way to advance the field of refractive surgery.

Mechanical versus alcohol-assisted epithelial debridement during photorefractive keratectomy: a confocal microscopic clinical trial

PURPOSE

To compare the effects of mechanical versus alcohol-assisted epithelial debridement on corneal cellular elements after photorefractive keratectomy (PRK) using confocal microscopy.

METHODS

This randomized, clinical trial included 66 eyes from 33 patients with spherical equivalent refraction <-4.00 diopters (D). Mechanical versus alcohol-assisted epithelial debridement was performed during PRK. The right eye of each patient was randomly assigned to one group (mechanical group or alcohol-assisted group) and the fellow eye to the alternate group. Confocal examination was performed preoperatively and at 3 and 6 months postoperatively. Main outcome measures were keratocyte density and maximum anterior stromal light reflectivity.

RESULTS

Mean epithelial healing time was 3.2 ± 0.4 and 3.0 ± 0.3 days in the mechanical and alcohol-assisted groups, respectively (P=.001). Anterior retroablation stromal keratocyte density was 704.3 ± 119.9 cells/mm² and 734.3 ± 103.7 cells/mm² at 3 months (P=.05) and 643.8 ± 134.4 cells/mm² and 696.7 ± 129.6 cells/mm² at 6 months (P=.02) in the mechanical and alcohol-assisted groups, respectively. No significant difference was noted in midstromal and posterior keratocyte density between the two groups. Maximum reflectivity was 61.56 ± 12.64 international units (IU) and 56.93 ± 7.86 IU in the mechanical and alcohol-assisted groups, respectively, 3 months after surgery (P=.018). Corresponding values were 49.46 ± 4.97 IU and 48.98 ± 4.60 IU, respectively, 6 months after surgery (P=.628).

CONCLUSIONS

Due to more adverse effects of mechanical epithelial debridement on anterior keratocyte density and anterior stromal reflectivity, alcohol-assisted epithelial debridement is recommended as the procedure of choice for epithelial removal during PRK in patients with mild myopia.