Phototherapeutic Keratectomy: Science and Art

Phototherapeutic keratectomy for corneal epithelial-stromal dystrophies in pediatric patients

Corneal dystrophies may develop gradually from early onset in childhood and persist for years to decades. Visual impairment or repeated ocular irritations caused by corneal dystrophies severely affect the quality of life. Although various surgical treatment options are indicated for adult patients, the treatment plan for pediatric patients remains unclear. Herein we describe clinical observations of phototherapeutic keratectomy for corneal epithelial-stromal dystrophies in three pediatric patients (five eyes). Corneal opacities were successfully removed, and visual acuity was greatly improved in all operated eyes. The procedure of phototherapeutic keratectomy seems to be feasible in the treatment of corneal epithelial-stromal dystrophies in c hildren, with advantages of minimal invasion and good visual outcomes.

Salzmann's Nodular Degeneration in Refractive Surgery: The Earlier Hit Hypothesis of EBM Injury-Related Fibrosis of the Subepithelial Space and Deeper Corneal Extension

PURPOSE

To review the atypical development of Salzmann's nodular degeneration (SND) after two cases of laser in situ keratomileusis (LASIK) and one case of photorefractive keratomileusis (PRK), and to highlight the pathophysiology of SND and its treatment.

METHODS

Three cases of SND (two following LASIK performed with microkeratomes and one following PRK) were reviewed and Pubmed.gov and internet searches were performed.

RESULTS

SND is myofibroblast-generated fibrosis in the subepithelial space between the epithelium and Bowman's layer that develops years or decades after traumatic, surgical, infectious, or inflammatory injuries to the cornea in which the epithelial basement membrane is damaged in one or more locations and does not fully regenerate. It is hypothesized based on these cases, and the previous immunohistochemistry of other investigators, that myofibroblast precursors, such as fibrocytes or corneal fibroblasts, that enter the subepithelial space are driven to develop into myofibroblasts, which slowly proliferate and extend the fibrosis, by transforming growth factor-beta from epithelium and tears that passes through the defective epithelial basement membrane. These myofibroblasts and the disordered collagens, and other extracellular matrix components they produce, make up the subepithelial opacity characteristic of SND. Nodules are larger accumulations of myofibroblasts and disordered extracellular matrix. If the injury is associated with damage to the underlying Bowman's layer and stroma, as in LASIK flap generation, then the myofibroblasts and fibrosis can extend into Bowman's layer and the underlying anterior stroma.

CONCLUSIONS

SND fibrosis often extends into Bowman's layer and the anterior stroma if there are associated Bowman's defects, such as incisions or lacerations. In the latter cases, SND frequently cannot be removed by simple scrape and peel, as typically performed for most common SND cases, but can be trimmed to remove the offending tissue. This condition is more accurately termed Salzmann's subepithelial fibrosis. [J Refract Surg. 2024;40(5):e279-e290.].

Topical Losartan Decreases Myofibroblast Generation But Not Corneal Opacity After Surface Blast-Simulating Irregular PTK in Rabbits

Purpose

To evaluate the efficacy of topical losartan after blast injury-simulating irregular phototherapeutic keratectomy (PTK) in rabbits.

Methods

Twelve NZW rabbits underwent 100 pulse 6.5 mm diameter PTK over a metal screen to generate severe surface irregularity and inhibit epithelial basement membrane regeneration. Corneas were treated with 0.8 mg/mL losartan in balanced salt solution (BSS) or BSS 50 µL six times per day for six weeks after PTK. All corneas had slit lamp photography, with and without 1% fluorescein at two, four, and six weeks after PTK, and were analyzed using immunohistochemistry for the myofibroblast marker α-smooth muscle actin (α-SMA), keratocyte marker keratocan, mesenchymal cell marker vimentin, transforming growth factor (TGF)-β1, and collagen type IV.

Results

Topical 0.8 mg/mL losartan six times a day significantly decreased anterior stromal α-SMA intensity units compared to BSS at six weeks after anterior stromal irregularity-inducing screened PTK (P = 0.009). Central corneal opacity, however, was not significantly different between the two groups. Keratocan, vimentin, TGF-β1, or collagen type IV levels in the anterior stroma were not significantly different between the two groups.

Conclusions

Topical losartan effectively decreased myofibroblast generation after surface blast simulation irregular PTK. However, these results suggest initial masking-smoothing PTK, along with adjuvant topical losartan therapy, may be needed to decrease corneal stromal opacity after traumatic injuries that produce severe surface irregularity.

Translational Relevance

Topical losartan decreased scar-producing stromal myofibroblasts after irregular PTK over a metal screen but early smoothing of irregularity would also likely be needed to significantly decrease corneal opacity.

Safety and Efficacy of the Phototherapeutic Keratectomy for Treatment of Recurrent Corneal Erosions: A Systematic Review and Meta-Analysis

BACKGROUND

Phototherapeutic keratectomy (PTK) has been increasingly used to treat severe recurrent corneal erosion syndrome (RCES) patients who do not respond to other treatments. However, the efficacy and complication of each study are currently uncertain due to varying rates.

OBJECTIVES

The objective of this study was to investigate the safety and efficacy of the PTK for recurrent corneal erosions.

METHODS

This article performed a systematic literature research in Cochrane, Embase, PubMed, Scopus, and the Web of Science for the literature on PTK treatment of RCES until December 20, 2022. The extracted data including recurrence rate and the adverse event rate were used for meta-analysis.

RESULTS

The recurrence rate was 18% (95% CI, 13%-24%) (129/700 eyes). Subgroup analysis showed that the RCE recurrence was 17% (95% CI, 9%-24%) after trauma and 22% (95% CI, 11%-32%) in the corneal dystrophy group. Treatment-related adverse events included subepithelial haze, hyperopic shift, and decrease of the best spectacle-corrected visual acuity. In this study, the incidence of these events was 13% (95% CI, 6%-21%), 20% (95% CI, 11%-28%), and 11% (95% CI, 5%-16%), respectively.

CONCLUSIONS

PTK represented a valuable treatment option for patients with recurrent corneal erosions, especially those with traumatic injuries, which had minimal side effects.

From bench to clinic: Emerging therapies for corneal scarring

Corneal diseases are one of the leading causes of moderate-to-severe visual impairment and blindness worldwide, after glaucoma, cataract, and retinal disease in overall importance. Given its tendency to affect people at a younger age than other blinding conditions such as cataract and glaucoma, corneal scarring poses a huge burden both on the individuals and society. Furthermore, corneal scarring and fibrosis disproportionately affects people in poorer and remote areas, making it a significant ophthalmic public health problem. Traditional medical strategies, such as topical corticosteroids, are not effective in preventing fibrosis or scars. Corneal transplantation, the only effective sight-restoring treatment for corneal scars, is curbed by challenges including a severe shortage of tissue, graft rejection, secondary conditions, cultural barriers, the lack of well-trained surgeons, operating rooms, and well-equipped infrastructures. Thanks to tremendous research efforts, emerging therapeutic options including gene therapy, protein therapy, cell therapy and novel molecules are in development to prevent the progression of corneal scarring and compliment the surgical options currently available for treating established corneal scars in clinics. In this article, we summarise the most relevant preclinical and clinical studies on emerging therapies for corneal scarring in recent years, showing how these approaches may prevent scarring in its early development.

Magic Bullets: The Coming Age of Meaningful Pharmacological Control of the Corneal Responses to Injury and Disease

Corneal injuries from chemical burns, mechanical trauma, infections, immunological rejections, surgical complications, and some diseases are commonly associated with persistent epithelial defects (PED), neurotrophic epitheliopathy, scarring fibrosis, corneal neovascularization (CNV), and/or corneal endothelial damage that lead to vision loss. Several Food and Drug Administration (FDA) approved medications have recently become available, are currently in clinical trials, or are likely to enter clinical trials in the near future. For example, a 2-week course of topical human recombinant nerve growth factor is frequently an effective treatment for corneal neurotrophic epitheliopathy associated with PEDs. Topical losartan, an angiotensin converting enzyme II receptor antagonist that also inhibits TGF beta signaling, has been shown to effectively decrease myofibroblast generation and scarring fibrosis in alkali burn injury and Descemetorhexis rabbit models. Small molecule topical tyrosine kinase inhibitors, such as sunitinib and axitinib, FDA approved as chemotherapeutic agents to treat specific cancers, have also been found to be effective topical inhibitors of CNV in animal and human trials. Rho-kinase inhibitors, such as ripasudil and netarsudil, that are currently approved agents for the treatment of glaucoma in some countries, have been shown to stimulate corneal endothelial proliferation in animal studies and human trials, and may accelerate the regeneration of Descemet's membrane. These agents, as well as other drugs in development, will be used in targeted combinations to treat corneal pathophysiology associated with epithelial healing disorders, stromal scarring fibrosis, CNV, and corneal endothelial injury during the next decade.

Contrast Sensitivity Changes after Phototherapeutic Keratectomy in Heterozygote Granular Corneal Dystrophy Type 2

Purpose: Contrast sensitivity, the ability to distinguish the relative difference in luminance of an object from its surrounding or adjacent objects, is a useful measure of visual function. In granular corneal dystrophy type 2 (GCD2), opacity of the corneal stroma causes deterioration in visual function. We compared the contrast sensitivity of GCD2 patients before and after phototherapeutic keratectomy (PTK) to evaluate the perioperative visual function in these patients.Methods: This study included 22 eyes of heterozygote GCD2 patients. The visual acuity and contrast sensitivity were measured before and after PTK. The contrast sensitivity was measured in mesopic and photopic background luminances, with glare (G) levels of 0-2 (G0, G1, and G2, respectively) and spatial frequencies at 1.5, 3, 6, 12, and 18 cycles per degree (cpd).Results: The contrast sensitivity increased after PTK at 1.5 and 3 cpd in mesopic and photopic conditions with G0-2 glare (p < 0.05). At 6 cpd, the contrast sensitivity increased in the mesopic condition with G1 glare, and in the photopic condition with G0-2 glare (p < 0.05). However, there was no change in contrast sensitivity at any glare level at 12 and 18 cpd after PTK.Conclusions: In GCD2 patients, the contrast sensitivity increased significantly after PTK. The vision of GCD2 patients, which is decreased due to corneal opacity, is improved after PTK.

Phototherapeutische Keratektomie bei rezidivierenden Hornhauterosionen verschiedener epithelialer Genese: Einfluss der Ablationstiefe auf Pachymetrie und Refraktion

Einführung

Die phototherapeutische Keratektomie gilt heute als etabliertes Therapieverfahren für Patienten, welche unter therapierefraktären genetisch bedingten Hornhautdystrophien oder rezidivierenden Erosiones ohne zugrunde liegende Basalmembrandystrophie leiden.

Ziel der Arbeit

Ziel der Arbeit war es, Änderungen der Refraktion und der Pachymetrie nach phototherapeutischer Keratektomie bei Patienten, welche eine epitheliale Basalmembrandystrophie oder rezidivierende Erosiones ohne zugrunde liegende Basalmembrandystrophie (traumatisch/nichttraumatisch bedingt) aufweisen, zu analysieren.

Material und Methoden

Die Patientendaten wurden retrospektiv aus dem Smart-Eye-Data-Datenbank-System der Augenklinik der LMU in den Jahren 2014 bis 2020 zusammen mit diagnostischen Daten aus Pentacam HR und Autorefraktometer ausgewertet. Als festes Therapieregime wurde eine Photoablation von 10 μm für epitheliale Basalmembrandystrophie und 6 μm für Patienten ohne Basalmembrandystrophie gewählt.

Ergebnisse

In beiden Kollektiven konnte eine Abnahme der Pachymetrie am Apex nachgewiesen werden (epitheliale Basalmembrandystrophie: Abnahme 25,8 μm, ±19,6 μm SD, Bandbreite −12–97 μm; keine Basalmembrandystrophie: Abnahme 12,3 μm, ±17,6 μm SD, Bandbreite −39–68 μm). Es kam zu keiner signifikanten Zu- oder Abnahme der „total corneal refractive power“ im epitheliale Basalmembrandystrophie-Kollektiv, im Kollektiv der rezidivierenden Erosiones ohne Basalmembrandystrophie zu einer signifikanten Zunahme von 42,3 dpt auf 42,6 dpt (Veränderung ±0,8 dpt SD, p < 0,05). Das sphärische Äquivalent zeigte keine Veränderung im Follow-up-Intervall für das epitheliale Basalmembrandystrophie Kollektiv. Hingegen zeigte das Kollektiv ohne Basalmembrandystrophie eine statistisch signifikante Abnahme des SE um 0,4 dpt (±0,7 dpt SD, p < 0,05). Das mittlere Follow-up-Intervall betrug 126 Tage (CI 95 %: 104 bis 147 Tage).

Schlussfolgerung

Ein signifikanter Einfluss auf die Refraktion konnte in der durchgeführten Studie in Bezug auf die „total corneal refractive power“ für beide Kollektive nur in geringem Maße festgestellt werden. Der finale Abtrag anhand der Pachymetrie am Apex hingegen kann auf das 2,3- bis 2,6-Fache der ursprünglichen Ablationstiefe geschätzt werden. Ursachen hierfür sind einerseits der Laserabtrag selbst sowie der Einfluss der reaktiven Wundheilung des kornealen Epithels.

Salzmann nodular degeneration in posterior keratoconus: a case report

Background

To report an unusual case of salzmann nodular degeneration (SND) in posterior keratoconus (PKC) after a corneal penetrating injury.

Case presentation

A 56-year-old woman presented with a history of recurrent light sensitivity, foreign body sensation, and tears after a corneal penetrating injury 20 years ago. The patient was diagnosed with SND accompanying with PKC by slit-lamp microscope, anterior segment optical coherence tomography (OCT), and corneal tomography. A combined therapy of medication (0.1% sodium hyaluronate eye drops, recombinant bovine basic fibroblast growth factor eye drops, and 0.1% fluorometholone eye drops) and bandage contact lens could not relieve the latest episode. A phototherapeutic keratectomy (PTK) treatment (laser ablation depth: 15 μm; treatment zone: 7.5 mm) was performed to remove nodules and smooth the surface. The best spectacle-corrected visual acuity improved from 20/63 preoperatively to 20/40 postoperatively. No SND relapse and corneal ectasia were recorded at follow-up 12 months later.

Conclusions

This is the first known, reported case of SND accompanying with PKC after corneal trauma. The PTK is a safe and effective option for SND with PKC.

Epithelial Basement Membrane Regeneration After PRK-Induced Epithelial-Stromal Injury in Rabbits: Fibrotic Versus Non-fibrotic Corneal Healing

PURPOSE

To study epithelial basement membrane (EBM) regeneration in non-fibrotic and fibrotic corneas after photorefractive keratectomy (PRK).

METHODS

Rabbits (120 total) had either epithelial scrape alone, -4.50 diopters (D) PRK, -9.00 D PRK, or no surgery. Immunohistochemistry was performed on cryofixed corneas at time points from unwounded to 8 weeks (four corneas at each time point in each group). Multiplex immunohistochemistry was performed for EBM components, including collagen type IV, laminin beta-3, laminin alpha-5, perlecan, and nidogen-1. Stromal cellular composition was studied by triplex immunohistochemistry for keratocan, vimentin, and alpha-smooth muscle actin (SMA).

RESULTS

PRK-injured EBM significantly regenerated by 4 days after surgery. However, early TGF-beta-regulating perlecan incorporation into the nascent EBM declined 4 to 7 days after surgery in fibrotic corneas. Non-fibrotic corneas that had fully regenerated EBM (with all five components incorporated into the EBM) were transparent and had few SMA-positive myofibroblasts in the stroma. Conversely, corneas with defective nascent EBM that lacked perlecan developed many anterior stromal myofibroblasts and fibrosis at 3 to 4 weeks after surgery and had large amounts of collagen type IV in the nascent EBM and anterior stroma. Myofibroblasts synthesized perlecan but were incompetent to incorporate the heparin sulfate proteoglycan into the nascent EBM. Corneal transparency was restored over several months even in fibrotic corneas, and this was associated with a return of EBM perlecan, myofibroblast disappearance, and reabsorption of disordered extracellular matrix.

CONCLUSIONS

Defective incorporation of perlecan into the regenerating EBM by subepithelial myofibroblasts, and likely their precursor cells, underlies the development and persistence of stromal fibrosis after PRK corneal injury. [J Refract Surg. 2022;38(1):50-60.].

[Combined transepithelial PTK and topography-guided PRK for treatment of trauma-related corneal scarring]

BACKGROUND

Corneal scars can severely impair visual performance and treatment can be challenging. The study aimed to evaluate a promising minimally invasive option in the treatment of corneal scars using transepithelial topography-guided ablation.

METHODS

This retrospective interventional study involved four eyes of four patients who developed corneal scarring and irregular surfaces due to trauma and were treated with topography-guided photorefractive keratectomy (TG-PRK) between 2017 and 2020. The ablation profile was calculated in all four cases using CRS-Master (Zeiss, Jena, Germany). The main outcome measures were uncorrected and best-corrected distance visual acuity, manifest refraction and corneal regularity by topographic images. The mean age was 34.75 ± 15.39 years and the follow-up time was 6 months for all patients.

RESULTS

In three cases full subjective refraction was corrected in one session and one patient had a refractive error of +0.5 D. Only corneal surface smoothing without additional refractive correction was performed in this case. All four patients showed improvement in uncorrected (2-3 Snellen lines) and corrected (3 Snellen lines) distance visual acuity. No complications occurred during or after the treatment and there was no reduction of visual acuity in any case.

CONCLUSION

The use of TG-PRK in patients with corneal scarring improves visual acuity in selected cases. In myopic patients most of the refractive error can also be corrected in a single session.

Phototherapeutic keratectomy: Indications, methods and decision making

Phototherapeutic keratectomy (PTK) involves treating anterior corneal lesions by superficial corneal ablation using an excimer laser (193 nm). Some of the commonly treated conditions include recurrent corneal erosions (RCE), corneal dystrophies, spheroidal degeneration, keratoconus, and corneal scars. We discuss various techniques of PTK including large area PTK, focal PTK, and multifocal PTK and alternatives to PTK. Masking agents like hyaluronate, methylcellulose, and dextran are recommended to help achieve a better outcome when ablating irregular corneal surfaces. Antifibrotic agents like mitomycin C reduce the chances of recurrence of the disease, apart from minimizing the postoperative scarring. Some of the complications include induced hyperopia and irregular astigmatism, haze, recurrence, and corneal thinning. However, earlier postoperative recovery, possibility of a repeat procedure, and ability to control the depth of ablation make PTK a promising, minimally invasive alternative to keratoplasty in cases with anterior corneal pathologies.

Visual rehabilitation by using corneal wavefront-guided transepithelial photorefractive keratectomy for corneal opacities after epidemic keratoconjunctivitis

PURPOSE

To evaluate long-term visual and refractive outcomes of corneal wavefront-guided transepithelial photorefractive keratectomy (t-PRK) with mitomycin C for the treatment of corneal opacities secondary to adenoviral epidemic keratoconjunctivitis.

METHODS

Records of patients who underwent corneal wavefront-guided t-PRK with excimer laser from January 2012 to December 2018 were retrospectively reviewed. Preoperative and postoperative uncorrected visual acuity, best-spectacle corrected visual acuity, slit-lamp biomicroscopic examination findings, manifest refraction, and corneal aberrations and fundus examination findings were evaluated.

RESULTS

Twenty-two eyes of 22 patients comprising 12 male (55%) and 10 female (45%) were treated. The mean age was 34.5 ± 10.8 years (range 19-55). The mean follow-up time was 34.4 ± 17.50 months (range 13-61 months). There was a statistically significant improvement in UCVA and BSCVA (p < 0.001 and p = 0.02), and there was a significant decrease in total higher-order aberrations, spherical, coma and trefoil aberration at postoperative first year (p < 0.001 in each). In two eyes of two patients, minimal haze formation was observed after the procedure, and both eyes were treated with topical steroid. No recurrence was observed in subepithelial infiltrates in any patient during long-term follow-up.

CONCLUSION

In long-term clinical follow-up, corneal wavefront-guided t-PRK treatment is an effective and reliable treatment method for rehabilitation of visual impairment due to corneal scars following adenoviral infections, in properly selected patients.

Fourier-domain optical coherence tomography-guided phototherapeutic keratectomy for the treatment of anterior corneal scarring

AIM

To evaluate the safety, visual and anatomic outcomes of fourier-domain optical coherence tomography (FD-OCT)-guided excimer laser phototherapeutic keratectomy (PTK) combined with photorefractive keratectomy (PRK) surgery in treating anterior corneal scarring.

METHODS

Clinical data of 23 eyes of 21 patients with anterior corneal scarring underwent FD-OCT-guided PTK and PRK from Dec. 2014 to Jul. 2016 were reviewed. Patients were assessed for preoperative and postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), contrast sensitivity (CS), FD-OCT, corneal topography and colour figures of anterior segments.

RESULTS

The preoperative corneal pathologic conditions included viral keratitis (7 patients, 7 eyes), band keratopathy (2 patients, 4 eyes), corneal dystrophy (4 patients, 4 eyes), traumatic corneal disease (2 patients, 2 eyes) and corneal chemical injury (6 patients, 6 eyes). Mean follow-up time was 10.65 (range, 3-19)mo. UCVA (in logMAR) improved from a mean of 0.79 (95%CI, 0.28-1.29) preoperatively to a mean of 0.45 (95%CI, 0.29-0.62) postoperatively (P=0.021). BSCVA (in logMAR) improved from 0.57 (95%CI, 0.27-0.88) preoperatively to a mean of 0.28 (95%CI, 0.15-0.41) postoperatively (P=0.001). Corneal topographic indices postoperatively showed significant improvement in corneal cylinder (P=0.009), the surface regularity index (P=0.007) and surface asymmetry index (P=0.00). Postoperative spherical equivalent averaged -0.53 diopters (-1.49 to 0.42). No complications were associated with the treatment.

CONCLUSION

FD-OCT-guided PTK combined with PRK is safe and effective for the treatment of anterior corneal scarring by eliminating or reducing corneal opacities.

Corneal nerves anatomy, function, injury and regeneration

The cornea is a highly innervated tissue, exhibiting a complex nerve architecture, distribution, and structural organization. Significant contributions over the years have allowed us to come to the current understanding about the corneal nerves. Mechanical or chemical trauma, infections, surgical wounds, ocular or systemic comorbidities, can induce corneal neuroplastic changes. Consequently, a cascade of events involving the corneal wound healing, trophic functions, neural circuits, and the lacrimal products may interfere in the corneal homeostasis. Nerve physiology drew the attention of investigators due to the popularization of modern laser refractive surgery and the perception of the destructive potential of the excimer laser to the corneal nerve population. Nerve fiber loss can lead to symptoms that may impact the patient's quality of life, and impair the best-corrected vision, leading to patient and physician dissatisfaction. Therefore, there is a need to better understand preoperative signs of corneal nerve dysfunction, the postoperative mechanisms of nerve degeneration and recovery, aiming to achieve the most efficient way of treating nerve disorders related to diseases and refractive surgery.

Combined Phototherapeutic Keratectomy and Peripheral Anterior Stromal Puncture for the Treatment of Recurrent Corneal Erosion Syndrome

PURPOSE

To investigate the efficacy of the combined phototherapeutic keratectomy (PTK) and peripheral anterior stromal puncture (ASP) compared with that of PTK alone in patients with recurrent corneal erosion syndrome (RCES).

METHODS

The medical records of 25 patients (25 eyes) who underwent combined treatment of PTK and peripheral ASP for RCES from March 2016 to May 2017 were retrospectively reviewed. Twenty-three patients (23 eyes) treated with PTK alone from March 2015 to February 2016 served as a control group. All surgeries were performed by a single surgeon. This retrospective clinical study comprised 48 patients (48 eyes) who were followed up for more than 18 months. Clinical records of age, sex, laterality, etiology of RCES, and history of recurrence after treatment were evaluated.

RESULTS

Twenty-five eyes were treated with combined PTK and ASP, and 23 eyes were treated with PTK only. The mean follow-up period was 19.63 ± 2.97 and 19.75 ± 6.83 months, respectively. There were no differences in baseline parameters between the groups. In the combined treatment group, one patient experienced recurrence 6 months after the surgery. In the single treatment group, five patients showed recurrence at 4, 7, 8, 11, and 13 months after the surgery, respectively. Compared to the single treatment group, the combined treatment group showed significantly lower recurrence rate (p < 0.05). All recurred patients required no additional treatment except temporary therapeutic contact lenses and topical lubricants.

CONCLUSIONS

Our findings suggest that combined treatment of PTK and peripheral ASP is effective in alleviation of symptoms and prevention of recurrence in refractory RCES compared with treatment using PTK alone.

Biology of keratorefractive surgery- PRK, PTK, LASIK, SMILE, inlays and other refractive procedures

The outcomes of refractive surgical procedures to improve uncorrected vision in patients-including photorefractive keratectomy (PRK), laser in-situ keratomileusis (LASIK), Small Incision Lenticule Extraction (SMILE) and corneal inlay procedures-is in large part determined by the corneal wound healing response after surgery. The wound healing response varies depending on the type of surgery, the level of intended correction of refractive error, the post-operative inflammatory response, generation of opacity producing myofibroblasts and likely poorly understood genetic factors. This article details what is known about these specific wound healing responses that include apoptosis of keratocytes and myofibroblasts, mitosis of corneal fibroblasts and myofibroblast precursors, the development of myofibroblasts from keratocyte-derived corneal fibroblasts and bone marrow-derived fibrocytes, deposition of disordered extracellular matrix by corneal fibroblasts and myofibroblasts, healing of the epithelial injury, and regeneration of the epithelial basement membrane. Problems with epithelial and stromal cellular viability and function that are altered by corneal inlays are also discussed. A better understanding of the wound healing response in refractive surgical procedures is likely to lead to better treatments to improve outcomes, limit complications of keratorefractive surgical procedures, and improve the safety and efficiency of refractive surgical procedures.

Oral l-Cysteine Supplementation Enhances the Long Term-Effect of Topical Basic Fibroblast Growth Factor (bFGF) in Reducing the Corneal Haze after Photorefractive Keratectomy in Myopic Patients

We aimed at evaluating the long-term effects of l-cysteine oral supplementation to basic fibroblast growth factor (bFGF) eye-drops on corneal re-epithelization and transparency in myopic patients subjected to photorefractive keratectomy (PRK). Forty patients subjected to bilateral PRK for myopia were enrolled and randomly divided into two groups receiving an additional therapy together with the standard postoperative treatment consisting in local tobramycin 0.3%, dexamethasone 0.1%, diclofenac 0.1%, and 0.2% hyaluronate. Group 1 included 20 patients (11 males and 9 females; 34.09 ± 8 years of age) receiving only bFGF eye-drops (10 μg/10 μL) four times a day for 7 days starting from the day of surgery; Group 2 included 20 patients (12 males and 8 females; 37.35 ± 11.5 years of age) who were postoperatively administered with topical basic fibroblast growth factor (bFGF; 10 μg/10 μL) four times a day for 7 days plus oral l-cysteine supplementation (500 mg/capsule) once a day for 15 days, starting 7 days before PRK. Patients were followed-up for 12 months. Clinical ophthalmologic parameters were recorded for all the 80 examined eyes. The corneal transparency was evaluated in vivo by slit lamp and confocal microscopy. The data showed that: (a) the corneal haze occurred in a smaller percentage of the patients who were postoperatively administered with topical bFGF plus oral l-cysteine supplementation (Group 2) compared to patients who received only bFGF (Group 1); (b) at 6 months of follow-up, the stromal mean image brightness of the patients belonging to Group 2 was significantly lower than that of the Group 1 (p < 0.03), and, interestingly, the difference was even more evident at 12 month from the treatment (p < 0.001). Moreover, the final mean of the spherical equivalent refraction was −0.06 ± 0.2 D in Group 1 and −0.08 ± 0.3 D in Group 2, whereas the final uncorrected distance visual acuity (UDVA) was equal or superior to 20/25 in 100% of eyes in both Group 1 and 2. Post refractive patients can benefit from the administration of l-cysteine before the surgery and in association with bFGF in the early postoperative period, showing a faster corneal re-epithelization able to prevent corneal haze in the long-term recovery.

Phototherapeutic Keratectomy in Macular and Granular Dystrophy: Two-year Results

PURPOSE

To evaluate two-year outcomes of phototherapeutic keratectomy in granular and macular dystrophy and to investigate the effects of dystrophy type on results.

METHODS

Sixty-three patients who underwent phototherapeutic keratectomy (PTK) for granular and macular dystrophy in the cornea funit of the University of Health Sciences Beyoglu Eye Research and Training Hospital were evaluated retrospectively. Patients under 18 years of age, patients with a follow-up period of less than 24 months, and patients who had previously undergone corneal surgery or excimer laser treatment were excluded from the study. Treatment values (ablation depth, optical zone, mitomycin-C (MMC) application time) and complications during and after treatment were recorded. Patients who had a decrease of two or more lines in their BCVA and those with recurrent or increased corneal opacities were considered to have severe recurrences. Uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) were recorded preoperatively and postoperatively at the 12th and 24th months. The values obtained before and after the PTK were compared with statistical methods.

RESULTS

A total of 41 eyes (27 with granular dystrophy and 14 with macular dystrophy) were included in this study. There were no statistically significant differences between patients with granular dystrophy and macular dystrophy in terms of preoperative UCVA and BCVA, MMC application time, and follow-up period (p > .05). The mean age of patients with macular dystrophy was statistically smaller than that of patients with granular dystrophy (p = .04). The amount of ablation applied to macular dystrophy was statistically higher than for granular dystrophy (p = .03). The mean UCVA and BCVA showed statistically significant improvements at the 24th postoperative month (p < .5). There was no statistically significant difference between the UCVA and BCVA values of the patients with granular and macular dystrophy at the 12th and 24th months after the procedure. No recurrence was observed in any patient after 24 months. However, when the follow-up continued, severe recurrence was encountered in 2 patients with macular dystrophy at 26th and 40th months. Re-treatment procedures were needed in these two patients who had severe recurrence.

CONCLUSIONS

Phototherapeutic keratectomy is an effective and safe option for treatment in both granular and macular corneal dystrophy. Recurrence is a more common problem in patients with macular dystrophy, and recurrent therapies or keratoplasty methods are needed more frequently.

Coordinated Modulation of Corneal Scarring by the Epithelial Basement Membrane and Descemet's Basement Membrane

PURPOSE

To provide an overview of the importance of the coordinated role of the epithelial basement membrane (EBM) and Descemet's basement membrane (DBM) in modulating scarring (fibrosis) in the cornea after injuries, infections, surgeries, and diseases of the cornea.

METHODS

Literature review.

RESULTS

Despite their molecular and ultrastructural differences, the EBM and DBM act in a coordinated fashion to modulate the entry of transforming growth factor beta (TGF-β) and other growth factors from the epithelium/tear film and aqueous humor, respectively, into the corneal stroma where persistent levels of these modulators trigger the development and persistence of myofibroblasts that produced disordered, opaque extracellular matrix not usually present in the corneal stroma. The development of these myofibroblasts and the extracellular matrix they produce is often detrimental to visual function of the cornea after penetrating keratoplasty, LASIK buttonhole flaps, persistent epithelial defects, microbial keratitis, Descemet stripping automated endothelial keratoplasty, or Descemet membrane endothelial keratoplasty, while being beneficial in other situations such as the scarred edge of LASIK flaps and donor-recipient interface in penetrating keratoplasty. Efforts to modulate the repair or replacement of the EBM and DBM, and thereby the development or disappearance of myofibroblasts, should be a major emphasis of treatments provided by refractive and corneal surgeries, infections, trauma, or diseases of the cornea.

CONCLUSIONS

The EBM and DBM are critical modulators of the localization of profibrotic growth factors, such as TGF-β, that modulate the development and persistence of myofibroblasts that produce corneal scars (stromal fibrosis). Therapeutic efforts to regenerate or repair EBM and/or DBM, and interfere with the development of myofibroblasts or facilitate their disappearance are often the key to clinical outcomes. [J Refract Surg. 2019;35(8):506-516.].

The Corneal Basement Membranes and Stromal Fibrosis

Purpose

The purpose of this review was to provide detailed insights into the pathophysiology of myofibroblast-mediated fibrosis (scarring or late haze) after corneal injury, surgery, or infection.

Method

Literature review.

Results

The epithelium and epithelial basement membrane (EBM) and/or endothelium and Descemet's basement membrane (BM) are commonly disrupted after corneal injuries, surgeries, and infections. Regeneration of these critical regulatory structures relies on the coordinated production of BM components, including laminins, nidogens, perlecan, and collagen type IV by epithelial, endothelial, and keratocyte cells. Whether a cornea, or an area in the cornea, heals with transparency or fibrosis may be determined by whether there is injury to one or both corneal basement membranes (EBM and/or Descemet's BM) and delayed or defective regeneration or replacement of the BM. These opaque myofibroblasts, and the disordered extracellular matrix these cells produce, persist in the stroma until the EBM and/or Descemet's BM is regenerated or replaced.

Conclusions

Corneal stromal fibrosis (also termed "stromal scarring" or "late haze") occurs as a consequence of BM injury and defective regeneration in both the anterior (EBM) and posterior (Descemet's BM) cornea. The resolution of fibrosis and return of stromal transparency depends on reestablished BM structure and function. It is hypothesized that defective regeneration of the EBM or Descemet's BM allows key profibrotic growth factors, including transforming growth factor beta-1 (TGF-β1) and TGF-β2, to penetrate the stroma at sustained levels necessary to drive the development and maintenance of mature opacity-producing myofibroblasts from myofibroblast precursors cells, and studies suggest that perlecan and collagen type IV are the critical components in EBM and Descemet's BM that bind TGF-β1, TGF-β2, platelet-derived growth factor, and possibly other growth factors, and regulate their bioavailability and function during homeostasis and corneal wound healing.

Femtosecond Laser-Assisted Ipsilateral Rotational Lamellar Autokeratoplasty

PURPOSE

To describe the surgical technique and report the outcomes of 2 patients treated with femtosecond laser-assisted ipsilateral rotational lamellar autokeratoplasty in central corneal scars.

METHODS

The corneal scar depth was mapped using preoperative optical coherence tomography. An eccentric lamellar lenticule was cut with a femtosecond laser and rotated to decenter corneal opacity and free the pupil area in 2 patients with nonprogressive central corneal scars. The surgical plan was set after simulating lenticule rotation with a digital corneal image and computer software.

RESULTS

In both cases, the corneal scar was decentered inferiorly, out of the pupillary area, with increased postoperative visual acuity but visual outcome limitations secondary to corneal irregularities and residual deep opacity.

CONCLUSIONS

Femtosecond laser-assisted ipsilateral rotational lamellar autokeratoplasty is effective for shifting central corneal opacities and can be considered in appropriate cases.

Pathophysiology of Corneal Scarring in Persistent Epithelial Defects After PRK and Other Corneal Injuries

PURPOSE

To analyze corneal persistent epithelial defects that occurred at 3 to 4 weeks after -4.50 diopter (D) photorefractive keratectomy (PRK) in rabbits and apply this pathophysiology to the treatment of persistent epithelial defects that occur after any corneal manipulations or diseases.

METHODS

Two of 168 corneas that had -4.50 D PRK to study epithelial basement membrane regeneration developed spontaneous persistent epithelial defects that did not heal at 3 weeks after PRK. These were studied with slit-lamp photographs, immunohistochemistry for the myofibroblast marker alpha-smooth muscle actin (α-SMA), and transmission electron microscopy.

RESULTS

Myofibroblasts developed at the stromal surface within the persistent epithelial defect and for a short distance peripheral to the leading edge of the epithelium. No normal epithelial basement membrane was detectable within the persistent epithelial defect or for up to 0.3 mm behind the leading edge of the epithelium, although epithelial basement membrane had normally regenerated in other areas of the zone ablated by an excimer laser where the epithelium healed promptly.

CONCLUSIONS

A persistent epithelial defect in the cornea results in the development of myofibroblasts and disordered extracellular matrix produced by these cells that together cause opacity within, and a short distance beyond, the persistent epithelial defect. Clinicians should treat persistent epithelial defects within 10 days of non-closure of the epithelium to facilitate epithelial healing to prevent long-term stromal scarring (fibrosis). [J Refract Surg. 2018;34(1):59-64.].