Evaluation of subbasal nerve morphology and corneal sensation after accelerated corneal collagen cross-linking treatment on keratoconus

A comparison of conventional and accelerated corneal crosslinking: corneal epithelial remodeling and in vivo confocal microscopy analysis

PURPOSE

To evaluate the effect of conventional and accelerated corneal crosslinking (CXL) on visual acuity, corneal topography, corneal epithelial thickness, and subbasal nerve morphology in progressive keratoconus patients.

METHODS

In this prospective and randomized study, twenty eyes of 20 patients were treated with conventional CXL (3 mW/cm2, 30 min, C-CXL) and 19 eyes of 19 patients were treated with accelerated CXL (9 mW/cm2, 10 min, A-CXL). The spherical equivalent, uncorrected visual acuity, best-corrected visual acuity, keratometric measurements, demarcation line measurement and epithelial thickness mapping analyses, and subbasal nerve morphology with in vivo confocal microscopy (IVCCM) were evaluated at baseline and at postoperative months 1, 3 and 6.

RESULTS

At postoperative 6 months, a significant improvement was observed in all keratometric values in both treatment groups (p < 0.05). All epithelial thickness indices, except central, temporal, and inferotemporal thickness, were reduced at 1 month postoperatively in both treatment groups. The epithelial map uniformity indices (standard deviation and difference between min-max thickness) were significantly lower than the baseline values at all time points after CXL in both treatment groups (p < 0.001). Compared with the preoperative values, there was a significant decrease in all IVCCM parameters at 1 month postoperatively (p < 0.05). At 6 months postoperatively, corneal nerve fiber density and corneal nerve branch density recovered to preoperative values in the A-CXL group, whereas corneal nerve regeneration was not complete in the C-CXL group.

CONCLUSION

Both conventional and accelerated CXL treatments appear to be effective in halting the progression of KC. Corneal epithelial irregularity slightly improves after CXL. The regeneration of subbasal nerves is faster after A-CXL treatment.

Evaluation of corneal nerves and dendritic cells by in vivo confocal microscopy after Descemet's membrane keratoplasty for bullous keratopathy

This study evaluated changes in corneal nerves and the number of dendritic cells (DCs) in corneal basal epithelium following Descemet membrane endothelial keratoplasty (DMEK) surgery for bullous keratopathy (BK). Twenty-three eyes from 16 consecutive patients that underwent DMEK for BK were included. Eyes of age-matched patients that underwent pre-cataract surgery (12 eyes) were used as controls. In vivo confocal microscopy was performed pre- and postoperatively at 6, 12, and 24 months. Corneal nerve length, corneal nerve trunks, number of branches, and the number of DCs were determined. The total corneal nerve length of 1634.7 ± 1389.1 μm/mm² before surgery was significantly increased in a time-dependent manner to 4485.8 ± 1403.7 μm/mm², 6949.5 ± 1477.1 μm/mm², and 9389.2 ± 2302.2 μm/mm² at 6, 12, and 24 months after DMEK surgery, respectively. The DC density in BK cornea pre- and postoperatively at 6 months was significantly higher than in the controls, and decreased postoperatively at 12 and 24 months and was significantly lower than that at 6 months postoperatively. Thus, our results suggest that DMEK can repair and normalize the corneal environment.

In Vivo Confocal Microscopy Evaluation in Patients with Keratoconus

Keratoconus is the most common primary corneal ectasia characterized by progressive focal thinning. Patients experience increased irregular astigmatism, decreased visual acuity and corneal sensitivity. Corneal collagen crosslinking (CXL), a minimally invasive procedure, is effective in halting disease progression. Historically, keratoconus research was confined to ex vivo settings. In vivo confocal microscopy (IVCM) has been used to examine the corneal microstructure clinically. In this review, we discuss keratoconus cellular changes evaluated by IVCM before and after CXL. Cellular changes before CXL include decreased keratocyte and nerve densities, disorganized subbasal nerves with thickening, increased nerve tortuosity and shortened nerve fibre length. Repopulation of keratocytes occurs up to 1 year post procedure. IVCM also correlates corneal nerve status to functional corneal sensitivity. Immediately after CXL, there is reduced nerve density and keratocyte absence due to mechanical removal of the epithelium and CXL effect. Nerve regeneration begins after 1 month, with nerve fibre densities recovering to pre-operative levels between 6 months to 1 year and remains stable up to 5 years. Nerves remain tortuous and nerve densities are reduced. Corneal sensitivity is reduced immediately postoperatively but recovers with nerve regeneration. Our article provides comprehensive review on the use of IVCM imaging in keratoconus patients.

Delayed Re-epithelialization After Epithelium-Off Crosslinking: Predictors and Impact on Keratoconus Progression

Purpose: To investigate the demographic and corneal factors associated with the occurrence of delayed reepithelialization (DRE) after epithelium-off crosslinking (epi-off CXL).

Design:Retrospective case series.

Methods:A chart review was performed to identify patients treated with epi-off CXL. DRE was defined as a corneal epithelial defect detected by fluorescein staining that persisted for more than 10 days. Slit-lamp examination, anterior segment optical coherence tomography, corneal topography, and corneal in vivo confocal microscopy (IVCM) were always performed preoperatively and at each follow-up visit (1, 3, 6, 12 months). A generalized estimating equation was used to assess the baseline factors associated with DRE.

Results:Data from 153 eyes were analyzed. The mean age of patients was 24.9 ± 8.5 years, and 47 (30.7%) were women. The average reepithelization time was 4.7 ± 1.8 days. Six eyes (3.9%) experienced DRE. In the multivariate model, both the age of the patient (OR = 1.30; p = 0.02) and the corneal steepest meridian (OR = 0.44, p = 0.047) were associated with DRE. Baseline nerve count was also associated with DRE (0.87, p = 0.03). Male gender was associated with a slower early nerve regrowth (1–6 months) (p = 0.048), but not with the occurrence of DRE (p = 0.27). Preoperative central corneal thickness was not related to DRE (p = 0.16). DRE was not associated with keratoconus progression after epi-off CXL (p = 0.520).

Conclusions:The association between DRE and age may reflect the age-related decrease in the corneal healing response. Also, low baseline corneal nerve count is associated with DRE. Gender seems to affect reinnervation measured by IVCM but not the reepithelization time. DRE does not seem to affect the efficacy of epi-off CXL.

[Methods of surgical treatment of keratectasia and analysis of postsurgical quality of vision]

Keratectasias are non-inflammatory dystrophic diseases of the cornea characterized by progressive bilateral thinning of the cornea that lead to deterioration in the quantitative and qualitative characteristics of vision reducing patient's quality of life. The changes can be asymmetrical and destructive. A number of surgeries have been proposed to reduce the negative effects of keratectasia including penetrating keratoplasty and its modifications, implantation of corneal ring segments, corneal cross-linking - alone and in combination with other methods, intrastromal keratoplasty. These methods can improve visual acuity to a certain degree and help slow the progression of keratectasia. This article studies various surgical methods used for treating keratectasia and analyses possible assessment of the quality of vision before and after the treatment.

Keratoconus Treatment Algorithm

Keratoconus management has significantly changed over the last two decades. The advent of new interventions such as cornea cross-linking, intrastromal corneal ring segments, and combined treatments provide corneal clinicians a variety of treatment options for the visual rehabilitation of keratoconus patients. This review summarizes current evidence for these treatments and highlights their place in keratoconus management while new promising emerging therapies are being investigated.

Role of corneal collagen fibrils in corneal disorders and related pathological conditions

The cornea is a soft tissue located at the front of the eye with the principal function of transmitting and refracting light rays to precisely sense visual information. Corneal shape, refraction, and stromal stiffness are to a large part determined by corneal fibrils, the arrangements of which define the corneal cells and their functional behaviour. However, the modality and alignment of native corneal collagen lamellae are altered in various corneal pathological states such as infection, injury, keratoconus, corneal scar formation, and keratoprosthesis. Furthermore, corneal recuperation after corneal pathological change is dependent on the balance of corneal collagen degradation and contraction. A thorough understanding of the characteristics of corneal collagen is thus necessary to develop viable therapies using the outcome of strategies using engineered corneas. In this review, we discuss the composition and distribution of corneal collagens as well as their degradation and contraction, and address the current status of corneal tissue engineering and the progress of corneal cross-linking.

Refractive, Topographic, and Aberrometric Results at 2-Year Follow-Up for Accelerated Corneal Cross-Link for Progressive Keratoconus

Purpose. To report the visual, refractive, and corneal topography and wavefront aberration results of accelerated corneal cross-linking (CXL) during a 24-month follow-up. Methods. Forty-seven eyes underwent riboflavin-ultraviolet A-induced accelerated CXL treatment (30 mW/cm² with a total dose of 7.2 joules/cm²). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical and cylindrical values, keratometry (K) measurements (K_steep, K_flat, K_avg, and K_apex), central corneal thickness, and anterior corneal aberrometric analyses including total wavefront error (WFE), total high order aberration (HOA), astigmatism, trefoil, coma, quadrafoil, secondary astigmatism, and spherical aberration were evaluated. Results. The mean UDVA and CDVA were significantly improved at 1 (p = 0.003 and p = 0.004, resp.) and 2 years after treatment (p = 0.001 and p = 0.001, resp.). The mean K_steep, K_flat, K_average, and K_apex values were significantly lower than baseline at 12 months (p = 0.008, p = 0.024, p = 0.001, and p = 0.014, resp.) and 24 months (p = 0.014, p = 0.017, p = 0.001, and p = 0.012, resp.). Corneal thickness showed a significant decrease at 1 month. Total HOA and coma decreased significantly at the 12-month (p = 0.001 and p = 0.009, resp.) and 24-month visits (p = 0.001 and p = 0.007, resp.). Conclusion. Accelerated CXL (30 mW/cm²) was found to be effective in improving UDVA, CDVA, corneal topography readings, total HOA, and coma aberrations during the 24-month follow-up.

Accelerated (18 mW/cm(2)) Corneal Cross-Linking for Progressive Keratoconus: 18-Month Results

PURPOSE

The aim of this study is to report the results of 18 months of follow-up after treatment with accelerated (18 mW/cm(2)) corneal cross-linking in patients with progressive keratoconus.

METHODS

Forty-two eyes of 42 patients with progressive keratoconus were included in this retrospective study. All patients underwent accelerated corneal cross-linking at an irradiance of 18 mW/cm(2) for 5 min (total surface dose 5.4 J/cm(2)). Visual acuity, topographic findings (Kflat, Ksteep, Kaverage, and apical keratometry), and central corneal thickness were evaluated during the 18-month follow-up period.

RESULTS

The mean ± standard deviation age of the 16 female and 26 male patients was 24.28 ± 6.32 years (range 14-36). Uncorrected distance visual acuity improved clinically significant from 0.52 ± 0.31 to 0.44 ± 0.25 logMAR (P = 0.031), and corrected distance visual acuity improved clinically significant from 0.34 ± 0.21 to 0.28 ± 0.19 logMAR (P = 0.018). At the last examination during the follow-up period, the flat keratometry (Kflat) decreased from a baseline of 45.65 ± 2.71 to 45.41 ± 2.72 diopters (D) (P = 0.001), the steep keratometry (Ksteep) decreased from 49.20 ± 3.54 to 48.96 ± 3.43 D (P = 0.023), and apical keratometry decreased from 56.62 ± 6.43 to 55.19 ± 5.69 D (P = 0.001), all of them were clinically significant at the 18-month visit. The preoperative values of central corneal thickness changed from 458.95 ± 38.79 to 461.85 ± 41.36 μm 18 months after the operation (P = 0.476).

CONCLUSION

The accelerated corneal cross-linking was found to be effective for the stabilization of progressive keratoconus during the 18 months of follow-up visits.

Corneal cross-linking

Since its inception in the late 1990s, corneal cross-linking has grown from an interesting concept to a primary treatment for corneal ectatic disease worldwide. Using a combination of ultraviolet-A light and a chromophore (vitamin B2, riboflavin), the cornea can be stiffened, usually with a single application, and progressive thinning diseases such as keratoconus arrested. Despite being in clinical use for many years, some of the underlying processes, such as the role of oxygen and the optimal treatment times, are still being worked out. More than a treatment technique, corneal cross-links represent a physiological principle of connective tissue, which may explain the enormous versatility of the method. We highlight the history of corneal cross-linking, the scientific underpinnings of current techniques, evolving clinical treatment parameters, and the use of cross-linking in combination with refractive surgery and for the treatment of infectious keratitis.