Impact of classifying keratoconus location based on keratometry or pachymetry on progression parameters.

BACKGROUND: This study sought to assess the impact of classifying keratoconus location based on thinnest pachymetry or maximum keratometry (Kmax) on progression parameters after corneal crosslinking (CXL). METHODS: In this observational study, patients were followed up at one, three, six and 12 months after CXL. All patients underwent visual acuity, Scheimpflug tomography and slitlamp assessment at all follow-ups. Keratoconus was classified as central, paracentral and peripheral based on X and Y co-ordinates of either thinnest pachymetry (Group 1) or Kmax (Group 2). Progression parameters Kmax, ABCD grading, anterior, posterior and total wavefront (WF) aberrations were compared between the groups. RESULTS: Fifty-two eyes (43 patients) were classified into Groups 1 and 2: there were 82.8 per cent, 13.4 per cent, 3.8 per cent and 42.3 per cent, 38.4 per cent, 19.2 per cent central, paracentral and peripheral cones respectively. Central cones: Group 1: 'C' decreased after three months, Kmax, 'A', anterior and total WF decreased after six months. Group 2: Kmax, anterior and total WF decreased after three months, 'A' decreased at 12 months, whereas 'C' increased from three months. Paracentral cones: Group 1: no significant changes. Group 2: Kmax and 'A' decreased after six months, 'C' increased after three months. Peripheral cones: Group 1: no significant changes. Group 2: 'C' increased only at one month. CONCLUSION: Thinnest pachymetry and Kmax should not be used interchangeably when categorising keratoconus. Although keratoconus may have thin cornea centrally, the Kmax may not be central. For the majority of parameters considered for monitoring progression, changes were noticed earlier when the keratoconus was classified based on Kmax.

Evaluation of preloaded intraocular lens injection systems: Ex vivo study.

PURPOSE: To compare preloaded intraocular lens (IOL) injection systems. SETTING: Sussex Eye Hospital, Brighton, United Kingdom. DESIGN: Experimental study. METHODS: In 30 porcine eyes, 5 preloaded +22.0 diopters IOLs were implanted from each of the following preloaded IOL systems: Ultrasert (U), iTec (iT), Eyecee (E), iSert (iS), Rayone (R), and CT Lucia (CT). External and internal wound size was measured. Nozzle damage was assessed using digital photography. The ease of opening the pack, ophthalmic viscosurgical device (OVD) injection, advancing into the nozzle, nozzle insertion, and IOL delivery was scored on a 4-point Likert scale, and the time was recorded. RESULTS: The iT, E, and iS injectors with acute angled bevels and shorter nozzle tips showed more damage after implantation. The fastest with regard to opening the pack and nozzle insertion was U, OVD injection and advancing into the nozzle was E, and IOL delivery was R. The maximum postimplantation wound stretch was 20% with the CT (mean 2.64 mm ± 0.1 [SD]), and the least was 11.8% with the iT (mean 2.46 ± 0.1 mm). Both the U and R scored 4 (very easy) for all parameters measured; the E, iS, iT, and CT scored 4 or less in some parameters with decreasing scores, respectively. CONCLUSIONS: The models, design, and injection systems varied with each brand; however, the longer and more parallel the nozzle and less acute the angle of the bevel tip, the lesser the stress with less nozzle damage after surgery. All preloaded systems varied in the ease-of-use and time for surgical steps, and all lead to postoperative wound stretch.

Iontophoresis-Assisted Corneal Collagen Cross-Linking with Epithelial Debridement: Preliminary Results.

Purpose. To report the early outcomes of iontophoresis-assisted corneal collagen cross-linking procedure with epithelial debridement (I-SCXL). Methods. Twenty eyes of twenty patients with progressive keratoconus were included in this prospective clinical study. Best spectacle corrected visual acuity (BSCVA), sphere and cylinder refraction, corneal topography, Scheimpflug tomography, aberrometry, anterior segment optical coherence tomography (AS-OCT), and endothelial cell count were assessed at baseline and at 1, 3, and 6 months of follow-up. The parameters considered to establish keratoconus progression were always proven with differential maps as change in curvature in the cone area of at least 1 diopter obtained with an instantaneous map. Results. Functional parameters showed a significant improvement (p < 0.05) of BSCVA after 3 and 6 months of follow-up. Morphological parameters indicated stabilization of the corneal ectasia during the follow-up; however, a positive trend was noted with a mean flattening of 1.73 D. Minimum pachymetry values showed thinning that remained constant after the treatment. The demarcation line was clearly visible in all patients, reaching a depth of 308.2 ± 37.74 µm. None of the patients had continuous progression of keratoconus or had to repeat cross-linking procedures. Endothelial cell counts did not change significantly (p > 0.05). Conclusion. The early results indicate that the I-SCXL may be able to reduce the treatment time and improve the riboflavin diffusion.

Corneal Cross-Linking: An Example of Photoinduced Polymerization as a Treatment Modality in Keratoconus.

The cornea is one of the principal refractive elements in the human eye and plays a crucial role in the process of vision. Keratoconus is the most common corneal dystrophy, found mostly among young adults. It is characterized by a reduced number of collagen cross-links in the corneal stroma, resulting in reduced biomechanical stability and an abnormal shape of the cornea. These changes lead to progressive myopia, corneal thinning, central scarring and irregular astigmatism, causing severely impaired vision. Hard contact lenses, photorefractive keratectomy or intracorneal rings are the most common treatment options for refractive error caused by keratoconus. However, these techniques do not treat the underlying cause of the corneal ectasia and therefore are not able to stop the progression of the disease. Riboflavin photoinduced polymerization of corneal collagen, also known as corneal cross-linking (CXL), has been introduced as the first therapy which, by stabilizing the structure of the cornea, prevents the progression of keratoconus. It stiffens the cornea using the photo-sensitizer riboflavin in combination with ultraviolet irradiation. This is a current review of the CXL procedure as a therapy for keratoconus, which relies on photoinduced polymerization of human tissue. We have focused on its biomechanical and physiological influences on the human cornea and have reviewed the previous and current biochemical theories behind cross-linking reactions in the cornea.