Epidemiology of Keratoconus

Customised Peripheral Corneal Cross-linking (P-CXL) for Ultra-thin Corneas with Stage III and IV Keratoconus

PURPOSE

This study aims to determine whether customised peripheral corneal cross-linking (P-CXL) can halt keratoconus progression in ultrathin corneas with stage 3 and 4 keratoconus, with thinnest pachymetry well below 400 μm and therefore excluded from most treatment protocols.

METHODS

This retrospective study included 21 eyes with progressive keratoconus and thinnest pachymetry ranging from 97 to 399 μm (mean 315 μm), who underwent P-CXL between 2007 and 2020. The procedure involved preoperative NSAIDs therapy, tomography-guided customized epithelial debridement, the use of both hypo-osmolar and iso-osmolar riboflavin solutions, and 9.0 mW/cm2 UV-A irradiation for 10 minutes. The outcome measures were best spectacle-corrected visual acuity (BSCVA), mean keratometry, maximum keratometry, and thinnest pachymetry.

RESULTS

After a minimum follow-up period of 12 months, P-CXL stabilized or improved mean keratometry and maximum keratometry in 85.7% of eyes (Kavg from 57.48 ± 9.38 to 56.43 ± 8.96 D, p < 0.001; Kmax from 72.77 ± 12.74 to 70.00 ± 11.50 D, p < 0.001), BSCVA in 90.5% of eyes (from 4.48 ± 2.85 to 5.72 ± 3.34 decimals, p < 0.001), and thinnest pachymetry in 81% of eyes (from 315.81 ± 90.05 to 342.33 ± 74.22 μm, p = 0.08). No adverse events and no loss of endothelial cell density occurred.

CONCLUSIONS

Customised peripheral corneal cross-linking (P-CXL) treated very severe keratoconus with a success rate of 85.7% and improved visual acuity and tomographic indicators in most cases. While a longer follow-up and a larger sample would help to support such conclusions to a greater extent, these results allow to broaden the treatment spectrum for patients with stage 3 and 4 keratoconus and contact lens tolerance.

Genetics vs chronic corneal mechanical trauma in the etiology of keratoconus

Both genetic and environmental factors have been considered to play a role in the etiology keratoconus. Eye rubbing, and more recently eye compression due to sleeping position, have been identified to be highly related to the condition, and are present in a high percentage of patients. Today, the predominant model is that these factors can provide the "second hit" necessary to generate the condition in a genetically susceptible individual. In addition, the extremely high prevalence in Arab populations, where endogamy could play a role, the high concordance rate in monozygotic twins, and the presence of family history of the condition between 5 and 23% of cases, support a genetic influence. Segregation analysis studies suggest that keratoconus is a complex non-Mendelian disease. Results from linkage analysis, next generation sequencing studies and genome-wide association studies also have suggested that genetic factors are involved in the condition. Recently, it has been proposed that mechanical trauma (i.e. eye rubbing or eye compression at night), is a sine quanon condition for the onset of keratoconus, and quite possibly its only cause. There are various arguments for and against this hypothesis. Indeed, it is possible, as initially suggested around 55 years ago, that the term "keratoconus" include diverse phenotypically similar conditions, which are actually of different etiology.

Keratoconus staging by decades: a baseline ABCD classification of 1000 patients in the Homburg Keratoconus Center

Background

This retrospective cross-sectional study aims to analyse the keratoconus (KC) stage distribution at different ages within the Homburg Keratoconus Center (HKC).

Methods

1917 corneae (1000 patients) were allocated to decades of age, classified according to Belin’s ABCD KC grading system and the stage distribution was analysed.

Results

73 per cent (n=728) of the patients were males, 27% (n=272) were females. The highest KC prevalence occurred between 21 and 30 years (n=585 corneae, 294 patients). Regarding anterior (A) and posterior (B) curvature, the frequency of A was significantly higher than B in all age groups for stage 0, 1 and 2 (A0>B0; A1>B1; A2>B2; p<0.03, Wilcoxon matched-pairs test). There was no significant difference between the number of A3 and B3, but significantly more corneae were classified as B4 than A4 in all age groups (p<0.02). The most frequent A|B combinations were A4|B4 (n=451), A0|B0 (n=311), A2|B4 (n=242), A2|B2 (n=189) and A1|B2 (n=154). Concerning thinnest pachymetry (C), most corneae in all age groups were classified as C0>C1>C2>C3>C4 (p<0.04, Wilcoxon matched-pairs test). For the best distance visual acuity (D), a significantly higher number of corneae were classified as D1 compared to D0 (p<0.008; D1>D0>D2>D3>D4).

Conclusion

The stage distributions in all age groups were similar. Early KC rather becomes manifest in the posterior than the anterior corneal curvature whereas advanced stages of posterior corneal curvature coincide with early and advanced stages of anterior corneal curvature. Thus, this study emphasises the necessity of posterior corneal surface assessment in KC as enabled by the ABCD grading system.