Corneal Endothelial Decompensation Following Collagen Cross Linking In Ultrathin Corneas. A Case Report.

The use of collagen cross linking to halt the progression of keratoconus has caused a paradigm shift in managing this condition. Ultrathin corneas, measuring less than 400 microns, require adjusting procedure parameters due to increased corneal fragility. Approximately 25% of keratoconus patients present with thin pachymetry. Furthermore, corneal thickness may decrease during the procedure as a result of corneal dehydration induced by ultraviolet (UV) exposure. Therefore, in borderline cases, even if corneal thickness exceeds 400 microns, intraoperative pachymetric measurement may be necessary to tailor cross linking parameters and minimize potential complications. 

Son Llàtzer University Hospital 

We present the case of a 19-year-old patient diagnosed with keratoconus in both eyes. Initially, the right eye had a visual acuity of 0.4, and slit-lamp examination revealed no signs of corneal ectasia. However, further assessment via topographic study confirmed advanced keratoconus, with minimum corneal thickness measuring 488 microns. Consequently, a decision was made to proceed with cross linking. The procedure adhered to the accelerated Avedro protocol, utilizing the epithelium-off technique and Vibex Rapid^TM induction for 10 minutes. The total irradiated energy administered was 7.2 mJ, with an UV power of 30 mW/cm2, and a total treatment time of 8 minutes, consisting of 4 minutes of UVA exposure followed by 4 minutes of darkness. 

After a favorable immediate postoperative period, topographic stromal edema developed one month following cross-linking, despite maintaining relatively good visual acuity (0.5). Medical treatment was initiated; however, six months later, there was a significant decline in visual acuity (reaching hand motion), accompanied by Descemet membrane detachment in the nasal area, epithelial bullae, and corneal edema. Urgent penetrating keratoplasty became necessary due to endothelial decompensation. 

Customizing cross-linking treatment is necessary for cases with corneal thickness below 400 microns, such as the sub-400 protocol. This approach allows penetration depths of up to 71 microns from the endothelium while simultaneously protecting it from radiation. Similarly, for corneas slightly thicker than 400 microns, tailored protocols might be considered, as topometric thickness may decrease after epithelial removal and riboflavin impregnation, potentially causing endothelial damage if standard corneal thickness values are applied.