Pachymetry during Cross-linking

Abstract

With great interest we read the article by Kymionis et al1Kymionis G.D. Kounis G.A. Portaliou D.M. et al.Intraoperative pachymetric measurements during corneal collagen cross-linking with riboflavin and ultraviolet A irradiation.Ophthalmology. 2009; 116: 2336-2339Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar who evaluated central corneal thickness (CCT) using ultrasound pachymetry during corneal cross-linking (CXL). An eyelid speculum was used while riboflavin drops were instilled every 3 minutes during 30 minutes, after which 30-minute ultraviolet-A (UVA) irradiation was performed. They demonstrated that CCT significantly decreased from 415.7 μm after epithelial removal to 340.7 μm after riboflavin instillation. They found no significant change in CCT during irradiation. We believe that the decreased CCT after the riboflavin solution instillation resulted from prolonged corneal dehydration. A significant decrease in CCT caused by corneal dehydration during corneal exposure has been demonstrated before (10.2% after 5 minutes exposure).2Aurich H. Wirbelauer C. Jaroszewski J. et al.Continuous measurement of corneal dehydration with online optical coherence pachymetry.Cornea. 2006; 25: 182-184Crossref PubMed Scopus (25) Google Scholar We evaluated CCT variations using ultrasound pachymetry (SP-100 Handy Pachymeter, Tomey, Nagoya, Japan) in 3 eyes of 3 patients with progressive keratoconus who underwent CXL. Central corneal thickness variations were evaluated during the 3 most relevant steps of the procedure (after epithelial removal, after riboflavin solution instillation and after 30 minutes of UVA irradiation). Contrary to Kymionis' findings, we found stable CCT values after the riboflavin solution instillation. We believe that this is related to the fact that we do not use the eyelid speculum during the 30-minute riboflavin instillation, thereby avoiding prolonged corneal dehydration. We instruct the patient to lie in a supine position and to keep both eyes closed, while we gently open the eyelids every 3 minutes for riboflavin solution instillation. After the 30-minute UVA irradiation, we did find decreasing CCT values, relating to the fact that during this step, the eyelid speculum is used (Table 1 and Figure 1; available at http://aaojournal.org).Table 1Central Corneal Thickness Variations During Corneal Cross-linkingUltrasound CCT (μm)Patient 1Patient 2Patient 3After epithelial removal427513485Post-riboflavin432513503Post-UVA irradiation470475439CCT = central corneal thickness; UVA = ultraviolet-A. Open table in a new tab CCT = central corneal thickness; UVA = ultraviolet-A. Therefore, we conclude that when the eyelid speculum is not used during riboflavin solution instillation, prolonged corneal dehydration can be avoided. Excess thinning of the cornea is undesirable because of potential UVA toxicity to the endothelium. Intraoperative Pachymetric Measurements during Corneal Collagen Cross-Linking with Riboflavin and Ultraviolet A IrradiationOphthalmologyVol. 116Issue 12PreviewTo study central corneal pachymetric variations during corneal collagen cross-linking (CXL) treatment with the use of riboflavin and ultraviolet A irradiation (UVA). Full-Text PDF Author replyOphthalmologyVol. 117Issue 10PreviewWe would like to thank the authors' for their comments. The point they are making is rather interesting but we would like to point out that our study1 was held in accordance with the original and standard corneal collagen cross-linking (CXL) protocol in which an eyelid speculum is used from the beginning of the procedure and throughout the 30-minute riboflavin instillation step. Full-Text PDF