Comparison of the Changes in Corneal Biomechanical Properties After Photorefractive Keratectomy and Laser In Situ Keratomileusis

Kamiya, Kazutaka; Shimizu, Kimiya; Ohmoto, Fumiko

doi:10.1097/ico.0b013e3181967082

Cited by 99 publications

(66 citation statements)

References 43 publications

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“…Previous investigators took two readings (16)(17) , three readings (18)(19) , Table 3 Pairwise comparison of ROC curve Table 2 Data summary from receiver operating characteristic curves of pentacam parameters in normal and keratoconic eyes and four readings (20)(21)(22)(23) in their experimental protocols. Is it worth use the average of two, three or four consecutive measurements if you can be used to measure the best score?…”

Section: Discussionmentioning

confidence: 99%

Best waveform score for diagnosing keratoconus

Luz¹,

Fontes²,

Lopes³

et al. 2013

Rev. bras.oftalmol.

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Purpose: To test whether corneal hysteresis (CH) and corneal resistance factor (CRF) can discriminate between keratoconus and normal eyes and to evaluate whether the averages of two consecutive measurements perform differently from the one with the best waveform score (WS) for diagnosing keratoconus. Methods: ORA measurements for one eye per individual were selected randomly from 53 normal patients and from 27 patients with keratoconus. Two groups were considered the average (CH-Avg, CRF-Avg) and best waveform score (CH-WS, CRF-WS) groups. The Mann-Whitney U-test was used to evaluate whether the variables had similar distributions in the Normal and Keratoconus groups. Receiver operating characteristics (ROC) curves were calculated for each parameter to assess the efficacy for diagnosing keratoconus and the same obtained for each variable were compared pairwise using the Hanley-McNeil test. Results: The CH-Avg, CRF-Avg, CH-WS and CRF-WS differed significantly between the normal and keratoconus groups (p<0.001). The areas under the ROC curve (AUROC) for CH-Avg, CRF-Avg, CH-WS, and CRF-WS were 0.824, 0.873, 0.891, and 0.931, respectively. CH-WS and CRF-WS had significantly better AUROCs than CH-Avg and CRF-Avg, respectively (p=0.001 and 0.002). Conclusion: The analysis of the biomechanical properties of the cornea through the ORA method has proved to be an important aid in the diagnosis of keratoconus, regardless of the method used. The best waveform score (WS) measurements were superior to the average of consecutive ORA measurements for diagnosing keratoconus.Keywords: Cornea/physiopathology; Keratoconus/diagnosis; Biomechanics/physiology; Dilatation, pathologic; Diagnostic techniques, ophthalmologic RESUMOObjetivo: Testar se a histerese corneana (CH) e o fator de resistência corneano (CRF) podem discriminar olhos com ceratocone e avaliar se a média de duas medidas consecutivas apresenta desempenho diferente da medida única com a melhor waveform score para diagnósticar o ceratocone. Métodos: Foram realizadas medidas do ORA de um olho por indivíduo, selecionados aleatoriamente a partir de 53 pacientes normais e de 27 pacientes com ceratocone. Dois grupos foram considerados: a média (CH-médio, o CRFmédio) e melhor waveform score (CH-WS, CRF-WS). O teste de Mann-Whitney U-teste foi utilizado para avaliar se as variáveis apresentaram distribuições semelhantes entre os grupos. As curvas (ROC) foram calculadas para cada parâmetro para avaliar eficácia no diagnóstico e as obtidas para cada variável foram comparadas usando o teste de Hanley-McNeil. Resultados: CH-médio, CRF-médio, CH-WS e CRF-WS diferiram significativamente entre os grupos (p<0,001). Já as áreas sob a curva ROC para CHmédio, CRF-médio, CH-WS, e CRF-WS foram 0,824, 0,873, 0,891, 0,931, respectivamente. CH-WS e CRF-WS obtiveram AUROCs significativamente melhores do que CH-médio e CRF-médio (p=0,001 e 0,002). Conclusão: A análise das propriedades biomecânicas da córnea através do ORA demonstrou ser um método auxiliar importante no diagnóstico de cera...

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Section: Discussionmentioning

confidence: 99%

Best waveform score for diagnosing keratoconus

Luz¹,

Fontes²,

Lopes³

et al. 2013

Rev. bras.oftalmol.

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“…28 The observation of the reduction in CH and CRF values after LASIK and surface ablation procedures have also been demonstrated. [29][30][31][32] The same authors who concluded that the Corvis ST may not be reliable to quantify the effect of CXL in KC eyes have published another study where they showed that it was possible to evaluate the corneal biomechanical properties after LASIK, ReLEx flex, and ReLEx smile. 33 If the changes induced by CXL on parameters, such as CH and CRF are too subtle to be documented unlike those in the abovementioned clinical situations, then would it not be logical to conclude that the effect of CXL on corneal biomechanics may be too modest to be clinically relevant?…”

Section: How Then Can We Explain the Lack Of Clearly Documented Biomementioning

confidence: 99%

Reevaluating the Effectiveness of Corneal Collagen Cross-linking and Its True Biomechanical Effect in Human Eyes

Gatinel¹

2017

International Journal of Keratoconus and Ectatic Corneal Diseases

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The induction of cross-links in corneal tissue appears to be a promising technique to increase its stiffness and this has been the basis of treatment of keratoconus (KC) and corneal ectatic disease. However, there exists a striking discrepancy between the reported biomechanical effects of corneal collagen cross-linking (CXL) in vitro compared to in vivo, and this has not received much attention in the literature. Despite the documentation of an increase in corneal stiffness in vitro by many investigators, reports that provide evidence of measurable and consistent biomechanical changes in corneal rigidity in vivo after CXL are lacking. Indeed, the absence of documented in vivo biomechanical improvement in CXL-treated corneas is a conundrum, which needs to be further explored. To explain this discrepancy, it has been postulated that biomechanical changes induced by CXL are too subtle to be measured by currently available diagnostic tools or have characteristics not discernible by these technologies. However, the dynamic bidirectional applanation device (Ocular Response Analyzer) and dynamic Scheimpflug analyzer instruments (Corvis ST) have demonstrated the ability to quantify even subtle biomechanical differences in untreated KC corneas of different ectatic degree, and document the reduction in corneal hysteresis (CH) and corneal resistance factor (CRF) in situations where the corneal stiffness is reduced, such as after laser in situ keratomileusis and surface ablation procedures. It has also been possible to demonstrate an altered CH and CRF in patients with diabetes, smoking habit, glaucoma, Fuchs’ dystrophy, and corneal edema. It is puzzling that these diagnostic tools could document subtle biomechanical changes in these situations, yet fail to measure the purported changes induced by CXL on corneas with progressive KC. This failure to document significant and consistent biomechanical changes in corneal rigidity could suggest that CXL does not induce a simple reversal of the particular biomechanical deficits that characterize KC, or make the cornea significantly more resistant to bending forces as has been widely postulated. The absence of measurable biomechanical change in living KC corneas after CXL could be a consequence of biomechanical strengthening which is insignificant compared to the marked weakening caused by preexisting alteration of the collagen structure, disorganization of collagen fiber intertwining, and compromised structural–mechanical homogeneity that are hallmarks of keratoconic disease, especially in corneas with progressive KC. The changes in the cornea induced by CXL that have been described in vivo may instead be driven by a wound healing process in response to the removal of the corneal epithelial layer and subsequent exposure to riboflavin and ultraviolet-A (UVA). This paper will present evidence that sustains this hypothesis. How to cite this article Gatinel D. Reevaluating the Effectiveness of Corneal Collagen Cross-linking and Its True Biomechanical Effect in Human Eyes. Int J Kerat Ect Cor Dis 2017;6(1):34-41.

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“…Studies have shown a greater decrease in both CH and CRF in LASIK eyes when compared with photorefractive keratectomy. 21 Thus patients with weaker biomechanics are more suitable for surface ablation with or without simultaneous crosslinking as compared to LASIK. Also, studies comparing SMILE and LASIK have found more reduction in biomechanics in patients that underwent LASIK, suggesting that the former may be more suitable for patients with pre-existing weaker biomechanics ( Figure 5).…”

Section: ) Refractive Surgerymentioning

confidence: 99%