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A Detailed Phenotypic Characterization of Keratoconus in a Large Portuguese Cohort

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Summary:	INTRODUCTION: Keratoconus (KC) is the most prevalent corneal ectatic disorder, defined by progressive thinning and steepening of the cornea. This study aims to provide a comprehensive phenotypic characterization of KC in a large Portuguese cohort, evaluating the correlation between disease severity, cone location, and clinical variables to enhance diagnostic accuracy and optimize treatment strategies. METHODS: Cross- sectional study including patients diagnosed between 2018 and 2023 at two Portuguese ophthalmologic centers. A detailed analysis of corneal tomography was performed at baseline. These parameters were used to classify patients into five distinct phenotypic groups, considering cone location, anterior corneal curvature, and the alignment of topographic and comatic axes. Maximum keratometry (Kmax) for each patient was stratified across the four severity stages of the Amsler Krumeich classification. Associations between cone location, phenotype, and clinical parameters were assessed, including variations in age and corneal steepness across phenotypes. RESULTS: A total of 411 eyes from 251 patients (65.9% male) were included. The mean baseline age was 23.14±5.20 years. The most prevalent keratoconus phenotypes were croissant (29.2%) and nipple (24.8%) followed by duck (20.0%), snowman (18.7%), and bowtie (7.3%). Patients with the snowman phenotype were significantly younger (21.00±6.43 years) than those with the croissant (23.83±4.15 years, p = 0.002) and nipple (24.26±5.09 years, p< 0.001) phenotypes. A significant association was found between keratoconus phenotype and sex (p = 0.001), with males predominating in almost all phenotypes. The nipple phenotype was predominantly linked to advanced stages at presentation (81.2% at stage IV). Significant differences in keratometric values and corneal parameters were observed across phenotypes (p< 0.001). Central cones, particularly those classified as nipple phenotype, were associated with steeper corneas and more severe disease at presentation. CONCLUSION: The phenotypic distribution of keratoconus in this Portuguese population is consistent with findings from other cohorts, except for a higher prevalence of nipple type. Different keratoconus phenotypes were shown to correlate with clinical variables such as age, sex, and disease severity. Central cones, especially the nipple phenotype, were linked to more severe disease at presentation and steeper corneas. These findings highlight the importance of phenotypic characterization in improving diagnostic accuracy and guiding treatment strategies for keratoconus.
Main Authors:	Francisco, Mariana
Other Authors:	Gil, Pedro; Gil, João; Alves, Nuno; Feijão, João; Costa, Esmeralda; Rosa, Andreia; Tavares, Cristina; Quadrado, Maria João; Murta, Joaquim
Subject:	Artigos Originais
Year:	2026
Country:	Portugal
Document type:	article
Access type:	open access
Associated institution:	Sociedade Portuguesa de Oftalmologia
Language:	English
Origin:	Revista Sociedade Portuguesa de Oftalmologia