New algorithm for corneal densitometry assessment based on anterior segment optical coherence tomography.

PURPOSE: To describe a new algorithm to measure corneal densitometry based on images obtained by swept source anterior segment ocular coherence tomography (SS-AS-OCT) and establish standard densitometry values in a group of normal eyes. METHODS: A total of 111 healthy participants (195 eyes) were enrolled in this study. Using a MATLAB designed algorithm, the cornea was segmented into three layers: anterior, posterior and mid-stroma, and it was divided into two concentric areas, 0-2 and 2-4 mm, resulting in nine areas for the analysis. The mean corneal densitometry values were calculated and expressed as grayscale units (GSU). RESULTS: The mean age was 57 years (range 22-87), with 100 (51.3%) right eyes and 95 (48.7%) left eyes. The total corneal densitometry was 86.9 ± 12.1 GSU. The mid-stroma layer had the highest densitometry values, 87.4 ± 12.1 GSU, and the anterior layer had the lowest values, 81.9 ± 14.2 GSU. Densitometry differences between the anterior layer and the mid-stroma layer (P < 0.001), as well as the anterior layer and the posterior layer (P < 0.05) were statistically significant. The 0-2 mm concentric area had higher mean densitometry values, 97.8 ± 12.7 GSU, and the differences were significant compared to the 2-4 mm concentric area (P < 0.001). No correlation was found between the corneal densitometry values and gender or age. CONCLUSIONS: The new MATLAB segmentation algorithm for the analysis of corneal SS-AS-OCT images is capable to objectively assess corneal densitometry. We provide standard and normal data for better clinical and research approach.

Tomographic and aberrometric assessment of first-time diagnosed paediatric keratoconus based on age ranges: a multicentre study.

PURPOSE: To describe paediatric keratoconus (KC) patients by tomographic and aberrometric characteristics at first diagnosis, in a multicentre study. METHODS: We included 278 eyes from 139 paediatric patients, with a first tomographic diagnosis (Pentacam® ) of KC prior to 18 years old. KC classification was based on the KC Index (≥ 1.07) and Topographic Keratoconus Classification (TKC ≥ 1). Patients were divided based on age ranges (14 and under and over 14 years) and gender. Statistical analysis was performed with SPSS statistics 25.0. ANOVA factor was carried out comparing to compare groups. RESULTS: 278 eyes were screened, and 230 eyes were diagnosed with paediatric KC. Mean age was 15.48 ± 2.33 (6 to 18) years. We found differences in terms of TKC (2.08 ± 0.89 and 2.38 ± 0.82, p < 0.05) and spherical aberration (-0.71 ± 0.97 and -1.07 ± 1.36, p < 0.05) among the 14 years old or under and above 14 years old groups, respectively. Overall, female paediatric KC patients presented a more severe TKC, Belin Ambrosio Display, maximum keratometry, asphericity and primary and secondary coma aberrations compared to male KC patients. We observed a correlation between CDVA and asphericity (r = 0.71, p < 0.01), as well as between CDVA and spherical aberration (r = 0.69, p < 0.01). CONCLUSION: Our findings revealed that the debut of KC is usually in a moderate to advanced stage in the paediatric population at first diagnosis, particularly in female patients. Corneal tomography should be systematically performed in children with recent onset of corneal astigmatism.

Could the percent tissue altered (PTA) index be considered as a unique factor in ectasia risk assessment?

PURPOSE: To evaluate the efficacy, safety, predictability and stability of the percent tissue altered (PTA) formula in post-LASIK (laser-assisted in situ keratomileusis) ectasia risk assessment. METHODS: One hundred and ninety-three eyes from 104 patients with low to moderate myopia that underwent femtosecond LASIK were included in this retrospective, observational and longitudinal study. Seventy-eight eyes were classified in the higher-PTA (> 40%) group and 115 eyes in the lower-PTA (< 40%) group. Spherical manifest refraction, cylinder manifest refraction, logMAR and Snellen previous corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), anterior face Baiocchi Calossi Versaci index (BCVf) and posterior face (BCVb), central corneal thickness (CCT), estimated residual stromal bed (RSB), spherical aberration (SA) and root mean square (RMS) were reported. All patients were followed up for 4 years. RESULTS: In the higher-PTA group, 97% of eyes reported UDVA 20/20 or better, and in the lower-PTA group, all eyes achieved 20/20 or better. No group reported decreased visual acuity. The higher-PTA group obtained 55% of eyes within ± 0.50 D and 90% within ± 1.00 D; and the lower-PTA group obtained 63% of eyes within ± 0.50 D and 90% within ± 1.00 D. Both groups showed a refraction correction of 0.50 D or more in 36% and 31% of eyes, in the higher-PTA and the lower-PTA groups, respectively. CONCLUSION: Percent tissue altered index should not be considered as a unique variable in post-LASIK ectasia risk assessment. Ectasia susceptibility screening should integrate tomography and biomechanical variables in order to help us to decide any refractive treatment choice and increasing refractive surgery safety.