**Background:** The Atlantic puffin (Fratercula arctica) is a vulnerable seabird with unique visual adaptations for aquatic, terrestrial, and aerial environments. Avian eyes possess distinctive structures like the sclerotic ring and pecten, which are critical for vision and behavior. While computed tomography (CT) is widely used in avian medicine, there are few publications on its application in ophthalmology, particularly for seabirds. This study aimed to use CT to perform a morphometric analysis of the ocular bulb and associated structures in the Atlantic puffin, providing reference values for clinical and biological research.
**Methods:** Twenty-nine Atlantic puffin carcasses (mean weight 0.251 kg, range 0.185–0.251 kg) were obtained from the Cabildo de Gran Canaria. CT scans of the skull were performed using a 16-slice helical CT scanner (Toshiba Astelion) with parameters: 120 kVp, 80 mA, 512×512 matrix, 0.6 mm slice thickness. Images were acquired in dorsal, transverse, and sagittal planes with bone and soft tissue windows. Measurements were taken by two observers using OsiriX MD software, including: lens diameter, internal and external diameters of the sclerotic ring, sclerotic ring thickness, ocular bulb height, width, and length, orbit depth, and attenuation (Hounsfield Units) of the lens, vitreous humor, and sclerotic ring. Statistical analysis used SPSS 19, with descriptive statistics, Shapiro-Wilk test for normality, Mann-Whitney U test for right vs. left eye comparisons, and Spearman correlation for relationships between variables (significance set at p<0.05).
**Key Results:** CT images clearly delineated the sclerotic rings, ocular bulbs, lens, vitreous and aqueous humors, and anterior/posterior chambers. For both eyes (n=58), mean values were: lens diameter 3.32 mm (range 2.7–4.2 mm, SD 0.32), internal sclerotic ring diameter 0.63 cm (range 0.59–0.7 cm, SD 0.03), external sclerotic ring diameter 1.44 cm (range 1.38–1.49 cm, SD 0.03), sclerotic ring thickness 2.16 mm (range 2.04–2.29 mm, SD 0.06), ocular bulb height 1.53 cm (range 1.41–1.61 cm, SD 0.05), width 1.28 cm (range 1.1–1.42 cm, SD 0.08), length 1.61 cm (range 1.46–1.71 cm, SD 0.07), and orbit depth 8.19 mm (range 7.9–8.5 mm, SD 0.18). Mean head length was 5.10 cm (range 4.8–5.32 cm, SD 0.13). Attenuation values: lens 69.53 HU (range 64–79 HU, SD 2.88), vitreous humor 35.38 HU (range 31–45 HU, SD 3.40), sclerotic ring 720.50 HU (range 687–752 HU, SD 17.87). No significant differences were found between right and left eyes (Mann-Whitney U test). Spearman correlation showed no significant relationship between eye measurements and head length. However, significant correlations included: ocular bulb height vs. width (rho=0.661, p<0.001), height vs. length (rho=0.403, p=0.002), width vs. length (rho=0.449, p=0.002), external vs. internal sclerotic ring diameter (rho=0.431, p<0.001), internal sclerotic ring diameter vs. ocular bulb height (rho=0.601, p<0.001) and length (rho=0.496, p<0.001), external sclerotic ring diameter vs. ocular bulb height (rho=0.688, p<0.001) and width (rho=0.642, p<0.001), and orbit depth vs. ocular bulb height (rho=-0.484, p<0.001) and width (rho=-0.294, p=0.025).
**Clinical Implications:** This study provides the first CT-based morphometric reference values for the ocular bulb and sclerotic ring in Atlantic puffins, which are essential for veterinary diagnosis and treatment of ocular diseases in this vulnerable species. The significant correlations between sclerotic ring dimensions and ocular bulb size suggest that these measurements can help infer visual capabilities and activity patterns (e.g., diurnal behavior) in puffins, similar to findings in other birds and extinct marine reptiles. The lack of correlation with head length indicates that eye size is not simply a function of overall head size, highlighting the need for species-specific reference data. CT proved effective for non-invasive ocular assessment in carcasses, though further studies in live animals are needed to validate these findings and account for potential postmortem changes. These data also support conservation efforts by enhancing understanding of puffin biology and ecology.