Performance of Vision–Language Models Compared with 252 Medical Students on Text-only and Image-based Dermatology Examinations

Vision–language models (VLMs) are increasingly evaluated in medical education, yet their performance on visually intensive assessments remains incompletely understood. We compared four state-of-the-art VLMs (ChatGPT-4o, ChatGPT-5, Gemini 2.5 Flash, and Gemini 3 Pro) with fifth-year medical students on ten consecutive dermatology clerkship examinations administered between September 2023 and January 2025. Examinations combined text-only questions (multiple-choice, multiple-select, and matching; 60% of total score) with image-based, structured open-ended questions (40%) spanning seven dermatologic sub-domains. Model outputs were evaluated using expert-validated answer keys and grading rubrics, with repeated runs to assess output variability. All VLMs significantly outperformed medical students on text-only examinations (mean scores > 95 vs. 84.9; p < 0.001), showing minimal sensitivity to exam difficulty. In contrast, image-based performance was heterogeneous: Gemini 3 Pro and ChatGPT-5 achieved higher scores than students, whereas students significantly outperformed ChatGPT-4o and Gemini 2.5 Flash. Medical students demonstrated the smallest performance gap between text-only and image-based components, indicating greater cross-modal consistency. Sub-domain analyses revealed that some models achieved accurate visual description and diagnosis but showed reduced performance in etiological and treatment reasoning. Gemini 3 Pro exhibited the highest overall accuracy and the lowest output variability across repeated evaluations. These findings indicate that while VLMs excel in text-based dermatologic assessment, multimodal competence remains uneven and model-dependent, supporting their use as complementary rather than standalone tools in dermatology education.