Marfan Syndrome — Arachnodactyly

A 7-year-old boy with tall stature and long slender fingers is brought to the pediatrics clinic for evaluation. On examination, the clinician asks the child to make a fist. The structure marked **B** in the diagram (Steinberg Thumb Sign) is positive—the thumb projects beyond the ulnar border of the hand when the fist is clenched. Genetic testing confirms a mutation in the FBN1 gene on chromosome 15. Which of the following ocular findings would most strongly support the diagnosis and distinguish this condition from homocystinuria?