Ectopia lentis or crystalline lens subluxation is one of the major criteria to diagnose Marfan syndrome. It may vary from mild lens subluxation to lens dislocation. Herewith is a case report of a 4-year-old autistic boy who had never been diagnosed with Marfan syndrome. He presented to the clinic after his parents noticed he had difficulty focusing on near objects. His bilateral best-corrected visual acuity was 6/60. On examination, there was bilateral lens subluxation superotemporally and lens equator blocking his visual axis. He was sent to the paediatric team and further Marfan workout showed dilated aortic root. He was then diagnosed with Marfan syndrome. He underwent bilateral lens aspiration, anterior vitrectomy, and iris-claw lens implantation. His postoperative bilateral visual acuity on day 1 was 6/30 and his best-corrected visual acuity 3 months after surgery was 6/9 for both eyes. In conclusion, ophthalmologists play an important role in diagnosing and managing Marfan syndrome. Early diagnosis is important to help preserve vision and improve quality of life.