Puyose: We present an unusual case of decreased vision from asteroid hyalosis, an entity not normally associated with decreased vision. Patients and methods: This 74-year-old male had vision gradually decreasing to 20/400 in the right eye. The left eye was 20/70, consistent with his lens changes, which were symmetrical. A dense clump of asteroid hyalosis was noted just posterior to the lens in the right eye, obscuring the fundus view. B-scan ultrasonography, pupil testing, and flash visually evoked potential testing were all normal, suggesting the potential for equal function between the eyes. A vitrectomy was performed on the right eye to remove the asteroid, which was confined to the anterior vitreous due to a posterior vitreous detachment. Results: Post operative vision was 20/60, now consistent with the lens changes. Conclusions: Since the only change between the pre and post operative state was the removal of the asteroid hyalosis, we conclude that the asteroid hyalosis was causing the decreased vision in the right eye. A posterior vitreous detachment allowed the asteroid to coalesce into a dense clump just posterior to the crystalline lens, which explains the unexpected, profound effect on the patient's vision.