This single-center, ambispective, observational study evaluates axial length acquisition in eyes with dense cataracts using the ARGOS swept-source optical coherence tomography biometer compared with the IOLMaster 700. Eligible subjects are pseudophakic adults who previously underwent complex cataract surgery because of poor visualization or poor red reflex from dense lens opacity and who had pre-operative biometry performed with both devices, with or without manual immersion A-scan ultrasonography. Enrolled subjects return for postoperative repeat biometry to confirm pre-operative measurements and to assess whether availability of an ARGOS axial length measurement may reduce the need for manual ultrasound A-scans in similar dense cataract cases. The planned sample size justification estimated that 61 patients were needed for statistical power, while 68 were originally targeted to allow for attrition in the prospective portion.