A 68-year-old man presents with progressive vision loss over 2 years. Slit-lamp examination reveals a cataract that starts at the nucleus and gradually progresses outward toward the cortex. Which feature best distinguishes this cataract type from a cortical cataract?

Explanation

## Nuclear vs. Cortical Cataract: Key Discriminators **Key Point:** Nuclear cataracts originate in the lens nucleus and progress centrifugally, whereas cortical cataracts originate in the cortex and progress centripetally toward the nucleus. ### Distinguishing Features | Feature | Nuclear Cataract | Cortical Cataract | |---------|------------------|-------------------| | **Origin** | Lens nucleus | Lens cortex | | **Progression** | Centrifugal (outward) | Centripetal (inward) | | **Color** | Brown/amber discoloration | White/opaque | | **Refractive change** | Myopic shift (increased power) | Hyperopic shift | | **Visual symptoms** | Gradual dimming, color desaturation | Glare, monocular diplopia | | **Slit-lamp finding** | Homogeneous nuclear density | Radial spokes/clefts | **High-Yield:** Nuclear cataracts cause a **myopic shift** due to increased refractive index of the hardened nucleus, whereas cortical cataracts cause a **hyperopic shift** due to swelling and increased lens thickness. **Clinical Pearl:** A patient with nuclear cataract may paradoxically report temporary improvement in near vision ("second sight") due to myopic shift, which is virtually pathognomonic for nuclear sclerosis. **Mnemonic:** **NUC** = **N**ucleus **U**niform color (brown) **C**entrifugal; **COR** = **C**ortex **O**paque (white) **R**adial spokes. ### Why This Matters in Exam The question stem explicitly states the cataract "starts at the nucleus and gradually progresses outward" — this is the definition of centrifugal progression, which is pathognomonic for **nuclear cataract**. The brown discoloration and myopic shift are the cardinal features that distinguish it from cortical cataracts.