A 68-year-old man from rural Maharashtra presents with progressive vision loss in both eyes over 2 years. He has a history of poorly controlled type 2 diabetes (HbA1c 9.2%) and hypertension. On examination, visual acuity is 6/60 in both eyes. Slit-lamp examination reveals a dense nuclear sclerotic cataract in both eyes with a brown discoloration. Intraocular pressure is 14 mmHg bilaterally. He is counselled for cataract surgery. During pre-operative assessment, his axial length is 23.5 mm and keratometry reading is 44 D. A monofocal IOL with a power of +20 D is planned. Post-operatively, the patient achieves 6/9 vision in the operated eye but complains of difficulty with near vision and requires reading glasses. Which of the following best explains the post-operative refractive outcome and the patient's visual complaint?

Explanation

## Post-operative Refractive Outcome with Monofocal IOL **Key Point:** Monofocal IOLs are designed to provide optimal vision at a single focal distance (usually distance), and patients require spectacle correction for near vision tasks. ### Understanding IOL Optics Monofocal IOLs have a fixed focal length determined by their power. When a +20 D IOL is implanted in an eye with the given biometric parameters (axial length 23.5 mm, keratometry 44 D), the calculations place the focal point at distance, allowing the patient to achieve 6/9 distance vision without glasses. ### Accommodation Loss in Pseudophakic Eyes Unlike the natural lens, IOLs are rigid and cannot change shape to accommodate. The ciliary muscle cannot adjust the power of an IOL, so: - **Distance vision:** Achieved without correction - **Near vision:** Requires additional convex lens power (reading glasses, typically +2.5 to +3.5 D) ### Why This Is the Expected Outcome | Lens Type | Distance Vision | Near Vision | Intermediate Vision | |-----------|-----------------|-------------|---------------------| | Monofocal | Excellent | Requires glasses | Requires glasses | | Multifocal | Good | Good | Fair | | Extended depth of focus (EDOF) | Good | Moderate | Good | **Clinical Pearl:** The patient's complaint of near vision difficulty is a **normal and expected** consequence of monofocal IOL implantation, not a complication. This should have been discussed during informed consent. **High-Yield:** In India, monofocal IOLs remain the most commonly implanted due to cost considerations, and patient counselling about spectacle dependence for near vision is crucial for satisfaction. [cite:Yanoff & Duker Ophthalmology 5e Ch 4]