what is diopters (D) ?

“diopter”在眼科和光學領域的標準中文翻譯是屈光度（qū guāng dù），它是測量透鏡或眼球屈光能力的單位，符號為D。

“diopter increment”在白內障手術或人工晶狀體（IOL）選擇語境中，通常翻譯為屈光度增量（qū guāng dù zēng liàng），指人工晶狀體功率的標準化步長（如0.5 D增量）。在中文醫學術語中，也常簡稱為“D增量”或“屈光度步長”。

 

In cataract surgery, the natural lens of the eye is replaced with an artificial intraocular lens (IOL). The power of the IOL is measured in diopters (D), a unit that quantifies the lens's focusing ability to correct vision and target a specific refractive outcome (e.g., distance vision without glasses).

The term **diopter increment** (or "D increment") refers to the standardized step size or interval between available IOL powers from manufacturers. IOLs are not custom-made to exact decimal places; instead, they are produced in discrete increments, most commonly **0.5 D** (half a diopter), though some advanced models offer finer **0.25 D** (quarter-diopter) steps for greater precision.

### Why It Matters in Lens Choice
- **Calculation and Selection**: Before surgery, biometry measurements (e.g., axial length of the eye, corneal curvature) are used with formulas (like SRK/T or Barrett Universal II) to calculate the ideal IOL power. The surgeon then selects the closest available IOL from the inventory that matches this calculation within the diopter increment.
  - Example: If calculations suggest +20.3 D, a 0.5 D increment might lead to choosing +20.0 D or +20.5 D.
- **Precision and Outcomes**: Finer increments (e.g., 0.25 D) allow for more accurate targeting of postoperative refraction, reducing the need for glasses or touch-up procedures like laser enhancement. However, 0.5 D is the "typical" or "highest practical" interval for most standard monofocal IOLs, balancing cost, availability, and clinical needs.
- **Trade-Offs**: Larger increments (e.g., 1.0 D in older or basic lenses) may result in slightly more refractive error post-surgery, while premium or toric IOLs (for astigmatism) often provide smaller steps for better customization.

This concept ensures efficient surgery while minimizing surprises in final vision correction. Your surgeon will discuss options based on your eye's anatomy and lifestyle goals.