## How is IOL calculated?

Modern instruments use separate sound velocities for the different eye components to obtain the total axial length. The measured transit time is converted to a distance using the formula d=t/v Where d is the distance, t is the time and v is the velocity. Two types of A-scan ultrasound biometry are currently in use.

## How is toric IOL power calculated?

Toric IOLs are labeled with cylinder power calculated at the IOL plane. This is higher than the cylinder value corrected at the corneal plane. The difference is correlated to the distance between the cornea and the IOL: The higher the distance, the higher the difference.

**What is DBR test?**

DBR: This is a very important test that enables one to calculate the desired power of intraocular lens during the cataract surgery. This artificial lens implanted in the same location as the natural lens permits one to have good vision without needing to use the thick glasses or contact lenses after cataract surgery.

**What is Angle Kappa?**

Angle kappa is defined as the angle between the visual axis (line connecting the fixation point with the fovea) and the pupillary axis (line that perpendicularly passes through the entrance pupil and the center of curvature of the cornea).

### What is the power of astigmatism?

Astigmatism is a common condition in which the surface of the eye, or cornea, is not curved in the normal way, leading to blurred vision. The abnormal curve of the cornea means that when light enters the eye, it is not correctly focused on the retina, resulting in an unclear image.

### What is Toricity?

Toricity may mean different things depending on the practitioner. Remember, toricity is two different curves separated by 90 degrees and oriented at a given axis. In optics those two different curves have dioptric power that induces astigmatism. When employing front surface toricity, the effect is optical.

**What is a pseudophakic patient?**

Pseudophakia translates from the Latin to mean false lens. The term refers to the implanting of an intraocular lens to replace a natural lens, the lens being the clear part of the eye that focuses light and images, enabling a person to see.

**What is the purpose of the SRK / T formula?**

The SRK/T formula is one of the third generation IOL calculation formulas. The purpose of this study was to evaluate the performance of the SRK/T formula in predicting a target refraction ±1.0D in short and long eyes using ultrasound biometry after phacoemulsification.

#### What is the SRK / T formula for corneal power?

SRK/T Formula ~ “Double K” Correction Method. Each of the two tables listed below assume an average pre-refractive surgery corneal power of 43 D and implantation of an Alcon SA60AT intraocular lens.

#### When was the SRK / T lens implant formula developed?

Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg. 1990 May;16 (3):333-40.

**What is the SRK / T formula for IOL power?**

The SRK/T (T for theoretical) is a formula, representing a combination of linear regression method with a theoretical eye model [ 6 ]. Ultrasound (US) biometry (A-Scan) and partial coherence interferometer (PCI)-based devices are the most commonly used methods for determining IOL power [ 10 ].