OCT uses light reflectance signal from the retina to measure RNFL thickness. Several software programs are there to perform segmentation of RNFL automatically by detecting the internal limiting layer and outer RNFL.
OCT imaging is influenced by cataract; image quality is reduced preoperatively and RNFL thickness measurements are slightly increased postoperatively. In individual patients, OCT scans remain reliable for gross clinical interpretation, even in the presence of cataract.
OCT imaging relies on near-infrared light. Similar to its effects in fundus photography and scanning laser ophthalmoscopy, a cataract is likely to increase light scattering and degrade OCT image quality. Some authors have reported variations in OCT measurements before and after uncomplicated cataract surgery, but these studies included only short series of healthy subjects and focused on a slight increase in retinal thickness after surgery, and on the apparent increase in RNFL thickness due to the resulting improved image quality.
Ultrasonic energy and fluidics produce mechanical effects that cause an inflammatory reaction that should also be taken into account as a risk factor that may affect the structure of the tissue in the eyeball.