Influence Of Pterygia On Cataract Surgery Planning And Intraocular Lens Selection

The primary aim of this study is to determine the effect of a growing pterygia on the intraocular lens (IOL) power calculation. In addition, we produced hypothetical calculations for a wide range of axial lengths (AL) for various sizes of pterygia, to see the extended impact on the IOL power selection where both corneal parameters and axial lengths are out of the normal range.

Pterygia are fibrovascular dysplasia occurring on the bulbar conjunctiva onto the corneal surface. Pterygia can impair vision, either by invading the central visual axis of the cornea, or by causing significant astigmatism. Treatment is excision with conjunctival autograft. As with other ocular surface disorders, pterygia can cause significant corneal irregularity, which could lead to variability in obtaining pre-operative measurements prior to cataract surgery, leading to refractive surprise.

Keratometry measurements using Scheimpflug technology (Pentacam) were conducted on consecutive pterygium excisions. Pterygium sizes were categorized into three groups: Group I – pterygium growth sparing the central 5mm of the cornea, Group II – pterygium involving between central 3mm to 5 mm of the cornea, Group III – pterygium involving central 3mm of the cornea. IOL power was calculated using Barrett’s Universal K formula using a range of hypothetical ALs from 20mm to 27mm. ALs were classified into Group A(short AL 20-22mm), Group B(mid-range AL 23-24mm) and Group C(long AL 25-27mm). All statistical analysis were performed using an artificial intelligence data scientist tool.

28 eyes of 27 patients were included in this study. There was a statistical significant difference in pre- and post-operative astigmatism, axial flat-axis keratometry(K1) and central 3mm tangential flat and steep axis keratometry. We also demonstrated statistical significant differences in IOL differences across the three pterygia grades for each individual hypothetical axial lengths(AL=20,21...27mm). There is also a wider range of predicted IOL differences in short and long AL (Groups A and C), as compared to medium AL group B. When comparing pre- and post-operative K1 and K2 values individually with predicted IOL differences, the strongest correlation was observed between pre-operative K1 and IOL difference with a coefficient of 0.87.

Grade II and III pterygia were associated with more significant changes in IOL predictions post-surgery, due to greater corneal irregularities caused by more advanced pterygium. A combined pterygium excision and cataract surgery may be possible if the pterygium does not affect the central 5 mm of the cornea. Extremes of axial lengths also showed a variation in IOL powers and ultimately highlighting additional impact on refractive outcome. This is relevant in refractive outcome discussions for cataract surgery with patients where a combined approach is being thought of. Patients with higher expectations may need more counselling and proper surgical planning.