AIM: To compare the accuracy of SRK-T, SRK-Ⅱ, Haigis and LSW1 used for intraocular lens(IOL)power calculations in patients with high axial myopia undergoing cataract surgery.

METHODS: A retrospective comparative study was carried out on 97 eyes of 72 patients with axial length(AL)>26mm, who were underwent phacoemulsification with IOL implantation. Preoperative AL was measured by the IOL master, postoperative refractive errors 1mo after surgery were measured by automatic refracto-keratometry(Nidek). IOL power was calculated by SKR-II, SRK-T, Haigis and a new formula developed by the author: LSW1 formula, Power(P)= P₁+P₀, P₁=(2xP_SRK-T+P_SRK-II)÷ 3; when 101≤ 15D, P₀=0.5D; when 51≤10D, P₀=1.0D; when 01≤5D, P₀=1.5D; when P₁≤0D, P₀=3D. According to the results of postoperative refraction calculated the theoretical IOL degree(IOL theory)that could achieve emmetropia. The difference between the IOL formula from four formulas and IOL theory was IOL predictive error(PE). Then IOL PE was converted into refractive PE and absolute prediction error(AE)of each formula. The AE and PE were also analyzed by SPSS 11.0 software.

RESULTS:(1)Among all the patients selected in this study, the average age was 63.25±9.65 years(41～82 years). Average K₁=43.97±1.75, average K₂=45.14±1.98, the average central anterior chamber depth(ACD)3.59±0.38mm, average AL measured by IOL master was 28.67±2.00(26.07～33.98)mm. The average IOL diopter was 8.06±4.33(-3～-14.5)D, the chosen IOL diopter was between the results measured by SRK-T and SRK-Ⅱ formulas.(2)Refractive PE values may be reacted refractive predictable trends. The average PE of LSW1 formula, SRK-T, SRK-Ⅱ, and Haigis were -0.60±0.66D, 0.82±0.92D, -0.52±0.84D, 0.55±0.74D, and the AE of these four formulas were 0.74±0.5D, 0.94±0.79D, 0.81±0.55D, 0.73±0.55D, respectively. The proportion of hyperopia in these four formulas were LSW1 14.4%(14/97), SRK-T 82.5%(80/97), SRK-Ⅱ 20.6%(20/97), Haigis 79.4%(77/97).

CONCLUSION: The PE of Haigis formula is the smallest among all the four formulas, followed by LSW1 formula, and SRK-Ⅱ formula, and SRK-T formula. LSW1 formula and SRK-Ⅱ formula indicate a slight tendency for myopia shift; while Haigis formula and SRK-T formula indicate a tendency for hyperopic shift. SRK-T formula has a larger tendency for hyperopic shift, and cannot provide accurate IOL power calculations in cataract patients with high AL. LSW1 formula has the smallest variability and is the most suitable formula for cataract patients with high AL.