Trial for new intraocular lens power calculation following phototherapeutic keratectomy.
OBJECTIVE
To determine an equation to calculate the intraocular lens (IOL) power for eyes that have undergone laser phototherapeutic keratectomy (PTK).


METHODS
The Gullstrand series was used to determine the power and radius of curvature of a convex-plane IOL, which will alter the focal point from the cornea to the conjugate point on the retina using the ray tracing method.


RESULTS
The radius of curvature of the anterior corneal surface (R), axial length (AXL), the predicted postoperative anterior chamber depth (ACD), and lens thickness (LT) were used in the following formula to calculate the refractive power of the IOL to be used: K = R/7.7, DC = 337.5/R, VC = lOOO/DC x 1.336 where VC is the posterior vertex focal length, A(1) = -(VC - ACD), B(1) = AXL - 0.5 x K - ACD - 0.103LT, S = l/A(1) + l/B(1), K is the proportional expression for anterior corneal curvature, DC = anterior corneal refractive power, A(1) = distance from anterior surface of IOL to posterior vertex focal point, B(1) = distance from the second principal point of IOL to the retina, S = 1/focal length of IOL in air. Using this equation, the power (in diopters) of the IOL in liquid was determined to be 1000/(l/S). 1. 336. In eyes that have undergone PTK, the keratometric value prior to cataract surgery is not used. Instead a value, R', is introduced. R' is defined as (R - 376/1376. dT), where R is the radius of corneal curvature prior to PTK and dT the amount of corneal tissue removed. The corneal thickness after cataract surgery, CT', was defined as CT - dT, where CT is the corneal thickness prior to PTK.


CONCLUSIONS
The new equation appears to be useful for determining the IOL power, although it is important to select a lens that has the accurate predicted anterior chamber depth.
Ishikawa
T
T
Department of Ophthalmology, Juntendo University, School of Medicine, Tokyo, Japan.
Hirano
A
A
Inoue
J
J
Nakayasu
K
K
Kanai
A
A
Takeuchi
K
K
Kanda
T
T
D000368:Aged; D000867:Anterior Chamber / Q000033:anatomy & histology / Q000601:surgery; D003315:Cornea / Q000033:anatomy & histology* / Q000601:surgery; D006801:Humans; D054018:Lasers, Excimer; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D055095:Optics and Photonics; D018903:Photorefractive Keratectomy; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000503:physiopathology; D054140:Refractive Surgical Procedures; D014792:Visual Acuity