Ultrasonic study of the refraction of patients with pseudophakos

doi:10.1016/0301-5629(74)90024-6

Ultrasound in Medicine & Biology

Volume 1, Issue 3, August 1974, Pages 267-273

https://doi.org/10.1016/0301-5629(74)90024-6 Get rights and content

Abstract

Ultrasonography and keratometry are used in the study of the refraction of the eye. The authors used the artificial implant lens after removal of the cataractous lens. The expected emmetropizing power of the implant lens can be calculated by a formula as well as the expected post-operative refraction which can also be calculated by second and third formulas. The authors compared the difference between the expected pre-operative and actual post-operative refraction. The factors giving this difference will be discussed. The expected emmetropizing power of the implant lens is not always the same as that of the iseikonizing power. A theoretical discussion of this problem is given.

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Cited by (9)

Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations
1997, Journal of Cataract and Refractive Surgery
Purpose: To provide a method and values that facilitate standardization of constants for ultrasonic biometry, keratometry, and intraocular lens (IOL) power calculations.
Setting: University of Texas Medical School, Houston, Texas, USA.
Methods: Keratometry and ultrasonic biometry provide the two measured input variables for the six variable vergence equations used to calculate the appropriate IOL power for a specific patient with a cataract. A review of the literature reflecting the past 156 years of research and development reveals the appropriate index of refraction to be used with the keratometer for net optical corneal power, the location of the principal planes of the cornea, the nominal value for retinal thickness, and the appropriate velocities for ultrasonic measurement of the axial length. The relationship of the thick IOL to the thin IOL is derived along with the physical location of the thick lens. Two methods are described that provide the best IOL constant to be used by a manufacturer to minimize the prediction error for a surgeon using the lens for the first time. The formulas for phakic IOLs and secondary piggyback IOLs are also derived and applied to methods described above for standard IOLs.
Results: Using a standardized net index of refraction of 4/3 for the cornea eliminates a variability of 0.56 diopter (D) in the predicted refraction. Using a standardized 1532 m/s velocity for axial length measurements and adding a value of 0.28 mm reduces the tolerance of axial length measurements to ±0.03 mm for any length eye. The physical location of the thick IOL's secondary principal plane must be anterior to the thin lens equivalent by approximately the separation of the principal planes of the thick lens. For biconvex poly(methyl methacrylate) IOLs, the separation in the principal planes is approximately 0.10 mm. Using these relationships, the physical position of the thick lens within the eye can be used to confirm the lens constant for any IOL style.
Conclusions: Standardizing the constants for keratometry, ultrasonic biometry, and IOL power calculations can significantly improve the predictability of refractive outcomes. Back-calculating and physically measuring the position of the lens within the eye can provide surgeons with an initial lens constant known to have a standard error of the mean of ±0.05 mm (±0.10 D). Other parameters such as the cardinal points of a lens, the shape factor, the lens-haptic plane, and the center lens thickness would allow further refinement of IOL power calculations.
Secondary IOL power calculations: A comparison of regression formula and refraction method in accurate prediction of emmetropia
1984, American Intra-Ocular Implant Society Journal
A retrospective review of 51 secondary intraocular lens (IOL) implantationswas made to determine the relative accuracy of the SRK^TM regression formula and the refraction method described by Holladay in preoperative prediction of emmetropic IOL power. The regression formula accurately predicted emmetropia within 1 diopter (D) in 63% of patients; the refraction method accurately predicted within 1 D in only 26% of cases. The emmetropic power predicted by the two formulas differed by at least 1 D in 76% of patients. Precise measurement of preoperative variables is imperative to ensure accurate prediction of emmetropic IOL power in the patient considered for secondary implantation.
Iseikonia and accommodation in the fellow eye in monocular IOL implantation
1983, American Intra-Ocular Implant Society Journal
In unilateral implantation of an intraocular lens (IOL), the main goal, for both distant and near vision, is iseikonia. After monocular IOL implantation, when the normal fellow eye accommodates for differdAnt distances, the changed magnification will result in aniseikonia. We have derived formulas for calculating the power of an iseikonizing IOL and of corresponding spectacles for both distant and near vision. Using the formulas, we can predict the degree of aniseikonia produced by accommodation in the normal eye. We suggest that accommodation in the fellow eye be avoided by using reading glasses.
A new intraocular lens calculation formula
1980, American Intra-Ocular Implant Society Journal
Triple procedure; analysis of outcome, refraction, and intraocular lens power calculation
1997, British Journal of Ophthalmology
Intraocular lens power calculations: The optimal approach
1985, Ophthalmologica

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Ultrasonic study of the refraction of patients with pseudophakos

Abstract

Am. J. Ophthal.

Über die endgültige Verträglichkeit künstlicher Augenlinsen bei der Aphakie und deren Verbesserung mittels Fixation der Linse in der Pupille

Klin. Mbl. Augenheilk.

Eigene Verfahren der Pseudophakie, Iris-clip-Pseudophakos und Irido-kapsulärer Pseudophakos

Klin. Mbl. Augenheilk.

Power of the prepupillary pseudophakos

Brit. J. Ophthal.