Search PubMed⌕ Search

Biomedical subjects

K J Hoffer

Publications and source records attributed to K J Hoffer.

At least 19 recordsLinked to original sources
PubMed2001

Pigment vacuum iridectomy for phakic refractive lens implantation.

I present a technique designed to ensure an atraumatic patent basal iridectomy for phakic refractive lens implantation. The technique divides the iridectomy procedure into 2 steps. First, the stromal layer is removed by surgical excision. Then, the pigment layer is removed by gentle vacuum aspiration with a 25 gauge cannula. Atraumatic, small, basal peripheral iridectomies that are functional and cosmetically pleasing have been performed in 12 eyes. There were no cases of large amounts of pigment debris deposited in the trabecular meshwork as checked by gonioscopy. Pigment vacuum iridectomy may be a reliable procedure to ensure a proper basal iridectomy in any type of anterior segment eye surgery.

Drainage↗
PubMed2000

Clinical results using the Holladay 2 intraocular lens power formula.

PURPOSE: To analyze the accuracy of the Holladay 2 formula, which has been proposed as an improvement over the original Holladay formula. METHODS: This retrospective analysis comprised 317 eyes operated on by 1 surgeon using 1 technique and 1 intraocular lens style in a specialty practice. Because the Holladay 2 formula has yet to be published, its accuracy can only be analyzed using the commercially available Holladay IOL Consultant computer program to compare it to the Holladay 1, Hoffer Q, and SRK/T formulas. Defined axial length ranges were analyzed individually. RESULTS: A lower mean absolute error (MAE) trend was found for the average length eye (22.0 to 24.5 mm) by the Holladay 1 and Hoffer Q formulas. For short eyes (< 22.0 mm), the Hoffer Q and Holladay 2 perform better. The SRK/T consistently showed a trend toward the lowest MAE in all long eyes (>24.5 mm) as well as the subdivisions of medium long (24.5 to 26.0 mm) and very long (>26.0 mm). The Holladay 2 trended toward the least accurate (MAE) of the 4 formulas in all ranges of axial length except the shortest and the very longest. It appears to perform poorer in average and medium long eyes. CONCLUSIONS: Although the Holladay 2 formula has improved its MAE accuracy in short eyes, it was not more accurate than the Hoffer Q. The changes made in the formula to effect this improvement in MAE seem to have sacrificed the accuracy of the original Holladay formula in eyes with average and medium long axial lengths.

Cornea↗
PubMed1994

Ultrasound velocities for axial eye length measurement.

Since 1974, I have used individual sound velocities for each eye condition encountered for axial length measurement. The calculation results in 1,555 M/sec for the average phakic eye. A slower speed of 1,549 M/sec was found for an extremely long (30 mm) eye and a higher speed of 1,561 M/sec was noted for an extremely short (20 mm) eye. This inversely proportional velocity change can best be adjusted for by measuring the phakic eye at 1,532 M/sec and correcting the result by dividing the square of the measured axial length (AL1,532)2 by the difference of the measured axial length (AL1,532) minus 0.35 mm. A velocity of 1,534 M/sec was found for all aphakic eyes regardless of their length, and correction is clinically significant. The velocity of an eye containing a poly(methyl methacrylate) intraocular lens is not different from an average phakic eye but it does magnify the effect of axial length change. I recommend measuring the pseudophakic eye at 1,532 M/sec and adding to the result (AL1,532), + 0.04 + 44% of the IOL thickness. The speed for an eye with a silicone IOL was found to be 1,476 M/sec (or AL1,532 + 0.04 - 56% of IOL thickness) and for glass, 1,549 M/sec (or AL1,532 + 0.04 + 75% of IOL thickness). A speed of 1,139 M/sec was found for a phakic eye with silicone oil filling most of the vitreous cavity and 1,052 M/sec for an aphakic eye filled with oil. For varying volumes of oil, each eye should be calculated individually. The speed was 534 M/sec for phakic eyes filled with gas. Eyes containing a silicone IOL or oil or gas will create clinically significant errors (3 to 10 diopters) if the sound velocity is not corrected.

Aphakia, Postcataract↗
PubMed1993

Axial dimension of the human cataractous lens.

OBJECTIVE: To determine the axial thickness of the human cataractous lens and analyze the effect of age and axial length on its thickness. METHOD: The axial thickness of the human lens was measured ultrasonically with immersion technique A-scan at 1641 m/s in 600 cataractous eyes immediately before cataract surgery for visual rehabilitation. The axial length was similarly measured but at 1555 m/s. RESULTS: The mean (+/- SD) thickness for all eyes in patients aged from 19 to 97 years was 4.63 (+/- 0.68) mm, with a mean age of 69 (+/- 12) years and a mean axial length of 23.65 (+/- 1.28) mm. The thickness of the cataractous lens was directly proportional to age, with a mean of 3.78 (+/- 0.21) mm in the third decade and a mean of 5.03 (+/- 0.46) mm in the 10th decade. Using one-way analysis of variance, the differences were statistically significant (P = .0002). The thickness of the lens was inversely proportional to the axial length of the eye (P < .003). The mean thickness was 5.03 (+/- 0.63) mm in eyes with axial length of less than 22 mm and 4.24 (+/- 0.58) mm in eyes with axial length of 27 mm or more. Eyes in patients younger than age 65 years (158 eyes) had a mean axial length of 24.08 (+/- 1.53) mm, eyes in patients aged from 65 to 75 years (252 eyes) had a mean axial length of 23.67 (+/- 1.19) mm, and eyes in patients older than age 75 years (190 eyes) had a mean axial length of 23.26 (+/- 1.03) mm. The differences were statistically significant using analysis of variance (P < .0001). CONCLUSIONS: The data confirm the fact that the lens thickens with age, at least in cataractous eyes. Axial length was shown to have an emmetropizing effect on lens thickness, being more optically powerful (thicker) in hyperopic eyes. These values are useful in determining average sound velocities for use with ultrasound A-scan instruments for measuring the axial length of the eye. Patients with axial myopia are more likely to develop cataracts at an earlier age than those with shorter axial lengths.

Adult↗
PubMed1993

The Hoffer Q formula: a comparison of theoretic and regression formulas.

A new formula, the Hoffer Q, was developed to predict the pseudophakic anterior chamber depth (ACD) for theoretic intraocular lens (IOL) power formulas. It relies on a personalized ACD, axial length, and corneal curvature. In 180 eyes, the Q formula proved more accurate than those using a constant ACD (P < .0001) and equal (P = .63) to those using the actual postoperative measured ACD (which is not possible clinically). In 450 eyes of one style IOL implanted by one surgeon, the Hoffer Q formula was equal to the Holladay (P = .65) and SRK/T (P = .63) and more accurate than the SRK (P < .0001) and SRK II (P = .004) regression formulas using optimized personalization constants. The Hoffer Q formula may be clinically more accurate than the Holladay and SRK/T formulas in eyes shorter than 22.0 mm. Even the original nonpersonalized constant ACD Hoffer formula compared with SRK I (using the most valid possible optimized personal A-constant) has a better mean absolute error (0.56 versus 0.59) and a significantly better range of IOL prediction error (3.44 diopters [D] versus 7.31 D). The range of error of the Hoffer Q formula (3.59 D) was half that of SRK I (7.31 D). The highest IOL power errors in the 450 eyes were in the SRK II (3.14 D) and SRK I (6.14 D); the power error was 2.08 D using the Hoffer Q formula. The series using overall personalized ACD was more accurate than using an axial length subgroup personalized ACD in each axial length subgroup. The results strongly support replacing regression formulas with third-generation personalized theoretic formulas and carefully evaluating the Holladay, SRK/T, and Hoffer Q formulas.

Aged↗
PubMed1992

Intraocular lens power calculations for multifocal intraocular lenses.

We performed calculations for anterior and posterior chamber intraocular lenses, determining the necessary power for emmetropia and 3 diopters of myopia for various axial lengths and corneal powers. Our results demonstrate that to achieve an effective add of 3.00 diopters at the spectacle plane (reading distance of 33 cm), the fabricated add (labeled add) on an intraocular lens must vary from 3.3 diopters for an anterior chamber lens in a patient with a flat cornea, to 5.1 diopters for a posterior chamber lens in a patient with a steep cornea. For most patients, targeting for an effective add of 3 diopters is appropriate, but factors such as availability of fabricated adds from the manufacturer and unusual patient requirements for near vision, may alter this target. We reviewed alternatives with monofocal lenses, such as monovision and compound myopic astigmatism.

Anterior Chamber↗