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Biomedical subjects

W Haigis

Publications and source records attributed to W Haigis.

At least 19 recordsLinked to original sources
PubMed2003

Laser interference biometry versus ultrasound biometry in certain clinical conditions.

PURPOSE: To compare laser interference biometry (LIB) with conventional ultrasound biometry in certain clinical conditions such as globe deformities, eccentric fixation, retinal detachment, macular edema or silicone oil-filled eyes. SETTING: Department of Ophthalmology, Würzburg University Eye Hospital, Germany. METHODS: We evaluated all patients who came to our university hospital for axial length measurement with our routine immersion biometry system (Grieshaber Biometry System) and compared the results with those obtained using the Zeiss IOLMaster of Carl Zeiss Jena, the commercially available LIB device. RESULTS: Selected case reports demonstrate the advantages and disadvantages of LIB. Advantages of LIB were found in patients with asymmetrically shaped globes, eccentric fixation, silicone oil-filled eyes and a fearful/nervous disposition. Disadvantages of the system were revealed in cases of retinal detachment, severe opacities along the visual axis and poor patient cooperation. CONCLUSION: We showed that LIB is a valuable addition to the choice of biometric devices, when used with medical understanding.

Aged↗
PubMed2001

[Determination of retinal thickness in relation to the age and axial length using optical coherence tomography].

PURPOSE: It is unknown whether the thickness of the retina depends on axial length or on age. We therefore used optical coherence tomography (OCT) to study this relationship. METHODS AND MATERIALS: We recruited 159 subjects aged 13-92 years (205 eyes) without macular pathology. OCT measurements included three horizontal scans and one vertical scan through the fovea. Axial length was determined by an analog high-resolution biometric unit. RESULTS: There was no correlation between retinal thickness and either axial length or age. Mean retinal thickness in the fovea was 142 +/- 18 microns. In the nasal retina thickness was significantly increased to 266 +/- 17 microns, compared to 249 +/- 18 microns in the temporal retina. Retinal thickness in subjects' two eyes was significantly correlated. CONCLUSIONS: Since retinal thickness does not depend upon age or length of the eye, no corrections are necessary when analyzing pathological retinal thickening, such as in diabetic retinal disease.

Adolescent↗
PubMed2001

Pseudophakic correction factors for optical biometry.

INTRODUCTION: The IOLMaster of Carl Zeiss Jena, which has recently become available, is a combined instrument for biometry and intraocular lens (IOL) planning for cataract surgery utilizing partial coherence interferometry for measuring axial length. Whereas measurement data from classical ultrasound biometry, e.g. in pseudophakic eyes, need to be corrected by +0.4 to -0.8 mm--depending on the lens material--smaller corrections are expected to be necessary in optical biometry. Correction factors for various modern IOL materials were estimated theoretically and checked in first clinical measurements. METHODS: Starting from the dispersion relation of PMMA and manufacturers' phase refractive index data at 546 nm, the group refractive indices of different IOL materials were estimated for the IOLMaster wavelength of lambda=780 nm. Then, for an average eye of 23.48 mm, the center thicknesses of emmetropizing lenses of different material were calculated. Finally, comparing the pseudophakic optical axial lengths thus deduced with the respective phakic value, individual material-specific correction factors were obtained. RESULTS: Expressing the true axial length ALtrue by the length ALphak measured in phakic mode and a correction factor delta (ALtrue=Alphak+delta), we obtained values of delta=0.12+/-0.01 mm for all IOL materials considered (PMMA, silicone, collamer, AcrySof, MemoryLens). For aphakic eyes, delta=0.20 mm was deduced. DISCUSSION: The calculations suffered from the fact that hardly any information relating to optical material specifications of IOLs is available from lens manufacturers. Therefore, calculations had to be based on--nevertheless realistic--assumptions. Early clinical results support our theoretical findings. Thus, optical biometry seems to be more reliable and forgiving in pseudophakic eyes than classical ultrasound.

Acrylic Resins↗
PubMed2000

Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis.

BACKGROUND: The precision of intraocular lens (IOL) calculation is essentially determined by the accuracy of the measurement of axial length. In addition to classical ultrasound biometry, partial coherence interferometry serves as a new optical method for axial length determination. A functional prototype from Carl Zeiss Jena implementing this principle was compared with immersion ultrasound biometry in our laboratory. PATIENTS AND METHODS: In 108 patients attending the biometry laboratory for planning of cataract surgery, axial lengths were additionally measured optically. Whereas surgical decisions were based on ultrasound data, we used postoperative refraction measurements to calculate retrospectively what results would have been obtained if optical axial length data had been used for IOL calculation. For the translation of optical to geometrical lengths, five different conversion formulas were used, among them the relation which is built into the Zeiss IOL-Master. IOL calculation was carried out according to Haigis with and without optimization of constants. RESULTS: On the basis of ultrasound immersion data from our Grieshaber Biometric System (GBS), postoperative refraction after implantation of a Rayner IOL type 755 U was predicted correctly within +/- 1 D in 85.7% and within +/- 2 D in 99% of all cases. An analogous result was achieved with optical axial length data after suitable transformation of optical path lengths into geometrical distances. CONCLUSIONS: Partial coherence interferometry is a noncontact, user- and patient-friendly method for axial length determination and IOL planning with an accuracy comparable to that of high-precision immersion ultrasound.

Adult↗
PubMed1997

[Intraoperative skiascopy for determining the refractive value of an implantable intraocular lens].

BACKGROUND: Preoperative biometry for calculation of the refractive power of intraocular lenses is not sufficiently reliable in certain cases. Most frequently inaccuracies tend to occur in highly myopic eyes. Preceding refractive procedures can also impair IOL-calculation or even make it impossible. PATIENTS: In a highly myopic patient IOL-power calculation was not possible with conventional calculation formulas due to a preexisting refractive silicone lens located between the cataractuous natural lens and the iris. In another myopic patient ultrasound measurement of axial eye length produced variable and unreliable results. Therefore retinoscopy was performed intraoperatively in the aphakic eye. Refractive power of the IOL was calculated using a new formula. For validation of the method retinoscopy was performed intraoperatively in a second group of 11 patients with unproblematic ultrasound biometry. RESULTS: In 3 eyes IOL power was chosen according to intraoperative retinoscopy. A maximal deviation of 1.25 D from the aimed refraction resulted. In the second group, the retinoscopic method produced partially considerably inaccurate results as compared to the ultrasound biometry. Inaccuracies increased with the extent of hyperopia. CONCLUSIONS: In cases of difficult or inaccurate preoperative ultrasound biometry IOL power can be estimated after intraoperative retinoscopy in the aphacic highly myopic eye. IOL power can be calculated instantly using computer programs or tables. This method additionally enables the surgeon to control the refractive result of intraocular lens implantation prior to wound closure. However this method lacks reliability in higher hyperopic eyes, as in these cases small changes in corneal vertex distance of the lens used for retinoscopy highly alter the result.

Adult↗
PubMed1996

Posterior chamber myopia lenses in phakic eyes.

OBJECTIVE: To determine the best technique for implanting a hypernegative intraocular lens (IOL) in the posterior chamber of phakic eyes to neutralize high myopia and its results. SETTING: Robert Koch Hospital, Hannover-Gehrden, Germany. METHODS: We implanted the Chiron-Adatomed silicone myopia IOL in 69 eyes of 37 patients between June 1992 and August 1994 and followed them prospectively. RESULTS: To avoid marked decentration, the IOL should merely touch the ciliary sulcus. Its best length should equal the horizontal diameter of the cornea (white to white). Iritis from implantation trauma was avoided by intravenous administration of 250 mg prednisone preoperatively. When inserting the Chiron-Adatomed myopia IOL, we avoided putting pressure on the crystalline lens with the spatula. In 53 eyes, the difference between precalculated postoperative refraction and achieved postoperative refraction at 3 months was +0.07 +/- 1.05 diopters (D) (mean +/- SD). No eye deviated more than 2.80 D. Eleven of 69 eyes had a follow-up of fewer than 6 months and 13 had marked preoperative cortical opacities. Eight of the remaining 45 eyes with clear or almost clear cortexes showed a central subcapsular opacity after 1 to 2 years, probably IOL induced. CONCLUSION: Use of the Chiron-Adatomed IOL should be confined to older patients with early cataract until its role as the cause of opacities has been clarified by further observation.

Cataract↗
PubMed1995

[New knowledge of echographic imaging of the optic nerve. Experimental and clinical studies].

The optic nerve can be displayed in vivo by A- and B-scan techniques. To achieve correlations between the anatomical structure of the optic nerve and the echograms and to answer the question if by the usual examination techniques the diameter of the nerve can be measured, experimental studies on bovine optic nerves were carried out: examination of the bovine optic nerve in vitro with the A-scan technique; measurement of the sound velocity in bovine optic nerves. Additionally, we compared the two most common A-scan techniques for the display of the optic nerve in vivo in 47 normal persons and in 35 patients with changes of the optic nerve. The experimental studies showed that the orbital fat and outer sheaths of the optic nerve cause refraction of the sound beam. The sound velocity of ultrasound in bovine optic nerves was measured to 1567 +/- 25 m/s. The two most common examination techniques in vivo showed no differences in normal persons, but significant differences in patients with increased subarachnoidal fluid.

Adipose Tissue↗
PubMed1994

Evaluation of eyes harbouring perfluorocarbon liquid with standardized ophthalmic echography.

For the detection of perfluorocarbon liquid (PFCL) left in the globe after vitreoretinal surgery, the method of standardized ophthalmic echography proved to be very helpful and effective. Larger amounts as well as only a few remnant drops of PFCL are represented in standardized A-scans and in contact B-scans by typical acoustic signals caused mainly by the slow velocity of ultrasound in PFCL. A safe differentiation from other intraocular conditions can be made with standardized echography.

Evaluation Studies as Topic↗
PubMed1993

[Calculating and development of refraction in theoretical intraocular lens implantation in early childhood].

BACKGROUND: For various reasons the implantation of an intraocular lens in very young children remains a controversial matter. Although an intraocular lens might solve the problems of aniseiconia and amblyopia better then other forms of correction, the growth of the eyeball remains a major problem for constant refraction. MATERIAL AND METHODS: Therefore we theoretically analysed the biometric data from small children with regard to the development of refraction in 29 children (40 eyes). RESULTS: These theoretic calculations demonstrate that with an aimed refraction of -2.0 diopters at the time of cataract-operation, refraction at an age of 10 years varies from -2.75 diopters to -32.0 diopters (mean -11.75 diopters). The calculated aniseiconia at the age of 10 varies between 1 and 76% (mean 11%). In analysing these biometric data according to the age of the children at the time of surgery it is evident, that refraction at an age of 10 years would be more within a normal range if the age at the time of operation was certainly above 12 month of age. CONCLUSIONS: According to this theoretical analysis implantation of an intraocular lens appears not to be meaningful at an age of less than 12 months at the time of operation. If lens implantation in older children is considered the further growth of the eyeball should be taken into account when calculating the power of an intraocular lens.

Anthropometry↗
PubMed1993

[Critical corneal radii may skew correct IOL calculation by using the SRK/T formula].

The popular SRK/T formula for IOL calculation is analysed with respect to the underlying optical model and identified as a "thin-lens formula". As far as the prediction algorithm for the "optical anterior chamber depth" is concerned, it is shown that mathematically there exists a critical value for the radius of corneal curvature which marks the onset of a nonphysiologic formula behaviour. Within the algorithmic framework of the SRK/T formula, this critical curvature is solely dependent on the axial length. Clinically, the effect of this insufficiency of the formula is not of great importance: a check through our biometry database showed that 4 out of every 1000 IOL calculations were affected.

Algorithms↗
PubMed1991

[Technique and results of nitrogen cryotherapy of eyelid basaliomas].

A new, low-cost and more handy equipment (Erbocryo SN) is presented. It may be used with cryoprobes (closed tip) or spray application. New thin-walled probes proved more effective. This was also true in treatment of patients. - The long-term results of cryotherapy are reviewed and shown in 4 patients as examples. Since 1979, 262 basalioma patients were treated at Würzburg with liquid nitrogen application. The long-term results of the first consecutive series (1979-1983) were published earlier in this journal. They confirmed the favorable results published by american authors and by Matthüs and coworkers. Surgical treatment is suitable as well in small tumours. If, however, larger parts of the lid or the lacrimal pathways would have to be excised in surgical treatment, liquid nitrogen cryotherapy is the better choice. The limitations of this method must be considered in case of deeply infiltrating basaliomas of the cheek. Thorough knowledge of the method and of the preconditions of its efficacy are mandatory.

Basal Cell Carcinoma↗
PubMed1988

[The development of standards for ophthalmologic ultrasound diagnosis].

The performance data of ultrasonic apparatus and transducer probes are decisive in view of the information content of the echograms. Clinically applicable measurement methods, therefore, were developed already in the early sixties for ophthalmic ultrasonography. The sensitivity of each probe apparatus combination was measured first by means of a variable absorption path, the working frequency by counting the oscillations per microsecond in the rf echo signal of a plane reflector. Depth and lateral resolution were determined using monofil filaments mounted to a micrometer gauge. These measurements resulted in marked improvement of safety of diagnosis. In view of the IEC document 854, we developed a test reflector. It reflects a standard echo which can be measured within the control range of most diagnostic machines without need of additional dB-calibrated attenuators. Now, each echo amplitude can be referred to this standard echo (whose difference to the ideal reflector echo is-17 dB). An electronic device (echo simulator) permits additional checking of distinct equipment parts (especially of the dB control, time scale and amplifier dynamics). The entirely empirical use of ultrasonic diagnostic apparatus without measurement of the diagnostically relevant performance data and without readjustment and documentation of comparable examination conditions is, in our opinion, an outdated approach. Repeated measurements at regular intervals and especially after repairs or change of transducer probes are mandatory.

Equipment Design↗
PubMed1982

[Differential echographic diagnosis in small tissue areas--exemplified by the orbits].

Measurement-based ultrasonography proved mandatory in ophthalmic diagnostic work. It provides comparable examination conditions and therefore, comparable results, in contrast to simple, empirical ultrasonic examination. Measurement methods which can be easily applied under clinical conditions have been developed for determination of those technical characteristics of the apparatus and transducer probes which proved decisive for the diagnostic results. Some echographic criteria can be additionally or better evaluated using this basis. All echo-amplitude measurements should be related to a well-defined test-reflector echo. In addition to sensitivity and resolution, frequency and frequency spectrum are especially important. Manufacturer's data have proved insufficient up to now, insufficient; even within one manufacturer's series of one equipment or transducer probe type considerable deviations from the declared data have been found. Such deviations may mimick pathologic alterations in the echograms. The size of a lesion area can be better evaluated when using well-defined technical conditions. The echographic presentation of tissue structures in the depth is especially dependent on frequency and on the frequency spectrum. Pathologic alterations of tissues may cause changes in the ultrasound attenuation which results in emphasized or reduced presentation of echoes from normal structures behind the lesion area. Tissue differentiation should be based on additional A-scan echograms. Computerized echogram averaging provides a more reliable evaluation of echo amplitudes and ultrasound attenuation. Use of measurement-based ultrasonography permits to compare measured echo-amplitudes and ultrasound attenuation with the results of other working groups, even if these are based on other equipment and transducers.

Equipment Design↗