One-handed phacoemulsification with low settings.

We describe a technique in which one-handed phacoemulsification with low aspiration flow and vacuum is performed with a peristaltic pump machine. With this technique, ultrasonic energy can be used for nucleus segmentation without the need for a second instrument. Measurements in cadaver eyes and clinical experience showed the technique to be simple, effective, and safe.

Diathermic capsulotomy versus capsulorhexis: a biomechanical study.

PURPOSE: To compare the mechanical quality of a capsulotomy opening performed by diathermy with that made by capsulorhexis (tearing). SETTING: Department of Ophthalmology, Vejle Hospital, Denmark. METHODS: This study included 12 pairs of human cadaver eyes and 20 pairs of pig eyes. One in each pair was randomly selected for one capsulotomy technique. The capsulotomy edge was stretched in a materials testing machine until break; force and elongation values were continuously recorded. RESULTS: In humans, the extensibility of the diathermic capsulotomy edge was approximately half that of the capsulorhexis edge (mean 38% +/- 4 [SD] versus 68% +/- 6), and the force required to break the edge was reduced by a factor of five (26 +/- 8 mN versus 134 +/- 36 mN). CONCLUSION: The mechanical quality of the diathermic capsulotomy edge is significantly less than that of the capsulorhexis edge, which indicates that the diathermic capsulotomy edge would withstand less surgical manipulation.

[Increasing waiting lists for cataract surgery in the county of Vejle]. / Stigende ventetider på operation for grå staer i Vejle Amt.

For several years the waiting list for cataract surgery has increased in the county of Vejle, Denmark. To reveal any change of indications for cataract surgery accounting for this increase, we analyzed referral notes and files in two samples of 86 and 72 patients examined preoperatively in 1991 and 1993. No significant difference was found between the groups regarding age, visual acuity, other eye diseases than cataract, diabetes, treatment with steroids, anisometropia or occupational disability due to poor vision. Thus no signs of changed indications for cataract surgery were found comparing the two samples. Median waiting time from referral to surgery had increased highly significantly from 1991 to 1993 (p << 0.01). The number of cataract operations per year was unchanged in the period. We propose that the increasing waiting time could be attributed to more people wanting cataract surgery, reflecting growing demands for good visual functioning and better expectations of the outcome after surgery.

Peribulbar anaesthesia. A clinical evaluation of two different anaesthetic mixtures.

Fifty-four consecutive cases of single injection peribulbar anaesthesia performed by the same ophthalmologist were evaluated concerning clinical effect on motility/akinesia and pain. The patients were randomly selected to one of two different mixtures of anaesthetics, one containing lidocaine, bupivacaine, adrenaline and hyaluronidase. The other lidocaine and bupivacaine. The mixture with adrenalin and hyaluronidase was significantly more effective than the other (success rates of 77.8% and 25.9%, p < 0.005).

Biomechanical aspects of the anterior capsulotomy.

We used the finite element method to evaluate different capsulotomy techniques. Nucleus expression was simulated in a computer model to visualize stress distribution in the anterior capsule. The finite element model demonstrated that the capsulorhexis edge is strong because of low and uniform stress distribution in the tissue. With can-opener and envelope capsulotomies, areas of high stress accumulation create the risk of tears during surgery.

Strength of the lens capsule during hydroexpression of the nucleus.

In planned extracapsular cataract extraction, hydroexpression of the nucleus has been introduced to facilitate nucleus delivery when performing capsulorhexis. The hydroexpression technique induces a fluid pressure in the capsular bag, which may rupture the posterior capsule. In a human cadaver eye model the pressure at the capsule's rupture point was determined in 16 cadaver eyes and compared to the fluid pressure in the capsular bag during hydroexpression of the nucleus in 32 eyes. The posterior capsule was able to withstand a pressure of 59 +/- 10 mm Hg (mean +/- SD) without rupturing. During hydroexpression of the nucleus the pressure was less than 12 mm Hg (3 mm Hg to 12 mm Hg) when the diameter of the capsulorhexis opening was 5.5 mm or more (measurement in the anterior chamber). Thus hydroexpression of the nucleus seems to be a safe technique when the diameter of the capsulorhexis is 5.5 mm or more.

Hydroexpression and viscoexpression of the nucleus through a continuous circular capsulorhexis.

When a continuous circular capsulorhexis (CCC) is performed, conventional nucleus expression may be impossible because of the strong capsular rim. Hydroexpression of the nucleus seems to overcome the problem if the capsulorhexis opening is large enough. Because a viscoelastic material may be an even more gentle tool than balanced salt solution (BSS), hydroexpression and viscoexpression were evaluated in 16 pairs of human cadaver eyes. The diameter of the capsulorhexis opening ranged from 4 mm to 6 mm; it was the same in each pair of eyes. Hydroexpression was performed in one eye using BSS and viscoexpression was performed in the fellow eye using sodium hyaluronate (Healon Yellow). The fluid pressure in the capsular bag was measured during both procedures. The pressure was higher during hydroexpression than during viscoexpression. The pressure difference between fellow eyes ranged from 0 to 32 mm Hg and was most marked when the CCC opening was small. This correlation was significant (P < .05). Viscoexpression may enhance the safety in cases with a small CCC opening or in those that are otherwise difficult.

Prediction of pseudophakic anterior chamber depth with the newer IOL calculation formulas.

Five methods for predicting pseudophakic anterior chamber depth (ACD) by five previously described intraocular lens power calculation formulas (Binkhorst II, Lepper and Trier, Holladay et al., Sanders-Retzlaff-Kraff (SRK/T), Olsen et al.) were evaluated in a series of 640 patients with a posterior chamber lens implant. Significant differences in formula performance were found in unusually short and long eyes. High errors were found in long eyes with the Lepper and Trier formula, the Holladay formula, and the SRK/T method. The highest accuracy was found with the Binkhorst formula and our previously described linear regression formula which expresses the pseudophakic ACD as a function of the average pseudophakic ACD for a given lens style, the preoperative ACD, and the axial length. The use of the preoperative ACD in combination with the axial length for the prediction of the pseudophakic ACD can therefore be expected to improve the accuracy of IOL power calculation.

Continuous circular capsulorhexis and nucleus delivery in planned extracapsular cataract extraction.

A technique for nucleus delivery through a continuous circular capsulorhexis in planned extracapsular cataract extraction is presented. The concept of hydro- and viscoexpression of the nucleus is explained, and a strongly bent cannula specially designed for the procedure is introduced.

[Clinical experience with a bifocal intraocular lens]. / Klinisk erfaring med en bifokal intraokulaer linse.

At cataract operation, the opaque cataractous lens is removed from the eye and is replaced by an artificial intraocular lens. Employing modern technology, development of a bifocal intraocular lens based on diffraction optic has now proved possible. The lens contains correction for distant vision and also for close work so that the patients may be independent of glasses. Sixty-two eyes with bifocal intraocular lenses were followed-up for approximately one year. The results are promising. 84% of the patients could read small print without corrective glasses. The accuracy by which the intraocular lens power can be calculated preoperatively and the surgical control of astigmatism in the eye are of decisive importance for the success of the lens.

Accuracy of the newer generation intraocular lens power calculation formulas in long and short eyes.

The accuracy of two newer generation theoretical intraocular lens (IOL) power calculation formulas and of the empirical SRK I and II formulas was evaluated in a series of 500 IOL implantations including a series of unusually long and short eyes. The prediction error of the theoretical formulas was found to be largely unaffected by the variation in axial length and corneal power, while the prediction of the SRK I formula was less accurate in the short and long eyes. The prediction of the SRK II formula was more accurate than the SRK I in that no systematic offset error with axial length could be demonstrated. However, because of a relatively larger scatter in the long eyes and a significant bias with the corneal power, the absolute error of the SRK II formula was higher than that of the theoretical formulas in the long eyes. The higher accuracy of the newer generation theoretical formulas was attributed to their improved prediction of the pseudophakic anterior chamber depth.

Stretching capacity of capsulorhexis and nucleus delivery.

The stretching capacity of the continuous circular capsulorhexis was studied in 30 human cadaver eyes. The capsulorhexis was found to have a remarkable stretching capacity, allowing safe nucleus delivery in planned extracapsular cataract extraction using hydroexpression. The difficulties encountered when trying to deliver the nucleus by external pressure to the sclera are discussed.

Prediction of postoperative intraocular lens chamber depth.

The postoperative intraocular lens (IOL) chamber depth was predicted using a multiple linear regression analysis of the postoperative chamber depth as a function of the corneal height, the preoperative chamber depth, and the axial length in 279 patients with a posterior chamber lens implant. Based on a linear regression formula incorporating these preoperatively defined parameters, the postoperative IOL chamber depth could be predicted with a correlation coefficient of 0.71 and an error of +/- 0.30 mm (SD). It is concluded that an individual prediction of the IOL chamber depth will improve the accuracy in IOL calculation.

Theoretical versus SRK I and SRK II calculation of intraocular lens power.

The predictability of a theoretical, computerized (PC-assisted) intraocular lens (IOL) power calculation method and of the Sanders-Retzlaff-Kraff [SRK] I and II methods was evaluated from preoperative and postoperative biometry in 202 cataractous patients who had extracapsular cataract extraction (ECCE). The theoretical method resulted in the lowest range and standard deviation of the error, and the highest correlation coefficient between the observed and the predicted refraction (P less than .05). The superiority of the theoretical approach was most clearly demonstrated when the postoperative measurements were used in the predictions (P less than .001). This demonstrated the potential accuracy of the formula used and the importance of incorporating methods to predict the IOL position after surgery. If the prediction of the IOL chamber depth was properly corrected for the axial length dependence, a high prediction accuracy could be obtained in short as well as in long eyes.

New multifocal intraocular lens design.

The first clinical experience with a new diffractive multifocal intraocular lens implanted in 55 eyes of 53 patients is reported. Excluding four patients with preoperative senile macular degeneration, the best corrected visual acuity was 20/40 or better and the near vision without any add to the best distance correction was J2 or better in all cases three, six, and 12 months postoperatively.

[Soft intraocular lenses]. / Bløde intraokulaere linser.

Hard intraocular polymethylmethacrylate (PMMA)-lenses have been implanted following cataract extractions since 1949, and their good properties are well proven. Soft intraocular lenses have only been implanted since 1976. Their chemical and physical properties, advantages and disadvantages are discussed with reference to the well known PMMA-lenses. In the short term the patients obtain the same visual acuity with soft intraocular lenses as with hard intraocular lenses, and it is the impression, that the soft lenses are more tissue compatible, but more prolonged follow up is required.

Intraocular pressure in the first days after implantation of posterior chamber lenses with the use of sodium hyaluronate (Healon).

Intraocular pressure (IOP) was measured before and 6, 24, 48 and 72 h after extracapsular cataract extraction with implantation of a posterior chambers lens in 3 groups of patients. Group I (30 patients): Sodium hyaluronate (Healon) was used during anterior capsulotomy and lens implantation and was aspirated at the end of surgery. Group II (22 patients): Healon as in group I + 500 mg acetazolamide at the end of surgery. Group III (17 patients): BSS and/or air was used instead of Healon during surgery. In all groups statistically significant rises in IOP after 6 h were followed by significant falls in the remaining post-operative period. The rise and subsequent fall in IOP was significantly greater in group I than in group III. Acetazolamide in group II did not prevent excessive rises in IOP. Aspiration probably shortens the period of Healon-induced hypertension. We recommend a meticulous aspiration of Healon at the end of surgery.