Biometry of the silicone oil-filled eye

Signal quality of biometry in silicone oil–filled eyes using partial coherence laser interferometry

PURPOSE

To assess the practical feasibility and signal quality of axial length measurements by partial coherence laser interferometry in silicone oil-filled eyes with previous complicated vitreoretinal surgery.

SETTINGS

Department of Ophthalmology, University Cologne, Cologne, Germany.

METHODS

Using a Zeiss IOLMaster, axial length measurements and signal-to-noise ratios of optical biometry in silicone oil-filled eyes (n=45) and contralateral eyes without tamponade (n=41) were analyzed.

RESULTS

Axial length measurements with signal-to-noise ratio > or =2 were feasible in 41 of 45 silicone oil-filled eyes (91%) and 37 of 41 eyes without tamponade (90%). Cataract, central retinal detachment, vitreous hemorrhage, and emulsified oil droplets attached to the intraocular lens were reasons for failure of partial coherence laser interferometry. The signal-to-noise ratio of the first 2 measurements was significantly smaller (P=.04) in silicone-filled eyes (4.4 +/- 2.0) than in eyes without tamponade (5.5 +/- 3.0). Axial lengths of the oil-filled eye and the contralateral eye showed a significant intraindividual correlation (P<.0001, Spearman r=0.84).

CONCLUSIONS

Partial coherence laser interferometry shows good clinical practicability in silicone oil-filled eyes with previous complicated vitreoretinal surgery. Further studies are needed to assess the reliability of these measurements with regard to postoperative refraction after combined oil removal and cataract surgery.

Intraoperative biometry for intraocular lens (IOL) power calculation at silicone oil removal

PURPOSE

Cataract development is common following retinal detachment surgery that necessitates silicone oil injection. Intraocular lens (IOL) power calculation in the presence of silicone oil is challenging for many reasons. The authors evaluated the accuracy of intraoperative biometry during cataract surgery in silicone-filled eyes.

METHODS

Twelve cases of cataract in eyes filled with silicone oil after retinal detachment surgery were included. Preoperatively, keratometric readings were documented. Intraoperative axial length was measured following removal of silicone oil using a sterile probe of the Nidek Echoscan US800 unit. IOL power calculation was computed using the SRK/T formula. This was followed by phacoemulsification and foldable lens implantation. Postoperative refraction allowed evaluation of the accuracy of intraoperative biometry. The predictability of three different formulas was also compared (Holladay, SRK/T, and SRK II).

RESULTS

Seven men and five women with a mean age of 50.2 years were included in the study. The mean postoperative spherical equivalent using the described technique was 6.77 +/- 0.43 diopters. SRK/T and Holladay formula had the best predictability for high axial length eyes, whereas the three studied formulas showed no significant differences in predictability in eyes with normal axial length.

CONCLUSIONS

Intraoperative biometry proved to have good predictability for the absolute postoperative refractive error in cataract surgery for eyes at the time of silicone oil removal. This predictability was accurate independent of axial length.

The problems of biometry in combined silicone oil removal and cataract extraction: a clinical trial

PURPOSE

To evaluate the problems and accuracy of biometry in eyes that have been operated on by silicone oil removal combined with cataract extraction with or without intraocular lens implantation.

SUBJECTS AND METHODS

Twenty-nine consecutive cases that have been operated on for silicone oil removal and cataract, with or without intraocular lens implantation, were included in a prospective study. Axial length measurement was done in silicone oil-filled eyes after changing the sound speed in vitreous cavity to 987 m/sec. The SRKT formula was used for intraocular lens calculation. The cataract was removed by phacoemulsification through corneal section or phacofragmentation through the standard vitrectomy sclerotomy. Intraocular lens implantation was done either on the peripheral anterior capsule (single piece, PMMA) or in the bag (acrylic foldable three pieces). The final refraction after at least 3 months' follow-up was measured. The difference between the predicted and the actual refraction was evaluated. A control group of 30 consecutive cases (20 nonmyopic and 10 highly myopic) of cataract extraction and intraocular lens implantation in eyes not filled with silicone oil was included using the same evaluation methods.

RESULTS

The mean deviation of the final from the predicted refraction was 1.87 +/- 2.11 diopters (range, +3.25 to -9 diopters). A total of 72.4% had a deviation of +/-2 diopters. The mean deviation in high myopia was 3.04 +/- 2.68 diopters (12 cases) (range, +/-1.75 to -9 diopters), while in nonmyopic patients, the mean deviation was 1.04 +/- 1.04 diopters (17 cases) (range, +3.25 to -3.25 diopters). The difference between highly myopic and nonmyopic eyes was statistically significant (P < 0.05). Most high errors occurred in highly myopic eyes. There was no statistical difference between the types of silicone oil (1000 versus 5000) or the mode of cataract extraction (phacoemulsification versus pars plana phacofragmentation). In the control group, the mean deviation in high myopia was 1.48 +/- 1.02 diopters (10 cases) (range, +/-0.5 to -3.5 diopters), while in nonmyopic patients, the mean deviation was 0.65 +/- 0.75 diopters (20 cases) (range, +2.75 to -1.75 diopters). The difference was statistically significant (P < 0.05).

CONCLUSION

Intraocular lens calculation in silicone oil-filled eyes is accurate in eyes that are not highly myopic. Some highly myopic eyes with posterior staphyloma have great deviation. Unsuitable formula, artifacts, or large eyes beyond the machine range may be the cause of errors of deviation of refraction. Comparable results are obtained in eyes regardless of the type of silicone oil (1000 or 5000) and techniques of intraocular lens implantation (in the sulcus or in the bag).