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

Optimization of biometry for best refractive outcome in cataract surgery

High-precision biometry and accurate intraocular lens (IOL) power calculation have become essential components of cataract surgery. In clinical practice, IOL power calculation involves measuring parameters such as corneal power and axial length and then applying a power calculation formula. The importance of posterior corneal curvature in determining the true power of the cornea is increasingly being recognized, and newer investigative modalities that can estimate both the anterior and posterior corneal power are becoming the standard of care. Optical biometry, especially using swept-source biometers, with an accuracy of 0.01-0.02 mm, has become the state-of-the-art method in biometry. With the evolution of IOL formulas, the ultimate goal of achieving a given target refraction has also moved closer to accuracy. However, despite these technological efforts to standardize and calibrate methods of IOL power calculation, achieving a mean absolute error of zero for every patient undergoing cataract surgery may not be possible. This is due to inherent consistent bias and systematic errors in the measurement devices, IOL formulas, and the individual bias of the surgeon. Optimization and personalization of lens constants allow for the incorporation of these systematic errors as well as individual bias, thereby further improving IOL power prediction accuracy. Our review provides a comprehensive overview of parameters for accurate biometry, along with considerations to enhance IOL power prediction accuracy through optimization and personalization. We conducted a detailed search in PubMed and Google Scholar by using a combination of MeSH terms and specific keywords such as "ocular biometry," "IOL power calculations," "prediction accuracy of refractive outcome in cataract surgery," "effective lens position," "intraocular lens calculation formulas," and "optimization of A-constants" to find relevant literature. We identified and analyzed 121 relevant articles, and their findings were included.

Topical Review: Causes of Refractive Error After Silicone-oil Removal Combined with Cataract Surgery

SIGNIFICANCE

This review summarizes the main factors of refractive error after silicone oil removal combined with cataract surgery.The post-operative refractive results of silicone oil removal combined with cataract surgery are closely related to the patient's future vision quality. This report summarizes the factors that influence the difference between the actual post-operative refractive power and the pre-operatively predicted refractive power after silicone oil removal combined with cataract surgery, including axial length, anterior chamber depth, silicone oil, commonly used tools for measuring intraocular lens power, and intraocular lens power calculation formulas, among others. The aim of the report is to assist clinical and scientific research on the elimination of refractive error after silicone oil removal combined with cataract surgery.

Accuracy of New Generation Intraocular Lens Calculation Formulas in Vitrectomized Eyes

PURPOSE

To compare the prediction accuracy of new intraocular lens (IOL) calculation formulas (Barrett Universal II [BUII], Emmetropia Verifying Optical [EVO], Kane and Ladas Super formula) and traditional formulas (Haigis, Hoffer Q, Holladay 1, and SRK/T) with Wang-Koch (WK) axial length (AL) adjustment in vitrectomized eyes.

DESIGN

Retrospective consecutive case-series study.

METHODS

One hundred eleven eyes of 111 patients underwent uneventful phacoemulsification and enVista MX60 implantation after vitrectomy were enrolled and divided into 4 groups according to whether the vitreous cavity was filled with silicone oil. The performance of each formula was evaluated with or without lens constant optimization.

RESULTS

Before lens constants optimization, the mean prediction errors (MEs) of all formulas were statistically different from zero (0.14-0.46 diopters [D]) in vitrectomized eyes, except for the Kane formula. The BUII, EVO, Kane, and Haigis had relatively lower mean absolute error (MAE) and median absolute error (MedAE) with optimized constants. No significant systemic bias was found in new formulas for vitrectomized eyes with AL >26 mm (P > .05). The Hoffer Q and Holladay 1 displayed significantly hyperopic shift (0.39 and 0.51 D) for long eyes, which was corrected by the WK adjustment. There were no significant differences in the prediction accuracy of all formulas among 4 subgroups (P > .05).

CONCLUSIONS

The BUII, EVO, Kane, and Haigis displayed comparable performance in vitrectomized eyes with optimized constants. In vitrectomized highly myopic eyes, the new formulas and traditional formulas with WK adjustment exhibited satisfactory prediction accuracy. Silicone oil tamponade did not affect the prediction accuracy of formulas using IOLMaster 700.

The influence of low signal-to-noise ratio of axial length measurement on prediction of target refraction, achieved using IOLMaster

Purpose

To evaluate the influence of low signal-to-noise ratio (SNR) of axial length measurement, achieved using IOLMaster, on prediction of target refraction.

Methods

A total of 131 eyes of 131 patients who underwent phacoemulsification with posterior chamber lens implantation were enrolled. Preoperative axial length measurements were performed with the IOLMaster 500 (Carl Zeiss Meditec, Germany); preoperative SNR values were used to divide the eyes into three groups (Group 1; SNR <10, Group 2; 10 ≤ SNR <50, Group 3; 50 ≤ SNR <100). One month and 6 months after cataract surgery, the manifest refraction spherical equivalents (MRSE) were measured. The mean numeric errors (MNE), the mean of the difference between postoperative MRSE, and preoperative target refraction, using the various intraocular lens (IOL) formulas, were calculated and compared among the three groups.

Results

One month after cataract surgery, postoperative MRSE was more hyperopic than preoperative target refraction, calculated by the Haigis formula in group 1, and by the SRK/T formula in group 2. After 6 months, for all formulas in group 1, there were significantly hyperopic results (approximately 0.35 diopter). Upon comparison of MNE among the three groups, group 1 was statistically significantly different from the other groups by Haigis formula.

Conclusions

When the SNR values in biometry, using IOLMaster, are <10, careful attention should be given to determining IOL power, as postoperative spherical equivalents are more hyperopic than preoperative target refraction by IOL formula.

Optical biometry features in silicon oil filled eyes

Background. The article presents results of axial length (AL) measurement in eyes filled with silicone oil and in those without silicone oil with IOLMaster and Lenstar LS 900 optical biometry methods. Materials and methods. The anteroposterior axis was measured in 27 eyes of 27 patients with silicone oil tamponade after surgical treatment of several vitreoretinal conditions. Using IOLMaster, the AL of eyes without silicone oil tamponade varied from 21.99 mm to 29.38 mm, Lenstar LS 900 biometry gave results from 21.96 mm to 29.41 mm. Results. According to data obtained and to their distribution, all cases were divided into 2 groups: I group — eyes with AL less than 23.63 mm, and II group — eyes with AL more than 23.63 mm. In the group II, the disparity of consecutive measurements was reliable and amounted to 0.28 ± 0.46 mm (р = 0.024) for IOLMaster and 0.23 ± 0.44 mm (р = 0.029) for Lenstar LS 900. Conclusion. So AL values at IOLMaster and Lenstar LS 900 biometry of silicone oil filled eyes may significantly overestimate the real ones when exceeding 23.63 mm. In case of simultaneous phacoemulsification with IOL implantation, this could lead to hypermetropic shift of postoperative refraction. Lenstar LS 900 measurement error in silicon oil filled eyes is less than that of IOLMaster, thus making the first biometry method preferable. In eyes with AL shorter than 23.63 mm, the measurement difference was not reliable, thus the biometry accuracy in silicone oil filled “short” eyes becomes higher.

Refractive outcomes after silicone oil removal and intraocular lens implantation

PURPOSE

To evaluate the accuracy of intraocular lens (IOL) calculations in eyes undergoing silicone oil removal and IOL implantation using ultrasound biometry and partial coherence interferometry (PCI) (IOLMaster).

METHODS

This was a retrospective consecutive series of eyes that underwent silicone oil removal and IOL implantation from 1999 to 2009. Data were collected on preoperative and intraoperative characteristics that could affect the refractive outcome. The predicted refraction, as measured with ultrasound biometry or PCI, was compared with the postoperative refraction.

RESULTS

Overall, the mean difference between observed and predicted refraction was -0.97 diopters (D). Thirty-five of 64 eyes (55%) were measured by ultrasound biometry, and 29 of 64 eyes (45%) were measured by PCI. The mean (SD) difference between the predicted refraction and the observed spherical equivalent was -1.34 D (2.18 D) when measured by biometry and -0.51 D (2.03 D) when measured by PCI (P = 0.13).

CONCLUSION

Refractive outcomes after silicone oil removal and secondary IOL implantation are fairly accurate, with most ending up slightly myopic. Measurement by PCI may be more accurate than biometry. The IOL power should be selected to yield a target refraction about 0.5 D to 1.25 D more hyperopic than desired, depending on the method used to measure it.

Accuracy and reliability of IOL master and A-scan immersion biometry in silicone oil-filled eyes

PURPOSE

To compare the accuracy and reliability of intraocular lens (IOL) master and A-scan immersion biometry in silicone oil (SO)-filled eyes.

METHODS

A prospective, consecutive, nonrandomized study was performed in 34 SO-filled eyes of 34 patients, who underwent a pars plana vitrectomy, with SO removal and cataract surgery, as well as IOL implantation. Both IOL master and immersion A-scan were performed to measure the axial length (AXL) before SO removal. Three months after removal of the SO, AXL measurements using IOL master and refraction was performed. Accuracy of the two techniques was determined by a mean postoperative AXL using an IOL master and reliability was determined by mean actual postoperative refractive error.

RESULTS

Preoperative mean AXL was 23.91±0.24 mm (range 21.33-28.61 mm) and 23.71±0.59 mm (range 19.27-36.18 mm) by IOL master and A-scan immersion, respectively. Postoperative mean AXL by IOL master was 23.90±0.23 mm (range 21.58-27.94 mm), which showed a statistically significant difference from the preoperative mean AXL by A-scan immersion (P=0.005). The AXL measurement by IOL master also was more accurate than A-scan immersion by Pearson's correlation (0.966 vs 0.410). For reliability of the two techniques, the predictive postoperative refractive error in A-scan immersion (mean 1.79±1.04 D, range -14.62 to 16.41 D) was greater than that in IOL master (mean 0.60±0.23 D, range -2.74 to 2.33 D), with a statistically significant difference (P=0.049).

CONCLUSION

IOL master had more accuracy and less deviation in predictive postoperative refractive error than A-scan immersion in SO-filled eyes.

Accuracy of intraocular lens power calculation using partial coherence interferometry in patients with high myopia

PURPOSE

Ultrasound-A-scan-biometry intraocular lens power calculation for cataract surgery sometimes shows lack of accuracy in patients with high myopia. The purpose of this retrospective study was to assess the accuracy of lens power calculation with optical biometry using the Zeiss IOLMaster across a large range of myopia levels.

METHODS

We included 37 consecutive, myopic eyes with an axial length >26.5mm (31 patients, 62±13years old, average preoperative refraction of -14.46±6.61D, range -3.5 to -32.0D which underwent phacoemulsification and implantation of an intraocular lens following biometry using the IOLMaster. For lens power calculation, the Haigis formula was used in all cases. For comparison, refraction was back-calculated using the SRK/T and Holladay I formulae.

RESULTS

  The preoperative mean axial length was 29.37±2.44 mm with a range of 26.50-35.52mm. Thirty eyes (81.1%) showed a postoperative spherical equivalent which differed 1.00D or less from the predicted value, in 20 cases (54.1%) the postoperative refractive error was within±0.50D. The mean absolute error (MAE) was 0.70±0.59D (Holladay I, 0.85±0.68; SRK/T, 1.01±0.61D).

CONCLUSIONS

  Optical biometry for intraocular lens power calculation seems to deliver reliable results for cataract surgery in patients with high myopia, although our data describe an increasing lack of accuracy beyond an axial length of 30mm. The Haigis formula provided the best predictability of postoperative refractive outcome for myopic eyes in general.

Assessment of a new averaging algorithm to increase the sensitivity of axial eye length measurement with optical biometry in eyes with dense cataract

PURPOSE

To assess the capability of new software to decrease the proportion of eyes that have insufficient signal-to-noise ratio (SNR) in optical biometry.

SETTING

Moorfields Eye Hospital NHS Foundation Trust, London, United Kingdom.

DESIGN

Evaluation of diagnostic test or technology.

METHODS

In a prospective study, consecutive cataract patients coming for biometry who were unsuccessfully measured with the former software (version 4) of the IOLMaster partial coherence interferometry (PCI) device were reevaluated with the new composite software (version 5). Subsequently, in a retrospective study, consecutive cataract patients were measured with software version 5. For unsuccessful scans, the type and intensity of cataract were assessed at the slitlamp.

RESULTS

Altogether, 2713 eyes (1956 patients) were included in the study. The prospective study comprised 458 eyes (244 patients), 10.6% of which could not be measured successfully with software version 4. With the composite software, 30% of cases were measured successfully, with a higher proportion (42%) in the posterior subcapsular cataract subgroup. In the retrospective study, of 2255 eyes (1712 patients), 4.7% were not measured successfully using the new algorithm because of white cataract (70 eyes), posterior subcapsular cataract (14 eyes), or dense nuclear cataract combined with posterior subcapsular cataract (13 eyes) or for other reasons (8 eyes).

CONCLUSION

The composite software (version 5) enhanced the SNR, allowing valid measurements in eyes in which optical biometry had previously failed, especially in cases of posterior subcapsular cataract.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned. Additional disclosure is found in the footnotes.

Advances in anterior segment imaging

PURPOSE OF REVIEW

Imaging of the crystalline lens and intraocular lens is becoming increasingly more important to optimize the refractive outcome of cataract surgery, to detect and manage complications and to ascertain advanced intraocular lens performance. This review examines recent advances in anterior segment imaging.

RECENT FINDINGS

The main techniques used for imaging the anterior segment are slit-lamp biomicroscopy, ultrasound biomicroscopy, scheimpflug imaging, phakometry, optical coherence tomography and magnetic resonance imaging. They have principally been applied to the assessment of intraocular lens centration, tilt, position relative to the iris and movement with ciliary body contraction.

SUMMARY

Despite the advances in anterior chamber imaging technology, there is still the need for a clinical, high-resolution, true anatomical, noninvasive technique to image behind the peripheral iris.