Comparison of a new image-guided system versus partial coherence interferometry, Scheimpflug imaging, and optical low-coherence reflectometry devices: Keratometry and repeatability

Calculation of Toric Intraocular Lens Power with the Barrett Calculator and Data from Three Keratometers

Aim

To investigate the interdevice agreement for differences in toric power calculated using data on anterior corneal astigmatism obtained with corneal topography/ray-tracing aberrometry (iTrace), partial coherence interferometry (IOLMaster 500), and Scheimpflug imaging (Pentacam).

Methods

The analysis included 101 eyes (101 subjects) with regular astigmatism. The main outcome measures were corneal cylinder power, axis of astigmatism, and keratometry values. Toricity and toric IOL power were calculated using the online Barrett toric calculator. Interdevice agreement for measurement and calculation was assessed using a paired sample t-test and a nonparametric test.

Results

Significant interdevice differences were noted in the magnitude of astigmatism and flat, steep, and mean keratometry values between iTrace and IOLMaster (all P < 0.01); in flat, steep, and mean keratometry values (all P < 0.001) but not in the magnitude of astigmatism (P=0.325) between iTrace and Pentacam; and in the magnitude of astigmatism and steep and mean keratometry values (all P < 0.01) but not in flat keratometry values (P=0.310) between IOLMaster and Pentacam. The toric IOL power calculated using data from the three devices showed the following trend: iTrace > IOLMaster (0.49 ± 0.36, P < 0.001) and Pentacam (0.39 ± 0.42, P < 0.001) and Pentacam was <IOLMaster (-0.10 ± 0.39, P=0.009). There were differences in toricity calculated using data from the three devices (P=0.004).

Conclusions

Differences in toric IOL power and toricity calculated using anterior keratometry data from iTrace, IOLMaster 500, and Pentacam should be noted in clinical practice.

Agreement between the Swept-Source Optical Coherence Tomography and the Image-Guided System for Biometry Assessment in Cataract Surgery

PURPOSE

To assess the agreement on biometric data obtained using the Verion image-guided surgery system and the swept-source-OCT biometer IOL Master 700.

MATERIALS AND METHODS

All patients underwent biometry using the SS-OCT and the Image-Guide System. The comparison between instruments was assessed using the Intraclass correlation coefficient (ICC). Level of Agreement (LoA) employing the Bland-Altman analysis.

RESULTS

The image-based system produced significantly higher keratometry values, evidencing a low LoA between the SS-OCT and the image-based system, ranging from -1.30 D to 0.65 D (1.95 D), -1.04 D to 0.72 D (1.76 D), and -1.31 D to 0.65 D (1.96 D), respectively. The LoA for the Cylinder ranged from -0.46 D to 0.74 D (1.2 D) and from 0.82 to 0.94 mm for WTW.

CONCLUSIONS

In our study, the SS-OCT biometer and the Image-based System evidenced statistically significant differences in measuring the main biometric parameters except for the WTW.

Megalocornea, anterior megalophthalmos, keratoglobus and associated anterior segment disorders: A review

Megalocornea and anterior megalophthalmos (megalocornea spectrum) disorders are typically defined by corneal diameter > 12.5 mm in the absence of elevated intraocular pressure. Clinical features overlap with keratoglobus but are distinct from buphthalmos and severe (globus) keratoconus. Megalocornea spectrum disorders and keratoglobus are primarily congenital disorders, often with syndromic associations; both can present with large and thin corneas, creating difficulty in diagnosis, however, only keratoglobus is typically progressive. Molecular genetics provide significant insight into underlying aetiologies. Nonetheless, careful clinical assessment remains intrinsic to diagnosis. Surgical management can be challenging due to the enlarged ciliary ring and weakened zonules in megalocornea spectrum disorders and the extreme corneal thinning of keratoglobus. In this review, the established literature on measurement of corneal diameter, diagnosis of megalocornea, anterior megalophthalmos and keratoglobus, differentiation from severe keratoconus, recent molecular genetics research and key surgical modalities in the management of these rare disorders are outlined and discussed.

Clinical Outcomes After Femtosecond Laser-Assisted Arcuate Corneal Incisions versus Manual Incisions

Purpose

To compare the relative effectiveness of Verion-LenSx guided femtosecond arcuate incisions and manual incisions in reducing postoperative refractive astigmatism.

Patients and Methods

This was a contralateral eye, prospective study that included subjects with 0.50 D to 1.75 D of corneal astigmatism who wanted less refractive astigmatism post cataract surgery. The surgeon used anterior keratometry and the Woodcock astigmatism nomogram for preoperative planning, while the LenSx femtosecond laser with the Verion Image Guided System was used to create all laser arcuate incisions. Manual incisions were planned using the Donnenfeld nomogram and made with a fixed-depth diamond knife. The primary outcome measure was the residual refractive astigmatism at 3 months postoperative. Secondary outcome measures included the manifest refraction, uncorrected distance visual acuity and the change in corneal astigmatism from 1 to 3 months postoperative.

Results

Forty-one subjects were successfully enrolled in the study, with data from 38 subjects available at 3 months. There were no statistically significant differences in refractive astigmatism, corneal astigmatism, uncorrected distance visual acuity or manifest refraction between the Manual and Femto groups at either 1 month or 3 months. Significant changes in refractive and corneal astigmatism were noted between 1 months and 3 months. Ninety percent of eyes in both groups had ≤0.50 D of refractive astigmatism at 3 months. Two minor non-serious adverse events (full-thickness incisions of the cornea) occurred in two eyes of two different subjects in the Manual group; they were resolved without incident.

Conclusion

Laser arcuate incisions appear to be an effective means of reducing postoperative refractive astigmatism at the time of cataract surgery. No significant clinical differences were observed between incisions made manually and those made with an image-guided femto-second laser system. The lower number of minor adverse events experienced with the femtosecond laser system is an apparent advantage.

Time-efficiency assessment of guided toric IOL cataract surgery: a pilot study

PURPOSE

To compare the time spent on toric intraocular lens (IOL) implantation during cataract surgery using a manual-marking versus a digital image-guided system (the Verion) for toric IOL alignment.

SETTINGS

All procedures were performed at the Instituto Oftalmológico Quirónsalud ophthalmology clinic (A Coruña, Spain).

DESIGN

We designed an experimental and longitudinal (1-month follow-up) study.

METHODS

A total of 98 eyes of 65 participants (68.2 ± 12.2 years) were divided into two groups: 49 eyes operated with toric IOL alignment using a manual-marking technique (manual group) and another 49 eyes operated using image-guided marking (Verion group). The primary variable for comparison between both groups was cataract surgery time. Other outcomes such as toric IOL misalignment, spherical equivalent (SE), astigmatism, uncorrected distance visual acuity (UDVA), and corrected distance visual acuity (CDVA) were also measured.

RESULTS

The total cataract surgery time was 2:09 minutes shorter (p  < 0.001) with the Verion system (12:12 ± 2:20) compared to the surgical procedure performed using manual marking (15:27 ± 3:04). One month after surgery, there were no statistical differences in terms of toric IOL misalignment between the Verion (3.38° ± 2.95°) and the manual group (4.66° ± 3.95°). No statistical differences were observed between groups for refractive and visual outcomes either (p ≥ 0.05).

CONCLUSIONS

The cataract surgery time was reduced when the procedure was assisted using the Verion system to align the IOL compared to manual marking, maintaining the same efficacy in terms of toric IOL misalignment, residual refraction, and visual acuity.

Progression Analysis with ABCD Grading System following Corneal Collagen Cross-Linking in Keratoconus

Objectives:

To evaluate the ABCD grading system used in follow-up of keratoconus progression after the corneal collagen cross-linking (CXL) treatment in different Kmax groups.

Methods:

This study included 57 eyes of 43 patients applied with CXL treatment for progressive keratoconus. All the patients were applied with the standard CXL protocol (Dresden). According to the changes in the Kmax value at the end of 12 months postoperatively (0–1D, 1–2D, >2D), the groups were separated as steepening and flattening. Scheimpflug progression parameters, such as ABCD keratoconus grading systems, were evaluated in six different groups. The Paired Samples t-test was used in the evaluation of parameters with normal distribution and the Wilcoxon test for parameters not showing normal distribution. A value of p<0.05 was accepted as statistically significant.

Results:

Mean age of patients was 18.37±3.86 years (11–28 years). According to the ABCD grading system, 0.19 significant regression was determined in grade A (p=0.014) and 0.24 in grade D (p<0.0001). 0.10 progression was seen in grade B (p=0.089), and 0.11 in grade C (p=0.011). In the mean Kmax value 0.25±0.42, D flattening was seen (p=0.137).

Conclusion:

The anterior corneal surface grade in ABCD system is correlated with Kmax in different groups. However, the posterior corneal surface parameter is not correlated with Kmax in 1-2 D steepening and >2D flattening groups. Although there is an increase in posterior elevation after CXL, despite excessive Kmax flattening, it would be inaccurate to consider this increase as an indicator of topographic progress.

Agreement between Pentacam and handheld Auto-Refractor/Keratometer for keratometry measurement

OBJECTIVE

This study was conducted to evaluate the level of agreement in keratometry measurements between a rotating Scheimpflug imaging-based system (Pentacam) and a handheld auto-refractokeratometer (handheld NIDEK ARK-30).

METHOD

This analytical cross-sectional study was conducted in the right eyes of 579 subjects. Keratometry measurements were conducted with the Pentacam and the handheld NIDEK ARK-30 systems. The SPSS Software version 22 and MedCalc V3 were applied to estimate descriptive statistics using paired t-test, Pearson correlation coefficient, 95% limits of agreement (LoA), and Bland-Altman plot.

RESULTS

In the total sample, the inter-device difference in the mean flat and steep keratometry values was -0.266 diopter (D) (P-value<0.001) and 0.052D (P-value=0.093), respectively. There was a significant difference in mean flat keratometry between the two devices in all groups of refractive errors (paired difference <0.5D and P-value<0.001). The difference in mean steep keratometry was significant only in myopic subjects (P-value=0.046). The 95% LoA between the two devices measurements was 2.51D, 3.98D, and 6.37D for flat keratometry and 2.6D, 3.2D, and 3.9D for steep keratometry in emmetropic, myopic, and hyperopic subjects, respectively.

CONCLUSION

Our study showed relatively wide limits of agreement between handheld NIDEK ARK-30 and Pentacam; therefore, these devices cannot be used interchangeably for measuring corneal curvature.

Image-guided lens extraction surgery: a systematic review

A systematic review of the recent literature regarding the current image-guided systems used for cataract surgery or refractive lens exchange was performed based on the PubMed and Google Scholar databases in March 2018. Literature review returned 21 eligible studies. These studies compared image-guided systems with other keratometric devices regarding their accuracy, repeatability and reproducibility in measurement of keratometric values, astigmatism magnitude and axis, as well as in IOL power calculation. Additionally, the image-guided systems were compared with conventional manual ink-marking techniques for the alignment of toric IOLs. In conclusion, image-guided systems seem to be an accurate and reliable technology with measurements of high repeatability and reproducibility regarding the keratometry and IOL power calculation, but not yet interchangeable with the current established and validated keratometric devices. However, they are superior over the conventional manual ink-marking techniques for toric IOL alignment.

Comparison of Holladay equivalent keratometry readings and anterior corneal surface keratometry measurements in keratoconus

PURPOSE

To compare the accuracy of the anterior corneal simulated keratometry (SimK) and the Holladay equivalent keratometry reading (EKR) provided by a Scheimpflug camera (Pentacam HR) with the keratometry (K) provided by a Placido system (T-Cone topography) in keratoconus and control eyes.

METHODS

This prospective study included 40 consecutive patients with keratoconus and 40 voluntary participants with no ocular complaints. Any patients with corneal scar, corneal trauma, history of corneal surgery or contact lens usage were excluded from the study. Mean SimK and Holladay EKR measurements were taken with Pentacam HR in the 2, 3, and 4.5 mm corneal zones, and these values were compared with the T-Cone mean K value with the Placido topography system attachment on the Lenstar LS 900. Statistical analysis was performed using the paired Student's t test and the Bland-Altman analysis.

RESULTS

A statistically significant difference was determined between the Placido K and the Scheimpflug EKR 2, 3, 4.5 mm and SimK values in the keratoconus group (p < 0.05). In the analyses which showed a difference between the SimK and Holladay EKR, it was observed that as the diameter of the corneal zone increased, the 95% LoA values were extended. No statistically significant difference was determined between the SimK and EKR 2 mm values (p > 0.05). In the control group, there was no statistically significant difference between any of the keratometric values.

CONCLUSION

In diseases which affect the posterior corneal surface, such as keratoconus, it is thought that because of the asymmetrical peripheral placement of the corneal apex, as the corneal diameter increases there could be an error increase of 1-3 mm in keratometric systems evaluating the anterior surface.

Assessment of Corneal Keratometric and Astigmatism Measurements Using Verion System and Other Instruments in Cataract Patient

PURPOSE

To compare keratometry and corneal astigmatism measurements obtained by the Verion Image Guided System to those obtained by automated keratometry (IOLMaster), manual keratometry (YZ38, Suzhou 66 visual Polytron Technologies Inc., China), and Scheimpflug imaging (Pentacam HR) in eyes with cataract.

METHODS

A total of 149 cataractous eyes of 149 patients were examined and categorized as low astigmatism (<1.0 D, N = 50), moderate astigmatism (1.0-2.0 D, N = 49), and high astigmatism (>2.0 D, N = 50). The flattest and the steepest keratometric values (Kf and Ks), the magnitude of astigmatism (Ast), the orientation of the steepest meridian (Axis), and power vectors J₀ and J₄₅ were compared.

RESULTS

Keratometry readings (Kf, Ks, and Km) obtained by the Verion system showed statistically significant differences as compared to the other three devices. The magnitude of astigmatism (Ast) measured by the Verion (1.50 ± 0.85 D) was similar to that measured by the YZ38 (1.45 ± 0.82 D, P = 0.110) and slightly lower than that by the IOLMaster (1.56 ± 0.87 D, P = 0.014), but much higher than that by the Pentacam (1.36 ± 0.81 D, P = 0.000) significantly. However, no statistically significant differences were observed in the J₀ and J₄₅ vectors in the whole sample, besides moderate and high astigmatism subgroups. A difference in astigmatism magnitude of 0.50 D or more was detected between the Verion system and other three devices most commonly in moderate astigmatism eyes (16.3-24.5%). The difference in the location of the steep meridian was greater than 10 degrees most frequently in the low astigmatism eyes (26.0-52.0%).

CONCLUSIONS

Keratometric and astigmatic results obtained with Verion were not completely interchangeable with those obtained with IOLMaster, manual keratometry, and Pentacam. The individual differences in power and orientation of the corneal cylinder should be considered while selecting the appropriate toric intraocular lens.

Comparison of corneal power obtained from VERION image-guided surgery system and four other devices

PURPOSE

To assess the corneal keratometric values obtained using the VERION image-guided surgery system and other devices.

METHODS

This study evaluated the right eyes of 115 cataract patients before intraocular lens (IOL) implantation through consecutive tests using 5 devices: VERION Reference Unit, Placido-based corneal topography (OPD-Scan III), monochromatic light-emitting diodes (LenStar LS900 and AL-Scan), and rotary prism technology (auto kerato-refractometer KR-8800). Analyzed parameters were corneal steep and flat keratometric values (Ks and Kf) and corneal astigmatism and axis. These parameters were evaluated using the one-sample two-tailed t-test and the 95% limits of agreement (95% LOAs) between the devices.

RESULTS

The mean corneal cylinder value measurements were -0.97±0.63 D, -0.88±0.60 D, -0.90±0.69 D, -0.90±0.67 D, and -0.83±0.60 D with VERION, LenStar, AL-Scan (2.4 mm), OPD III, and KR-8800, respectively. Only KR-8800 showed a significant difference from VERION in the corneal cylinder value (P<0.05). The mean differences in the Kf and Ks of VERION compared to those of OPD III were 0.18±0.45 D and 0.17±0.38 D (P<0.05), respectively. The 95% LOAs of Bland-Altman analysis for the corneal astigmatism axis of the VERION with LenStar, AL-Scan (2.4 mm), OPD III, and KR-8800 were -26.25° to 58.71°, -20.61° to 47.44°, -25.03° to 58.98°, and -27.85° to 65.17°, respectively.

CONCLUSION

None of the VERION parameters were significantly different from those of AL-Scan and LenStar. AL-Scan (2.4 mm zone) was especially similar to VERION. Wide LOAs are potential contributors to axis error in patients with toric IOL implants.

Pseudophakic astigmatism reduction with femtosecond laser-assisted corneal arcuate incisions: a pilot study

Purpose

The aim of this study was to assess the effectiveness of the Verion-LenSx guided arcuate incision technique to reduce refractive astigmatism in a pseudophakic population.

Patients and methods

A prospective single-arm study was conducted in which one or both eyes of subjects required reduction of 1.0–2.0 D of refractive astigmatism after previous cataract surgery or refractive lens exchange. The surgeon used the refractive cylinder in the eye and the Woodcock astigmatism nomogram for preoperative planning, while the LenSx femtosecond laser with the Verion Image Guided System was used to create all arcuate incisions. The primary outcome measure was the uncorrected monocular distance visual acuity (UCVA). Secondary outcome measures included the change in corneal astigmatism, the change in refractive astigmatism, the best-corrected visual acuity and spectacle independence at distance from preoperative stage to 1 month and 2 months postoperatively.

Results

Twenty-eight eyes of 18 subjects were treated. The best-corrected visual acuity at the 2-month postoperative (PO) stage was not statistically significantly different from the preoperative visual acuity (0.02 logarithm of the minimum angle of resolution [logMAR] in both cases, P>0.05). Uncorrected visual acuity was statistically significantly better at the 2-month PO stage relative to the preoperative value (0.14 versus 0.34 logMAR, P<0.01). The mean change in refractive cylinder from the preoperative stage to the 2-month PO stage was 1.0 D. At the 2-month PO stage, two-thirds of the subjects (12/18) reported that they did not use glasses for distance vision and that their spectacle use for distance vision at 2 months was “lower” or “much lower” than the preoperative stage; in 71% of eyes (20/28), the residual refractive cylinder was ≤0.50 D. Vector changes in keratometric astigmatism were weakly associated with changes in refractive cylinder.

Conclusion

Arcuate incisions made with a femtosecond laser to treat moderate levels of residual refractive astigmatism after previous cataract surgery may reduce dependence on spectacles for distance vision.