Accuracy of Intraocular Lens Formulas in Eyes With Keratoconus

Comparison of Barrett TK Universal II and Barrett Universal II TCRP Formulas in Power Calculations for 3 Presbyopia-Correcting Intraocular Lenses

Purpose

To compare Barrett TK Universal II and Barrett Universal II TCRP calculations in the power calculations for 3 presbyopia-correcting intraocular lenses (PC-IOL).

Methods

This observational study involved 64 eyes from 64 patients who prepared to undergo extraction of crystalline lenses combined with PC-IOL (Symfony ZXR00, PanOptix TFNT00, or AT LISA tri 839MP) implantation. All eyes underwent ocular biometric measurements with IOLMaster 700 and Pentacam HR, and the interdevice agreement of measurements including total keratometry (TK, IOLMaster 700) and total corneal refractive power (TCRP, Pentacam HR) was evaluated. IOL power calculations were performed using TK-based Barrett TK Universal II and TCRP-based Barrett Universal II calculations, respectively.

Results

Paired t-tests showed that the differences in white-to-white diameter, central corneal thickness, anterior chamber depth, and mean TK between IOLMaster 700 and Pentacam HR were slight but significant (all P<0.05), and the differences in recommended IOL power for emmetropia between two Barrett calculations were also significant in 3 PC-IOLs (all P<0.05). The ROC curve showed that the AUC was 0.917 (95% CI, 0.820-0.971) for the absolute value of the difference between TK and TCRP in discriminating the difference of ≥ ±0.5 D in predicted IOL power with best cutoff values of 0.4 D.

Conclusion

The novel Barrett TK Universal II formula built in IOLMaster 700 is comparable to TCRP-based Barrett Universal II calculation for IOL power calculation of PC-IOLs, and the convenience of using the Barrett TK Universal II formula should be founded on measurement consistency between devices.

[Evaluation of the accuracy of modern intraocular lens calculation formulas when optical biometry is not possible]

PURPOSE

This study evaluates the accuracy of modern intraocular lens (IOL) calculation formulas using axial length (AL) data obtained by ultrasound biometry (UBM) compared to the third-generation SRK/T calculator.

MATERIAL AND METHODS

The study included 230 patients (267 eyes) with severe lens opacities that prevented optical biometry, who underwent phacoemulsification (PE) with IOL implantation. IOL power calculation according to the SRK/T formula was based on AL and anterior chamber depth obtained by UBM (Tomey Biometer Al-100) and keratometry on the Topcon KR 8800 autorefractometer. To adapt AL for new generation calculators - Barrett Universal II (BUII), Hill RBF ver. 3.0 (RBF), Kane and Ladas Super Formula (LSF) - the retinal thickness (0.20 mm) was added to the axial length determined by UBM, and then the optical power of the artificial lens was calculated. The mean error and its modulus value were used as criteria for the accuracy of IOL calculation.

RESULTS

A significant difference (p=0.008) in the mean IOL calculation error was found between the formulas. Pairwise analysis revealed differences between SRK/T (-0.32±0.58 D) and other formulas - BUII (-0.16±0.52 D; p=0.014), RBF (-0.17±0.51 D; p=0.024), Kane (-0.17±0.52 D; p=0.029), but not with the LSF calculator (-0.19±0.53 D; p=0.071). No significant differences between the formulas were found in terms of mean error modulus (p=0.238). New generation calculators showed a more frequent success in hitting target refraction (within ±1.00 D in more than 95% of cases) than the SRK/T formula (86%).

CONCLUSION

The proposed method of adding 0.20 mm to the AL determined by UBM allows using this parameter in modern IOL calculation formulas and improving the refractive results of PE, especially in eyes with non-standard anterior segment structure.

Intraocular Lens Power Calculations in Keratoconus Eyes Comparing Keratometry, Total Keratometry, and Newer Formulae

PURPOSE

To compare the utility of keratometry vs total keratometry (TK) for intraocular lens power calculations in eyes with keratoconus (KCN) using KCN and non-KCN formulae.

DESIGN

Retrospective cohort study.

METHODS

This study was conducted at 2 academic centers and included 87 eyes in 67 patients who underwent cataract surgery between 2019 and 2021. Biometry measurements were obtained using a swept-source optical coherence tomography biometer (IOL Master 700). Refractive prediction errors, including root mean square error (RMSE), were calculated for 13 formulae. These included 4 classical formulae (Haigis, Hoffer Q, Holladay 1 [H1], and SRK/T), 5 new formulae (NF) (Barrett Universal II [BU2], Cooke K6, EVO 2.0, Kane, and Pearl-DGS), 3 KCN formulae (BU2 KCN: M-PCA, BU2 KCN: P-PCA, and Kane KCN), and H1 with equivalent keratometry reading values (H1-EKR). Formulae were ranked by RMSE. Friedman analysis of variance with post hoc analysis and H-testing was used for statistical significance testing.

RESULTS

KCN formulae had the lowest RMSEs in all eyes, and BU2 KCN:M-PCA performed the best among KCN formulae in all subgroups. In eyes with severe KCN, if TK values are unavailable, the BU2 KCN: P-PCA performed better than the top-ranked non-KCN formula (SRK/T). In eyes with nonsevere KCN, if TK values are unavailable, EVO 2.0 K was statistically superior to the next competitor (Kane K). H1-EKR had the highest RMSE.

CONCLUSIONS

KCN formulae and TK are useful for intraocular lens power calculations in KCN eyes, especially in eyes with severe KCN. The BU2 KCN: M-PCA using TK values performed best for eyes with all severities of KCN. For eyes with nonsevere KCN, the EVO 2.0 TK or K can also be used.

Factors Predictive of Refractive Error After Toric Lens Implantation

Purpose

To identify factors related to suboptimal refractive outcomes after toric intraocular lens implantation.

Patients and Methods

A retrospective case-control chart review of 446 eyes with toric lens insertion by the same surgeon at a university hospital from 2016 to 2020 was conducted. Pre-operative exam findings, biometry, and one month and three month post-operative vision and refraction were noted. Reviewed charts were considered cases if uncorrected distance visual acuity (UDVA) was worse than 20/40, spherical equivalent (SE) >1 diopter (D) off target, or cylinder >1 D off target.

Results

Overall, 93.7% (n = 343) of eyes achieved UDVA of 20/40 or better, 92.7% (n = 306) were within 1 D of target SE, and 90.9% (n = 300) were within 1 D of target cylinder. UDVA cases had more eyes with prior LASIK (21.7% vs 7.0%, p = 0.01) and keratoconus (8.7% vs 0.6%, p < 0.001) than controls. More SE cases had prior radial keratotomy (RK) (8.3% vs 0%, p < 0.001) and keratoconus (12.5% vs 0%, p < 0.001) than controls. More cylinder cases had prior LASIK (30.0% vs 8.7%, p < 0.001) and higher mean astigmatism (2.3 vs 1.5 D, p = 0.02) than controls. More cases in all three analyses had higher toric cylinder power (T5-T9) than controls. Age, sex, eye laterality, axial length, anterior chamber depth, lens power, dry eye, anterior basement membrane dystrophy, and Fuchs' endothelial dystrophy differences were not significant.

Conclusion

Prior LASIK or RK, keratoconus, and higher astigmatism may increase the chance of a suboptimal outcome.

Visual Outcomes of Cataract Surgery in Patients With Keratoconus Using Toric and Non-toric Lenses

PURPOSE

To compare the accuracy and outcomes of different intraocular lens (IOL) power calculation formulas in eyes with keratoconus undergoing cataract surgery with toric and non-toric IOLs.

METHODS

This was a consecutive retrospective case series study including patients from the Cornea Service at the Department of Ophthalmology and Visual Sciences at the University of British Columbia, Vancouver, Canada, from 2000 to 2020. Keratoconus was diagnosed based on corneal topography and clinician opinion. Patients who underwent topography-guided photorefractive keratectomy, intracorneal ring segments implantation, or corneal transplant were excluded. The manifest spherical equivalent, prediction errors, and median absolute errors were calculated. Descriptive statistics were expressed as mean ± standard deviation.

RESULTS

There were 160 eyes from 101 patients; 136 eyes received non-toric lenses and 24 eyes received toric lenses. Most patients had mild disease (< 48.00 diopters [D]) when stratified by steep keratometry values. Patients with severe disease (> 53.00 D) were significantly more hyperopic following surgery (P < .05). The Barrett Universal II (0.26 D, inter-quartile range [IQR] = 0.4), Holladay 2 (0.31, IQR = 1.2), and SRK/T (0.42, IQR = 0.86) formulas had the lowest median absolute error. The postoperative prediction error following toric lens insertion was not significantly different than following non-toric lens insertion, and the mean absolute astigmatism was significantly reduced with toric lenses.

CONCLUSIONS

The Barrett Universal II, Holladay 2, and SRK/T were the most accurate IOL power calculation formulas in patients with keratoconus undergoing cataract surgery. Hyperopic surprise was increased in severe keratoconus. Toric IOLs may be considered in patients with mild keratoconus. [J Refract Surg. 2023;39(5):319-325.].

Accuracy of intraocular lens calculations in eyes with keratoconus

PURPOSE

To compare the prediction accuracy of the Barrett True-K for keratoconus with standard formulas (SRK/T, Barrett Universal II, and Kane) and the Kane keratoconus formula.

SETTING

Shaare Zedek Medical Center, Jerusalem, Israel, and University Eye Clinic, Maastricht, the Netherlands.

DESIGN

Multicenter retrospective case series.

METHODS

Eyes with stable keratoconus undergoing cataract surgery were included. The predicted refractions were calculated for SRK/T, Barrett Universal II, Barrett True-K for keratoconus (predicted and measured), Kane, and Kane adjusted for keratoconus formulas. Primary outcomes were prediction error (PE), absolute error (AE), and percentage of eyes with PE ±0.25 diopters (D), ±0.50 D, and ±1.00 D. Subgroup analyses were performed based on the severity of the keratoconus.

RESULTS

57 eyes were included in the study. The PE was not significantly different from zero for SRK/T, Barrett True-K (predicted and measured), and Kane keratoconus formulas (range 0.09 to 0.22 D, P > .05). The AE of Barrett True-K predicted (median 0.14 D) and Barrett True-K measured (median 0.10 D) were significantly lower from Barrett Universal II (median 0.47 D) and Kane (median 0.50 D), P < .001.

CONCLUSIONS

The Barrett True-K formulas for keratoconus had higher prediction accuracy as compared with new generation formulas and a similar prediction accuracy as compared with the Kane keratoconus formula.

Cataract surgery in Keratoconus revisited - An update on preoperative and intraoperative considerations and postoperative outcomes

PURPOSE

This review aims to evaluate and simplify the recent literature on preoperative surgical planning, intraoperative considerations, postoperative surprises, and their management in patients with keratoconus undergoing cataract surgery.

METHODS

A review of the literature was done to analyze all the pertinent articles on Keratoconus and cataract surgery.

RESULTS

The surgical planning of cataracts in eyes with keratoconus needs a multifaceted approach. Preoperatively, techniques such as cross-linking or the use of intra-corneal rings help stabilize the progression. Unreliable biometric measurements are a significant problem in keratoconus patients, especially in an advanced stage of the disease. It is better to consider actual K readings if the K value is less than 55D but for a K value, more than 55D using standard K values will prevent postoperative refractive surprises. For calculation of K values, an elevation-based device like pentacam gives better repeatability in mild to moderate cases whereas for advanced keratoconus none of the keratometers is reliable. Recently, the Kane keratoconus formula performed better in all stages of disease whereas previous studies showed good results with SRK/T formula is a mild and moderate disease. Monofocal intraocular lenses are a better choice in these patients. Toric lenses can be used in mild and stable keratoconus. Intraoperatively, the use of a customized RGP lens can overcome the challenge of image distortion and loss of visual perspective. Despite taking necessary measures, postoperative refractive surprise can occur and can be managed with IOL exchange or Secondary IOLs.

CONCLUSION

There is a spectrum of challenges in managing cataracts in keratoconus which makes thorough preoperative planning important for good surgical outcomes. Despite the measures, there might be post-operative surprises and the patients need to be informed regarding the same.

Cataract surgery considerations in patients with prior history of keratoconus and ectasia

PURPOSE OF REVIEW

Preoperative workup for cataract surgery in patients with keratoconus poses certain challenges, particularly in patients with moderate-to-severe disease. This review aims to outline the appropriate preoperative, intraoperative, and postoperative considerations and provides an algorithm to help guide the workup prior to surgery.

RECENT FINDINGS

A new system for keratoconus progression and staging has been proposed and additional studies comparing intraocular lens (IOL) formulas calculations and biometry devices have been conducted.

SUMMARY

Patients with severe keratoconus have unpredictable results and have an increased risk of a hyperopic refraction postoperatively. Although studies have compared IOL calculation formulas, there is no consensus on management. Clinical considerations and an approach to the workup are presented; however, additional studies are required to determine the most appropriate management of cataracts in severe keratoconus.

Cataract surgery in patients with underlying keratoconus: focused review

An underlying diagnosis of keratoconus (KC) can complicate cataract surgery. In this study, the results of a focused review of the literature pertaining to cataract surgery in patients with KC are detailed. Topics essential for the appropriate management of this patient population are discussed. First, the individual and shared epidemiology and pathophysiology of cataract and KC are reviewed. Then, the theory and approach to intraocular lens power calculation are discussed, highlighting particularities and pitfalls of this exercise when performed in patients with KC. Finally, several special-although not uncommon-management scenarios and questions are addressed, such as surgical planning in cases where corneal stabilization or tissue replacement interventions are also necessitated.

Refractive Outcomes of Non-Toric and Toric Intraocular Lenses in Mild, Moderate and Advanced Keratoconus: A Systematic Review and Meta-Analysis

Background: To perform a systematic review and meta-analysis of the refractive outcomes of non-toric and toric intraocular lenses (IOLs) in keratoconus (KC) using different IOL power calculation formulas. Methods: A systematic search was conducted to identify studies that report on refractive outcomes of different IOL power calculation formulas in KC patients undergoing cataract surgery. Inclusion criteria were primary posterior chamber non-toric and toric monofocal intraocular lens implantation, data on the degree of KC, explicit mention of the formula used for each stage of KC, and the number of eyes in each category. We calculated and compared the absolute and mean prediction errors, percentage of eyes within 0.5 D and 1 D from target, and the weighted absolute prediction errors of IOL formulas, all were given for KC degrees I–III. Results: The bibliographic search yielded 582 studies published between 1996 and 2020, 14 of which (in total 456 eyes) met the criteria: three studies on non-toric IOL (98 eyes), eight studies on toric IOLs (98 eyes) and three studies of unknown separation between non-toric and toric IOLs (260 eyes). The lowest absolute prediction error (APE) for mild, moderate, and advanced KC was seen with Kane’s IOL power formula with keratoconus adjustment. The APE for the top five IOL power formulas ranged 0.49–0.73 diopters (D) for mild (83–94%) of eyes within 1 D from the target), 1.08–1.21 D for moderate (51–57% within 1 D), and 1.44–2.86 D for advanced KC (12–48% within 1 D). Conclusions: Cataract surgery in eyes with mild-to-moderate KC generally achieves satisfactory postoperative refractive results. In patients with advanced KC, a minority of the eyes achieved spherical equivalent refraction within 1 D from the target. The Kane’s formula with keratoconus adjustment showed the best results in all KC stages.

New treatment algorithm for keratoconus and cataract: small-aperture IOL insertion with sequential topography-guided photorefractive keratectomy and simultaneous accelerated corneal crosslinking

PURPOSE

To describe a new treatment algorithm aimed at optimizing refractive outcomes for patients with keratoconus and cataract.

SETTING

Private practice in Sydney, Australia.

DESIGN

Retrospective case series.

METHODS

This procedural approach involves cataract extraction with small-aperture intraocular lens (IOL) insertion, IC-8 IOL (AcuFocus, Inc.), followed by topography-guided photorefractive keratectomy (T-PRK) with simultaneous corneal crosslinking (CXL). Cataract surgery was performed with an initial 2.4 mm clear corneal incision enlarged to 3.5 mm to accommodate IC-8 IOL insertion. Once eyes demonstrated stable corneal tomography and refraction, T-PRK was performed using Schwind excimer laser (500 Hz) with the Vancouver custom topographical neutralization technique, aiming to achieve low myopia. CXL was performed immediately after T-PRK using Optolink hypotonic riboflavin with LIGHTLink-CXL (Lightmed) with 5.4 J total energy delivered at an 18 mw/cm2 irradiance.

RESULTS

Outcomes of 4 eyes are reported with all achieving rigid gas-permeable (RGP) contact lens independence, improved corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA), and regularization of corneal curvature with cone reduction. The mean CDVA improved from 0.43 preoperatively to 0.07 postoperatively (P = .00), and the mean UDVA improved from 0.81 preoperatively to 0.29 postoperatively (P = .04). Postoperative UNVA ranged from N.8 to N.12.

CONCLUSIONS

This treatment algorithm demonstrates unique combination of existing corneal and cataract surgical procedures to achieve satisfactory refractive outcomes and RGP contact lens independence in patients with keratoconus and cataract.

Intraocular Bag-in-the-Lens Exchange: Indications, Outcomes and Complications

PURPOSE

To report the indications, outcomes, and complications regarding the Bag-in-the-lens (BIL) intraocular lens (IOL) exchanges over a period of 13 years in a tertiary ophthalmologic centre.

SETTING

Department of Ophthalmology of the University Hospital of Antwerp (UZA).

DESIGN

Observational retrospective study.

PATIENTS AND METHODS

Between 2003 and 2020, 12 176 patients were operated using the BIL technique. We included adult patients who underwent an intraocular BIL exchange and recorded the demographics, indications, outcomes, and complications.

RESULTS

Fifty-nine eyes of 59 patients who underwent a BIL exchange between 2007 and 2020 were included (0.48%). The mean age was 61.15 ±13.53 years. The mean time between primary surgery and IOL exchange was 25.73 ± 41.88 months. The main indication for explantation was refractive surprise mostly related to the patients' risk factors e.g. preoperative corneal and refractive surgery. The mean preoperative uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) were 0.36 ± 0.24 and 0.79 ± 0.24 respectively. The postoperative 1 month-UDVA and CDVA were 0.66 ± 0.28 and 0.86 ± 0.19 respectively. The improvement in UDVA was statistically significant (<0.0001). The most common peroperative complication was damage to the anterior hyaloid in 9 eyes (15%), which did not prohibit reimplantation of a secondary BIL.

CONCLUSIONS

BIL to BIL exchange is an viable and successful technique that provides good refractive results with few, manageable complications. Because of the tertiary profile of our centre with referral of complex cases, BIL was our preferred IOL in patients at risk of postoperative refractive surprise.

Toric intraocular lens implantation - atypical cases

Objective: To describe the results of toric intraocular lens (IOL) implantation in three atypical cases (four eyes) with cataract and corneal astigmatism: one with bilateral keratoconus, one with pellucid marginal degeneration and one with buphthalmos due to congenital glaucoma.

Methods: Three patients (four eyes) with corneal astigmatism (one with bilateral keratoconus, one with pellucid marginal degeneration and one with buphthalmos due to congenital glaucoma) underwent cataract surgery by standard phacoemulsification and the implantation of toric IOLs in the capsular bag. The presence of corneal astigmatism was identified by automated keratometry and confirmed by Scheimpflug-based corneal tomography. The toric IOL implanted in all cases was a single-piece AcrySof Toric IOL (Alcon Laboratories, Inc.). Postoperative visual acuity, the reduction in the refractive astigmatism, the spherical equivalent (SE) and the rotational stability of the toric IOL were recorded for all the patients.

Results: Visual acuity increased and the refractive astigmatism decreased in all cases. In Case 1, the right eye achieved a postoperative uncorrected visual acuity (UCVA) of 20/ 20, a decrease in the refractive astigmatism from -3 DCyl to -0.75 DCyl and a spherical equivalent (SE) of -0.25. The left eye presented with a best-corrected visual acuity (BCVA) of 20/ 20, a decrease in the refractive astigmatism from -1.50 DCyl to -1.25 DCyl and a SE of -0.25. In Case 2, the postoperative UCVA was 20/ 20, with a decrease in the refractive astigmatism from -5.5 DCyl to -1 DCyl and a SE for the right eye of 0.00 D. In Case 3, the postoperative BCVA was 20/ 20, with a decrease in the refractive astigmatism from -4.75 DCyl to -1.50 DCyl and a SE of +1.25. No misalignment of the axis of the toric IOL was observed in any patient at subsequent follow-ups. The postoperative visual acuity was satisfactory for all the patients.

Conclusions: Toric intraocular lenses can be an effective option for implantation in patients with cataract and corneal astigmatism in atypical situations such as mild to moderate keratoconus, pellucid marginal degeneration and buphthalmos due to congenital glaucoma. Predicting the refractive outcome is difficult in atypical cases and the surgeon should have accuracy and consistency in the preoperative measurements, for achieving satisfactory postoperative results.

Corneal Topography for Intraocular Lens Selection in Refractive Cataract Surgery

The purpose of this review is to evaluate the usefulness of corneal topography to select premium intraocular lenses (IOLs), including aspherical IOLs, toric IOLs, and multifocal IOLs, in refractive cataract surgery. Corneal topography can detect corneal regular astigmatism, corneal irregular astigmatism (higher-order aberrations [HOAs]) including spherical aberration, and corneal shape abnormalities after corneal refractive surgery. Surgeons can explain to the patients with significant corneal HOAs about its effect on postoperative visual function before surgery. Multifocal IOLs should not be selected for such eyes. For eyes with abnormal corneal shape, appropriate IOL power calculation formulae can be applied. In the case of toric IOLs, regular astigmatism and corneal HOAs should be checked. Before implanting an aspheric IOL, it is ideal to confirm spherical aberration of the cornea is not below the normal range. Because corneal HOAs, abnormal corneal shape after corneal refractive surgery, corneal regular astigmatism, and corneal spherical aberration increase postoperative refractive errors and poor vision quality with premium IOLs, corneal topography before cataract surgery is helpful in screening patients who are not appropriate candidates for premium IOLs.

Accuracy of intraocular lens calculation formulas in cataract patients with steep corneal curvature

OBJECTIVE

To compare the accuracy of five kinds of intraocular lens calculation formulas (SRK/T, Haigis, Hoffer Q, Holladay and Barrett Universal Ⅱ) in cataract patients with steep curvature cornea ≥ 46.0 diopters.

METHODS

This is a retrospective study of cataract phacoemulsification combined with intraocular lens implantation in patients with steep curvature cornea (corneal curvature ≥ 46D). The refractive prediction errors of IOL power calculation formulas (SRK/T, Haigis, Holladay, Hoffer Q, and Barrett Universal II) using User Group for Laser Interference Biometry (ULIB) constants were evaluated and compared. Objective refraction results were assessed at one month postoperatively. According to axial length (AL), all patients were divided into three groups: short AL group (<22mm), normal AL group (>22 to ≤24.5mm) and long AL group (>24.5mm). Calculate the refractive error and absolute refractive error (AE) between the actual postoperative refractive power and the predicted postoperative refractive power. The covariance analysis was used for the comparison of five formulas in each group. The correlation between the absolute refractive error and AL from every formula were analyzed by Pearson correlation test, respectively.

RESULT

Total 112 eyes of 83 cataract patients with steep curvature cornea were collected. The anterior chamber depth (ACD) was a covariate in the short AL group in the covariance analysis of absolute refractive error (P<0.001). The SRK/T and Holladay formula had the lowest mean absolute error (MAE) (0.47D), there were statistically significant differences in MAE between the five formulas for short AL group (P = 0.024). The anterior chamber depth had no significant correlation in the five calculation formulas in the normal AL group and long AL group (P = 0.521, P = 0.609 respectively). In the normal AL group, there was no significant difference in MAE between the five calculation formulas (P = 0.609). In the long AL group, Barrett Universal II formula had the lowest MAE (0.35), and there were statistically significant differences in MAE between the five formulas (P = 0.012). Over the entire AL range, the Barrett Universal II formula had the lowest MAE and the highest percentage of eyes within ± 0.50 D, ± 1.00 D, and ± 1.50 D (69.6%, 93.8%, and 98.2% respectively).

CONCLUSION

Compared to SRK/T, Haigis, Hoffer Q, and Holladay, Barrett Universal Ⅱ formula is more accurate in predicting the IOL power in the cataract patients with steep curvature cornea ≥ 46.0 diopters.

[Phacosurgery features in keratoconus]

The review summarizes the results of surgical treatment of cataracts in patients with keratoconus. The major challenges of phacosurgery in keratoconus are associated with intraocular lens (IOL) power calculation, choice of the most appropriate IOL model and additional interventions required to stabilize keratectasia and reduce corneal irregularity.

Long-term refractive outcomes in patients with cataracts and keratoconus after phacoemulsification with toric intraocular lens implant

PURPOSE

To determine the refractive stability of patients with keratoconus and cataracts after the implantation of a toric intraocular lens.

METHODS

This is a cross-sectional, retrospectivestudy. Clinical records from patients with non-progressive keratoconus and cataracts that underwent non-complicated phacoemulsification with toric IOL implantation were reviewed. Mean keratometry (Km), refractive cylinder (RC), spherical equivalent (SE), steeper keratometry (K), and axis were evaluated at the 1-month, 6-month, 12-month, and 24-month follow-up visits.

RESULTS

Fifty-four eyes from 41 patients were included. Thirty-seven (68.5%) female and 17 (31.5%) male patients, with a mean age of 67.52 ± 8.22. Refractive cylinder at postoperative 30 days was -1.61 ± 1.23, 6-month -1.22 ± 0.80, 12-month -1.10 ± 0.83 and 24-month visit after surgery was -1.37 ± 0.77(p = 0.290). SE at the 30-day visit was -0.82 ± 1.90, 6-month -0.64 ± 1.23, 12-month -0.78 ± 1.91 and at 24-month postoperative visit -1.02 ± 1.87 (p = 0.210). Km value at the 1-month visit was 47.23 ± 1.95, 6-month 47.87 ± 1.61, 12-month 46.39 ± 2.52 and 24-month postoperative visit 46.92 ± 1.26 (p = 0.877). The steeper K axis in the 30-day control was 78.53 ± 30.12, 6-month 77.29± 37.68, 1-year 93.13 ± 62.42, 24-month 67.31 ± 38.49 (p = 0.632).

CONCLUSIONS

Our findings suggest a low variation in the refractive outcome for patients with mild and moderate keratoconus and cataracts, without evident progression signals, a demonstrated keratoconus clinical stability. No statistically significant postoperative changes in the refractive cylinder, SE, mean K, and steeper K axis were observed, which suggests good predictability for toric IOL implant.

Refractive approaches to visual rehabilitation in patients with keratoconus

PURPOSE OF REVIEW

As keratoconus is a chronic disease affecting young people, vision-related quality of life is often significantly impaired in patients with this disease. However, successful management of keratoconus, including visual rehabilitation strategies, can improve quality of life in these patients. This review will describe clinical approaches that improve vision-related quality of life in patients with stable keratoconus.

RECENT FINDINGS

Several types of contact lenses including scleral lenses have been used successfully to manage keratoconus. Eyes with severe keratoconus, even those in which fitting with other types of lenses is challenging, can be successfully fitted with scleral lenses. Although laser ablative procedures, such as photorefractive keratectomy (PRK) have been traditionally contraindicated in patients diagnosed with or suspected of having keratoconus, PRK has been attempted to partially correct refractive errors in keratoconus. Although phototherapeutic keratectomy and radial keratotomy have been reported to be used in eyes with keratoconus, effectiveness and safety results have varied. Implantation of phakic intraocular lenses and intraocular lenses, including toric intraocular lenses, which primarily correct regular astigmatism, with cataract extraction or refractive lens exchange can improve vision-related quality of life in patients with keratoconus by significantly reducing cylinder while improving uncorrected visual acuity.

SUMMARY

Appropriate selection and application of treatment options based on consideration of multiple factors will help patients with keratoconus, improving their vision-related quality of life and delaying or avoiding keratoplasty.

Intraocular lens calculations in patients with keratoectatic disorders

PURPOSE OF REVIEW

Intraocular lens (IOL) calculations in patients with keratoconus and other keratoectatic disorders continues to be a challenge for today's cataract surgeon. In this article, we review data published over the past 18 months (June 2018 to January 2020).

RECENT FINDINGS

Cataract surgery in keratoconus patients has the potential to greatly improve patients' vision. However, keratoconic eyes are notorious for unpredictable outcomes because of difficulty in obtaining proper preoperative biometry and lack of data and consensus on IOL calculation formulas that can reliable in providing the desired outcome. Recent studies suggest the Barrett II Universal calculation is the most accurate in mild-to-moderate keratoconic eyes. All studies note the level of predictability decreases with the steepness of keratometric readings. Historically, the SRK/T has been shown to provide the most reliable calculations.

SUMMARY

There is still no consensus on which formula is best for IOL calculation in keratoconic eyes. On the basis of the most recent literature, we recommend using the Barrett II Universal in conjunction with the SRK/T formula for mild-to-moderate eyes. Preoperative counseling of expectations with the patient is the key to achieving a satisfied patient and avoiding an unpleasant situation in the result of refractive surprise.

Update on Intraocular Lens Formulas and Calculations

Investigators, scientists, and physicians continue to develop new methods of intraocular lens (IOL) calculation to improve the refractive accuracy after cataract surgery. To gain more accurate prediction of IOL power, vergence lens formulas have incorporated additional biometric variables, such as anterior chamber depth, lens thickness, white-to-white measurement, and even age in some algorithms. Newer formulas diverge from their classic regression and vergence-based predecessors and increasingly utilize techniques such as exact ray-tracing data, more modern regression models, and artificial intelligence. This review provides an update on recent literature comparing the commonly used third- and fourth-generation IOL formulas with newer generation formulas. Refractive outcomes with newer formulas are increasingly more and more accurate, so it is important for ophthalmologists to be aware of the various options for choosing IOL power. Historically, refractive outcomes have been especially unpredictable in patients with unusual biometry, corneal ectasia, a history of refractive surgery, and in pediatric patients. Refractive outcomes in these patient populations are improving. Improved biometry technology is also allowing for improved refractive outcomes and surgery planning convenience with the availability of newer formulas on various biometry platforms. It is crucial for surgeons to understand and utilize the most accurate formulas for their patients to provide the highest quality of care.