Cataract surgery in eyes with keratoconus: a review of the current literature

Functional Approach to IOL Selection in Eyes With Combined Cataract and Keratoconus With an Option for Refractive Lens Exchange

PURPOSE

To evaluate spherical intraocular lens (IOL) implantation for cataracts in keratoconic eyes followed by optional refractive toric lens exchange to improve uncorrected visual acuity.

METHODS

This retrospective study evaluated cataract surgery outcomes in keratoconic eyes. Eyes treated with a spherical IOL targeted for -2.00 diopters (D) either achieved acceptable manifest refraction and desired exchange with a toric IOL (Group 1); achieved satisfactory manifest refraction and chose to use spectacles or contact lenses (Group 2); or did not achieve acceptable refraction and used contact lenses (Group 3). Group 4 had single-stage toric IOL implantation with plano target. Corrected and uncorrected distance visual acuity (CDVA and UDVA) and keratometry were analyzed.

RESULTS

Groups 1 to 4 had 18, 23, 18, and 26 eyes, respectively. A staged toric exchange resulted in significantly better (P = .02) UDVA (mean: 0.15 logMAR; 20/25 Snellen) than initial toric IOL implantation (0.24 logMAR; 20/30 Snellen). All toric IOL exchange eyes achieved 20/30 or better CDVA and 94% had 20/40 or better UDVA. Mean manifest cylinder significantly decreased from 3.39 D before lens exchange to 1.10 D postoperatively.

CONCLUSIONS

Initial implantation of a spherical IOL in keratoconic eyes allows basing toric calculations on the manifest refraction, which may be more reliable than keratometry measurements in keratoconic eyes. UDVA after staged toric IOL exchange was significantly better than after initial toric IOL implantation. Importantly, by staging use of toric lenses, the authors avoided cases where patients required a rigid contact lens after a toric IOL was implanted. [J Refract Surg. 2024;40(4):e207-e217.].

Current concepts in the management of cataract with keratoconus

This review analyzed all pertinent articles on keratoconus (KCN) and cataract surgery. It covers preoperative planning, intraoperative considerations, and postoperative management, with the aim of providing a simplified overview of treating such patients. Preoperatively, the use of corneal cross-linking, intrastromal corneal ring segments, and topo-guided corneal treatments can help stabilize the cornea and improve the accuracy of biometric measurements. It is important to consider the advantages and disadvantages of traditional techniques such as penetrating keratoplasty and deep anterior lamellar keratoplasty, as well as newer stromal augmentation techniques, to choose the most appropriate surgical approach. Obtaining reliable measurements can be difficult, especially in the advanced stages of the disease. The choice between toric and monofocal intraocular lenses (IOLs) should be carefully evaluated. Monofocal IOLs are a better choice in patients with advanced disease, and toric lenses can be used in mild and stable KCN. Intraoperatively, the use of a rigid gas permeable (RGP) lens can overcome the challenge of image distortion and loss of visual perspective. Postoperatively, patients may need updated RGP or scleral lenses to correct the corneal irregular astigmatism. A thorough preoperative planning is crucial for good surgical outcomes, and patients need to be informed regarding potential postoperative surprises. In conclusion, managing cataracts in KCN patients presents a range of challenges, and a comprehensive approach is essential to achieve favorable surgical outcomes.

Development of a Web-Based Algorithm for Understanding the Intraocular Lens-Based Surgery in Stable and Progressing Keratoconus for Non-Specialist Ophthalmologists

PURPOSE

To propose an algorithm to facilitate lens-based surgery in keratoconus.

METHODS

A literature review was performed to prepare a software algorithm based on cone location, stability, best spectacle-corrected distance visual acuity (BSCVA) level and whether there is a clear or cataractous lens. The software usability was assessed through a 10-question questionnaire and two hypothetical keratoconus case histories (moderately simple and moderately complex) given to 15 trainees. The usability questionnaires were graded on a Likert scale (1 = strongly disagree to 5 = strongly agree) and two case histories (1 = very difficult to 7 = very easy).

RESULTS

The algorithm can be found at https://www.sussexeyelaserclinic.co.uk/keratoconus/. Thirteen trainees completed the questionnaire. 91.9% would frequently use it; for 100%, it was easy to use independently without technical support; for 63.7%, it was strongly integrated; for 100%, it was consistent; 100% thought that most people would learn to use it quickly, 91.9% found the system not cumbersome to use, felt very confident to use it and need not learn a lot to use it. The first case was found easy by 63.7% and the second by 45%.

CONCLUSION

We present an algorithm as a guide for lens-based surgery in stable and progressing keratoconus, which is classified based on cone location. This algorithm will help trainee and "non-specialist" ophthalmic surgeons understand the pre-operative planning for the surgery and referral to the "specialist" corneal surgeon, considering factors such as progression, BSCVA, keratometry, topography and apex location of the cone in keratoconus patients.

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.

Measuring the agreement of keratometry readings of four devices in eyes with keratoconus

PURPOSE

To determine the keratometry measurement agreement using Sirius corneal topography and Scheimpflug camera, Tomey corneal topography, Topcon autokeratorefractometer, and Tomey OA-2000 optical biometry in eyes with different severity of keratoconus.

METHODS

In this retrospective study 115 eyes in different stages of keratoconus were divided into 2 groups of mild (stage 1), and moderate to severe keratoconus (stages 2, 3), according to the Amsler-Krumeich classification. Keratometry measurements were obtained using Sirius corneal topography and Scheimpflug camera (phoenix V3.7.01.08), Tomey corneal topography (Tms SW22C-200S-200), Topcon autokeratorefractometer (KR8900), and Tomey optical biometry (OA-2000 Opt-Meas V.4E).

RESULTS

In group 1 All devices demonstrated fair agreement in average keratometry values (95% LoA range > 1 D). However, it was poorer for group 2 (95% LOA range > 3 D). In group 1 Bonferroni test revealed statistically significant difference in average K readings among (Topcon autokeratorefractometer 8900 and Tomey OA-2000 biometry, p < 0.01), and between (Tomey topography and Topcon autokeratorefractometer, p < 0.05). Also in group 2 significant difference was observed in the average keratometry of the most instruments (p < 0.01) except for the (Tomey topography and Topcon autokeratorefractometer) and (Tomey topography and Tomey OA-2000 biometry.

CONCLUSIONS

According to our investigation in mild, moderate and severe keratoconus the agreement in K reading between Topcon autokeratorefractometer, OA-2000 optical biometry, Sirius topography and Tomey topography was poor. The agreement declines especially in the steep meridian and it was not acceptable clinically. These devices should not be applied interchangeably.

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.

Correction of Asymmetric Bowtie Corneal Astigmatism with a Toric Intraocular Lens: Outcomes and Accuracy of Measurement Modes

The outcomes of toric intraocular lens (IOL) implantation in correcting asymmetric bowtie corneal astigmatism remain uncertain. The accurate measurement of corneal astigmatism is essential for surgical planning. In this prospective cohort study, patients with asymmetric or symmetric bowtie corneal astigmatism who underwent toric IOL implantation were recruited. Preoperative corneal astigmatism was measured with an IOLMaster and Pentacam (including the simulated keratometry (SimK), total corneal refractive power (TCRP), and wavefront aberration (WFA) modes). At 3 months after surgery, the refractive outcomes and residual astigmatic refractive errors were compared with patients with symmetric bowtie astigmatism. The prediction errors (the differences between the calculated actual corneal astigmatism and the measured corneal astigmatism) were compared among the different measurement modes in the asymmetric group. There were no differences in residual astigmatism between the asymmetric and symmetric groups. However, the mean absolute residual astigmatic refractive error was greater in the asymmetric group than in the symmetric group (0.72 ± 0.42 D vs. 0.53 ± 0.24 D, p = 0.043). In the asymmetric group, the mean absolute prediction errors for the IOLMaster, SimK, TCRP and WFA modes were 0.53 ± 0.40, 0.56 ± 0.47, 0.68 ± 0.52, and 0.43 ± 0.40 D, respectively. The Pentacam WFA mode was the most accurate mode (p < 0.05). The absolute prediction error of the WFA mode was positively correlated with the total corneal irregular astigmatism higher-order aberrations and coma (r = 0.416 and r = 0.473, respectively; both p < 0.05). Our study suggests toric IOL implantation effectively corrected asymmetric bowtie corneal astigmatism. The Pentacam WFA mode may be the most accurate measurement mode, although its accuracy decreased as asymmetry increased.

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.

Two-stage treatment of ametropia in patients with keratoconus and cataracts

Keratoconus (KC) is a progressive degenerative corneal disease, leads to the aberration of biomechanical and optical properties and thinning of the cornea, causes astigmatism and decreases visual acuity.Materials and methods. 33 patients (35 eyes) with stages II–III of non-progressive keratoconus and concomitant cataracts of various stages of maturity were operated on. The average age of the patients was 46.5 ± 2.7 (41–63) years old. The operations were performed according to our proposed two-stage method of treating ametropia in patients with KC and cataracts (Patent of the Russian Federation No. 2748634 of 28.05.2021). The first stage was the implantation of FERRARA intrastromal corneal ring segments (ICRS) with thickness from 150 to 350 μm. To correct residual refractive error in 5–7 months after stage 1, patients underwent stage 2: cloudy lens was removed and replaced with toric posterior chamber intraocular lens (TIOL) – AcrySof IQ Toric (Alcon, USA), T-fl ex Toric RayOne (Rayner, UK).Results and discussion. After stage 1 of the operation (ICRS implantation), the uncorrected visual acuity (NCVA) was 0.2 ± 0.03, the best corrected visual acuity (BCVA) was 0.4 ± 0.02. In 1 month after stage 2 (phacoemulsifi cation + TIOL) NCVA was 0.64 ± 0.11 and BCVA was 0.74 ± 0.12. During the entire follow-up period after the surgery visual functions, refraction, and rotational stability of TIOL were stable.Conclusions. Conducting a two-stage surgical intervention in patients with keratoconus and cataracts allows to stop the progression of the disease and effectively correct the ametropia concomitant with keratoconus.

Comparison of Four Intraocular Power Calculation Formulas in Keratoconus Eyes

Introduction:

This study aimed to evaluate the differences in Intraocular Lens (IOL) power in keratoconus (KC) eyes between calculations obtained clinically with the most commonly used formulas in healthy eyes (SRK T, Holladay 1, Hoffer Q and Haigis) as well as to define predictive factors for such differences.

Methods:

This retrospective study comprised 43 keratoconus eyes of 22 patients with no previous ocular surgery. IOL powers were calculated with SRK T, Holladay 1, Hoffer Q, and Haigis formulas, considering the Effective Lens Position (ELP) of each formula and the desired refraction of 0 D (Rdes=0 D).

Results:

All differences between formulas were statistically significant and clinically relevant. Haigis formula always provided higher values compared to the rest of the formulas, with the highest differences observed when comparing Haigis with Hoffer (0.84 D) and Hoffer Q (1.17 D) formulas. The lowest difference was obtained for the comparison between SRK-T and Holladay 1 formulas (0.22 D). Differences of the Haigis formula compared to the rest were higher as the magnitude of the IOL power calculated decreased, becoming the patient more myopic. Increased differences between Haigis and Hoffer formulas were observed in eyes with deep anterior chambers, steeper anterior and posterior corneal surfaces, and high axial lengths.

Conclusion:

The most comparable results in IOL power in keratoconus are provided by the Holladay 1 and SRK T formulas, whereas the Haigis formula provides the most discrepant outcome. The consideration of the curvature of the second corneal surface in IOL power calculations in keratoconus may decrease the variability between calculation methods. However, other factors as anterior chamber depth or axial length are also relevant.

Lamellar Keratoplasty for Advanced Keratoconus

Ectatic corneal diseases are a group of disorders resulting in progressive corneal steepening and thinning. Keratoconus, keratoglobus, pellucid marginal degeneration, post-keratorefractive ectasia, and corneal graft ectasia are the types of corneal ectasia. Early diagnosis with appropriate diagnostic tools can help prevent progression, eliminating the need for corneal transplantation. Lamellar or full thickness corneal transplantation are the treatment options for advanced diseases. Although the visual outcomes of penetrating keratoplasty are comparable to anterior lamellar keratoplasty (ALK) especially in keratoconus, ALK is the preferred treatment of choice considering benefits including reduced graft rejection, less long-term complications, and better graft survival. This article reviews the various surgical techniques in ALK with its clinical outcomes in advanced keratoconus.

[Intraocular correction of ametropia in patients with keratoconus]

This review was conducted due to the growing number of patients with keratoconus requiring cataract surgery and the complexity of surgical planning. The article reviews preoperative planning, intraoperative options, and postoperative management, which can help obtain high functional results. Treatment of cataracts in keratoconic eyes requires a multifaceted approach. In some cases, in the preoperative period, interventions such as crosslinking and implantation of intrastromal segments or corneal ring may be required to ensure stable keratometry values for accurate intraocular lens (IOL) calculations. The use of stabilizing procedures prior to optical biometrics can assist in preoperative lens selection and provide predictable surgical outcomes. To achieve targeted refraction and reduce unwanted optical effects, it is necessary to take a critical approach when choosing the type of lens (toric, monofocal). This is due to the appearance of aberrations of different order after preliminary surgical interventions on the cornea. The intraoperative decision plays important role in choosing the position of the corneal incisions, how to use sutures for wound adaptation, choosing scleral approaches to minimize possible postoperative complications. In the postoperative period, the degree of irregular astigmatism and the need for rigid gas-permeable or scleral lenses should be assessed.

An innovative approach for determining the customized refractive index of ectatic corneas in cataractous patients

The aim of this study is to determine the customized refractive index of ectatic corneas and also propose a method for determining the corneal and IOL power in these eyes. Seven eyes with moderate and severe corneal ectatic disorders, which had been under cataract surgery, were included. At least three months after cataract surgery, axial length, cornea, IOL thickness and the distance between IOL from cornea, and aberrometry were measured. All the measured points of the posterior and anterior parts of the cornea converted to points cloud and surface by using the MATLAB and Solidworks software. The implanted IOLs were designed by Zemax software. The ray tracing analysis was performed on the customized eye models, and the corneal refractive index was determined by minimizing the difference between the measured aberrations from the device and resulted aberrations from the simulation. Then, by the use of preoperative corneal images, corneal power was calculated by considering the anterior and posterior parts of the cornea and refractive index of 1.376 and the customized corneal refractive index in different regions and finally it was entered into the IOL power calculation formulas. The corneal power in the 4 mm region and the Barrett formula resulted the prediction error of six eyes within ± 1 diopter. It seems that using the total corneal power along with the Barrett formula can prevent postoperative hyperopic shift, especially in eyes with advanced ectatic disorders.

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.

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.

Intracorneal ring segments followed by toric pseudoaccomodating IOL for treatment of patients with corneal ectasia and cataract

Purpose

Surgical management of keratoconus aims to improve corneal curvature, prevent progression of corneal ectasia, and manage refractive error. In older individuals with concurrent cataracts, management can be challenging due to topographic irregularity and difficult-to-interpret IOL calculations. We describe a sequential combination of two surgical techniques—intrastromal corneal ring segments (e.g. intacs) insertion and toric pseudoaccomodating lens implantation—to successfully manage concurrent keratoconus and cataracts.

Observations

In this case series, we present three eyes with corneal ectasia in two cataractous patients successfully managed by (1) Intacs placement to normalize corneal contour/asymmetry and enable more regular keratometry measurements, followed by (2) correction of astigmatism and presbyopia by placement of toric pseudoaccommodating IOL (Trulign) after cataract extraction.

Conclusions and Importance

This is the first description, to the authors’ knowledge, of the use of intraocorneal ring segments + toric pseudoaccommodating intraocular lenses for the management of concurrent keratoconus, cataract, and presbyopia.

Intraocular lens power calculation in eyes with keratoconus

The purpose was to review and document the methods used to calculate the power of the intraocular lens (IOL) to be implanted in cataract surgery in the specific scenario of eyes with keratoconus. This review included all scientific articles published in English that focused on the parameters and formulas used to calculate the power of the IOL to be implanted in eyes with keratoconus undergoing cataract surgery. There are few publications that show in detail how IOL power is calculated in these particular cases. If the keratometric value used was based on the standard refractive index (1.3375), it resulted in a postoperative refractive error with a tendency to hyperopia. The SRK/T formula yielded the best outcomes. The greater the severity of keratoconus the greater was the deviation of the postoperative refractive status from the target outcome.

Management of cataract in keratoconus: early visual outcomes of different treatment modalities

A review of 31 eyes with keratoconus who developed cataract and underwent phacoemulsification. Visual acuities were measured 1mo postoperatively. Six eyes with a history of good corrected distance visual acuity (CDVA) and a similar refractive and topographic astigmatic axis were implanted with toric intraocular lenses (IOLs). The mean postoperative uncorrected distance visual acuity (UDVA) was 0.2 logMAR with a spherical equivalent (SE): 0.75D. Eleven eyes with a history of good CDVA and different refractive and topographic axis were implanted with monofocal IOL+/-Toric implantable collamer lenses to treat anisometropia and ametropia; mean UDVA was 0.25 logMAR with a mean SE: -0.51 D postoperatively. Six eyes with poor CDVA were first treated with intra-corneal ring segments, followed by phacoemulsification, the mean postoperative UDVA was 0.82 logMAR with an SE: 0.22 D. Eight eyes had advanced ectesia and received combined phacoemulsification and penetrating keratoplasty. Our approach is efficient in addressing ametropia after cataract surgery in keratoconic eyes.

Current Trends in Modern Visual Intraocular Lens Enhancement Surgery in Stable Keratoconus: A Synopsis of Do's, Don'ts and Pitfalls

Keratoconus is a relatively common ectatic, non-inflammatory corneal disorder that involves gradual visual deterioration through progressive alteration of the shape of the cornea. The corneal thinning, irregular astigmatism and higher order aberrations that occur as the disease progresses pose major challenges in the visual rehabilitation of such patients. This paper summarizes the current literature regarding the results of visual enhancement procedures in patients with stable keratoconus treated with standalone anterior or posterior chamber phakic intraocular lens implantation and monofocal, toric or multifocal toric intraocular lens implantation following phacoemulsification for age-related cataract extraction or refractive lens exchange.

Intraocular lens power calculation in keratoconus; A review of literature

Purpose

To review the published literature regarding cataract surgery in keratoconus (KCN) patients with emphasis on challenges encountered during intraocular lens (IOL) power calculation and their solutions.

Methods

A literature review was performed to investigate all the relevant articles on the advancements of IOL calculations in KCN patients.

Results

Cataract surgery in keratoconic eyes can improve patients' refraction, and proper patient selection and IOL calculation methods are necessary to get the best results. The main problem in KCN patients is unreliable biometric measurements. It is more difficult to make conclusions in more advanced keratoconic corneas, as the steep keratometric values in these eyes will result in the selection of a low-power IOL. Presence of a low-power IOL will yield in extreme postoperative hyperopia, and IOL exchange might be mandatory. In cases in which keratoplasty may be needed in the future, contact lens fitting can help surgeons make a better decision preoperatively. Axial length (AL) measurements may have better repeatability and reproducibility than keratometry (K) readings in keratoconic eyes. SRK II formula may provide the most accurate IOL power in mild KCN. There is still not a comprehensive consensus of which formula is the best one in moderate and severe KCN, as the literature is limited in this subject.

Conclusions

Various methods of IOL power calculation optimization and recommendations may hold the key to improve surgical outcomes in keratoconic eyes. There are multiple sources of biometric error in KCN patients, hence IOL calculation methods may not be as efficient as expected in these eyes.

Preoperative evaluation for cataract surgery

PURPOSE OF REVIEW

To provide a consolidated update regarding preoperative evaluation for cataract surgery.

RECENT FINDINGS

Visual acuity alone is a poor gauge of cataract disability. Modalities such as wave front aberrometry, lens densitometry, and light-scatter assessments can quantify optical aspects of cataract and may prove clinically useful in surgical evaluation. Advances in biometry are driving improvements in refractive outcomes, which in turn have increased patient expectations. Future advances in biometry technology may include three-dimensional imaging of the cornea and lens. Screening for ocular comorbidities has become increasingly important, particularly to guide lens selection. Risk stratification systems can help guide surgical decisions and may decrease intraoperative complication rate. A comprehensive medical history and physical is currently mandated for all Medicare patients undergoing cataract surgery but may be of limited utility for low-risk patients.

SUMMARY

Rising patient expectations and a growing number of surgical choices have expanded the cataract preoperative evaluation. A systematic and comprehensive examination which includes identifying any ocular comorbidity is essential for surgical planning and counseling on visual prognosis. New technologies will continue to inform, but not replace, sound clinical judgment.

Two-stage procedure in the management of selected cases of keratoconus: clear lens extraction with aspherical IOL implantation followed by WFG-PRK

AIM

To assess the objective and subjective results of a two-stage procedure for management of keratoconus: clear lensectomy with aspherical intraocular lens (IOL) implantation followed by wave front-guided photorefractive keratotomy (WFG-PRK).

METHODS

This prospective interventional non-randomized study included patients aged 35 years old or more with grade I and II stable keratoconus, a clear visual axis, minimal corneal thickness (MCT) 420 µm or more and average keratometric reading (K) less than 54 diopter (D). Refraction of all selected eyes should be -8.00 D sphere or more with less than -6.00 D cylinder and could be corrected two lines or more with spectacles or contact lenses. All studied eyes underwent a two-stage approach treatment: first refractive lens exchange and aspherical IOL implantation followed, after at least 3mo, by WFG-PRK. Pre and postoperative complete ophthalmological examination were performed. Topographical, visual and aberrometric results were recorded and evaluated during 6mo follow up period. Moreover, patient satisfaction and other subjective outcomes were also analyzed.

RESULTS

The 13 eyes of 11 patients diagnosed with stable keratoconus and aged from 39 to 49y (42.4±6.2y) were enrolled in the study. At baseline, 8 eyes had grade I and 5 eyes had grade II keratoconus. The manifest sphere was -10.3±4.2 D (ranged from -8.0 to -14.0 D) and the manifest cylinder was -4.2±1.2 D (ranged from -1.75 to -5.50 D). After the two-stage procedure, sphere and cylinder reduced significantly to -0.43±0.22 D and -1.3±0.72 D respectively (P<0.001). There was also a highly significant improvement in the mean uncorrected distance visual acuity (UDVA) from logMAR 1.41±0.49 preoperatively to 0.51±0.16 postoperatively (P<0.001) and the mean corrected distance visual acuity (CDVA) from 0.76±0.24 preoperatively to 0.49±0.13 after the operation (P<0.001). All aberrometric and mesopic vision parameters and most of the topographical indices demonstrated highly significant improvement that remains stable until the end of follow up. All recorded subjective data revealed a high degree of patient satisfaction.

CONCLUSION

Two-stage approach (clear lens exchange with monofocal IOL followed by WFG-PRK) in selected cases of keratoconus is a safe, effective and highly predictable procedure with satisfactory visual and refractive results.