An Advanced Lens Measurement Approach (ALMA) in post refractive surgery IOL power calculation with unknown preoperative parameters

Lens Factor Choice in IOL Power Calculation after Laser Refractive Surgery: The Right Constant for Advanced Lens Measurement Approach (ALMA)

Background/Objectives: To evaluate the advanced lens measurement approach (ALMA) formula accuracy using different lens constants available on the user group for laser interference biometry (ULIB) and IOL Con platforms. Methods: In this retrospective, comparative, case-series study, 150 eyes of 160 patients with previous myopic Photorefractive Keratectomy (PRK) or laser-assisted in situ keratomileusis (LASIK), who underwent uneventful cataract surgery and IOL implantation, were examined. The ALMA formula was evaluated to calculate the refractive prediction error (PE), analysing four different categories of lens constants: both nominal and optimized A-Constant for SRKT, which are available on the ULIB and IOL Con platforms. An additional analysis was carried out in this study, evaluating if a decreased ULIB optimized constant (DUOC) with different fixed factors (-1.2 -1.3 -1.4 -1.5) could improve refractive outcomes. Median absolute error (MedAE) and percentage of eyes within ±0.50 and ±1.00 diopters (D) of prediction error were measured as the main outcomes. Results: Comparing the lens factors available on ULIB and IOL Con platforms, the ALMA formula reported a lower MedAE and higher percentages of eyes with a refractive PE within 1.0 D using ULIB nominal constants (all p < 0.05). Using DUOC (-1.3), and there was a statistically significant improvement of both MedAE and of the percentages of eyes with PE within ±0.50 D with the ALMA method compared to nominal ULIB constants (all p < 0.05). Conclusions: The impact of different lens factors in the IOL power calculation after myopic LRS should be carefully evaluated. The ALMA formula, in the absence of optimized constants by zeroing the mean error, should be used by subtracting 1.3 from the optimized ULIB constants available on the IOL Con website. This finding suggests further studies to test which of these constants could work better with the other post-refractive surgery formulas.

The Development of a Thick-Lens Post-Myopic Laser Vision Correction Intraocular Lens Calculation Formula

PURPOSE

To describe the development of the post-myopic laser vision correction (LVC) version of the PEARL-DGS intraocular lens (IOL) calculation formula and to evaluate its outcomes on an independent test set.

DESIGN

Retrospective, single-center case series.

METHODS

A modified lens position prediction algorithm was designed along with methods to predict the posterior corneal curvature radius and correct the corneal power measurement error. A different set of previously operated eyes that underwent LVC was used to evaluate the prediction precision of the post-LVC formula.

RESULTS

Post-LVC PEARL-DGS formula significantly reduced mean absolute error of prediction in comparison to Haigis-L, Shammas, and American Society of Cataract and Refractive Surgery (ASCRS) average formulas (P < .001). It exhibited similar postoperative refractive precision as the Barrett True-K No History formula (P = .61).

CONCLUSION

The post-LVC formula development process described in this article performed as well as the state-of-the-art post-LVC formula on the present test set. Further studies are required to assess its efficacy in other independent sets.

Intraocular Lens Power Calculation Formulas-A Systematic Review

PURPOSE

The proper choice of an intraocular lens (IOL) power calculation formula is an important aspect of phacoemulsification. In this study, the formulas most commonly used today are described and their accuracy is evaluated.

METHODS

This review includes papers evaluating the accuracy of IOL power calculation formulas published during the period from January 2015 to December 2022. The articles were identified by a literature search of medical and other databases (PubMed/MEDLINE, Crossref, Web of Science, SciELO, Google Scholar, and Cochrane Library) using the terms "IOL formulas," "Barrett Universal II," "Kane," "Hill-RBF," "Olsen," "PEARL-DGS," "EVO," "Haigis," "SRK/T," and "Hoffer Q." Twenty-nine of the most recent peer-reviewed papers in English with the largest samples and largest number of formulas compared were considered.

RESULTS

Outcomes of mean absolute error and percentage of predictions within ±0.5 D and ±1.0 D were used to evaluate the accuracy of the formulas. In most studies, Barrett achieved the smallest mean absolute error and PEARL-DGS the highest percentage of patients with ±0.5 D in short eyes, while Kane obtained the highest percentage of patients with ±0.5 D in long eyes.

CONCLUSIONS

The third- and fourth-generation formulas are gradually being replaced by more accurate ones. The Barrett Universal II among vergence formulas and Kane and PEARL-DGS among artificial intelligence-based formulas are currently most often reported as the most precise.

Evaluation of Tropicamide-Phenylephrine Mydriatic Eye Drop Instillation on Choroidal Thickness

The purpose of this study is to evaluate choroidal thickness (ChT) at the subfoveal and peripheral level after the instillation of 0.5% tropicamide + 10% phenylephrine 9 hydrochloride eye drops by using OCT scans in enhanced depth image (EDI) mode. In total, 53 patients (30 males and 23 females) were involved, and the mean age was 25.62 ± 2.41 (age range: 23-36). The dominant eye was treated with tropicamide + phenylephrine (Visumidriatic Fenil 100 mg/mL + 5 mg/mL, Visufarma) while the nondominant eye was used as the control. An OCT analysis was performed on both eyes before and 30 min after the instillation of a drop of mydriatic in the dominant eye. The ChT was measured by using the OCT software measurement tool (Spectralis; Heidelberg Engineering; Heidelberg, Germany, version 6.0). The results showed a statistically significant ChT decrease (p = 0.009) in the temporal sector after the treatment with tropicamide + phenylephrine. In the subfoveal and nasal sectors, no statistically significant ChT changes were detected (p = 0.94; p = 0.85) following the administration of the mydriatic eye drops. The ChT thinning in the temporal sector following the instillation of the tropicamide + phenylephrine eye drops suggests that in the case of ChT studies, mydriatic administration should be avoided.

Challenges of refractive cataract surgery in the era of myopia epidemic: a mini-review

Myopia is the leading cause of visual impairment in the world. With ever-increasing prevalence in these years, it creates an alarming global epidemic. In addition to the difficulty in seeing distant objects, myopia also increases the risk of cataract and advances its onset, greatly affecting the productivity of myopes of working age. Cataract management in myopic eyes, especially highly myopic eyes is originally more complicated than that in normal eyes, whereas the growing population of cataract with myopia, increasing popularity of corneal and lens based refractive surgery, and rising demand for spectacle independence after cataract surgery all further pose unprecedented challenges to ophthalmologists. Previous history of corneal refractive surgery and existence of implantable collamer lens will both affect the accuracy of biometry including measurement of corneal curvature and axial length before cataract surgery, which may result in larger intraocular lens (IOL) power prediction errors and a compromise in the surgical outcome especially in a refractive cataract surgery. A prudent choice of formula for cataract patients with different characteristics is essential in improving this condition. Besides, the characteristics of myopic eyes might affect the long-term stability of IOL, which is important for the maintenance of visual outcomes especially after the implantation of premium IOLs, thus a proper selection of IOL accordingly is crucial. In this mini-review, we provide an overview of the impact of myopia epidemic on treatment for cataract and to discuss new challenges that surgeons may encounter in the foreseeable future when planning refractive cataract surgery for myopic patients.

Comparing the Accuracy of the Kane, Barrett Universal II, Hill-Radial Basis Function, Emmetropia Verifying Optical, and Ladas Super Formula Intraocular Lens Power Calculation Formulas

Purpose

To assess the accuracy of five new-generation intraocular lens (IOL) power formulas: Barrett Universal II (BUII), Emmetropia Verifying Optical (EVO) Formula, Hill-Radial Basis Function (Hill-RBF), Kane Formula, and Ladas Super Formula (LSF).

Patients and Methods

This is a retrospective single-surgeon study from a refractive clinic and clinical research center in Draper, UT, USA. The primary outcome measures were mean absolute error (MAE) and median absolute error (MedAE). Secondary outcome measures were the standard deviation (SD) of each formula's refractive prediction errors (RPE) and the percentage of eyes within ±0.50D. Refractive predictions were compared to the postoperative spherical equivalent to determine the RPE for each formula. RPEs were optimized, and MAE, MedAE, SD of the AME, and percent of eyes achieving RPEs within the specified ranges of ±0.125 D, ±0.25 D, ±0.50 D, ±0.75 D, ±1.0 D were calculated. Subgroup analysis between different axial lengths was attempted but yielded insufficient statistical power to draw meaningful conclusions.

Results

A total of 103 eyes of 103 patients were included in our study after applying inclusion and exclusion criteria to 606 eyes from 2019 to 2021. Formulas ranked in ascending order by MAE were Kane, EVO, BUII, Hill-RBF, and LSF. The ascending rankings of MedAE were Kane, BUII, Hill-RBF, EVO, Ladas. Kane had a significantly lower MAE than Hill-RBF (p<0.001). EVO had the lowest SD of AMEs and the highest percentage of eyes within ±0.50 D. According to heteroscedastic testing, EVO also had a statistically significant lower SD than Hill-RBF.

Conclusion

Kane was the most accurate formula in terms of MAE and MedAE. EVO and BUII achieved marginally higher MAEs than Kane, suggesting these three formulas are comparable in performance. With the exception EVO and Hill-RBF, the heteroscedastic test yielded no significant differences in SD between the formulas. Although there were multiple statistically significant differences between the formulas in terms of MAE, MedAE, and SD, these differences may not be appreciable clinically. Lastly, there were no statistically significant differences in the percent of eyes with RPEs within ±0.50 D, suggesting similar clinical performance between formulas.

Bibliometric and visualized analysis of myopic corneal refractive surgery research: from 1979 to 2022

Background

Myopic corneal refractive surgery is one of the most prevalent ophthalmic procedures for correcting ametropia. This study aimed to perform a bibliometric analysis of research in the field of corneal refractive surgery over the past 40 years in order to describe the current international status and to identify most influential factors, while highlighting research hotspots.

Methods

A bibliometric analysis based on the Web of Science Core Collection (WoSCC) was used to analyze the publication trends in research related to myopic corneal refractive surgery. VOSviewer v.1.6.10 was used to construct the knowledge map in order to visualize the publications, distribution of countries, international collaborations, author productivity, source journals, cited references, keywords, and research hotspots in this field.

Results

A total of 4,680 publications on myopic corneal refractive surgery published between 1979 and 2022 were retrieved. The United States has published the most papers, with Emory University contributing to the most citations. The Journal of Cataract and Refractive Surgery published the greatest number of articles, and the top 10 cited references mainly focused on outcomes and wound healing in refractive surgery. Previous research emphasized "radial keratotomy (RK)" and excimer laser-associated operation methods. The keywords containing femtosecond (FS) laser associated with "small incision lenticule extraction (SMILE)" and its "safety" had higher burst strength, indicating a shift of operation methods and coinciding with the global trends in refractive surgery. The document citation network was clustered into five groups: (1) outcomes of refractive surgery: (2) preoperative examinations for refractive surgery were as follows: (3) complications of myopic corneal refractive surgery; (4) corneal wound healing and cytobiology research related to photorefractive laser keratotomy; and (5) biomechanics of myopic corneal refractive surgery.

Conclusion

The bibliometric analysis in this study may provide scholars with valuable to information and help them better understand the global trends in myopic corneal refractive surgery research frontiers. Two stages of rapid development occurred around 1991 and 2013, shortly after the innovation of PRK and SMILE surgical techniques. The most cited articles mainly focused on corneal wound healing, clinical outcomes, ocular aberration, corneal ectasia, and corneal topography, representing the safety of the new techniques.

Choroidal involvement in mediterranean fever

Standardized measurements are needed to obtain reliable data, therefore the aim of this letter is to clarify some points.

A No-History Multi-Formula Approach to Improve the IOL Power Calculation after Laser Refractive Surgery: Preliminary Results

This retrospective comparative study proposes a multi-formula approach by comparing no-history IOL power calculation methods after myopic laser-refractive-surgery (LRS). One-hundred-thirty-two eyes of 132 patients who had myopic-LRS and cataract surgery were examined. ALMA, Barrett True-K (TK), Ferrara, Jin, Kim, Latkany and Shammas methods were evaluated in order to back-calculate refractive prediction error (PE). To eliminate any systematic error, constant optimization through zeroing-out the mean error (ME) was performed for each formula. Median absolute error (MedAE) and percentage of eyes within ±0.50 and ±1.00 diopters (D) of PE were analyzed. PEs were plotted with corresponding mean keratometry (K), axial length (AL), and AL/K ratio; then, different ranges were evaluated. With optimized constants through zeroing-out ME (90 eyes), ALMA was better when K ≤ 38.00 D-AL > 28.00 mm and when 38.00 D < K ≤ 40.00 D-26.50 mm < AL ≤ 29.50 mm; Barrett-TK was better when K ≤ 38.00 D-AL ≤ 26.50 mm and when K > 40.00 D-AL ≤ 28.00 mm or AL > 29.50 mm; and both ALMA and Barrett-TK were better in other ranges. (p < 0.05) Without modified constants (132 eyes), ALMA was better when K > 38.00 D-AL ≤ 29.50 mm and when 36.00 < K ≤ 38.00 D-AL ≤ 26.50 mm; Barrett-TK was better when K ≤ 36.00 D and when K ≤ 38.00 D with AL > 29.50 mm; and both ALMA and Barrett-TK were better in other ranges (p < 0.05). A multi-formula approach, according to different ranges of K and AL, could improve refractive outcomes in post-myopic-LRS eyes.

Impact of Total Corneal Astigmatism Estimated With the Abulafia-Koch Formula Versus Measured With a SS-OCT Biometer on the Refractive Outcomes of a Toric Intraocular Lens in Cataract Surgery

PURPOSE

To compare the impact of total corneal astigmatism (TCA) estimated with the Abulafia-Koch formula (TCA^ABU) versus measured by Total Keratometry (TK), swept-source optical coherence tomography (OCT) coupled with telecentric keratometry (TCA^TK) on the refractive outcomes after cataract surgery with toric intraocular lens (IOL) implantation.

METHODS

Two hundred one eyes of 146 patients who underwent cataract surgery with toric IOL implantation (XY1AT; HOYA Corporation) were included in this single-center, retrospective study. For each eye, TCA^ABU (estimated from the anterior keratometry values measured with the IOLMaster 700 [Carl Zeiss Meditec AG]) and TCA^TK (measured using TK IOLMaster 700) were entered into the HOYA Toric Calculator. Patients were operated on based on TCA^ABU. For each eye, centroid and mean absolute error in predicted residual astigmatism (EPA) were calculated according to TCA used (TCA^ABU or TCA^TK). The cylinder power and the axis of the posterior chamber IOL were compared.

RESULTS

The mean uncorrected distance visual acuity was 0.07 ± 0.12 logMAR, the mean spherical equivalent was 0.11 ± 0.40 D, and mean residual astigmatism was 0.35 ± 0.36 D. Mean centroid EPA was 0.28 D at 132° with TCA^ABU and 0.35 D at 148° with TCA^TK (P(x) < .001; P(y) < .01). Mean absolute EPA was 0.46 ± 0.32 D with TCA^ABU and 0.50 ± 0.37 D with TCA^TK (P < .01). In the with-the-rule astigmatism subgroup, a deviation from the target of less than 0.50 D was achieved in 68% of eyes with TCA^ABU versus 50% of eyes with TCA^TK. The proposed posterior chamber IOL was different depending on the calculation methods used in 86% of cases.

CONCLUSIONS

Both calculation methods showed excellent results. However, the predictability error was significantly reduced when TCA^ABU was used compared to TCA^TK measured with the IOLMaster 700 in the whole cohort. Finally, TCA was overestimated by TK in the with-the-rule astigmatism subgroup. [J Refract Surg. 2023;39(3):171-179.].

Agreement between a new optical low coherence reflectometry biometer and an anterior segment optical coherence tomographer

BACKGROUND

To assess agreement of measurements between a new optical low coherence reflectometry (OLCR) biometer (SW-9000, Suoer, Tianjin, China) and a spectral-domain optical coherence tomographer (SD-OCT)/Placido topographer (MS-39, CSO, Florence, Italy) in healthy subjects.

METHODS

A total of 66 right eyes from 66 healthy subjects were enrolled in this prospective study. Three consecutive measurements were randomly obtained with both devices by the same experienced operator to assess agreement. Bland-Altman plots and 95% limits of agreement (LoA) were used to verify the agreement between the devices. Results are presented as mean ± standard deviation (SD).

RESULTS

The SD-OCT/Placido tomographer showed high agreement with the OLCR biometer for all parameters included in this study. The mean differences of central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AQD), mean keratometry (Km) and corneal diameter (CD) were 2.21 ± 2.67 μm (P < 0.001), - 0.10 ± 0.03 mm (P < 0.001), - 0.10 ± 0.04 mm (P < 0.001), - 0.01 ± 0.22 D (P = 0.773) and 0.20 ± 0.16 mm (P < 0.001), respectively. This implies that the inter-device difference in Km was not statistically significant, while the differences in CCT, ACD, AQD, CD were statistically but not clinically significant. The 95% LoAs of CCT, ACD, AQD, Km and CD were - 3.01 to 7.44 μm, - 0.16 to - 0.05 mm, - 0.18 to - 0.03 mm, - 0.45 to 0.43 D, and - 0.12 to 0.51 mm, respectively.

CONCLUSIONS

For CCT, ACD, AQD, Km, and CD in healthy subjects, the new OLCR biometer has high agreement with the SD-OCT/Placido tomographer and can be used interchangeably due to the narrow range of 95% LoAs.

Application of total keratometry in ten intraocular lens power calculation formulas in highly myopic eyes

Background

The accuracy of using total keratometry (TK) value in recent IOL power calculation formulas in highly myopic eyes remained unknown.

Methods

Highly myopic patients who underwent uneventful cataract surgery were prospectively enrolled in this prospective comparative study. At one month postoperatively, standard deviation (SD) of the prediction errors (PEs), mean and median absolute error (MedAE) of 103 highly myopic eyes were back-calculated and compared among ten formulas, including XGboost, RBF 3.0, Kane, Barrett Universal II, Emmetropia Verifying Optical 2.0, Cooke K6, Haigis, SRK/T, and Wang-Koch modifications of Haigis and SRK/T formulas, using either TK or standard keratometry (K) value.

Results

In highly myopic eyes, despite good agreement between TK and K (P > 0.05), larger differences between the two were associated with smaller central corneal thickness (P < 0.05). As to the refractive errors, TK method showed no differences compared to K method. The XGBoost, RBF 3.0 and Kane ranked top three when considering SDs of PEs. Using TK value, the XGboost calculator was comparable with the RBF 3.0 formula (P > 0.05), which both presented smaller MedAEs than others (all P < 0.05). As for the percentage of eyes within ± 0.50 D or ± 0.75 D of PE, the XGBoost TK showed comparable percentages with the RBF 3.0 TK formula (74.76% vs. 66.99%, or 90.29% vs. 87.38%, P > 0.05), and statistically larger percentages than the other eight formulas (P < 0.05).

Conclusions

Highly myopic eyes with thinner corneas tend to have larger differences between TK and K. The XGboost enhancement calculator and RBF 3.0 formula using TK showed the most promising outcomes in highly myopic eyes.

Unexpected ocular morphological changes after corneal refractive surgery: A review

Corneal refractive surgery (CRS) currently is widely used to correct refractive errors because of its efficacy and reliability. Several studies dealt with the corneal modification induced by this type of surgery, but it is still debated if CRS can induce unexpected changes namely anterior chamber depth (ACD) and axial length (AL). A literature review was performed, including all articles regarding CRS and eye-variations from 1999 to December 2021. Excluding articles about specific systemic conditions (e.g., pregnancy), pathological conditions, post-surgical complications or about only corneal flattening and thinning post CRS, we found nine studies that met the search criteria. We divided the found articles according to the type of surgery performed (radial keratotomy, PRK/LASEK, lasik) and analyzed the results about ACD and AL. Finally, according to the literature, we can conclude that CRS not only gives a corneal flattening, thinning and biomechanical changes, but also induces AL and ACD decrease. This makes the AL and ACD measurements obtained before CRS uselessness in case of IOL power calculation.

Comparison between dynamic contour tonometry and Goldmann applanation tonometry correcting equations

In order to investigate the reliability of correcting GAT formulas in comparison with dynamic contour tonometry (DCT), this study included 112 right eyes of 112 healthy subjects aged from 21 to 77 years, whose eyes underwent to a full ophthalmologic exam. IOP was measured in each eye with DCT and then with GAT. IOP values obtained with GAT were corrected with 10 equations and then compared with those provided by DCT. Participants mean age was 42.24 ± 14.08 years; mean IOP measured with DCT was 17.61 ± 2.87 and 15.50 ± 2.47 mmHg, measured with GAT. The mean discordance between DCT and GAT measurements was 2.11 ± 2.24 mmHg. All the correcting formulas, but Srodka one (p ˂ 0.001), tend to increase the difference between GAT and DCT. According to these results Śródka equation provides the best correction, reducing the difference between the two IOP measurement methods of - 0.03 ± 0.85 mmHg. Other equations do not provide a valid improvement of the agreement between the two methods or they provide a worsening of the agreement.

A formula to improve the reliability of optical axial length measurement in IOL power calculation

To verify the influence of axial length (AL) variations after cataract surgery in IOL power calculation. Patients underwent ophthalmic evaluation before surgery, including optical biometry with IOLMaster 500. Same exams were repeated 2 months after surgery: AL of operated eye was evaluated using two modes (pseudophakic/aphakic options). Mean Keratometry and AL changes were analyzed. Furthermore, refractive prediction error (PE) was back-calculated with Barrett Universal-II, Hoffer-Q, Holladay-1 and SRK/T formulas. To eliminate any systematic error, the mean error (ME) was zeroed-out for each formula. MEs and median absolute errors (MedAEs) of PEs were analyzed. Two-hundred-one operated eyes of 201 patients and 201 opposite eyes were evaluated. In operated eyes, mean AL difference was - 0.11 ± 0.07 mm (p < 0.001) with pseudophakic option and 0.00 ± 0.07 mm (p = 0.922) with aphakic option. There were not-statistically significant differences between MedAE of PEs calculated after zeroing-out the ME with different ALs (p > 0.05). Instead, only MEs of PEs obtained with postoperative ALs-pseudophakic option were not-statistically different from zero (p > 0.05). AL measurement change after cataract surgery is probably due to a systematic error in optical biometer in case of phakic eyes. A correction factor applied to preoperative AL could eliminate any systematic error in IOL power calculation without modifying the lens constant.

Optical Coherence Tomography Analysis of Retinal Layers in Celiac Disease

Celiac disease is an immune-mediated, chronic, inflammatory, and systemic illness which could affect the eye. The aim of this study is to look for possible signs of retinal involvement in celiac disease that could be utilized as biomarkers for this disease. Sixty-six patients with celiac disease and sixty-six sex-matched healthy subjects were enrolled in this observational case–control study. A comprehensive ophthalmological evaluation, axial length measurements, and SD-OCT evaluation were performed. The thickness of the retinal layers at the circle centered on the fovea (1 mm in diameter) and the average of the foveal and parafoveal zones at 2 and 3 mm in diameter were evaluated, together with retinal volume and the peripapillary retinal nerve fiber layer (RNFL). Concerning the thicknesses of the retinal layers in each analyzed region, no statistically significant differences were found. The same results were obtained for the total volume. Regarding peripapillary RNFL, the celiac patients showed slightly thicker values than the healthy controls, except for temporal and nasal-inferior quadrants, with no statistically significant differences. All the analyzed parameters were similar for the celiac patients and the healthy individuals. This could be related either to the non-involvement of the retinal layers in celiac disease pathophysiology or to the gluten-free diet effect.

Recent Evidence of Tea Tree Oil Effectiveness in Blepharitis Treatment

The purpose of our study is to see how beneficial is tea tree oil (TTO) for treating chronic blepharitis topically, with a focus on the Demodex mite. To discover all possibly relevant published papers, an accurate Pubmed database search analysis of the current literature was undertaken from 2012 to December 2021. Fourteen papers dealing with the use of TTO to treat chronic blepharitis have been found. The effectiveness of TTO treatment was tested in vitro by 4 authors and in vivo by 10 authors. All studied confirmed efficacy of TTO treatment, even cyclic, on Demodex mite blepharitis. TTO can be used for lid scrubs, facial cleanser, eyelid patch, eyelid gel, eyelash shampoo or, more commonly, as TTO impregnated eyelid wipes. The scientific evidence of TTO for chronic blepharitis treatment gives a lot of confidence for the progress that this treatment may have in the future clinical practice.

Reply to Cione et al. Comment on "Iida et al. Development of a New Method for Calculating Intraocular Lens Power after Myopic Laser In Situ Keratomileusis by Combining the Anterior-Posterior Ratio of the Corneal Radius of the Curvature with the Double-K Method. J. Clin. Med. 2022, 11, 522"

We appreciate the insightful comments [...].

Conditional Process Analysis for Effective Lens Position According to Preoperative Axial Length

PURPOSE

To predict the effective lens position (ELP) using conditional process analysis according to preoperative axial length.

SETTING

Yeouido St. Mary hospital.

DESIGN

A retrospective case series.

METHODS

This study included 621 eyes from 621 patients who underwent conventional cataract surgery at Yeouido St. Mary Hospital. Preoperative axial length (AL), mean corneal power (K), and anterior chamber depth (ACD) were measured by partial coherence interferometry. AL was used as an independent variable for the prediction of ELP, and 621 eyes were classified into four groups according to AL. Using conditional process analysis, we developed 24 structural equation models, with ACD and K acting as mediator, moderator or not included as variables, and investigated the model that best predicted ELP.

RESULTS

When AL was 23.0 mm or shorter, the predictability for ELP was highest when ACD and K acted as moderating variables (R2 = 0.217). When AL was between 23.0 mm and 24.5 mm or longer than 26.0 mm, the predictability was highest when K acted as a mediating variable and ACD acted as a moderating variable (R2 = 0.217 and R2 = 0.401). On the other hand, when AL ranged from 24.5 mm to 26.0 mm, the model with ACD as a mediating variable and K as a moderating variable was the most accurate (R2 = 0.220).

CONCLUSIONS

The optimal structural equation model for ELP prediction in each group varied according to AL. Conditional process analysis can be an alternative to conventional multiple linear regression analysis in ELP prediction.

Ocular anterior segment and corneal parameters evaluation in celiac disease

This observational case-control study evaluated the anterior ocular segment parameters of patients with celiac disease with a Scheimpflug imaging system and compared them with those of a healthy controls group, highlighting potential differences related to the underlying pathogenetic mechanisms of the disease. Seventy celiac patients and 70 healthy subjects were assessed with a comprehensive ophthalmological evaluation, including clinical history, Snellen best-corrected visual acuity, axial length (AL) measurements with IOLMaster, and anterior segment tomographic evaluation with Pentacam HR. The measurements of all keratometry values, astigmatism, steep axis, anterior and posterior Q value (asphericity), pupil diameter, pupil center, corneal apex, the thinnest point, corneal volume, anterior chamber depth from the epithelium, anterior chamber depth from endothelium, anterior chamber volume, and iridocorneal angle were also appraised. The two study groups were comparable and similar for gender, age, and AL, with no statistically significant differences regarding all analyzed tomographic parameters. Thus, ocular anterior segment parameters of celiac patients are not significantly different from those of healthy subjects, suggesting no underlying pathogenetic implications of celiac disease affecting the assessed structures. Nevertheless, a routine ophthalmological examination for all celiac patients should be recommended throughout their lifetimes due to the potential ocular manifestations of the disease.

Intraocular lens power calculation in eyes with previous corneal refractive surgery

Intraocular lens (IOL) power calculation after corneal refractive surgery (CRS) becomes an expanding challenge for ophthalmologists as more and more cataract surgeries after CRS are required. These patients typically also have high expectations as to visual performance. Conventional IOL power calculation schemes frequently provide inaccurate results in these cases. This review aims to summarize and recommend currently available IOL power calculation methods for eyes with the most common CRS methods: radial keratotomy (RK), photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE). To this end, biometry measuring methods and IOL formulas will be explained and combinations of both are proposed. In synopsis, it is evident that the latest generation of vergence formulas exhibit favorable IOL power prediction accuracy in post-CRS eyes, even though the predictive precision of methods in eyes without CRS is not attained. Ray tracing computation, intraoperative aberrometry, and machine learning–based formulas hold potential to further improve refractive outcomes in post-CRS eyes.

Comparison between two devices in the detection of corneal thickness changes after cataract surgery

This study compared corneal thickness (CT) changes obtained with specular microscopy (SM) and a rotating Scheimpflug camera (RSC) after conventional phacoemulsification surgery (PS). One hundred sixty six eyes of 83 patients were analyzed before and one month after PS. One eye underwent PS, while the fellow phakic one was used as control. CT was measured with SM at the center of the cornea and with RSC at the pupil center, at the corneal apex and at the thinnest point. In the operated eye, SM showed a larger CT mean increase than those one detected at the three different measurements’ points evaluated by RSC. Inversely, in the fellow phakic eye, SM showed a greater CT mean decrease than those one registered by RSC at its three measurement’s points. Thus, one month after surgery, even if cornea appears clear at the slit-lamp, a significant thickness increase is still present. This is even more evident if the slight decrease of the fellow phakic eye is considered. The differences between the two devices are probably related to the different measured areas.

Corneal thickness evaluation in healthy eyes: Comparison between two different Scheimpflug devices

Purpose

To evaluate the correlation between corneal thickness (CT) measurements obtained with two Scheimpflug devices, Pentacam HR and Precisio, and to elaborate, if necessary, a regression formula which could make these results comparable.

Design

Retrospective, Comparative, Observational study.

Setting

Department of Medicine, Surgery and Dentistry, “Scuola Medica Salernitana” University of Salerno, Italy

Methods

One hundred twenty four healthy eyes of 124 volunteers (65 males; range: 20–32 years; mean age of 24.8 ± 1.7) were included in this study. CT was measured using Pentacam HR and Precisio in three different points: the pupil center (PC), the corneal apex (CA) and the thinnest point (TP).

Results

CT obtained with both devices at the PC, at the CA and at the TP showed a good correlation (r = 0.97, r = 0.97, r = 0.97, respectively), but Pentacam HR measurements were significantly thicker than those provided by Precisio (p < 0.01). The differences between Pentacam HR and Precisio were 21.9 ± 8.8 μm at the PC, 21.9 ± 8.9 μm at the CA, 19.1 ± 9.0 μm at the TP. The calculated regression formulas were: y = 0.9558x + 2.3196 for the PC, y = 0.9519x + 4.5626 for the CA, y = 0.9364x + 15.436 for the TP, where x is the CT measured with Pentacam HR and y is the Precisio measurement.

Conclusions

The findings provided by this study highlight that Precisio measures thinner corneas compared to Pentacam HR. The identified regression formulas could be utilized to make interchangeable the results obtained with these two devices.