Flatter Corneas Research Articles

Laser-Assisted In Situ Keratomileusis in Flat, Normal, and Steep Corneas.

To compare laser-assisted in situ keratomileusis (LASIK) outcomes in patients with different corneal curvatures. This is a retrospective comparative chart review. Patients included in this study underwent wavefront-optimized myopic LASIK between January 2013 and December 2022 at Care-Vision Laser Center, Tel-Aviv, Israel. Patients were divided into 3 groups based on the steepness of the cornea (steep keratometry) (flat: <42 diopters [D], normal: 42-46 D, and steep: >46 D). Case-by-case matching was performed to verify that baseline parameters (age, preoperative visual acuity, and refractive error) were similar between groups. Primary outcome measures were postoperative corrected/uncorrected distance visual acuity, efficacy index, safety index, spherical equivalence, and astigmatism. After matching, 300 eyes were included in each group, which were similar in baseline parameters. There were no significant postoperative differences between flat, normal, and steep corneas regarding safety index (1.01 vs. 1.02 vs. 1.01, P = 0.95), efficacy index (1.03 vs. 1.02 vs. 1.02, P = 0.94), logarithm of the minimum angle of resolution corrected distance visual acuity (0.01 vs. 0.01 vs. 0.01, P = 0.17), logarithm of the minimum angle of resolution uncorrected distance visual acuity (0.02 vs. 0.03 vs. 0.02, P = 0.65), proportion of patients with spherical equivalence within 0.50 D (73.0% vs. 73.7% vs. 69.3%, P = 0.45) or 1.00 D (93.3% vs. 94.7% vs. 91.7%, P = 0.34) of the target, and proportion of patients with astigmatism within 0.50 D (86.7% vs. 82.3% vs. 80.3%, P = 0.11) or 1.00 D (98.7% vs. 98.7% vs. 99.0%, P = 0.91) of the target. Longer term follow-up of a smaller set of patients revealed similar results. No significant differences were found between flat, normal, and steep corneas following wavefront-optimized myopic LASIK. Thus, this procedure may be safely and effectively performed across a wide range of corneal curvatures.

Comparison of IOL power formulas in eyes with a flat cornea

PurposeTo assess and compare accuracy of intraocular lens (IOL) power calculation performed with old generation, new generation and artificial intelligence (AI)-based formulas in eyes with flat corneas. DesignPatients with a tomography-derived mean keratometry <42 D were retrospectively recruited among those who underwent uncomplicated phacoemulsification with intracapsular IOL implantation in two different tertiary care centers. Mean prediction error (ME), mean absolute prediction error (MAE) and incidence of MAE>0.25D were calculated for Barrett Universal II (BUII),EVO 2.0, Hoffer QST, Kane, Olsen-C, Pearl-DGS and SRK/T formulas. Linear correlation between MAE and axial length was also calculated for each formula. ResultsEighty (80) eyes with a mean keratometry of 41.4 ± 0.6 D (range 40.6–41.9 D) were recruited. The SRK/T significantly differed from both the Olsen-C (p = 0.022) and the BUII (p = 0.048) in ME. The EVO 2.0, the Hoffer QST, the Kane and the PEARL-DGS showed a significantly lower MAE compared to all other formulas (p < 0.001) and a significant lower incidence of MAE>0.25D (p < 0.001), MAE>0.50 D (p < 0.001) and MAE>1.0 D (0.002). ConclusionFormulas based on AI and on the theory of vergence show superior accuracy in IOL power calculation in corneas with low mean keratometry; their MAE is not correlated to axial length.

The effect of corneal power on the accuracy of 14 IOL power formulas

BackgroundThis study evaluates the impact of corneal power on the accuracy of 14 newer intraocular lens (IOL) calculation formulas in cataract surgery. The aim is to assess how these formulas perform across different corneal curvature ranges, thereby guiding more precise IOL selection.MethodsIn this retrospective case series, 336 eyes from 336 patients who underwent cataract surgery were studied. The cohort was divided into three groups according to preoperative corneal power. Key metrics analyzed included mean prediction error (PE), standard deviation of PE (SD), mean absolute prediction error (MAE), median absolute error (MedAE), and the percentage of eyes with PE within ± 0.25 D, 0.50 D, ± 0.75 D, ± 1.00 D and ± 2.00 D.ResultsIn the flat K group (Km < 43 D), VRF-G, Emmetropia Verifying Optical Version 2.0 (EVO2.0), Kane, and Hoffer QST demonstrated lower SDs (± 0.373D, ± 0.379D, ± 0.380D, ± 0.418D, respectively) compared to the VRF formula (all P < 0.05). EVO2.0 and K6 showed significantly different SDs compared to Barrett Universal II (BUII) (all P < 0.02). In the medium K group (43 D ≤ Km < 46 D), VRF-G, BUII, Karmona, K6, EVO2.0, Kane, and Pearl-DGS recorded lower MAEs (0.307D to 0.320D) than Olsen (OLCR) and Castrop (all P < 0.03), with RBF3.0 having the second lowest MAE (0.309D), significantly lower than VRF and Olsen (OLCR) (all P < 0.05). In the steep K group (Km ≥ 46D), RBF3.0, K6, and Kane achieved significantly lower MAEs (0.279D, 0.290D, 0.291D, respectively) than Castrop (all P < 0.001).ConclusionsThe study highlights the varying accuracy of newer IOL formulas based on corneal power. VRF-G, EVO2.0, Kane, K6, and Hoffer QST are highly accurate for flat corneas, while VRF-G, RBF3.0, BUII, Karmona, K6, EVO2.0, Kane, and Pearl-DGS are recommended for medium K corneas. In steep corneas, RBF3.0, K6, and Kane show superior performance.

Прогнозирование остроты зрения на близких расстояниях для линз с увеличенной глубиной фокуса на основании данных дооперационной биометрии

Abstract Original article Prediction of near visual acuity for intraocular lens with an extended range of focus technology based on preoperative biometry data E.V. Danilenko, A.N. Kulikov, N.V. Nevin S.M. Kirov Medical Militar y Academy Ministr y of Defense of the Russian Federation, Saint-Petersburg, Russian Federation Purpose. To develop a method for predicting near visual acuity at 40 cm after TECNIS Symphony IOL implantation based on preoperative biometry data. Material and methods. 2 groups of patients were enrolled in the study – the test group (50 eyes), where IOL TECNIS ZCB00 was implanted, and the main group (30 eyes), who received the TECNIS Symphony lens. Preoperatively all patients underwent Lenstar LS900 measurement and OCT of the anterior segment Cassia 2. There were no differences in biometry and demographic parameters between the groups. In the postoperative period, the measurements were repeated, refraction, distance and near visual acuity were also determined in the main group. The follow-up period was 6,48±0,15 months. Results. The posterior surface of the TECNIS IOL was 0.06±0.17 mm (p=0.022) closer to the cornea than the center of the crystalline lens. Center of the crystalline lens depth had correlation with the distance between cornea and the anterior (R=0.76 and R=0.74 according to Cassia 2 and Lenstar, respectively, p=0.000 in both cases) and posterior IOL surface (R=0.74 and R=0.86, p=0.000 in both cases). The average near visual acuity in the main group was 0.50±0.20 and did not depend on the axial length of the eye, IOL power, length of the vitreous chamber, residual ametropia and gender. Based on the results of regression analysis, an equation was derived for predicting near visual acuity after implantation of the TECNIS Symphony IOL (sum of squares 0.83, p=0.000), which included center of the crystalline lens depth, flat cornea meridian power and its thickness. Conclusion. Near visual acuity at 40 cm after implantation of TECNIS Symphony IOL can be reliably predicted based on center of the crystalline lens depth, flat cornea meridian power and its thickness. It is also possible to use the simplified nomogram proposed by the authors. Key words: EDOF, near vision acuity prediction, presbyopia

Association between body stature with ocular biometrics and refraction among Chinese preschoolers

PurposeTo evaluate the association of body stature with ocular biometrics and refraction in preschool children.MethodsA cross-sectional, school-based study was conducted in Shenzhen, China. Preschool children aged 3 to 6 from 10 randomly-selected kindergartens were recruited. Ocular biometric parameters, including axial length (AL), anterior chamber depth (ACD), vitreous chamber depth (VCD), corneal radius curvature (CR), axial length to corneal radius ratio (AL-to-CR ratio) and lens thickness (LT) were measured using non-contact partial-coherence laser interferometry. Cycloplegic refractions were obtained by a desktop autorefractor. Body height and weight were measured using standard procedures. The association between body stature and ocular biometrics were analyzed with univariable and multivariable regression model.ResultsA total of 373 preschoolers were included. AL, ACD, VCD, CR, and AL-to-CR ratio, were positively associated with height and weight (p < 0.05), whereas LT was negatively associated with height and weight (p < 0.01). No association was observed between stature and central cornea thickness and refraction. After adjusted for age and gender in a multivariable regression model, AL had positive associations with height (p < 0.01) and weight (p < 0.01). However, refraction had no significant association with stature parameters.ConclusionTaller and heavier preschoolers had eyes with longer AL, deeper vitreous chamber, and flatter cornea. The significant associations between body stature and ocular biometric parameters reveal the driving influence of body development on the growth of eyeballs in preschoolers.

Quantitative analysis of dynamic iris changes in primary angle-closure disease with long axial lengths: the Handan Eye Study.

To investigate dynamic iris changes in patients with primary angle-closure disease (PACD) with long axial length (AL) compared to those with short and medium AL. This observational cross-sectional study enrolled participants aged 35 years or older from the Handan Eye Study follow-up examination who were diagnosed with PACD and underwent Visante anterior segment optical coherence tomography (ASOCT) imaging under light and dark conditions. The right eye of each participant was included in the analysis. AL was categorized as short (<22.0 mm), medium (≥22.0 to ≤23.5 mm), or long (>23.5 mm). Anterior segment parameters, including iris dynamic changes, were compared among the three groups with different ALs. Data from 448 patients with PACD were analyzed. We found that 10.9% of included eyes had a long AL with a flatter cornea; larger central anterior chamber depth, angle opening distance, anterior chamber width, anterior chamber area, and volume; and smaller lens thickness and lens vault (LV) (P < 0.05) than those with short AL. No significant difference existed between the three groups in iris thickness, iris cross-sectional area (IA), iris curvature, or pupil diameter (PD) change between light and dark (P > 0.05). The significant associated factors for IA changes were area recess area (ARA) in the dark, LV in the dark, and PD change from light to dark (P < 0.05). Dynamic and static iris parameters were consistent across patients with PACD with short, medium, or long AL and may contribute to the pathogenesis of angle closure in atypical PACD.

Relationship between biometry, fovea, and choroidal thickness in Nigerian children with myopia

Background: Understanding the relationship between biometric and structural changes in childhood myopia is necessary to effectively manage myopia progression.Aim: To determine the relationship between ocular biometry, fovea and sub-fovea choroidal thickness in school-aged children with myopia of Nigerian descent.Setting: Abuja, Nigeria.Methods: This study involved 189 children (117 girls and 72 boys), and myopia was defined as cycloplegic spherical equivalent refraction (SER) of ≤ −0.50 D. Keratometry values, biometry data, fovea and sub-foveal choroidal thickness (SFChT) values were obtained from medical records retrospectively and analysed.Results: The median age was 13 years (interquartile range [IQR]: 5). The median SER, fovea and SFChTs were −2.63 D (IQR: 3.38), 249 μm (IQR: 118) and 225 μm (IQR: 341), respectively. Male children had flatter corneas, thicker fovea and thinner SFChT compared to female children. The vitreous chamber and axial length were longer and sub-fovea choroid was thinner in children with high myopia. There was a weak but significant positive correlation between myopia and sub-fovea choroidal thickness (r = 0.270 respectively, P 0.01). A moderate negative correlation was found between myopia and vitreous chamber depth (r = −0.536, P 0.001), and a strong negative correlation was found between myopia and axial length (r = −0.706, P 0.001).Conclusion: Myopia in school-aged Nigerian children is associated with sub-fovea choroidal thinning, increased vitreous chamber depth and axial elongation.Contribution: This study provides data on the relationship between ocular biometry, fovea and sub-foveal choroidal thickness in school-aged Nigerian children with myopia.

Photorefractive keratectomy in flat, normal, and steep corneas.

To compare photorefractive keratectomy (PRK) outcomes in patients with different corneal steepness. Care-Vision Laser Center, Tel-Aviv, Israel. Retrospective comparative chart review. Patients included in this study underwent wavefront optimized myopic PRK between January 2013 and December 2019. Patients were divided into 3 groups based on the steepness of the cornea (steep keratometry) (flat: <42 diopters [D], normal: 42 to 46 D and steep: >46 D). One to one matching was performed to verify that baseline parameters (age, preoperative visual acuity and refractive error) were similar between groups. Primary outcome measures were: postoperative corrected/uncorrected distance visual acuity (CDVA/UDVA), efficacy index (postoperative UDVA/preoperative CDVA), safety index (postoperative CDVA/preoperative CDVA), spherical equivalence (SEQ) and cylinder. After matching, 650 eyes were included in each group, which were similar in baseline parameters. There were no significant postoperative differences between flat, normal, and steep corneas in terms of safety index (1.02 vs 1.03 vs 1.03, P = .28), efficacy index (1.01 vs 1.01 vs 1.02, P = .57), logMAR CDVA (0.01 vs 0.02 vs 0.01, P = .76), logMAR UDVA (0.02 vs 0.03 vs 0.02, P = .68), %SEQ within 0.50 D (73.9% vs 74.2% vs 74.6%, P = .95) or 1.00 D of target (91.9% vs 92.5% vs 92.2%, P = .92), %cylinder within 0.50 D (82.8% vs 82.2% vs 81.4%, P = .81) or 1.00 D of target (96.9% vs 97.1% vs 97.2%, P = .95). No significant differences were found between flat, normal and steep corneas following wavefront-optimized myopic PRK. Thus, this procedure may be safely and effectively performed in both flat and steep corneas.

Relationship between anterior segment biometry and primary angle-closure glaucoma in Hubei region: a retrospective case-control study.

To investigate the pathogenesis of Primary Angle-Closure Glaucoma (PACG) and its relationship with the anatomical structure of the anterior segment by obtaining biometric parameters using the IOL-Master 700. A retrospective case-control study was conducted. Clinical data from 39 PACG patients and 40 normal controls treated at the Aier Eye Hospital affiliated with Wuhan University from January to December 2022 were collected. Anterior chamber depth (AC), white-to-white (WTW), lens thickness (LT), central corneal thickness (CCT), axial length (AL), corneal curvature (K1), corneal curvature (K2), and lens position (LP) were measured using the IOL-Master 700 to analyze the characteristics and differences in the anterior segment structure of both groups. Statistical methods included independent sample t-tests and logistic regression analysis. Significant differences were found in the anterior segment biometric parameters between PACG patients and normal controls (p < 0.05). Anterior chamber depth, white-to-white, lens thickness, central corneal thickness, axial length, and K2 were all related to the occurrence of PACG (p < 0.05). The occurrence of PACG was negatively correlated with ACD, CCT, and AL (OR = 0.12-0.64, p < 0.05), and positively correlated with LT. Compared to the normal control group, PACG patients in the Hubei region have a smaller anterior segment space, narrower angles, thicker lens, thinner cornea, shorter axial length, flatter cornea, and more anteriorly positioned lens.

Deep learning prediction of steep and flat corneal curvature using fundus photography in post-COVID telemedicine era.

Recently, fundus photography (FP) is being increasingly used. Corneal curvature is an essential factor in refractive errors and is associated with several pathological corneal conditions. As FP-based examination systems have already been widely distributed, it would be helpful for telemedicine to extract information such as corneal curvature using FP. This study aims to develop a deep learning model based on FP for corneal curvature prediction by categorizing corneas into steep, regular, and flat groups. The EfficientNetB0 architecture with transfer learning was used to learn FP patterns to predict flat, regular, and steep corneas. In validation, the model achieved a multiclass accuracy of 0.727, a Matthews correlation coefficient of 0.519, and an unweighted Cohen's κ of 0.590. The areas under the receiver operating characteristic curves for binary prediction of flat and steep corneas were 0.863 and 0.848, respectively. The optic nerve and its peripheral areas were the main focus of the model. The developed algorithm shows that FP can potentially be used as an imaging modality to estimate corneal curvature in the post-COVID-19 era, whereby patients may benefit from the detection of abnormal corneal curvatures using FP in the telemedicine setting.

Intraocular lens power calculation for silicone oil-dependent eyes.

Silicone oil tamponade is widely used in vitreoretinal surgery. In some cases, silicone oil may not be extracted for a long time or even permanently and is referred to as silicone oil-dependent eyes. In this study, we aimed to deduce a theoretical formula for calculating intraocular lens power for silicone oil-dependent eyes and compare it with clinical findings. A theoretical formula was deduced using strict geometric optical principles and the Gullstrand simplified eye model. The preoperative and postoperative refractive statuses of patients with silicone oil-dependent eyes who underwent intraocular lens implantation were studied (Group A, n = 13). To further test our derived theoretical formula, patients with silicone oil tamponade and first-stage intraocular lens implantation were included (Group B, n = 19). In total, 32 patients (32 eyes) were included in the study. In group A, the calculated intraocular lens power based on our formula was 24.96 ± 3.29 diopters (D), and the actual refraction of the patients was 24.02 ± 4.14D. In group B, the theoretical intraocular lens power was 23.10 ± 3.08D, and the clinical intraocular lens power was 22.84 ± 3.42D. There was no significant difference between the theoretical and clinical refractive powers, and the intraclass correlation coefficient was 0.771 for group A and 0.811 for group B (both p ≤ 0.001). The mean absolute error for silicone oil-dependent eyes of the formula was 1.66 ± 2.09D. After excluding data for two patients with a flat cornea (corneal refractive power < 42D), the mean absolute error decreased to 0.83 ± 0.62D. A strong correlation between the theoretical and clinical intraocular lens powers was observed, and the formula we deduced can be used to calculate the intraocular lens power for silicone oil-dependent eyes. This formula will help clinicians select a more appropriate intraocular lens for patients with silicone oil-dependent eyes, especially when the corneal refractive power is ≥42D.

Choice of intraocular lens calculation formula for cataract patients with prior pars plana vitrectomy.

To determine the optimal intraocular lens (IOL) calculation formula for vitrectomized eyes with diverse surgical and biometric characteristics. Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. Retrospective consecutive case series study. This study included 974 vitrectomized eyes (974 patients) scheduled for phacoemulsification with IOL implantation. 11 formulas were evaluated: Barrett Universal II (BUII), Emmetropia Verifying Optical, Hoffer-QST, Kane, Ladas Super Formula, Pearl-DGS, Radial Basis Function (RBF), Haigis, HofferQ, Holladay1, and SRK/T. Risk factors for prediction error (PE) exceeding 1 diopter (D) were determined using multiple logistic regression. Subgroup analyses were performed based on surgical history and biometric parameters. The risk of hyperopic PE (>1 D) was higher in patients with silicone oil tamponade (odds ratio [OR], 1.82) and longer axial length (AL) (OR, 1.55), while patients with previous scleral buckling (OR, 2.43) or ciliary sulcus IOL implantation (OR, 6.65) were more susceptible to myopic PE (<-1 D). The Kane formula had the highest overall prediction accuracy, and also the best in silicone oil-filled eyes and the flat cornea subgroup. The BUII and RBF displayed the optimal performance in eyes with previous scleral buckle and steep cornea, respectively. In eyes with an AL ≥ 26 mm, the Holladay1 with the nonlinear version of the Wang-Koch AL adjustment (Holladay1-WKn) showed the lowest absolute PE and highest percentage within ± 1.0 D of PE. The Kane achieved the highest overall prediction accuracy in vitrectomized eyes. The optimal formula for eyes with previous scleral buckle, steep cornea, or long AL was BUII, RBF, and Holladay1-WKn, respectively.

Extensive misalignment of plate-haptic rotationally asymmetric multifocal toric intraocular lens.

Plate-haptic rotationally asymmetric multifocal toric intraocular lenses (IOL) (Lentis Comfort Toric) occasionally rotate extensively after surgery. We conducted the current study to investigate the incidence of extensive misalignment of this IOL and its association with clinical parameters. Retrospective case series. Data were collected from patients who had undergone phacoemulsification and implantation of a plate-haptic multifocal toric IOL. Among 332 eyes, extensive misalignment of toric IOLs ≥ 45º occurred in 3.3% (11 eyes). The amount of misalignment in eyes with extensive misalignment was 81.6 ± 22.9º, while in those without extensive misalignment, it was 3.0 ± 2.7º. The eyes with extensive misalignment showed significantly greater axial length (p < 0.001), larger corneal diameter (p = 0.034), and flatter corneas (p = 0.044) than those without extensive misalignment. Repositioning surgery to correct toric IOL misorientation was conducted in 9 eyes between 7 and 28 days after cataract surgery. In 2 eyes, repositioning surgery was carried out twice. In majority of cases plate-haptic multifocal toric IOLs showed satisfactory rotational stability, but extensive misalignment ≥ 45º occurred in 3.3% of cases.

Comment on: Influence of ocular biometric parameters such as effective lens position, keratometry, and axial length on near add power of multifocal intraocular lens.

We read with interest the manuscript by Wu et al.1 The authors conduced a review about the variability of multifocal intraocular lens (mIOL) addition depending on biometric eye parameters, compiling the theoretical background provided in the scientific literature. The main clinical implication is that this variability should be considered in surgical planning, as the authors remark in the conclusion. Beyond the theoretical background, which was already described by Savini et al.,2 the review missed some important clinical evidence for translation to real practice in mIOL selection. We would like to give our point of view about some important messages for clinical practice and comment on the possible corrections needed. “In clinic, myopic patients with steep cornea often have longer effective lens position (ELP), which reduces near focal point of mIOLs, whereas hyperopic patients with flat cornea have the opposite situation.” This situation is not commonly observed in clinical practice. Patients with a longer axial length (AXL) have a longer ELP, and corneal power is inversely correlated with AXL, which means that eyes with a longer AXL usually have flatter corneas, contrary to the authors' sentence. Thus, the formula considering all the parameters should be used for a correct estimation of the addition (EA) because the higher EA due to lower corneal power is usually dominated by a lower EA due to a longer ELP in longer eyes.3 Wu et al. state: “A larger ELP should be more suitable for a higher near add power of mIOLs and a lower ELP should be more suitable for a higher near add power of mIOLs.”1 We assume the authors based this recommendation on the study by Savini et al., but there is a mistake in the second half of the sentence, which we believe should read: “…lower ELP should be more suitable for a lower near add power of mIOLs.”2 Wu et al. state: “They also found that variations in ELP had a greater effect on the position of the near focal point than K.”1 This is true, the ELP dominates the EA in comparison with keratometry (K), but other factors should be considered beyond the EA calculation. According to clinical evidence, near vision goes beyond the EA. Keratometry has demonstrated frequent relationships with near vision performance, whereas relationships between EA and near visual performance could depend on mIOL design.4 Wu et al. state: “Considering that the defocusing curve can roughly reflect the real near addition of mIOLs,….”1 Clinical evidence supports that EA could underestimate the effective addition calculated from defocus curves.5 In conclusion, beyond the EA calculation for mIOL selection, near vision could be influenced by other eye biometric parameters and mIOL optical characteristics (such as light distribution). Some clinical evidence has demonstrated that eyes with higher corneal power (steeper corneas related to short eyes) have lower areas under the visual acuity defocus curve in the near range.4 Therefore, although the theoretical basis of EA recommends low-addition mIOLs for short eyes, our clinical studies suggest that caution should be exercised when selecting low-addition mIOLs in short eyes in patients with higher expectations of spectacle independence. The theory of EA for mIOL selection is more valid if the same optical design is used for different additions; however, different additions come from different manufacturers and optical designs. Surgeons should consider that EA theory might not always be accomplished. In addition, it should not be forgotten that selecting a higher EA for improving near vision might also lead to poorer intermediate vision, and nowadays, decisions should be made considering patient needs throughout the entire range of vision.

An Overview of the Penguin Visual System.

Penguins require vision that is adequate for both subaerial and submarine environments under a wide range of illumination. Here we provide a structured overview of what is known about their visual system with an emphasis on how and how well they achieve these goals. Amphibious vision is facilitated by a relatively flat cornea, the power in air varying from 10.2 dioptres (D) to 41.3 D depending on the species, and there is good evidence for emmetropia both above and below water. All penguins are trichromats with loss of rhodopsin 2, a nocturnal feature, but only deeper diving penguins have been noted to have pale oil droplets and a preponderance of rods. Conversely, the diurnal, shallow-diving little penguin has a higher ganglion cell density (28,867 cells/mm2) and f-number (3.5) than those that operate in dimmer light. In most species studied, there is some binocular overlap, but this reduces upon submergence. However, gaps in our knowledge remain, particularly with regard to the mechanism of accommodation, spectral transmission, behavioural measurements of visual function in low light, and neural adaptations to low light. The rarer species also deserve more attention.

Comparison of anterior segment parameters in myopia with and without primary open-angle glaucoma.

To compare anterior segment parameters between myopes with and without primary open-angle glaucoma using Pentacam scheimpflug tomography. This was a single-center retrospective cross-sectional study. Records of patients examined with a Pentacam scheimpflug tomographer (Wavelight-Allegro Oculyzer, GmbH, Erlangen, Germany) were reviewed. Variables studied were recorded from the topographic map and included anterior chamber angle, anterior chamber volume, anterior chamber depth, keratometric readings, and corneal thickness. A general linear model for age-and spherical equivalent refraction-adjusted intergroup comparisons of the anterior segment parameters was conducted. The study included myopes previously diagnosed with primary open-angle glaucoma (POAG) [Mild defect, n = 81; Moderate-severe defect, n = 50] and non-glaucomatous myopes (n = 247). The results revealed a smaller anterior chamber angle, shallower anterior chamber depth, and flatter cornea curvature in the mildly glaucomatous group compared to the non-glaucomatous group (p < 0.05). Smaller anterior chamber angle, shallower anterior chamber depth, and thinner cornea thickness were also observed in the moderate-severely glaucomatous group compared to the non-glaucomatous group (p < 0.05). Glaucomatous damage in myopic patients with POAG was associated with comparatively small anterior chamber angle, shallow anterior chamber depth, flat cornea curvature, and thin cornea.

Accuracy of Intraocular Lens Power Calculation Based on Total Keratometry in Patients With Flat and Steep Corneas

To analyze the accuracy of the current intraocular lens power calculation formulas using standard keratometry (K) and total keratometry (TK) data in patients with flat and steep corneas. Retrospective consecutive cross-sectional study. An optical biometer with swept-source optical coherence tomography was used in this retrospective study. The standard deviation (SD), mean absolute error (MAE), median absolute error (MedAE), and the proportion of eyes with prediction error (PE) within ±0.25 diopter (D), ±0.5 D, ±0.75 D, and ±1.00 D were calculated to evaluate the refractive outcomes of each formula. A total of 231 eyes from 231 patients were included. In the entire study cohort, the Emmetropia Verifying Optical (EVO) formula using TK data showed the lowest SD (0.383) and MAE (0.30) and the highest percentage of cases with a PE within ±0.5 D (81.4%). In the flat keratometry group, the EVO (P=.042), Haigis (P=.043), Hoffer Q (P=.038) and Holladay 1 (P=.013) formulas using TK data had significantly lower SD than using K data. The EVO formula using TK data showed the lowest SD (0.357) and MAE (0.28). In the steep keratometry group, the Hoffer Q (P=.036) and SRK/T (P=.029) formulas using TK data had significantly lower SD than using K data. The BUII TK formula showed the lowest SD (0.431), MedAE (0.26), and MAE (0.32). The TK data set showed a better trend of refractive outcomes, especially in the flat and steep keratometry groups. EVO (TK) and BUII TK formulas were suggested for eyes with K values lower than 42 D and K values higher than 46 D, respectively.

Selected ocular dimensions of three penguin species

Penguins (Spheniscidae) are a diverse clade of flightless, marine birds. Their eyes, likely a primary driver of behaviour, have been noted to have anatomic adaptations to their amphibious lifestyle. In particular, they have a relatively flat cornea, which would make the transition from a subaerial to a submarine environment require less accommodative effort. However, the ocular dimensions are not known for many penguin species, despite the diversity within the family, and their accommodative abilities have been the source of some dispute. In this study we undertook to establish the basic dimensions of the eye of the smallest, a mid-sized penguin and the second largest penguin. The power of the front surface of the cornea was inversely related to the size of both the eye and penguin, being 41.3 D in the little penguin (Eudyptula minor), a power greater than previously measured in any other penguin species, 26.3 D in the gentoo (Pygoscelis papua) and 19.1 D in the king penguin (Aptenodytes patagonicus). All other dimensions increased or decreased in line with the size of the eye. All penguins were able to achieve emmetropia in air. The gentoo appeared to be emmetropic underwater. A finding of central corneal thickening in some penguins may be artefactual. Calculations using the ocular dimensions demonstrated that the mean retinal illumination of an extended source of light in the little penguin eye is less than that of its larger, deeper-diving relatives.

Refractive error characteristics and influence on ocular parameters in patients with unilateral congenital ptosis

BackgroundThe study aimed to investigate the difference in refractive status and ocular parameters between ptotic and fellow eyes in patients with unilateral congenital ptosis.MethodsThirty patients (53% males, age 22.00 ± 11.41 years) with unilateral congenital ptosis diagnosed and treated at the First Affiliated Hospital of Sun-yat Sen University were enrolled and underwent detailed refractive examinations from March 2019 to February 2022. Ocular biometric measurements were performed by an IOL Master 700 biometer. The differences in refractive error characteristics, best-corrected visual acuity (BCVA), and ocular parameters including axial length (AL), central corneal thickness (CCT), aqueous depth (AQD), anterior chamber depth (ACD), lens thickness (LT), and keratometry values between ptotic and fellow eyes were analysed.ResultsA lower BCVA (logMAR, median (IQR), 0.00 (− 0.13,0.00), P = 0.009) and a higher incidence of amblyopia (n (%), 7(23%), P = 0.016) were observed in ptotic eyes. The CCT of ptotic eyes was greater than that of fellow eyes (mean ± SD, 539.83 ± 26.73 μm, P < 0.001). The keratometry values at the flat axis (K1) and mean corneal power (Km) were smaller in ptotic eyes (mean ± SD, 42.11 ± 1.49 D, 42.68 ± 1.52 D, respectively, both P = 0.001). There was no significant difference in AL between ptotic and fellow eyes.ConclusionsCongenital ptosis influences ocular parameters, mainly causing a thicker and flatter cornea. Patients with unilateral congenital ptosis might have lower BCVA in the ptotic eyes.

Accuracy of Formulas for Intraocular Lens Power Calculation After Myopic Refractive Surgery.

To assess the accuracy of the following intraocular lens (IOL) power formulas: Barrett True-K No History (BTKNH), Emmetropia Verifying Optical 2.0 Post Myopic LASIK/PRK (EVO 2.0), Haigis-L, American Society of Cataract and Refractive Surgery (ASCRS) average, and Shammas, designed for patients who have undergone previous myopic refractive surgery, independent of preexisting clinical history and corneal tomographic measurements. Data from 302 eyes of 302 patients who previously underwent myopic refractive surgery and had cataract surgery done by a single surgeon with only one IOL type inserted were included. The predicted refraction was calculated for each of the formulas and compared with the actual refractive outcome to give the prediction error. Subgroup analysis based on the axial length and mean keratometry was performed. On the basis of mean absolute prediction error (MAE), the formulas were ranked as follows: Haigis-L (0.61 diopters [D]), ASCRS average (0.63 D), BTKNH (0.67 D), EVO 2.0 (0.68 D), and Shammas (0.69 D). The Haigis-L had a statistically significant lower MAE compared with all formulas (P < .05) except the ASCRS average. Hyperopic mean prediction errors were seen in all formulas for axial lengths of greater than 30 mm or mean keratometry values of 35.00 diopters or less. The Haigis-L and the ASCRS average formulas provided the most accurate results in the overall population evaluated in this study. Moreover, according to data observed, it is important to be careful handling very long eyes and very flat corneas because hyperopic refractions could be more common. [J Refract Surg. 2022;38(7):443-449.].