Corneal Topographic Analysis Research Articles

Epithelial and stromal thickness profile and lens decentration in myopic orthokeratology

PurposeTo study topographic epithelial and total corneal thickness changes in myopic subjects undergoing successful orthokeratology treatment in connection with the objective assessment of contact lens decentration. MethodsA prospective-observational and non-randomized study in 32 Caucasian myopic eyes undergoing Ortho-k for 3 months. Total, epithelial, and stromal thicknesses were studied before and after Ortho-k treatment, using optical coherence tomography with anterior segment application software. Central, paracentral, and mid-peripheral values are taken along 8 semi-meridians. ResultsThe central average total corneal thickness was 4.72 ± 1.04 μm thinner after Ortho-K. The paracentral corneal thickness showed no significant changes (p = 0.137), while the mid-peripheral corneal thickness was increased by 3.25 ± 1.6 μm associating this increase exclusively to the epithelial plot (p<0.001). When lens centration was assessed, a lens fitting decentration less than 1.0 mm was found for the whole sample, predominantly horizontal-temporal (87.5%) and vertical-inferior (50%) decentring. Corneal topographical analysis revealed a horizontal and vertical epithelial thickness asymmetric change profile with paracentral temporal thinnest values, and mid-peripheral nasal thickest values. ConclusionsThe present study found a central corneal thinning induced by Ortho-k lenses in subjects with moderate myopia, only associated with a change in epithelial thickness, as well as mid-peripheral thickening, that seems to be mainly epithelial in origin. The authors also found a tendency of contact lens decentration toward temporal and inferior areas conditioning an asymmetric epithelial redistribution pattern.

Ophthalmic Manifestations in Fabry Disease: Updated Review.

Fabry disease (FD) is an X-linked lysosomal storage disorder, causing Gb-3 (globotriaosylceramide) buildup in cellular lysosomes throughout the body, in particular in blood vessel walls, neuronal cells, and smooth muscle. The gradual accumulation of this glycosphingolipid in numerous eye tissues causes conjunctival vascular abnormalities, corneal epithelial opacities (cornea verticillata), lens opacities, and retinal vascular abnormalities. Although a severe vision impairment is rare, these abnormalities are diagnostic indicators and prognostics for severity. Cornea verticillata is the most common ophthalmic feature in both hemizygous men and heterozygous females. Vessel tortuosity has been linked to a faster disease progression and may be useful in predicting systemic involvement. New technologies such as optical coherence tomography angiography (OCTA) are useful for monitoring retinal microvasculature alterations in FD patients. Along with OCTA, corneal topographic analysis, confocal microscopy, and electro-functional examinations, contributed to the recognition of ocular abnormalities and have been correlated with systemic involvement. We offer an update regarding FD ocular manifestations, focusing on findings derived from the most recent imaging modalities, to optimize the management of this pathology.

The effect of anterior segment parameters on surgical success of Descemet membrane endothelial keratoplasty: a prospective study.

To investigate how anterior segment parameters affect the success of Descemet membrane endothelial keratoplasty (DMEK) in patients with endothelial insufficiency without stromal opacities and to identify factors predisposing them to repeat keratoplasty. Our prospective observational study included patients who underwent primary DMEK for Fuchs' endothelial dystrophy and pseudophakic bullous keratopathy between March 2019 and March 2020. After a detailed ophthalmologic examination, corneal topographic analysis, anterior segment optical coherence tomography (AS-OCT) scans, endothelial cell density (ECD) and axial length (AL) measurements were performed. Surgical success was defined as no endothelial dysfunction during follow-up. Changes in the parameters and how preoperative parameters affect surgical success were investigated. In 43 eyes of 43 patients (mean age: 68.58 ± 8.51years), mean visual acuity was 1.73 ± 0.74 LogMAR before DMEK and 0.31 ± 0.29 LogMAR in the final visit. Central corneal thickness (CCT, p = 0.026) and mean anterior chamber depth (ACD, p = 0.001) affected surgical success. Preoperative CCT values greater than 770µm increased the risk of repeat keratoplasty by 8.75-fold, whereas preoperative ACD values less than 2.5mm increased the risk by 2.92-fold. Preoperative higher CCT and lower ACD values were associated with surgical failure after DMEK. Early surgery may be considered for more successful results. This prospective study has been registered on the ClinicalTrials.gov system with the registration number NCT04420429 on 06/06/2020.

Comparison of Amsler–Krumeich and Sandali Classifications for Staging Eyes with Keratoconus

Keratoconus (KC) is the most common corneal ectasia characterized by progressive corneal thinning, protrusion, and irregular astigmatism. The Amsler–Krumeich classification based on the analysis of corneal topography, corneal thickness, refraction and biomicroscopy is the most commonly used; recently, a new classification based on anterior segment Optical Coherence Tomography was introduced by Sandali and colleagues. Since there is no information about the possible agreement between these two classifications, the aim of this study is to compare the stratification of consecutive KC patients using the Amsler–Krumeich and Sandali classifications, and to further ascertain KC cases in which one classification is preferred over the other. Overall, 252 eyes of 137 patients (41.45 ± 16.93 years) were analyzed: in 156 eyes (61.9%), the Amsler and Sandali staging differed in one stage while in 75 cases (29.8%) it differed in two or more stages. In 222 eyes (88.1%), the Sandali staging was higher compared to the Amsler one. These results show that the two classifications are not fully interchangeable: the Amsler–Krumeich classification is more appropriate in identifying and longitudinally monitoring patients with early stages of KC, while the Sandali classification for the diagnosis and follow-up of patients with more advanced stages, particularly when a surgical planning has to be chosen.

Corneal Topographic Analysis in Patients with Involutional Lower Eyelid Entropion

ABSTRACT Purpose: To analyze the corneal morphology before and after surgery by the advancement of posterior lower eyelid retractors (LERs) alone or in combination with a lateral tarsal strip (LTS) for lower eyelid involutional entropion. Methods: We retrospectively analyzed the cases of 24 consecutive elderly patients (24 eyelids) who underwent posterior layer advancement of LERs alone or in combination with an LTS for involutional entropion. All patients underwent general ophthalmological examinations including best-corrected visual acuity (BCVA), fundus examination, and slit lamp microscopy. The degree of corneal damage was evaluated using the area (A) and density (D) classification of corneal fluorescein staining. Corneal topography was measured using anterior segment optical coherence tomography (AS-OCT). The parameters were steep keratometry (Ks), flat keratometry (Kf), average keratometry (AveK), cylindrical power (CYL), central corneal thickness (CCT), and total higher-order aberrations (HOAs) within a 4-mm diameter. Results: There was no significant difference in the Ks, Kf, AveK, CYL or CCT values between before and after surgery. The HOAs were significantly decreased after surgery. In the AD classification, both the A and D values were significantly decreased after surgery. Significant correlations were observed between preoperative mean HOAs and the mean of A classification, and between preoperative mean HOAs and the mean of D classification. Conclusion: Involutional entropion does not appear to significantly affect corneal morphology before or after posterior LER advancement alone or in combination with an LTS. However, this surgery is thought to result in an improvement of corneal disorders and consequent improvement of HOAs.

Corneal topography in keratoconus evaluated more than 30\xa0years after penetrating keratoplasty: a Fourier harmonic analysis

The aim of this observational study was to examine the characteristics of anterior and posterior corneal topography in keratoconic eyes more than 30 years after penetrating keratoplasty (PK). Patients who maintained clear grafts for more than 30 years after PK were included and divided into the keratoconus (KC) group or other diseases (Others) group, based on the primary indication. Twenty-six eyes of 26 patients were included. The KC group and the Others group included 14 eyes and 12 eyes, respectively. The KC group participants were younger at the time of surgery (P = 0.03). No differences were found in best-spectacle-corrected visual acuity, keratometric power, and central-corneal-thickness. Based on corneal topography using Fourier harmonic analyses, regular astigmatism in the anterior cornea was significantly larger (P = 0.047) and the spherical component in the posterior cornea was significantly lower (P = 0.01) in the KC group. The area under the receiver operating characteristic curve of the spherical component, regular astigmatism, asymmetry component, and higher-order irregularity were 66.07%, 63.10%, 57.14%, and 59.23%, respectively, in the anterior cornea and 80.65%, 52.98%, 63.10%, and 63.99%, respectively, in the posterior cornea. Our results suggested that Fourier harmonic analysis of corneal topography could be useful for patients with KC long after PK.

Relationship between Corneal Morphogeometrical Properties and Biomechanical Parameters Derived from Dynamic Bidirectional Air Applanation Measurement Procedure in Keratoconus.

The morphogeometric analysis of the corneal structure has become a clinically relevant diagnostic procedure in keratoconus (KC) as well as the in vivo evaluation of the corneal biomechanical properties. However, the relationship between these two types of metrics is still not well understood. The current study investigated the relationship of corneal morphogeometry and volume with two biomechanical parameters: corneal hysteresis (CH) and corneal resistance factor (CRF), both provided by an Ocular Response Analyzer (Reichert). It included 109 eyes from 109 patients (aged between 18 and 69 years) with a diagnosis of keratoconus (KC) who underwent a complete eye examination including a comprehensive corneal topographic analysis with the Sirius system (CSO). With the topographic information obtained, a morphogeometric and volumetric analysis was performed, defining different variables of clinical use. CH and CRF were found to be correlated with these variables, but this correlation was highly influenced by corneal thickness. This suggests that the mechanical properties of KC cornea contribute only in a partial and limited manner to these biomechanical parameters, being mostly influenced by morphogeometry under normal intraocular pressure levels. This would explain the limitation of CH and CRF as diagnostic tools for the detection of incipient cases of KC.

Corneoscleral contact lenses for visual rehabilitation after keratoplasty surgery

PurposeTo report the use of corneoscleral lenses (CSL) in keratoconus patients who were unsatisfied with their visual outcomes after keratoplasty surgery. MethodsEleven consecutive cases with unsatisfactory vision with spectacles, due to irregular astigmatism, preferred to try CSL before SL due to handling or economic issues. An eye examination included refraction and visual acuity assessment, anterior eye biomicroscopy, ocular fundus examination, corneal topographic analysis, endothelial-cell count (ECC) and evaluation of corneal biomechanical parameters (corneal resistance factor, CRF; corneal hysteresis, CH; corneal-compensated intraocular pressure, IOPcc). The fitting process was performed using a diagnostic fitting set. Subjective visual quality and comfort, and CSL usage time were also recorded. Patients were monitored for 1 year. ResultsTwo patients presented intolerance to CSL. Therefore, nine patients (6 males and 3 females; the mean±SD age, 44.56 ± 17.33 years, range 27–82) were fitted with CSL. The log MAR visual acuity of these eyes improved significantly with CSL in relation to the best spectacle-corrected vision (0.02 ± 0.06 vs 0.22 ± 0.15, respectively; p = 0.007). Patients reported prolonged usage times (an average of 9.78 ± 1.99 h; range, 8–14). No significant adverse ocular effects or clinically relevant changes in ocular parameters (ECC, CH, IOPcc, central corneal thickness and keratometry; all p > 0.05), visual quality, comfort rating or usage time were found during the 1-year follow-up. ConclusionCorneoscleral lenses could be fitted in non-severe cases after keratoplasty surgery with optimal visual results as they can be a safe and healthy alternative option.

Comparison of outcomes after topography-modified refraction versus wavefront-optimized versus manifest topography-guided LASIK

BackgroundTo compare the outcomes of myopia and myopic astigmatism corrected with topography-modified refraction laser in situ keratomileusis (TMR-LASIK), wavefront-optimized (WFO) LASIK, and topography-guided (TG) LASIK with a correction target based on the manifest refraction (manifest TG-LASIK).MethodsThis observational, retrospective cohort study included patients who underwent LASIK using the WaveLight® EX500 excimer laser to correct myopia and myopic astigmatism between August 2016 and July 2017. Patients who underwent TMR-LASIK (85 patients), WFO-LASIK (70 patients), or manifest TG-LASIK (40 patients) were enrolled, and only one eye from each patient was analyzed. All participants underwent measurement of the uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (BCVA), manifest refraction, vector analysis of astigmatic change, corneal topography, and corneal wavefront analysis at baseline and at every posttreatment visit.ResultsThree months postoperatively, a UDVA of 0.0 logMAR or better and manifest refraction spherical equivalent (MRSE) within ±0.5 diopters (D) did not differ across the TMR-, WFO-, and manifest TG-LASIK groups. However, the residual cylinder in the TMR group was significantly larger than that in the WFO and manifest TG groups. The magnitude of error in the TMR group measured using astigmatism vector analysis was significantly higher than that in the WFO and manifest TG groups.ConclusionsAlthough these three LASIK platforms achieved the predicted surgical outcomes, TMR-LASIK overcorrected astigmatism and showed a higher residual postoperative astigmatism compared with WFO- and manifest TG-LASIK.

Comparison of Excimer Laser Versus Femtosecond Laser Assisted Trephination in Penetrating Keratoplasty: A Retrospective Study.

To compare the impact of non-mechanical excimer-assisted (EXCIMER) and femtosecond laser-assisted (FEMTO) trephination on outcomes after penetrating keratoplasty (PK). In this retrospective study, 68 eyes from 23 females and 45 males (mean age at time of surgery, 53.3 ± 19.8years) were included. Inclusion criteria were one surgeon (BS), primary central PK, Fuchs' dystrophy (FUCHS) or keratoconus (KC), no previous intraocular surgery, graft oversize 0.1mm and 16-bite double running suture. Trephination was performed using a manually guided 193-nm Zeiss Meditec MEL70 excimer laser (EXCIMER group: 18 FUCHS, 17 KC) or 60-kHz IntraLase™ femtosecond laser (FEMTO group: 16 FUCHS, 17 KC). Subjective refractometry (trial glasses) and corneal topography analysis (Pentacam HR; Casia SS-1000 AS-OCT; TMS-5) were performed preoperatively, before removal of the first suture (11.4 ± 1.9months) and after removal of the second suture (22.6 ± 3.8months). Before suture removal, mean refractive/AS-OCT topographic astigmatism did not differ significantly between EXCIMER and FEMTO. After suture removal, mean refractive/Pentacam/AS-OCT topographic astigmatism was significantly higher in the FEMTO (6.2 ± 2.9 D/7.1 ± 3.2 D/7.4 ± 3.3 D) than in the EXCIMER patients (4.3 ± 3.0 D/4.4 ± 3.1 D/4.0 ± 2.9 D) (p ≤ 0.005). Mean corrected distance visual acuity increased from 0.22 and 0.23 preoperatively to 0.55 and 0.53 before or 0.7 and 0.6 after suture removal in the EXCIMER and FEMTO groups, respectively. Differences between EXCIMER and FEMTO were only pronounced in the KC subgroup. Non-mechanical EXCIMER trephination seems to have advantages regarding postoperative corneal astigmatism and visual acuity compared with FEMTO trephination, especially in KC. A bigger sample size and longer follow-up are needed to evaluate the long-term impact of EXCIMER and FEMTO trephination on postoperative topographic and visual outcomes.

Accuracy of Scheimpflug-derived corneal biomechanical and tomographic indices for detecting subclinical and mild keratectasia in a South Asian population

To test the predictive accuracy of the Belin-Ambrósio deviation index (BAD-D), the stiffness parameter A1 (SPA1), the Corvis biomechanical index (CBI), and the tomographic and biomechanical index (TBI) assessments for distinguishing subclinical and mild keratoconic eyes from normal eyes. Medical Research Foundation, Sankara Nethralaya, Chennai, India. Retrospective case series. In this cross-sectional clinical study, the following 3 groups of eyes were analyzed: very asymmetric ectasia with normal topography (very asymmetric-normal topography), mild keratoconus, and normal control. All eyes had comprehensive assessment with corneal topography (TMS-IV), Scheimpflug tomography (Pentacam HR), and dynamic Scheimpflug biomechanical analysis (Corvis ST). The outcomemeasures were the BAD-D, SPA1, CBI, and TBI. Receiver operating characteristic (ROC) curve analysis was performed to determine each parameter's predictive accuracy in distinguishing between eyes with subclinical or mild keratoconus and control eyes. The area under the curve (AUC) ROC values for the very asymmetric-normal topography and normal control comparison were 0.81 (BAD-D), 0.76 (SPA1), 0.78 (CBI), and 0.90 (TBI). The TBI (using cutoff value 0.16) showed the highest diagnostic accuracy (85%), with 84% sensitivity and 86% specificity. The AUC ROC values for the mild keratoconus and normal control comparison were 0.998 (BAD-D), 0.91 (SPA1), 0.97 (CBI), and 0.999 (TBI). The TBI (with a 0.63 cutoff) showed the highest accuracy (99.5%), with 99% sensitivity and 100% specificity. The TBI also showed the weakest correlation with mean keratometry, biomechanically corrected intraocular pressure, and central corneal thickness in normal eyes and keratoconic eyes. The TBI best distinguished eyes with mild ectasia from normal eyes and had the weakest correlation with biomechanical confounding factors, reinforcing the hypothesis that the TBI represents corneal biomechanical susceptibility.

A clinical study to describe the corneal topographic pattern and estimation of the prevalence of keratoconus among diagnosed cases of vernal keratoconjunctivitis

BackgroundAssociation of keratoconus with vernal keratoconjunctivitis is well known, but there are few topographic studies describing actual prevalence especially in India where it is a common condition. There is also scarce literature on the topographic patterns and subclinical topographic anomalies in cases of vernal catarrh and their relationship with various subtypes. This study was conducted to estimate the prevalence of subclinical keratoconus among Indian subjects with vernal keratoconjunctivitis and describe the various topographic abnormalities which can help in screening for these cases. MethodsIn the cross-sectional study conducted at a tertiary care center, 76 established cases of vernal keratoconjunctivitis were evaluated with placido disc–based videokeratography for topographic abnormalities and early keratoconus based on modified Rabinowitz–McDonnell criteria. ResultsSeventeen (11.2%) eyes satisfied both the modified Rabinowitz–McDonnell criteria of keratoconus. Corneal topographic pattern analysis showed asymmetric bowtie with inferior steepening in 17.11% of the patients. None of these patients had clinical evidence of keratoconus. ConclusionsThe study showed 11.2% prevalence of keratoconus in patients suffering from vernal keratoconjunctivitis. The findings highlight the importance of using a simple placido disc–based corneal topography system for screening the patients with vernal keratoconjunctivitis for keratoconus. This can help in early detection and preventive intervention.

Visual quality with corneo-scleral contact lenses after intracorneal ring segment (ICRS) implantation for keratoconus management

To evaluate the visual quality results when fitting a corneo-scleral contact lens (CScL) after intracorneal ring segment (ICRS) implantation for keratoconus management. Twenty-seven eyes of 27 patients with keratoconus underwent ICRS implantation and had CScL fitted as their visual quality was unsatisfactory with their spectacles or contact lenses. Patients received a complete eye examination, refraction and visual acuity assessment, anterior eye biomicroscopy, ocular fundus examination, corneal topographic analysis, endothelial-cell count, and visual quality assessment using contrast sensitivity and aberrometry tests. A diagnostic trial set was used in the fitting process, and patients were assessed according to a standardised methodology, including subjective visual quality and comfort, and contact lens usage time. The follow-up period was one year. After fitting CScL, log-MAR visual acuity values improved significantly in relation to the best spectacle-corrected vision (0.22 ± 0.17 vs 0.00 ± 0.12; p < 0.001). Total high-order aberrations decreased 33% (2.62 ± 1.31 vs 1.75 ± 1.81 μm; p < 0.009) and the spatial frequencies of contrast sensitivity all improved (all p < 0.05). Furthermore, 70.37% of patients reported high ratings of subjective visual quality (favourable and very favourable) and prolonged usage times (11.78 ± 3.93 h). After wearing CScL for one year, no adverse ocular effects or clinically relevant changes in corneal parameters, visual quality, comfort ratings or usage time were found. This CScL appears to be an alternative reasonable option for keratoconic eyes with ICRS placement, providing an improvement in subjective visual quality.

Visual quality with corneo-scleral contact lenses for keratoconus management.

To assess the visual quality achieved by fitting corneo-scleral contact lenses (CScL) for keratoconus management. Thirty patients with keratoconus presented to have CScL fitted because of the unsatisfactory visual quality they experienced with their contact lenses or spectacles. The eye examination included visual acuity assessment, anterior eye biomicroscopy, ocular fundus examination, corneal topographic analysis, endothelial-cell count, contrast sensitivity and aberrometry. The fitting process was performed using a diagnostic trial set. Subjective visual quality and comfort, and contact lens wear time were also reported. Patients were monitored for one year. Three patients discontinued CScL wear before one year. Therefore, 27 eyes of 27 patients (19 male and 8 female) participated in this study. The mean age was 36.1 ± 13.1 (mean ± SD) years. Statistically significant differences were found in logMAR visual acuity between the best spectacle-corrected vision and after CScL fitting (mean ± SD, 0.23 ± 0.30 and 0.00 ± 0.14, respectively; p < 0.001). The total high-order aberrations decreased significantly (55%), and the spatial frequencies of contrast sensitivity all improved to normal range values of the population. Furthermore, high subjective visual quality and comfort ratings, and prolonged usage times (mean ± SD, 13.44 ± 2.38 h a day) were reported. No adverse ocular effects or clinically relevant changes in corneal parameters, visual quality, comfort or usage time were found one year after wearing CScL. This CScL seems to be safe and healthy, providing optimal visual quality, comfort and prolonged usage times in patients with keratoconus.

Evaluation of anterior segment parameters in patients with Turner syndrome using Scheimpflug imaging

To compare the anterior segment parameters in patients with Turner syndrome (TS) as measured by the Pentacam HR-Scheimpflug imaging system with those of healthy control subjects. This cross-sectional prospective study included 35 patients with TS and 30 age-matched controls. Corneal topographic analysis was performed using the Pentacam HR-Scheimpflug imaging system (Oculus, Wetzlar, Germany). The power of the corneal astigmatism, mean keratometry (Km) values for the both front and back surfaces of the cornea, maximum keratometry (Kmax), central corneal thickness (CCT), corneal volume (CoV), white-to-white diameter (WTW), chamber volume (CaV), angle and anterior chamber depth (ACD) values were recorded. The mean age of TS subjects was 17.2±6.1years; of controls, 16.4±5.7years. All participants were female. There was a significant difference in the mean values of WTW (11.3±0.5mm vs 12.0±0.4mm [P<0.001]), CaV (148.4±33.5mm3 vs 191.9±27.6mm3 [P<0.001]), and ACD (2.8±0.3mm vs 3.1±0.2mm [P<0.001]) between TS versus group and the control group. The mean values of the power of the corneal astigmatism, Km values for the both front and back of the corneal surface, Kmax, CCT, CoV, and angle values were similar between groups (P>0.05 for each one). There was a reduction in CaV, ACD, and WTW measurements in TS patients compared with controls.

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Effect of Limbal Relaxing Incisions on Corneal Aberrations.

To study the effect of limbal relaxing incisions on corneal aberrations after phacoemulsification with aspheric intraocular lens (IOL) implantation. Forty-five eyes underwent microincision cataract surgery with on-axis phacoemulsification incision. These eyes were divided into two groups: limbal relaxing incision group (23 eyes) and control group (22 eyes). In the limbal relaxing incision group, a single limbal relaxing incision was performed on the steepest meridian of corneal topography and the degrees of arc were determined using the DONO-Donnenfeld nomogram. The eyes in the control group were operated on by microincision cataract surgery without limbal relaxing incision. Corneal topography and wavefront analysis over 6-mm pupil size were performed preoperatively and 1 month postoperatively in both groups. Target induced astigmatism vector, surgically induced astigmatism vector, difference vector, magnitude of error, flattening effect, and torque were analyzed using the Alpins vectorial method. The limbal relaxing incision group showed significant reduction in topographic astigmatism by 51.87% of preoperative topographical astigmatism (P < .0001). The mean surgically induced astigmatism of limbal relaxing incision was 1.29 ± 0.71 diopters (D), which was close to the mean target induced astigmatism (1.33 ± 0.20 D), whereas the control group did not show a significant change in topographic astigmatism (0.17 ± 0.11 D; P = .73). Higher order aberrations of the cornea did not show significant change in either group except quatrefoil aberration, which significantly increased in the limbal relaxing incision group but not in the control group, with no significant difference between the two groups regarding corneal aberrations. Limbal relaxing incision is an effective method in reducing corneal astigmatism with neutral effect on corneal aberrations.

Analysis of corneal topography in patients with pure microphthalmia in Eastern China

To determine the typical corneal changes in pure microphthalmia using a corneal topography system and identify characteristics that may assist in early diagnosis. Patients with pure microphthalmia and healthy control subjects underwent corneal topography analysis (Orbscan IIZ® Corneal Topography System; Bausch and Lomb, Bridgewater, NJ, USA) to determine degree of corneal astigmatism (mean A), simulation of corneal astigmatism (sim A), mean keratometry (mean K), simulated keratometry (sim K), irregularities in the 3 - and 5-mm zone, and mean thickness of nine distinct corneal regions. Patients with pure microphthalmia (n = 12) had significantly higher mean K, sim K, mean A, sim A, 3.0 mm irregularity and 5.0 mm irregularity, and exhibited significantly more false keratoconus than controls (n = 12). There was a significant between-group difference in the morphology of the anterior corneal surface and the central curvature of the cornea. Changes in corneal morphology observed in this study could be useful in borderline situations to confirm the diagnosis of pure microphthalmia.

Effect of translation and rotation fitting on analysis of corneal topography

The purpose was to assess the suitability of quadratic equations for the accurate representation of corneal topography and consider the effect of translation and rotation fitting on the quality of fit and the curvature results. Topography images were recorded for the anterior and posterior surfaces of 490 corneas of 490 myopic patients using Pentacam. Elevation data were fitted to four shape models, three of which considered translational and/or rotational fitting. Differences between the models in the estimates of radii of curvature (R) and asphericity coefficients (Q) and in the quality of fit (as measured by the root mean square (RMS) error and the structural similarity index (SSIM)) were statistically analysed. The general shape model that considered both translational and rotational misalignments provided the best fit for the anterior (RMS = 1.18 ± 0.56 µm, SSIM = 0.99 ± 0.01) and posterior (RMS 3.64 ± 1.23 µm, SSIM = 0.99 ± 0.01) corneal surfaces in all subjects. The quality of fit degraded significantly (with p < 0.01 in all cases) when misalignments were not considered, increasing RMS to 5.20 ± 2.27 µm (anterior) and 17.10 ± 6.08 µm (posterior) and decreasing SSIM to 0.84 ± 0.18 (anterior) and 0.68 ± 0.22 (posterior) when both translational and rotational misalignments were ignored. The estimates of Rx, Ry, Qx and Qy as obtained when both forms of misalignment were considered varied, respectively, by as much as 0.18 mm, 0.23 mm, 0.27 and 0.54 for the anterior surface, and 0.25 mm, 0.39 mm, 0.32 and 0.37 for the posterior surface when misalignments were ignored. The variations were statistically significant, with p remaining below 0.01 in all cases. In conclusion, consideration of geometric misalignments helps improve the accuracy of describing corneal topography. The effects of misalignments on the estimates of corneal radius and asphericity are statistically significant and may in some cases be clinically significant.

Clinical utility of femtosecond laser-assisted astigmatic keratotomy after cataract surgery.

To examine the clinical utility of femtosecond laser-assisted astigmatic keratotomy (FSL-AK) for eyes after cataract surgery. Eight eyes of 6 patients with an intraocular lens and corneal astigmatism of 2.0 diopters (D) or more underwent FSL-AK. The mean preoperative manifest cylindrical refraction was 2.88 ± 0.64 D and the mean corneal astigmatism was 2.84 ± 0.83 D. Paired symmetrical arcuate incisions were created with the same settings, except for the incision depth. Uncorrected distance visual acuity (UDVA), manifest cylindrical power, and surgically induced astigmatism (SIA) were measured at 1 day, 1 week, and 1 month postoperatively. Fourier analysis of corneal topography and incision depths measured with anterior-segment optical coherence tomography were evaluated 1 month postoperatively. In all eyes, the UDVA improved at 1 week and 1 month postoperatively, and the manifest cylinder also decreased postoperatively, while the SIA showed overcorrections in 6 eyes. Fourier analysis showed decreases in spherical and regular astigmatic components and increases in higher-order irregularity. The mean incision depth was measured as 60 µm deeper than the intended depth. The FSL-AK effectively reduced corneal astigmatism and improved the UDVA, although it was demonstrated that the deeper incisions led to overcorrection.