Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Postoperative changes of posterior corneal surface height after small incision lenticule extraction and femtosecond laser <i>in situ</i> keratomileusis / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To explore the posterior corneal surface height after femtosecond laser small incision lenticule extraction(SMILE)or femtosecond laser <i>in situ</i> keratomileusis surgery(Fs-LASIK). <p>METHODS: A retrospective analysis of 113 cases of patients(226 eyes)with myopia underwent laser corneal refractive surgery in our hospital from January to December 2016 was taken. There were 51 cases(102 eyes)with SMILE and 62(124 eyes)with Fs-LASIK. Postoperative posterior corneal surface height, uncorrected visual acuity, spherical equivalent change, operation safety were analyzed and compared between the two groups.<p>RESULTS: The preoperative posterior corneal surface height had no statistical difference between the two groups(<i>P</i>>0.05). Corneal surface height at 1, 3 and 6mo after operation were significantly higher than those before operation(<i>P</i><0.05), but the differences between the two groups at different time points after operation were not significant(<i>P</i>>0.05). Preoperative uncorrected visual acuity had no statistical difference between the two groups(<i>P</i>>0.05); postoperative uncorrected visual acuity at 1, 3 and 6mo were significantly better than those before operation(<i>P</i><0.05), but the differences between the two groups at different time points after operation were not significant(<i>P</i>>0.05). Preoperative spherical equivalent had no statistical difference between the two groups(<i>P</i>>0.05); postoperative spherical equivalent at 1wk were significantly better than those before operation(<i>P</i><0.05), but the differences between the two groups after operation were not significant(<i>P</i>>0.05). Postoperative incidence of adverse reactions such as corneal edema, corneal infection, diffuse lamellar keratitis and postoperative glare had no statistical difference between the two groups at 6mo after operation(<i>P</i>>0.05).<p>CONCLUSION: SMILE and Fs-LASIK can be safely and effectively correcting visual acuity, but posterior corneal surface partial forward occurred after either operation.

Characteristics of posterior corneal astigmatism and aberration in cataract patients with high myopia / 中华实验眼科杂志

Objective This study was to investigate the characteristics of posterior corneal astigmatism (PCA) and aberration in cataract patients with high myopia.Methods A retrospective study was designed.Two hundred and eighty-two eligible eyes of 190 cataract patients were enrolled in Eye and ENT Hospital of Fudan University from September to December,2014.The eyes were classified into two groups according to axial length (AL):high myopia group with 139 eyes (AL≥26 mm) and control group with 143 eyes (AL was 20 to 25 mm).The mean keratometric mid-radius of curvature (Km),corneal central thickness (CCT),astigmatism and aberrations were measured by the rotating Scheimpflug System (Pentacam),and the AL were measured by the partial coherence interferometry (IOL Master).This study followed the Helsinki declaration,and was approved by the Ethic Committee of Eye and ENT Hospital,Fudan University.Informed consent was signed from each patient.Results In high myopia group,the mean PCA was 0.3 D (range 0 ～ 0.9 D) and 92.8％ eyes had PCA values ＜0.5 D.The steep corneal meridian was aligned vertically (60°～ 120°) in 87.1％ eyes for the posterior corneal surface.There was no significant difference in PCA between the high myopia group and the control group (P =0.797).Significant positive linear correlations was found between PCA and anterior corneal astigmatism (ACA),PCA and anterior corneal root mean square (RMS),PCA and anterior lower-order RMS,PCA and posterior corneal RMS,PCA and posterior high-order RMS,PCA and posterior lower-order RMS (r =0.235,P =0.005;r =0.217,P =0.010;r =0.229,P =0.007;r =0.395,P =0.000;r =0.243,P =0.004;r =0.384,P =0.000).Compared with total corneal astigmatism (TCA),anterior corneal measurements overestimated with-the-rule astigmatism (WTR) by a mean of (0.27 ± 0.18) D in 65.67％ eyes,underestimated against-the-rule astigmatism (ATR) by (0.27 ± 0.18) D in 88.10％ eyes and underestimated oblique astigmatism (Obl) by (0.22 ± 0.10) D in 63.33％ eyes.Compared with total corneal aberrations,anterior corneal aberrations measurements overestimated by (0.275 ±0.176) μm in 87.05 ％ eyes,and the anterior corneal astigmatism types had no effect on the result.Conclusions In high myopia group,92.8％ eyes had PCA values ＜0.5 D and the main astigmatism type in posterior corneal surface was ATR.The posterior corneal astigmatism and aberration were needed to consider in choosing intraocular lens (IOL) before cataract surgery.

Caracterización morfológica de la superficie corneal posterior en córneas normales / Morphological characterization of the posterior corneal surface in normal corneas

OBJETIVO: describir las características de la superficie corneal posterior en córneas normales y las modificaciones de esta en pacientes a quienes se les realizó queratomileusis con láser in situ. MÉTODOS: fue realizado un estudio descriptivo, longitudinal y prospectivo en 282 ojos de pacientes que asistieron a la consulta de cirugía refractiva. Las variables estudiadas fueron: queratometría media central posterior, equivalente esférico, paquimetría óptica en la posición más delgada, astigmatismo topográfico anterior y posterior, astigmatismo refractivo y variación morfológica del mapa topográfico de elevación posterior respecto a la esfera de mejor ajuste. Fueron escogidos 27 ojos, los cuales reunían los criterios para cirugía refractiva láser y se les realizó la técnica queratomileusis con láser in situ. Se analizaron también las variables cantidad de ablación, estroma residual y diferencia de elevación posterior corneal, esta última obtenida del mapa de diferencia del tomógrafo Pentacam HR. RESULTADOS: la queratometría media posterior fue de -6,37 ± 0,22 dioptrías; la correlación entre la queratometría media posterior con respecto a la paquimetría óptica fue muy significativa (p= 0,008). La media de la diferencia de elevación máxima con respecto a la esfera de mejor ajuste posterior fue 5,33 µm; el 93,3 % de la muestra se encontraba dentro de valores normales. La diferencia de elevación posterior a través del tiempo fue de 18,38 µm ± 7,47 al mes y 14,95 µm ± 10,02. Se observó relación con la paquimetría y el estroma residual. CONCLUSIONES: la queratomileusis con láser in situ determina modificaciones en la superficie corneal posterior. El estroma residual es el factor más relacionado con estas modificaciones.

OBJECTIVE: to describe the characteristics of the posterior corneal surface in normal corneas and its changes in patients who underwent laser in situ keratomileusis. METHODS: prospective, longitudinal and descriptive study of 282 eyes from patients who went to the refractive surgery service. The studied variables were posterior central mean keratomery, spheral equivalent, optical pakimetry at the thinnest position, anterior and posterior topographic astigmatism, refractive astigmatism and morphological variation of the posterior elevation topographic map in relation to the best fit sphere. In this group, 27 eyes were selected, which met the criteria for laser refractive surgery using the laser in situ keratomileusis. Other analyzed variables were ablation amount, residual stroma and posterior corneal elevation difference, being the latter taken from the difference map outlined with the Pentacam HR tomography. RESULTS: mean posterior keratometry was -6,37 ± 0,22 dioptries; the correlation between mean posterior keratometry and optical pakimetry was very significant (p= 0,008). The mean difference of maximum elevation with respect to the best posterior fit sphere was 5,33 µm; 93,3 % of the sample was within the normal values. The correlation between the posterior elevation and the spheral equivalent was also significant (p= 0,019). The difference of the posterior elevation throughout the period was 18,38 µm ± 7,47 after a month and 14,95 µm ± 10,02 at the end of the period. There was correlation with pakimetry and residual stroma. CONCLUSIONS: laser in situ keratomileusis causes changes in the posterior corneal surface. The residual stroma is the factor most related with these changes.

Effect of related factors on the stability of posterior corneal surface after LASIK / 国际眼科杂志(Guoji Yanke Zazhi)

AIM:To discuss the related factors that affected the stability of posterior corneal surface after laser in situ keratomileusis ( LASIK) . METHODS:About 64 patients (64 eyes) were enrolled. The correlation among the changes in posterior corneal surface 6 month after LASIK, surgery method, corneal flap thickness ( FT ) , ablation thickness ( AT ) , postoperative residual corneal stroma thickness ( RCST ) , preoperative thinnest corneal thickness ( CT ) , flap thickness/preoperative thinnest corneal thickness ( FT/CT ) , ablation thickness/preoperative thinnest corneal thickness ( AT/CT) , postoperative residual corneal stroma thickness/preoperative thinnest corneal thickness ( RCST/CT) , anterior and posterior preoperative corneal height, the difference of the forward shift in posterior corneal surface ( diff value ) of preoperative and preoperative intraocular pressure were analyzed. RESULTS: The changes of diff value between preoperative and postoperative were related with diopter (r=0.419, P=0.014), AT (r=0.394, P=0.023), AT/CT (r=0.501, P=0.004), Diff value of preoperative (r=0.501, P=0. 004), RCST (r=-0. 385, P=0. 033) and RCST/CT (r=-0. 401, P=0. 025). The changes of height value from posterior corneal surface between preoperative and postoperative were related with diopter (r=0. 520, P=0. 002), AT (r=0.504, P=0. 003), AT/CT (r=0. 442, P=0. 013), Diff value of preoperative (r=0. 624, P=0. 000) and RCST/CT (r=-0. 394, P=0. 028). CONCLUSION: AT, RCST, AT/CT, RCST/CT and diff value of preoperative should be the key index that predicted the stability of posterior corneal surface after LASIK,the further research will give the range of safety value.

Reasearch progress in posterior corneal surface anterior protrusion after the excimer laser corneal refractive surgery / 中华实验眼科杂志

With the mature of techniques and development of equipments in excimer laser corneal refractive surgery,the postoperative complications are decreasing gradually.As the center of cornea become thin after laser in situ keratomileusis (LASIK)and laser subepithelial keratomileusis ( LASEK ),the strength of cornea and the intraocular pressure relatively step down,which can cause cornea anterior protrusion more or less.Because the posterior surface which is not directly affected by surgical process and healing process,so it is usually used to evaluate the protrusion of cornea.As the application of.ophthalmic anterior segment imaging and analysis system,we can get more message of cornea posterior surface.The manifestation,principle and precautionary measures of corneal posterior surface anterior protrusion after the excimer laser corneal refractive surgery were reviewed.

The Changes of Posterior Corneal Surface and High-Order Aberrations after Refractive Surgery in Moderate Myopia

PURPOSE: To compare forward shift of posterior corneal surface and higher-order aberration (HOA) changes after LASIK, LASEK, and wavefront-guided LASEK surgery in moderate myopia METHODS: One hundred eighty four eyes undergoing LASIK, LASEK and wavefront-guided LASEK with VISX STAR S4 were included in this study. The posterior corneal elevation was measured with Orbscan before, 2 and 4 months after surgery. Changes of the elevation were assessed using the difference map generated from preoperative and postoperative elevation maps. The values of higher-order aberrations were evaluated preoperatively and 2 months postoperatively with Wavefront aberrometer. RESULTS: The posterior corneal surface displayed forward shift of 27.2+/-11.45 micrometer, 24.3+/-9.76 micrometer in LASIK group, 23.4+/-10.5 micrometer, 23.6+/-10.55 micrometer in LASEK group, 24.0+/-14.95 micrometer, 28.4+/-14.72 micrometer in wavefront-guided LASEK group at 2 months and 4 months, respectively. There were no statistically significant differences among those three groups, and between 2 and 4 months. The root mean score (RMS) of HOA was increased after LASIK and LASEK (p=0.000, p=0.000, respectively). The mean change of HOA-RMS was significantly smaller in wavefront-guided LASEK than LASIK or LASEK (p=0.000, p=0.000, respectively, Bonferroni-corrected). CONCLUSIONS: The changes of posterior corneal surface forward shift showed no difference among LASIK, LASEK and wavefront-guided LASEK in moderate myopia. HOAs were significantly increased after LASIK and LASEK. The changes of HOAs were significant smaller in wavefront-guided LASEK than LASIK or LASEK.

Comparison of Anterior and Posterior Corneal Surface Change after Laser In Situ Keratomileusis and Laser Epithelial Keratomileusis

PURPOSE: To compare the time course of the change in corneal surface between LASIK and LASEK groups, which show the difference in residual bed thickness. METHODS: Twenty-one eyes of 15 patients who underwent LASIK and 20 eyes of 12 patients who underwent LASEK were included in this study and were evaluated on a review retrospectively. Corneal topography was performed preoperatively, 1 week, 2 months, 6 months, and 1 year postoperatively. The change in corneal surface was measured with the Orbscan II. The change in the elevation of the anterior corneal surface was assessed using the difference map produced from the first postoperative week and the subsequent postoperative maps. The elevation of the posterior corneal surface was measured using the difference map generated from the preoperative and postoperative elevation maps. RESULTS: After LASIK and LASEK, the posterior corneal surface was shifted anteriorly by 18.87 +/- 5.91 micrometer and 28.77 +/- 15.46 micrometer at 1 week, 15.43 +/- 6.49 micrometer and 16.03 +/- 11.32 micrometer at 2 months, 15.58 +/- 6.19 micrometer and 15.14 +/- 7.17 micrometer at 6 months, and 16.38 +/- 6.67 micrometer, 12.81 +/- 9.94 micrometer at 1 year, respectively. Compared to the 1 week postoperative measurement, average posterior corneal surface in the LASIK group reduced by 3.44 micrometer at 1 year (p=.175) ; in the LASEK group, it reduced by 23.24 micrometer at 1 year (p=.020). CONCLUSIONS: In conclusion, in both groups, the posterior corneal surface shifted forward in the early time point postoperatively, and thereafter, it showed a trend toward gradual progressive backward shift over time, but not to the preoperative levels. The elevation of the posterior corneal surface was reduced relatively more in LASEK than in LASIK at 1 year after surgery.

Change of Posterior Corneal Surface after Laser In Situ Keratomileusis; One Year Fallow-up

PURPOSE: To investigate the change of the posterior corneal surface for 1 year after LASIK METHODS: Ninety-nine eyes of 57 patients who underwent LASIK were evaluated retrospectively. The posterior corneal surface was evaluated before surgery and at 1 week, 2 months, 6 months and 1 year postoperatively. The patients were divided into two groups based on the preoperative mean spherical equivalent (Group I; -2.5 ~ -6.0 D, Group II; -6 ~ -10 D) and two groups based on the residual bed thickness (RBT: Group A; 250 ~ 300 micrometer, Group B; 300 ~ 350 micrometer). We also grouped them based on the ablation percentage of the total corneal thickness (P/TCT: Group 1; below 10%, Group 2; 10-15%, Group 3; 15-20%) RESULTS: The posterior corneal surface in Group I was shifted forward 14.19 +/- 8.98 micrometer at 1 week, 7.93 +/- 5.64 micrometer at 1 year after LASIK, and 19.77 +/- 6.97 micrometer and 14.93 +/- 6.95 micrometer in Group II, respectively. It was displayed forward shift 19.48 +/- 8.54 micrometer at 1 week and 13.04 +/- 7.14 micrometer at 1 year in Group A and 11.64 +/- 6.09 micrometer and 7.07 +/- 5.26 micrometer in Group B, respectively. The values at the same times were 8.49 +/- 5.83 micrometer and 5.45 +/- 4.18 micrometer in Group 1, 17.21 +/- 7.73 micrometer and 9.12 +/- 5.26 micrometer in Group 2 and 20.25 +/- 8.16 micrometer and 16.05 +/- 7.24 micrometer in Group 3, respectively. CONCLUSIONS: The posterior corneal surface shifted forward early time after LASIK, but showed a trend toward gradual backward shifted over time. The eyes with higher myopia, thinner RBT and higher P/TCT were more shifted forward the posterior corneal surface at l year after LASIK.

Factors Affecting the Anterior Displacement of Posterior Corneal Surface after Laser In Situ Keratomileusis

PURPOSE: To determine factors which influence forward displacement of the posterior surface of conea after performing LASIK with residual corneal thickness greater than 250 micro meter. METHODS: We studied 100 eyes of 50 myopic patients with an expected residual corneal thickness of greater than 250 micro meter after underwent LASIK. Residual corneal thickness, amount of laser ablation, intraocular pressure, spherical equivalent of cornea (keratometer), corneal diameter, corneal thickness, and anterior chamber depth were obtained at the preoperative stage, the postoperative one week, one month. Computed topography of cornea was performed between before and after LASIK. We evaluated the influence the forward displacement of posterior surface of conea by LASIK procedure. RESULTS: Average forward displacement of posterior surface of the cornea was 38+/-12 micro meter, and among preoperative factors, preoperative corneal thickness showed relatively high correlation with r=0.462 (P<0.001), having influence on the forward displacement. The displacement measured 1 month after LASIK was shown to decrease slightly (31+/-8 micro meter) compared that the displacement measured at 1 week after LASIK. CONCLUSIONS: Despite performing LASIK with residual corneal thickness of greater than 250 micro meter, if pre- operative corneal thickness is thin, one should be careful about anterior displacement of corneal posterior surface, and this change usually occurs within 1 week.

Factors Associated with the Posterior Corneal Surface Elevation in Mmyopic Eye

PURPOSE: To know the factors associated with the posterior corneal surface elevation in myopic eye. METHODS: The posterior corneal surface elevation (PCSE), keratometry, central corneal thickness (CCT), peripheral corneal thickness (PCT), thinnest corneal thickness (TCT) were measured in 64 right myopic eyes with the Orbscan topography system. The correlation between PCSE and age, refractive error, intraocular pressure (IOP), keratometry, CCT, TCT, PCT, PCT-CCT, PCT/CCT, PCT-TCT, and PCT/TCT was evaluated. RESULTS: The posterior corneal surface elevation has correlation with CCT (r:.0.3306, p:0.0071), TCT ( r :.0.4094, p:0.0007), PCT-CCT(r:0.3326, p:0.0068), PCT/CCT (r:0.3759, p:0.0020), PCT-TCT (r: 0.4750, p:0.0001), and PCT/TCT (r:0.5145, p:0.0001) but does not have correlation with age, keratometry, refractive error, IOP (r:.0.0627, p:0.6225), and PCT. CONCLUSIONS: In myopic eyes, the posterior corneal surface elevation correlates with central corneal thickness and specifically the ratio PCT to TCT.