Near-term analysis of corneal epithelial thickness after cataract surgery and its correlation with epithelial cell changes and visual acuity

Corneal Epithelial Thickness Mapping: A Major Review

The corneal epithelium (CE) is the outermost layer of the cornea with constant turnover, relative stability, remarkable plasticity, and compensatory properties to mask alterations in the underlying stroma. The advent of quantitative imaging modalities capable of producing epithelial thickness mapping (ETM) has made it possible to characterize better the different patterns of epithelial remodeling. In this comprehensive synthesis, we reviewed all available data on ETM with different methods, including very high-frequency ultrasound (VHF-US) and spectral-domain optical coherence tomography (SD-OCT) in normal individuals, corneal or systemic diseases, and corneal surgical scenarios. We excluded OCT studies that manually measured the corneal epithelial thickness (CET) (e.g., by digital calipers) or the CE (e.g., by confocal scanning or handheld pachymeters). A comparison of different CET measuring technologies and devices capable of producing thickness maps is provided. Normative data on CET and the possible effects of gender, aging, diurnal changes, refraction, and intraocular pressure are discussed. We also reviewed ETM data in several corneal disorders, including keratoconus, corneal dystrophies, recurrent epithelial erosion, herpes keratitis, keratoplasty, bullous keratopathy, carcinoma in situ, pterygium, and limbal stem cell deficiency. The available data on the potential role of ETM in indicating refractive surgeries, planning the procedure, and assessing postoperative changes are reviewed. Alterations in ETM in systemic and ocular conditions such as eyelid abnormalities and dry eye disease and the effects of contact lenses, topical medications, and cataract surgery on the ETM profile are discussed.

Real-time corneal thickness changes during phacoemulsification cataract surgery

PURPOSE

To observe the changes in corneal thickness during phacoemulsification cataract surgery and to analyze the influencing factors.

METHODS

One hundred two patients (102 eyes) with cataracts undergoing phacoemulsification cataract surgery at Shandong Eye Hospital between July and October 2021 were included. Intraoperative OCT was applied to capture real-time images preoperatively, before and after ultrasonic emulsification, at the end of irrigation aspiration and the end of surgery. Then, the corneal thickness at the above time points was measured using Photoshop software.

RESULTS

The corneal thickness of 102 cataract patients was 511.79 ± 31.46 μm before operation and 512.71 ± 31.51 μm at the beginning of phacoemulsification, which increased by 0.91 ± 1.48 μm (0.2%). At the end of ultrasonic emulsification, the corneal thickness was 521.58 ± 32.75 μm and 8.87 ± 8.71 μm (1.7%) thicker than that before the procedure. After irrigation aspiration, the corneal thickness reached 528.09 ± 33.87 μm, which increased by 6.52 ± 6.38 μm (1.3%) compared with that of the previous step. At the end of the operation, the corneal thickness was 539.19 ± 33.88 μm, 11.09 ± 10.92 μm, and 27.37 ± 13.64 μm thicker than that of the previous step and the preoperative thickness, respectively, with an overall increase of 5.3%. The differences were statistically significant at all time points (all P < 0.001). Correlation analysis showed that postoperative corneal thickness changes were correlated with age, cataract lens nuclear grade, actual phacoemulsification time (APT), effective phacoemulsification time (EPT), average phacoemulsification energy (APE), total surgery time (TST), cell density (CD), maximum cell area (MAX), and cell area standard deviation (SD) (all P < 0.05), while the changes in thickness were not correlated with gender, cell area coefficient of variation (CV), percentage of hexagonal cells (6A), average cell area (AVE), or minimum cell area (MIN) (all P > 0.05).

CONCLUSIONS

During phacoemulsification cataract surgery, corneal thickness gradually increases in real time with the increase of perfusion pressure and intraocular manipulation time. The real-time magnitude of intraoperative corneal thickness change is closely related to lens nucleus hardness, corneal endothelial cell density, ultrasound energy, and time for emulsification.

Comparison of central corneal thickness in corneal edema by ultrasound pachymetry, specular microscopy, and anterior segment optical coherence tomography

PURPOSE

The purpose of this study was to compare ultrasound pachymetry Ultrasound pachymetry (UP), specular microscopy (SM), and anterior segment optical coherence tomography (ASOCT) in the measurement of central corneal thickness (CCT) in cases of corneal edema before and after uncomplicated phacoemulsification.

METHODS

Preoperative pachymetric measurements were performed in all patients before cataract surgery. Sixty -seven patients who developed corneal edema after routine faoemulsification surgery were included in the study. CCT measurements were made the day before surgery and on the 1^st, 7^th, and 14^th days after surgery. Correlation and agreement between the devices were quantified with the intraclass correlation coefficient (ICC), limits of agreement, and Bland-Altman plots.

RESULTS

The mean age of the patients was 70.99 ± 9.56 (36-92) years. While CCT could be measured in all eyes with ASOCT after surgery, the number of eyes measured with UP and SM were 24 (11.7%) and 27 (16.1%), 55 (82.1%) and 52 (77.6%), and 46 (88.8%) and 45 (86.9%) on postoperative days 1, 7, and 14, respectively. ICC values between UP and SM, UP and ASOCT, and SM and ASOCT, respectively, were: preoperative 0.91, 0.94, and 0.92; 1^st postoperative day 0.93, 0.86, and 0.93; 7^th postoperative day 0.94, 0.85, and 0.96; and 14^th postoperative day 0.95, 0.92, and 0.96.

CONCLUSION

In all eyes with corneal edema, CCT measurements can be taken with ASOCT; however, in some cases, CCT measurements with SM and UP cannot be taken. However, there is a good correlation between measurements taken with these devices.

Change Patterns in Corneal Intrinsic Aberrations and Nerve Density after Cataract Surgery in Patients with Dry Eye Disease

This study aimed to evaluate the change patterns in corneal intrinsic aberrations and nerve density after cataract surgery in dry eye disease. The preoperative, 1- and 3-month postoperative dry eye-related parameters were obtained by the Oculus keratograph and the ocular surface disease index questionnaire. The corneal intrinsic aberrations were measured using the Pentacam HR system. In vivo confocal microscopy was performed to observe the vortical and peripheral corneal nerves. An artificial intelligence technique run by the deep learning model generated the corneal nerve parameters. Corneal aberrations on the anterior and total corneal surfaces were significantly increased at 1 month compared with the baseline (p < 0.05) but gradually returned to the baseline by 3 months (p > 0.05). However, the change in posterior corneal aberration lasted up to 3 months (p < 0.05). There was a significant decrease in the corneal vortical nerve maximum length and average density after the operation (p < 0.05), and this damage lasted approximately 3 months. The corneal vortical nerve maximum length and average density were negatively correlated with the anterior corneal surface aberrations before and 1 month after the operation (correlation coefficients, CC = −0.26, −0.25, −0.28; all p < 0.05). Corneal vortex provided a unique site to observe long-term corneal nerve injury related to eye dryness. The continuous damage to the corneal vortical nerve may be due to the continuous dry eye state.

Density and distribution of dendritiform cells in the peripheral cornea of healthy subjects using in vivo confocal microscopy

PURPOSE

To establish dendritiform cell (DC) density and morphological parameters in the central and peripheral cornea in a large healthy cohort, using in vivo confocal microscopy (IVCM).

METHODS

A prospective, cross-sectional, observational study was conducted in 85 healthy volunteers (n = 85 eyes). IVCM images of corneal center and four peripheral zones were analyzed for DC density and morphology to compare means and assess correlations (p < 0.05 being statistically significant).

RESULTS

Central cornea had lower DC density (40.83 ± 5.14 cells/mm²; mean ± SEM) as compared to peripheral cornea (75.42 ± 2.67 cells/mm², p < 0.0001). Inferior and superior zones demonstrated higher DC density (105.01 ± 7.12 and 90.62 ± 4.62 cells/mm²) compared to the nasal and temporal zones (59.93 ± 3.42 and 51.77 ± 2.98 cells/mm², p < 0.0001). Similarly, lower DC size, field and number of dendrites were observed in the central as compared to the average peripheral cornea (p < 0.0001), with highest values in the inferior zone (p < 0.001 for all, except p < 0.05 for number of dendrites in superior zone). DC parameters did not correlate with age or gender. Inter-observer reliability was 0.987 for DC density and 0.771-0.922 for morphology.

CONCLUSION

In healthy individuals, the peripheral cornea demonstrates higher DC density and larger morphology compared to the center, with highest values in the inferior zone. We provide the largest normative cohort for sub-stratified DC density and morphology, which can be used in future clinical trials to compare differential changes in diseased states. Furthermore, as DC parameters in the peripheral zones are dissimilar, random sampling of peripheral cornea may be inaccurate.

Defining the surgical footprint in cataract surgery: patient-related outcomes dependent on the experience of the surgeon

PURPOSE

To investigate which patient-related outcomes are dependent on the experience of the cataract surgeon.

METHODS

The study was designed as a prospective observational study. Novice (<150 surgeries performed) and experienced (>1000 surgeries performed) cataract surgeons from the Department of Ophthalmology, Rigshospitalet - Glostrup and Nordsjaellands Hospital - Hillerød were included in the study. Patients operated by the included surgeons were examined preoperatively, 1 day, 3 days, and 3 weeks after standard, noncomplicated cataract surgery. Primary outcomes were change in central corneal thickness and endothelial cell loss. Secondary outcomes were best-corrected visual acuity, intraocular pressure, aqueous flare, central macular thickness, and surgical complications.

RESULTS

Surgery performed by novice surgeons resulted in significantly lower visual acuity (mean -3.6 letters (Early Treatment Diabetic Retinopathy Study (ETDRS)); 95% CI: -7.3; -0.4, p = 0.03) and greater corneal thickness (mean 26.7 µm; 95% CI: 6.8; 46.6, p = 0.01) on the first day postoperative than surgery performed by experienced surgeons.

CONCLUSION

The experience of the cataract surgeon affected visual acuity and central corneal thickness in the immediate postoperative period. In the future, these patient-related outcomes may be used to assess the technical proficiency of surgical trainees and investigate the effect of different training programs.

Femtosecond laser-assisted cataract surgery in eyes with shallow anterior chamber depth: comparison with conventional phacoemulsification

PURPOSE

To compare the postoperative outcomes between femtosecond laser-assisted cataract surgery (FLACS) and conventional phacoemulsification in eyes with shallow anterior chamber depth (ACD).

SETTING

Eye Clinic, NEUROFARBA Department, University of Florence, Italy.

DESIGN

Prospective case series.

METHODS

Forty eyes of 40 patients with senile cataract and true ACD less than 2.00 mm underwent FLACS (femto group, n = 20) or manual phacoemulsification (phacoemulsification group, n = 20). Preoperatively and 1 week and 1 month and 6 months postoperatively, central corneal thickness (CCT) and endothelial cell density were evaluated; basal epithelial cell (BEC) and Langerhans dendritic cell (LDC) densities and keratocyte activation were assessed using in vivo corneal confocal microscopy. Intraoperative parameters such as cumulative dissipated energy (CDE) and ultrasound (US) power were recorded.

RESULTS

Endothelial cell loss (ECL) was significantly lower in the femto group at all timepoints (P ≤ .001). In the phacoemulsification group, the CCT was significantly higher 1 week (P < .001) and 1 month (P < .001) postoperatively than preoperatively; conversely, in the femto group, it was higher only after 1 week (P < .001). BECs and LDCs significantly increased at 1 postoperative week (P < .001), returning to preoperative values after 1 month in both groups. Keratocyte activation remained significantly higher at 1 postoperative month only in the phacoemulsification group (P = .005). CDE and US power were lower in the femto group (P = .017 and P = .001, respectively); they were correlated with ECL (r = 0.662, P = .000; r = 0.389, P = .013).

CONCLUSIONS

In eyes with shallow ACD, FLACS was a safe and an effective technique, significantly reducing the postoperative ECL and corneal inflammation compared with conventional phacoemulsification.

Evaluation of Safety Following Optic Exchange of a Modular Intraocular Lens

PURPOSE

To characterize safety of optic exchange using a modular lens.

SETTING

3 study sites (New Zealand, Philippines).

DESIGN

Prospective clinical study.

METHODS

Harmoni modular intraocular lens (HMIOL) with separate base and optic components was implanted in the study eye (monovision target -1.5 D). Contralateral eyes received standard monofocal lenses. Subjects could elect optic exchange 3 months after primary implantation. Adverse events (AEs) and endothelial cell loss (ECL) were assessed through 12-months follow-up.

RESULTS

114 subjects successfully received HMIOL and 114 received control lens in contralateral eye. At month 3, 65 HMIOL eyes had optic exchange due to unsatisfactory visual outcome from high monovision (Exchange cohort); 49 eyes received no exchange (No Exchange cohort). Exchange, No Exchange, and Control cohorts reported ocular AEs in 10 (15%), 6 (12%), and 14 (12%) eyes. No posterior capsular rupture occurred during optic exchange procedures. Short-term (12-month) posterior capsule opacification (PCO) evaluation showed all eyes had PCO grade ≤1 at month 12; no YAG capsulotomy was performed in the Exchange cohort. No Exchange and Exchange cohorts had similar ECL at 3 months versus preoperative baseline (-4.5%, n=48 and -4.0%, n=65). In the Exchange cohort, additional 2.7% ECL occurred 3 months after optic exchange compared with pre-exchange baseline; ECL was significantly below the 14% threshold (P<0.001) and was 5.8% at 12 months.

CONCLUSIONS

HMIOL safety outcomes were comparable with standard monofocal lenses; HMIOL may provide an effective method for correcting postoperative refractive errors.

Triphasic polymeric corneal coating gel versus a balanced salt solution irrigation during cataract surgery: A postoperative anterior segment optical coherence tomography analysis and confocal microscopy evaluation

PURPOSE

To investigate the safety and efficacy of the intraoperative use of a triphasic polymeric gel as corneal coating during cataract surgery and its effect on postoperative ocular comfort.

SETTING

Eye Clinic, University of Florence, Italy.

DESIGN

Longitudinal observational retrospective study.

METHODS

Data on patients who received an application of a polysaccharide blend of hydroxypropyl methylcellulose, xanthan gum, and carrageenan (EyeDRO) on the corneal surface and data on patients who received a balanced salt solution during phacoemulsification surgery were analyzed. The central corneal thickness (CCT) and epithelial thickness were examined using anterior segment optical coherence tomography, and the corneal basal epithelial cell (BEC) and Langerhans cell densities by in vivo confocal microscopy. The ocular surface disease index (OSDI) score, tear breakup time (TBUT), and Schirmer test I values were evaluated.

RESULTS

The study comprised data on 28 patients in the coating gel group and 26 patients in the balanced salt solution group. In the coating gel group, the CCT and epithelial thickness values returned to the baseline value within 5 and 15 postoperative days, respectively; the BEC and Langerhans cell densities returned to baseline levels within 15 and 30 postoperative days. In the balanced salt solution group, the mean BEC and Langerhans cell densities were significantly different from the preoperative values at all follow-up assessments. The TBUT returned to the preoperative level at day 5 in the coating gel group. The OSDI scores returned to the preoperative values after 15 days in the coating gel group and 30 days in the balanced salt solution group.

CONCLUSIONS

The use of a tripolymeric gel as a corneal coating during cataract surgery played a protective role on the corneal surface and reduced postoperative discomfort symptoms.

Long-Term Visual Quality after Microincision Cataract Surgery

Purpose

Few studies have focused on long-term postoperative visual quality. This study aimed to evaluate the long-term visual quality after microincision cataract surgery (MICS).

Methods

96 patients (144 eyes) diagnosed with age-related cataracts were enrolled in this one-year study. The patients underwent MICS and received aspheric monofocal intraocular lens implants. Uncorrected distance visual acuity (UDVA) was evaluated together with best-corrected distance visual acuity (BCDVA), best-corrected near visual acuity (BCNVA), contrast sensitivity, and surgically induced astigmatism (SIA).

Results

Compared to preoperative measurements, UDVA, BCDVA, and BCNVA were significantly better after surgery (P < 0.001), and they remained stable throughout follow-up. Contrast sensitivity was also significantly better after surgery (P < 0.001). Mean SIA during follow-up was 0.57 ± 0.33 D at 1 week, 0.36 ± 0.25 D at 3 months, and 0.18 ± 0.16 D at 1 year. SIA decreased significantly during the postoperative period (P < 0.001). The 1-year postoperative absolute residual diopter value was 0.32 ± 0.28 D.

Conclusion

MICS can provide excellent visual quality as soon as on postoperative day 1, which persists during the follow-up period of 1 year. In contrast to previous studies, SIA decreases over time and may not completely stabilize for as long as 1 year postoperatively.

Epithelial Remodeling Following Phacoemulsification in Diabetic Patients Using Anterior-Segment Optical Coherence Tomography: A Comparative Study

Purpose

To compare the effect of phacoemulsification on corneal epithelial thickness in diabetic and nondiabetic cataract patients.

Methods

Fifty eyes with cataracts were enrolled in a prospective comparative interventional study. They were divided into two groups: group A (diabetics) and group B (nondiabetics) and underwent uneventful phacoemulsification. Epithelial thickness was assessed in the central, paracentral, and peripheral cornea on the first day and at 1 week, 1 month, and 3 months postoperatively using spectral-domain ocular coherence tomography.

Results

A significant increase in the first-day postoperative central epithelial thickness was noticed in both groups (57.16±3.5 µm and 55.96±2.81 µm in groups A and B, respectively), with increased baseline epithelial thickness of 3.8±2.1 µm and 3.4±2.14 µm in groups A and B, respectively (P<0.001). A significant decrease in epithelial thickness was noticed in both groups after 1 week (−2.40±3.1 µm and −2.76±2.71 µm in group A and B, respectively). No further significant change was noticed in the nondiabetic group at 1 month; however, significant reductions in for central epithelial thickness were found in the diabetic group up to the first month (−0.80±1.9 µm, P=0.05). Central corneal thickness followed the same pattern of change as the epithelium. A nonsignificant delay in visual acuity improvement was noticed in diabetic patients.

Conclusion

Phacoemulsification induces a temporary increase in corneal and epithelial thickness that should resolve by the first week postoperatively. However, diabetic patients had slower epithelial recovery that took up to 1 month, which could be reflected in delayed visual recovery with no effect on the final visual outcome.

[Changes in corneal nerve fibers after microinvasive cataract surgery (a preliminary report)]

INTRODUCTION

Potential changes in corneal nerve fibers (CNF) induced by cataract phacoemulsification remain insufficiently studied. The need for research in this direction is dictated by a number of circumstances: introduction of corneal confocal microscopy into clinical practice, the need for phaco surgery in the presence of corneal changes of various genesis, the possible negative impact of laser radiation during hybrid (femtosecond laser-assisted) phacoemulsification.

PURPOSE

To assess the changes in CNF after various methods of microinvasive cataract surgery.

MATERIAL AND METHODS

The studies were conducted in patients aged 50 to 60 years who underwent standard ultrasound and hybrid phacoemulsification; the patients were respectively divided into two groups (30 surgeries each). The algorithm for assessing the state of CNF involved laser confocal microscopy using original software. To quantify the state of the nerves, two coefficients were used: CNF orientation anisotropy (KΔL) and CNF orientation symmetry (K_sym).

RESULTS

Regardless of the surgery technique, tendencies were noted for the orientation anisotropy coefficient to decrease and the orientation symmetry coefficient to increase, which are conditionally comparable with previously identified age-related changes in CNF. After hybrid phacoemulsification, a decrease in the orientation anisotropy coefficient 2-2.5 months after the intervention turned out to be statistically less significant compared to the standard ultrasound technique.

CONCLUSION

Further research should be aimed at analyzing the long-term results of both microinvasive phacosurgery techniques and the «classical» extracapsular cataract extraction, which remains the method of choice in a number of clinical situations.

[Phacosurgery effects on the condition of corneal nerve fibers]

The question of potential changes in the nerve fibers of the cornea induced by phacosurgery remains poorly investigated. This is a review of results of many individual studies aimed at assessing the condition of corneal nerve fibers following different techniques of cataract removal. The authors substantiate the necessity for structural analysis of fiber changes based on in vivo confocal microscopy of the cornea. Functional assessment of corneal sensitivity (esthesiometry) does not allow objective conclusions, for several reasons. Further studies on corneal nerve changes after phacosurgery could be directed at improving software products for objective quantitative assessment of corneal nerve fibers and analyzing long-term results of various phacosurgery techniques.

Central corneal epithelial thickness changes after half-moon supracapsular nucleofractis phacoemulsification technique

PURPOSE

To find out the effect of half-moon supracapsular nucleofractis technique on central corneal epithelial thickness (CET) measured by spectral domain anterior segment optical coherence tomography (AS-OCT).

MATERIALS AND METHODS

Patients who underwent uneventful cataract surgery by the same surgeon with the same technique were recruited in this study. The effective phaco time (EPT) was recorded in each surgery. Central CET was measured by AS-OCT 1 day before and 1, 3, 7 days after surgery. CET was measured without precorneal tear film layer, and non-epithelial central corneal thickness was also calculated manually. Preoperative and postoperative values were compared by statistical analysis.

RESULTS

Thirty-one eyes of 31 patients were included in this study. The mean age of patients was 65.03 ± 11.47 years. On the first day of surgery, increase in mean CET was statistically significant, but on the 3rd and 7th day after surgery, this increase was declined (p = 0.001, p = 0.367, p = 1, respectively). A statistically significant positive correlation was found between mean EPT and mean CET on the first postoperative day (p = 0.013, r = 0.470). On the 3rd and 7th day, this correlation was not statistically significant (p = 0.055, p = 0.454, respectively).

CONCLUSION

Mean central CET was statistically thicker and positive correlated with EPT on the first postoperative day. But on the 7th day, it declined to preoperative values.

Post-lens tear turbidity and visual quality after scleral lens wear

BACKGROUND

The aim was to evaluate the turbidity and thickness of the post-lens tear layer and its effect on visual quality in patients with keratoconus after the beginning of lens wear and before lens removal at the end of eight hours.

METHODS

Twenty-six patients with keratoconus (aged 36.95 ± 8.95 years) participated voluntarily in the study. The sample was divided into two groups: patients with intrastromal corneal ring (ICRS group) and patients without ICRS (KC group). Distance visual acuity (VA), contrast sensitivity, pachymetry, post-lens tear layer height and post-lens tear layer turbidity (percentage area occupied and number of particles per mm² ) were evaluated with optical coherence tomography before and after wearing a scleral lens.

RESULTS

A significant increase of turbidity was found in all groups assessed (p < 0.05). The number of particles per square millimetre was eight times higher after scleral lens wear than at the beginning of wearing the lens for all groups. VA decreases in all groups after scleral lens wear (p < 0.001). All patients showed a statistical diminishing of contrast sensitivity after scleral lens wear (p < 0.05). A significant correlation was found for both turbidity parameters with distance VA but no correlation between turbidity and post-lens tear layer thickness at the beginning was found (p > 0.05). A strong correlation in all groups between the post-lens tear layer at the beginning and differences of tear layer thickness between two measures was also found (p < 0.05).

CONCLUSION

The VA decrease during the scleral lens wearing, filled with preserved saline solution, was due to the increasing post-lens tear layer turbidity.