Anatomic Predictive Factors of Acute Corneal Hydrops in Keratoconus

Scheimpflug-Based Tomographic Risk Factors for the Development of Acute Corneal Hydrops in Keratoconus

PURPOSE

The purpose of this study was to assess the risk factors that predispose patients with keratoconus to develop acute corneal hydrops (ACH), including both clinical and tomographic risk factors. We additionally describe tomographic changes of the cornea over time after ACH.

METHODS

We retrospectively reviewed patients with keratoconus who were followed at our institution from January 2015 to May 2023. Control eyes, defined as eyes with advanced keratoconus (stage IV Amsler-Krumeich classification on initial examination) were compared with eyes that developed ACH. Demographic, clinical, and tomographic factors were investigated. Visual acuity, keratometry, and corneal thickness were assessed at each follow-up visit to monitor progression over time.

RESULTS

Twenty-three eyes of 19 patients developed ACH over the follow-up period. The incidence of known clinical associations including seasonal allergies, eye rubbing, snoring, asthma, and eczema was similar between the hydrops and control groups. There was a higher incidence of Down syndrome in the hydrops group ( P = 0.04). Eyes that developed hydrops had similar best corrected visual acuity on initial examination, but had steeper keratometry ( P = 0.003) and thinner corneas ( P < 0.001) than controls at baseline. After hydrops, progressive corneal flattening and reduced maximum keratometry occurred over time. However, final best corrected visual acuity was worse compared with initial examination before hydrops ( P = 0.03), as well as compared with control eyes ( P < 0.001).

CONCLUSIONS

Risk factors of developing ACH include steep keratometry and thin corneas as well as Down syndrome. Although corneal flattening will occur after resolution of acute corneal edema, visual acuity worsened after ACH.

Comparison of different corneal imaging modalities using artificial intelligence for diagnosis of keratoconus: a systematic review and meta-analysis

PURPOSE

This review was designed to compare different corneal imaging modalities using artificial intelligence (AI) for the diagnosis of keratoconus (KCN), subclinical KCN (SKCN), and forme fruste KCN (FFKCN).

METHODS

A comprehensive systematic search was conducted in scientific databases, including Web of Science, PubMed, Scopus, and Google Scholar based on the PRISMA statement. Two independent reviewers assessed all potential publications on AI and KCN up to March 2022. The Critical Appraisal Skills Program (CASP) 11-item checklist was used to evaluate the validity of the studies. Eligible articles were categorized into three groups (KCN, SKCN, and FFKCN) and included in the meta-analysis. The pooled estimate of accuracy (PEA) was calculated for all selected articles.

RESULTS

The initial search yielded 575 relevant publications, of which 36 met the CASP quality criteria and were included in the analysis. Qualitative assessment showed that Scheimpflug and Placido combined with biomechanical and wavefront evaluations improved KCN detection (PEA, 99.2, and 99.0, respectively). The Scheimpflug system (92.25 PEA, 95% CI, 94.76-97.51) and a combination of Scheimpflug and Placido (96.44 PEA, 95% CI, 93.13-98.19) had the highest diagnostic accuracy for the detection of SKCN and FFKCN, respectively. The meta-analysis outcomes showed no significant difference between the CASP score and accuracy of the publications (all P > 0.05).

CONCLUSIONS

Simultaneous Scheimpflug and Placido corneal imaging methods provide high diagnostic accuracy for early detection of keratoconus. The use of AI models improves the discrimination of keratoconic eyes from normal corneas.

Double-Docking Technique for Femtosecond Laser-Assisted Deep Anterior Lamellar Keratoplasty: A Retrospective Consecutive Case Series Study of Advanced Keratoconus

PURPOSE

The aim of this study was to report the clinical outcomes and prognosis of femtosecond laser (FSL)-assisted double-docking deep anterior lamellar keratoplasty (DD-DALK) for advanced keratoconus (AK).

METHODS

Records of consecutive patients with keratoconus who underwent FSL-assisted DALK (DD-DALK) were reviewed.

RESULTS

We analyzed 37 eyes from 37 patients who underwent DD-DALK. Sixty-eight percent of eyes had a successful big-bubble formation and 27% had a manual dissection to achieve the DALK deep dissection. Stromal scarring was associated with not achieving a big bubble. Intraoperative conversion to penetrating keratoplasty was conducted in 2 cases (5%). The best-corrected visual acuity improved from a median (± interquartile range) of 1.55 ±0.25 logMAR preoperatively to 0.2 ±0.2 logMAR ( P < 0.0001). The median postoperative spherical equivalent was -5.75 ±2.75 D with a median astigmatism of -3.5 ±1.3 D. BCVA, SE, and astigmatism were not statistically different between patients who underwent DD-DALK and patients who underwent manual DALK. Stromal scarring was associated with big-bubble (BB) formation failure ( P = 0.003). All patients with failed BB requiring manual dissection had anterior stromal scarring.

CONCLUSIONS

DD-DALK is safe and reproducible. The success rate of BB formation is hampered by stromal scarring.

Corneal Hydrops - Aetiology and Advanced Therapeutic Strategies

Acute hydrops refers to sudden corneal edema caused by rupture of Descemet's membrane (DM) - often in progressive keratectasia. It leads to a sudden decrease in visual acuity, pain, and foreign body sensation as well as an increased glare sensation. Acute hydrops usually heals with scarring within months, but complications such as corneal perforation, infectious keratitis, and corneal vascularization may occur. The prevalence in keratoconus patients is 2.6 to 2.8%. Risk factors include keratoconjunctivitis vernalis, atopic dermatitis, high keratometry, male gender, and eye rubbing. Keratoplasty should be avoided in the acute phase. The prognosis of the graft is reduced, and after scar healing of the hydrops, wearing contact lenses or glasses may be possible again. Conservative therapy alone with lubricants and hyperosmolar eye drops, prophylactic antibiotic eye drops to prevent superinfection, and topical steroids was long considered the only possible form of treatment. However, healing under conservative therapy takes an average of over 100 days. In the meantime, there are different surgical strategies that rapidly shorten the healing and thus the recovery phase of the patients to a few days. If the DM is detached without tension, a simple injection of gas into the anterior chamber can already lead to reattachment and thus to almost immediate deswelling of the cornea. If the DM is under tension, predescemetal sutures combined with a gas injection into the anterior chamber can flatten the cornea and reattach the DM. Mini-Descemet membrane endothelial keratoplasty (mini-DMEK) allows for sutureless closure of the DM defect by transplantation of a small (< 5 mm) graft. In cases of particularly large DM tears and very pronounced hydrops, suture loosening and relapse may occur after the placement of predescemetal sutures. Mini-DMEK can then lead to permanent healing, but in contrast to simple corneal sutures, it is usually performed under general anesthesia and by aid of intraoperative optical coherence tomography. The very good results with regard to the rapid healing prove that surgical therapy makes sense in the vast majority of patients with acute hydrops and should be initiated quickly.

Early Visibility of Cellular Aggregates and Changes in Central Corneal Thickness as Predictors of Successful Corneal Endothelial Cell Injection Therapy

(1) Background: Cell injection therapy is an emerging treatment for bullous keratopathy (BK). Anterior segment optical coherence tomography (AS-OCT) imaging allows the high-resolution assessment of the anterior chamber. Our study aimed to investigate the predictive value of the visibility of cellular aggregates for corneal deturgescence in an animal model of bullous keratopathy. (2) Methods: Cell injections of corneal endothelial cells were performed in 45 eyes in a rabbit model of BK. AS-OCT imaging and central corneal thickness (CCT) measurement were performed at baseline and on day 1, day 4, day 7 and day 14 following cell injection. A logistic regression was modelled to predict successful corneal deturgescence and its failure with cell aggregate visibility and CCT. Receiver-operating characteristic (ROC) curves were plotted, and areas under the curve (AUC) calculated for each time point in these models. (3) Results: Cellular aggregates were identified on days 1, 4, 7 and 14 in 86.7%, 39.5%, 20.0% and 4.4% of eyes, respectively. The positive predictive value of cellular aggregate visibility for successful corneal deturgescence was 71.8%, 64.7%, 66.7% and 100.0% at each time point, respectively. Using logistic regression modelling, the visibility of cellular aggregates on day 1 appeared to increase the likelihood of successful corneal deturgescence, but this did not reach statistical significance. An increase in pachymetry, however, resulted in a small but statistically significant decreased likelihood of success, with an odds ratio of 0.996 for days 1 (95% CI 0.993-1.000), 2 (95% CI 0.993-0.999) and 14 (95% CI 0.994-0.998) and an odds ratio of 0.994 (95% CI 0.991-0.998) for day 7. The ROC curves were plotted, and the AUC values were 0.72 (95% CI 0.55-0.89), 0.80 (95% CI 0. 62-0.98), 0.86 (95% CI 0.71-1.00) and 0.90 (95% CI 0.80-0.99) for days 1, 4, 7 and 14, respectively. (4) Conclusions: Logistic regression modelling of cell aggregate visibility and CCT was predictive of successful corneal endothelial cell injection therapy.

The Evolution of Diagnostics for Keratoconus: From Ophthalmometry to Biomechanics

PURPOSE

To enumerate the various diagnostic modalities used for keratoconus and their evolution over the past century.

METHODS

A comprehensive literature search including articles on diagnosis on keratoconus were searched on PUBMED and summarized in this review.

RESULTS

Initially diagnosed in later stages of the disease process through clinical signs and retinoscopy, the initial introduction of corneal topography devices like Placido disc, photokeratoscopy, keratometry and computer-assisted videokeratography helped in the earlier detection of keratoconus. The evolution of corneal tomography, initially with slit scanning devices and later with Scheimpflug imaging, has vastly improved the accuracy and detection of clinical and sub-clinical disease. Analyzing the alteration in corneal biomechanics further contributed to the earlier detection of keratoconus even before the tomographic changes became evident. Anterior segment optical coherence tomography has proven to be a helpful adjuvant in diagnosing keratoconus, especially with epithelial thickness mapping. Confocal microscopy has helped us understand the alterations at a cellular level in keratoconic corneas.

CONCLUSION

Thus, the collective contribution of the various investigative modalities have greatly enhanced earlier and accurate detection of keratoconus, thus reducing the disease morbidity.

The Development and Clinical Application of Innovative Optical Ophthalmic Imaging Techniques

The field of ophthalmic imaging has grown substantially over the last years. Massive improvements in image processing and computer hardware have allowed the emergence of multiple imaging techniques of the eye that can transform patient care. The purpose of this review is to describe the most recent advances in eye imaging and explain how new technologies and imaging methods can be utilized in a clinical setting. The introduction of optical coherence tomography (OCT) was a revolution in eye imaging and has since become the standard of care for a plethora of conditions. Its most recent iterations, OCT angiography, and visible light OCT, as well as imaging modalities, such as fluorescent lifetime imaging ophthalmoscopy, would allow a more thorough evaluation of patients and provide additional information on disease processes. Toward that goal, the application of adaptive optics (AO) and full-field scanning to a variety of eye imaging techniques has further allowed the histologic study of single cells in the retina and anterior segment. Toward the goal of remote eye care and more accessible eye imaging, methods such as handheld OCT devices and imaging through smartphones, have emerged. Finally, incorporating artificial intelligence (AI) in eye images has the potential to become a new milestone for eye imaging while also contributing in social aspects of eye care.

The Role of Hi-Tech Devices in Assessment of Corneal Healing in Patients with Neurotrophic Keratopathy

To prove the role of high-tech investigation in monitoring corneal morphological changes in patients with neurotrophic keratopathy (NK) using Keratograph 5M (K5M) and anterior segment OCT (AS-OCT), corneal healing was monitored with Keratograph 5M (Oculus, Wetzlar, Germany) and AS-OCT (DRI, Triton, Topcon, Tokyo, Japan) in 13 patients (8F and 5M), aged from 24 to 93 years (67.8 ± 19) with severe NK, who were treated with Cenegermin 0.002% (20 μg/mL) (Oxervate^®, Dompè, Farmaceutici Spa, Milan, Italy). The surface defects were evaluated on Keratograph 5M with ImageJ software and the corneal thickness variations were measured using DRI-Triton OCT software. Instrumental procedures were performed at baseline, and after 4 and 8 weeks of the treatment, respectively. The main outcome measures were reduction of the ulcers’ area and corneal thickness recovery. The mean area of the corneal ulcers was reduced between baseline and 4 weeks examination in all patients, and at 8 weeks all ulcers were completely healed. An increase of the corneal thickness was evidenced between the baseline visit and after the 4- and 8-week follow-up, respectively. Additionally, only in collaborating subjects the In Vivo Confocal Microscopy (IVCM) was performed with HRT Rostock Cornea Module (Heidelberg Eng GmbH) to study the corneal nerves fibres. High-tech diagnostics with K5M, AS-OCT and IVCM proved useful in the assessment of corneal morphology and the healing process in patients with NK and could be extended to assess other corneal pathologies.

Changes in Corneal Epithelial Thickness Induced by Topical Antiglaucoma Medications

Corneal thickness measurement is important for assessing intraocular pressure in patients with glaucoma. This study investigated the changes in corneal epithelial thickness (CET) induced by antiglaucoma medications and explored the factors affecting CET measurement. CET was measured over a 9.0 mm diameter area by using Fourier domain optical coherence tomography in 125 patients with primary open-angle glaucoma and 125 age-matched controls without glaucoma. The influence of sex, age, benzalkonium chloride (BAK)-containing instillations, disease severity, and types and numbers of medications was analyzed using simple and multiple regression analyses. CET over 25 sectors was smaller in the glaucoma group than in the control group (mean difference of 4.2 µm in the central 2.0 mm zone; 52.8 ± 3.6 vs. 48.5 ± 3.9, p < 0.001). Simple regression analysis revealed age, use of β-blockers, prostaglandin, carbonic anhydrase inhibitors, total number of medications, and number of daily BAK-containing instillations were associated with a thinner epithelium. Multiple regression analysis revealed β-blockers, prostaglandin, and number of BAK-containing instillations were significant factors. Use of β-blockers and number of BAK-containing instillations were also associated with a thinner epithelium in the monotherapy subgroup analysis. CET was significantly smaller in patients with glaucoma receiving topical medications and was affected by the use of β-blockers, prostaglandin, and BAK.

The role of environment in the pathogenesis of keratoconus

PURPOSE OF REVIEW

This study was conducted to demonstrate the importance of the environment in keratoconus (KC) genesis.

RECENT FINDINGS

Genetic-related connective tissue disorders demonstrate the inconsistency of theories regarding KC pathogenesis since no corneal steepening was observed in the majority of these patients. Despite recent advances and decades of research into the genetics of KC, the identification of disease-causing KC genes has been frustrating. Variants found based on genome-wide and next-generation sequencing only seem to account for a small number of cases or play a limited role in KC pathogenesis.

SUMMARY

The literature shows that mechanical manipulation may be the common underlying factor or the indispensable act precipitating the cascade of events leading to permanent corneal deformation. Hence, ophthalmologists have the opportunity to increase patient awareness about eye manipulation repercussions and treatment for ocular surface disorders.

VIDEO ABSTRACT

http://links.lww.com/COOP/A42.

Deep learning for identifying corneal diseases from ocular surface slit-lamp photographs

To demonstrate the identification of corneal diseases using a novel deep learning algorithm. A novel hierarchical deep learning network, which is composed of a family of multi-task multi-label learning classifiers representing different levels of eye diseases derived from a predefined hierarchical eye disease taxonomy was designed. Next, we proposed a multi-level eye disease-guided loss function to learn the fine-grained variability of eye diseases features. The proposed algorithm was trained end-to-end directly using 5,325 ocular surface images from a retrospective dataset. Finally, the algorithm's performance was tested against 10 ophthalmologists in a prospective clinic-based dataset with 510 outpatients newly enrolled with diseases of infectious keratitis, non-infectious keratitis, corneal dystrophy or degeneration, and corneal neoplasm. The area under the ROC curve of the algorithm for each corneal disease type was over 0.910 and in general it had sensitivity and specificity similar to or better than the average values of all ophthalmologists. Confusion matrices revealed similarities in misclassification between human experts and the algorithm. In addition, our algorithm outperformed over all four previous reported methods in identified corneal diseases. The proposed algorithm may be useful for computer-assisted corneal disease diagnosis.

Fourier-Domain OCT Imaging of the Ocular Surface and Tear Film Dynamics: A Review of the State of the Art and an Integrative Model of the Tear Behavior During the Inter-Blink Period and Visual Fixation

In the last few decades, the ocular surface and the tear film have been noninvasively investigated in vivo, in a three-dimensional, high resolution, and real-time mode, by optical coherence tomography (OCT). Recently, OCT technology has made great strides in improving the acquisition speed and image resolution, thus increasing its impact in daily clinical practice and in the research setting. All these results have been achieved because of a transition from traditional time-domain (TD) to Fourier-domain (FD) technology. FD-OCT devices include a spectrometer in the receiver that analyzes the spectrum of reflected light on the retina or ocular surface and transforms it into information about the depth of the structures according to the Fourier principle. In this review, we summarize and provide the state-of-the-art in FD-OCT imaging of the ocular surface system, addressing specific aspects such as tear film dynamics and epithelial changes under physiologic and pathologic conditions. A theory on the dynamic nature of the tear film has been developed to explain the variations within the individual compartments. Moreover, an integrative model of tear film behavior during the inter-blink period and visual fixation is proposed.

Anterior segment optical coherence tomography scanning protocols and corneal thickness repeatability

PURPOSE

To examine the influence of anterior segment optical coherence tomography imaging protocols on the intraobserver and intrasession repeatability of epithelial, stromal, and total corneal thickness measurements.

METHODS

Repeated anterior segment optical coherence tomography (AS-OCT) images (Spectralis, Heidelberg) were obtained from 15 adults using single 8.3 mm wide horizontal line scans with an average of 2, 10, 20, 30, 50 and 100 B-scans. Volumetric scans consisting of nine 8.3 mm horizontal line scans encompassing a 1.3 mm vertical region were also captured (with 20 B-scans per line scan). Single point thickness measures (at the normal to the tangent of the anterior corneal surface) were compared with thickness measures averaged over the central 6 mm. The impact of B-scan averaging and intraobserver variability were examined for single line scans. For volumetric scans, the impact of the number of line scans upon intraobserver and intrasession variability were calculated.

RESULTS

Intraobserver repeatability did not vary significantly as a function of the number of averaged B-scans per line scan, but was lowest for 20-30 averaged B scans. For volumetric scans, increasing the number of line scans did increase scan duration (p < 0.001), with minimal impact upon the average scan quality index (p = 0.06). Averaging more than 3 line scans did not significantly improve intraobserver or intrasession repeatability for either single point or average thickness measurements.

CONCLUSION

AS-OCT volumetric scans with 3 lines each consisting of 20 B-scans with measurements averaged over a central 6 mm of the cornea provide highly repeatable measures of epithelial, stromal and total corneal thickness (95 % LoA ≤ ±3.2 μm for intraobserver repeatability and ≤ ±3.7 μm for intrasession repeatability). This scanning protocol can provide reliable information when monitoring subtle changes in corneal thickness.

Severity Assessment of Acute Hydrops Due to Recurrent Keratoconus after Penetrating Keratoplasty Using Anterior Segment Optical Coherence Tomography

Purpose: To compare the clinical characteristics of acute hydrops between eyes with recurrent keratoconus and eyes with treatment-naïve keratoconus.Methods: Six eyes with acute hydrops caused by recurrent keratoconus (recurrent group) and 29 eyes with acute hydrops due to treatment-naïve keratoconus (naïve group) were included. We collected data from anterior-segment optical coherence tomography (AS-OCT), corneal topography and medical records. With AS-OCT, we investigated the location of Descemet's membrane break, the length and frequency of Descemet's membrane detachment, and the speed of corneal thinning before acute hydrops.Results: Descemet's membrane breaks were detectable in 6 cases in the recurrent group (100%) and 7 cases in the naïve group (70%). Distance from the break to the central line was 2-3 mm in the recurrent group, and less than 1 mm in the naïve group (p < .001). Detachment length was significantly greater in the recurrent group than in the naïve group (p = .003). Steep corneal power values tended to increase before acute hydrops in the recurrent group, but the difference between groups was not significant (observation period; 6.03 ± 2.67, 7.36 ± 5.53 years, respectively). Penetrating keratoplasty was required in 5 cases (83%) in the recurrent group, and 8 cases (28%) in the naïve group (p = .02).Conclusions: Acute hydrops due to recurrent keratoconus occurred around graft-host junctions and was more severe than that in eyes with treatment-naïve keratoconus. Severity assessment of Descemet's membrane detachment using AS-OCT provided clues not only for diagnosis, but also for predicting prognosis.

Predictive Factors for Successful Type 1 Big Bubble during Deep Anterior Lamellar Keratoplasty

Objective

Big bubble (BB)-deep anterior lamellar keratoplasty (DALK) has become the reference transplantation technique for corneal stromal disorders. Type 1 BB is the desired aspect but it is not constant. We aimed to determine the predictive factors of type 1 BB success.

Methods

Observational cohort study including 77 consecutive eyes of 77 patients undergoing DALK by one surgeon at a single reference center without any selection. Clinical and spectral domain optical coherence tomography data were collected pre- and postoperatively.

Results

Stromal scars were found in 91.8% of cases and were located in the anterior (90.9%), mid (67.5%), and posterior (36.4%) stroma. Type 1 BB (49.3% of cases) was significantly associated with the absence of scars in the posterior stroma, stage 1-3 keratoconus, and deep trephination. Among eyes with posterior scars, type 1 BB was associated with higher minimal corneal thickness, maximum-minimum corneal thickness < 220 μm, and diagnosis other than keratoconus. Eyes with type 1 BB featured significantly thinner residual stromal bed (22 ± 8 µm versus 61 ± 28 µm), thinner corneas at 12, 24, and 36 months, and better visual acuity at 12 months compared with eyes with no type 1 BB. Conversely, no significant differences between both groups were observed for graft survival, visual acuity at 24 and 36 months, and endothelial cell density at 12 and 36 months.

Conclusion

OCT assessment before DALK is useful for choosing trephination depth that should be as deep as possible and for looking for posterior scars. The BB technique may not be the most appropriate method in keratoconus with posterior scars. Follow-up data do not support the need for conversion to penetrating keratoplasty when type 1 BB cannot be obtained nor does it support the need for performing a penetrating keratoplasty as a first-choice procedure in eyes with posterior stromal scars.

Anterior segment optical coherence tomography: its application in clinical practice and experimental models of disease

Optical coherence tomography (OCT) provides non-invasive, high-resolution in vivo imaging of the ocular surface and anterior segment. Over the years, it has become an essential tool for evaluating the anterior segment of the eye to monitor ocular development and ocular pathologies in both the clinical and research fields of ophthalmology and optometry. In this review, the clinical applications relating to the use of anterior segment OCT for imaging and quantifying normal and pathological features of the ocular surface, cornea, anterior chamber, and aqueous outflow system are summarised in a range of human ocular diseases. Applications of anterior segment OCT technology that have improved imaging and quantitation of ocular inflammation in experimental animal models of ocular diseases, such as anterior uveitis, microbial keratitis and glaucoma, are also described. The capacity to longitudinally evaluate anterior segment anatomical changes during development, and inflammation facilitates the understanding of the dynamics of tissue responses, and further enhances the intra-operative in vivo imaging during procedures, such as corneal transplantation and drug delivery. Future developments including in vivo ultrahigh-resolution anterior segment OCT, automated analyses of anterior segment OCT images and functional extensions of the technique, may revolutionise the clinical evaluation of anterior segment, corneal and ocular surface diseases.

Optical coherence tomography for ocular surface and corneal diseases: a review

The advent of optical coherence tomography (OCT) imaging has changed the way ophthalmologists image the ocular surface and anterior segment of the eye. Its ability to obtain dynamic, high and ultra-high resolution, cross-sectional images of the ocular surface and anterior segment in a noninvasive and rapid manner allows for ease of use. In this review, we focus on the use of anterior segment OCT, which provides an “optical biopsy” or in vivo imaging of various ocular surface and corneal pathologies, allowing the clinician to diagnose diseases otherwise not visualized by traditional methods. The utility of anterior segment OCT for various anterior segment pathologies is reviewed.

An unusual hydrops in keratoconus

A young 19-year-old male was referred for the management of acute hydrops in the left eye. During follow-up, other eye cornea developed edematous bands as if hydrops was developing at two parallel sites. Edema progressed very slowly and new edema bands continued to develop. This creeping type of hydrops took 4 months to develop into typical hydrops. To the best of our knowledge, hydrops has always been reported to develop in an acute manner and at a single site. Our case is unusual because hydrops progressed very slowly and developed at multiple sites in a creeping manner.

Advanced anterior segment imaging in keratoconus: a review

Advances in anterior segment imaging have enhanced our ability to detect keratoconus in its early stages and characterize the pathologic changes that occur. Computerized corneal tomography has elucidated the alterations in shape of the anterior and posterior corneal surfaces and alterations in thickness as the disease progresses. Automated screening indices such as the keratoconus screening index were developed to assist in detecting keratoconus in suspicious cases. In vivo assessment of keratoconic corneas has revealed that compromised corneal biomechanics can now be measured clinically. Optical coherence tomography has demonstrated alterations in corneal epithelial thickness and distribution in keratoconus, has a role in assessing Descemet's membrane detachment in acute corneal hydrops (ACH) and the depth of the demarcation line following corneal collagen cross-linking. In vivo confocal microscopy has exhibited cellular changes that occur in keratoconus and provided insight into cellular events that may be related to the development of neovascularization in ACH.

Stromal striae: a new insight into corneal physiology and mechanics

We uncover the significance of a previously unappreciated structural feature in corneal stroma, important to its biomechanics. Vogt striae are a known clinical indicator of keratoconus, and consist of dark, vertical lines crossing the corneal depth. However we detected stromal striae in most corneas, not only keratoconus. We observed striae with multiple imaging modalities in 82% of 118 human corneas, with pathology-specific differences. Striae generally depart from anchor points at Descemet’s membrane in the posterior stroma obliquely in a V-shape, whereas in keratoconus, striae depart vertically from posterior toward anterior stroma. Optical coherence tomography shear wave elastography showed discontinuity of rigidity, and second harmonic generation and scanning electron microscopies showed undulation of lamellae at striae locations. Striae visibility decreased beyond physiological pressure and increased beyond physiological hydration. Immunohistology revealed striae to predominantly contain collagen VI, lumican and keratocan. The role of these regions of collagen VI linking sets of lamellae may be to absorb increases in intraocular pressure and external shocks.

Imaging Microscopic Features of Keratoconic Corneal Morphology

Purpose:

To search for gold-standard histology indicators using alternative imaging modalities in keratoconic corneas.

Methods:

Prospective observational case–control study. Fourteen keratoconic corneas and 20 normal corneas (10 in vivo healthy subjects and 10 ex vivo donor corneas) were examined. Images of corneas were taken by spectral domain optical coherence tomography (SD-OCT) and in vivo confocal microscopy (IVCM) before keratoplasty. The same removed corneal buttons were imaged after keratoplasty with full-field optical coherence microscopy (FFOCM) and then fixed and sent for histology. Controls consisted of normal subjects imaged in vivo with IVCM and donor corneas imaged ex vivo with FFOCM. Corneal structural changes related to pathology were noted with each imaging modality. Cell density was quantified by manual cell counting.

Results:

Keratoconus indicators (ie, epithelial thinning/thickening, cell shape changes, ferritin deposits, basement membrane anomalies, Bowman layer thinning, ruptures, interruptions, scarring, stromal modifications, and appearance of Vogt striae) were generally visible with all modalities. Additional features could be seen with FFOCM in comparison with gold-standard histology, particularly in the Bowman layer region, whereas the combination of SD-OCT plus IVCM detected 76% of those features detected in histology. Three-dimensional FFOCM imaging aided interpretation of two-dimensional IVCM and SD-OCT data. Basal epithelial cell and keratocyte densities were significantly lower in patients with keratoconus than those in normals (P < 0.0001).

Conclusions:

Structural and cellular assessment of the keratoconic cornea by means of either in vivo SD-OCT combined with IVCM or ex vivo FFOCM in both cross-sectional and en face views can detect as many keratoconus indicators as gold-standard histology.

New parameters in assessment of human donor corneal stroma

PURPOSE

To provide quantitative parameters for assessment of human donor corneal stroma by imaging stromal features of diseased and normal human corneas with full-field optical coherence microscopy (FFOCM), using confocal microscopy (CM) and histology as reference techniques.

METHODS

Bowman's layer (BL) thickness and keratocyte density were assessed ex vivo in 23 human donor corneas and 27 human pathological corneas (keratoconus and other corneal disorders) with FFOCM, CM and histology. Stromal backscattering was assessed with FFOCM. Additionally, 10 normal human corneas were assessed in vivo with CM.

RESULTS

In FFOCM, the logarithm of the normalized stromal reflectivity was a linear function of stromal depth (R²  = 0.95) in human donor corneas. Compared with keratoconus corneas, human donor corneas featured higher BL thickness (p = 0.0014) with lower coefficient of variation (BL-COV; p = 0.0002), and linear logarithmic stromal reflectivity with depth (higher R² , p = 0.0001). Compared with other corneal disorders, human donor corneas featured lower BL-COV (p = 0.012) and higher R² (p = 0.0001). Using the 95% confidence limits of the human donor cornea group, BL thickness < 6.5 μm (sensitivity, 57%; specificity, 100%), BL-COV > 18.6% (79%; 100%) and R²  < 0.94 (93%; 71%) were revealed as indictors of abnormal cornea. In CM, keratocyte density decreased with stromal depth (r = -0.56). The mean overall keratocyte density (cells/mm² ) was 205 in human donor corneas, 244 in keratoconus, 176 in other corneal disorders and 386 in normal corneas.

CONCLUSION

Full-field optical coherence microscopy (FFOCM) provides precise and reliable parameters for non-invasive assessment of human donor corneal stroma during storage, enabling detection of stromal disorders that could impair the results of keratoplasty.

Applications of Anterior Segment Optical Coherence Tomography in Cornea and Ocular Surface Diseases

Optical coherence tomography (OCT) is a noncontact technology that produces high-resolution cross-sectional images of ocular tissues. Anterior segment OCT (AS-OCT) enables the precise visualization of anterior segment structure; thus, it can be used in various corneal and ocular surface disorders. In this review, the authors will discuss the application of AS-OCT for diagnosis and management of various corneal and ocular surface disorders. Use of AS-OCT for anterior segment surgery and postoperative management will also be discussed. In addition, application of the device for research using human data and animal models will be introduced.

Case-control study of risk factors for acute corneal hydrops in keratoconus

PURPOSE

To determine risk factors for the development of acute corneal hydrops in keratoconus in the UK in a case-controlled study.

METHODS

Between November 2009 and December 2010, we prospectively identified 73 individuals who developed acute corneal hydrops. We then identified 174 controls from nine regions in the UK with keratoconus who had not had hydrops. For cases and controls we recorded demographics and clinical features. Univariate and multivariable logistic regressions were performed to identify risk factors.

RESULTS

Univariate analysis suggested strong associations between the odds of hydrops and each of vernal keratoconjunctivitis (OR 4.08, 95% CI 1.45 to 11.49, p=0.008), asthma (OR 2.70, CI 1.34 to 5.47, p=0.006), atopic dermatitis (OR 3.13, CI 1.50 to 6.56, p=0.002), learning difficulties (OR 7.84, CI 2.86 to 21.46, p<0.001), previous hydrops (OR 40.2; CI 6.2 to ∞, p<0.001), black ethnicity (OR 2.98, CI 0.98 to 8.99; p=0.05), visual acuity in the worse eye (OR 8.76 CI 3.86 to 19.88; p<0.001) and minimum keratometry of ≥48 D prior to the hydrops (OR 4.91, CI 1.07 to 22.6, p=0.041). The use of a contact lens correction was also found to be associated with the odds of hydrops (OR 0.08; CI 0.03 to 0.19, p<0.001). Multiple variable regression indicated that having vernal keratoconjunctivitis (adjusted OR (AOR) 15, 95% CI 1.30 to 173.7; p=0.03), asthma (AOR 4.92, CI 1.22 to 19.78; p=0.025), visual acuity in worse eye (AOR 4.11, CI 1.18 to 14.32; p=0.026) and a high keratometry value (AOR 4.44, CI 0.85 to 23.18; p=0.077) were independently associated with the odds of hydrops in subjects with keratoconus.

CONCLUSION

Some individuals with keratoconus are at high risk of developing acute corneal hydrops. These patients could be managed more aggressively to reduce their risk of developing this complication of their disease.