Calculation of ophthalmic viscoelastic device-induced focus shift during femtosecond laser-assisted cataract surgery

PURPOSE

To assess if a change in refractive index of the anterior chamber during femtosecond laser-assisted cataract surgery can affect the laser beam focus position.

METHODS

The index of refraction and chromatic dispersion of six ophthalmic viscoelastic devices (OVDs) was measured with an Abbe refractometer. Using the Gullstrand eye model, the index values were used to predict the error in the depth of a femtosecond laser cut when the anterior chamber is filled with OVD. Two sources of error produced by the change in refractive index were evaluated: the error in anterior capsule position measured with optical coherence tomography biometry and the shift in femtosecond laser beam focus depth.

RESULTS

The refractive indices of the OVDs measured ranged from 1.335 to 1.341 in the visible light (at 587 nm). The error in depth measurement of the refilled anterior chamber ranged from -5 to +7 μm. The OVD produced a shift of the femtosecond laser focus ranging from -1 to +6 μm. Replacement of the aqueous humor with OVDs with the densest compound produced a predicted error in cut depth of 13 μm anterior to the expected cut.

CONCLUSIONS

Our calculations show that the change in refractive index due to anterior chamber refilling does not sufficiently shift the laser beam focus position to cause the incomplete capsulotomies reported during femtosecond laser-assisted cataract surgery.

Long-term follow-up of epikeratophakia

We report a 28-year follow-up of epikeratophakia surgery after extracapsular extraction of a congenital cataract. The patient's ocular history included the diagnosis of bilateral cortical congenital cataracts at 2 years of age, which was more severe in the right eye than in the left. One year later, the visual acuity in the right eye progressively worsened, and extracapsular cataract extraction without intraocular lens implantation was performed. After contact lens fitting failed, an epikeratophakia procedure was performed in the right eye. Twenty-eight years after the procedure, the patient was referred to Bascom Palmer Eye Institute for progressive loss of visual acuity in the left eye. It was discovered that the right eye had remained stable; the corrected distance visual acuity was 20/30 with a manifest refraction of -8.75 + 0.50 × 105.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

In vivo effects of femtosecond laser-assisted keratoplasty

IMPORTANCE

The femtosecond laser is reported to cut lamellar surfaces with varying degrees of smoothness depending on the depth of the cut, with deeper cuts leaving less smooth surfaces. We attempted to evaluate the smoothness of the deeper lamellar surface as cut by the femtosecond laser after allowing 3 months of in vivo healing.

OBSERVATIONS

Two patients underwent penetrating keratoplasty 3 months after inadequate visual rehabilitation following femtosecond laser-assisted sutureless anterior lamellar keratoplasty for the treatment of anterior stromal scars. In vivo confocal microscopy that was performed before penetrating keratoplasty demonstrated an acellular zone with a hyperintense signal consistent with a mild interface opacification. Light microscopy in one patient demonstrated scarring limited primarily to the posterior stroma; in the other patient, the interface was smooth with mild scarring of the anterior lamellae. When studied with electron microscopy, the cut surfaces revealed a smooth to very mild stuccolike appearance that was smoother than anticipated.

CONCLUSIONS AND RELEVANCE

After 3 months of in vivo healing, the lamellar interface produced by the femtosecond laser, as imaged by electron microscopy, appeared to be nearly smooth with minimal roughness to the cut surfaces. We attribute this to the effects of in vivo healing and remodeling.

Assessment of rose bengal versus riboflavin photodynamic therapy for inhibition of fungal keratitis isolates

PURPOSE

To compare the in vitro effect of rose bengal and riboflavin as photosensitizing agents for photodynamic therapy (PDT) on fungal isolates that are common causes of fungal keratitis.

DESIGN

Experimental study.

METHODS

Three isolates (Fusarium solani, Aspergillus fumigatus, Candida albicans) recovered from patients with confirmed fungal keratitis were used in the experiments. Isolates were grown on Sabouraud-Dextrose agar, swabbed, and prepared in suspension, and 1 mL aliquots were inoculated onto test plates in triplicate. Test plates were separated into 5 groups: Group 1, no treatment; Group 2, 0.1% rose bengal alone; Group 3, 518 nm irradiation alone; Group 4, riboflavin PDT (riboflavin + 375 nm irradiation); and Group 5, rose bengal PDT (rose bengal + 518 nm irradiation). Irradiation was performed over a circular area using either a green light-emitting diode (LED) array (peak wavelength: 518 nm) or an ultraviolet-A LED array (peak wavelength: 375 nm). Test plates were irradiated with an energy density of 5.4 J/cm(2). Later, plates were placed in a 30 C incubator and observed for growth.

RESULTS

Rose bengal-mediated PDT successfully inhibited the growth of all 3 fungal isolates in the irradiated area. All other groups exhibited unrestricted growth throughout the plate.

CONCLUSIONS

Rose bengal-mediated PDT successfully inhibited the growth of 3 types of fungi. No other experimental groups, including riboflavin-mediated PDT, had any inhibitory effect on the isolates. The results might be useful for the treatment of patients suffering from corneal infection.

A new, specular reflection-based, precorneal tear film stability measurement technique in a rabbit model: viscoelastic increases tear film stability

PURPOSE

To develop a safe, noninvasive, noncontact, continuous in vivo method to measure the dehydration rate of the precorneal tear film and to compare the effectiveness of a viscoelastic agent in maintaining the precorneal tear film to that of a balanced salt solution.

METHODS

Software was designed to analyze the corneal reflection produced by the operating microscope's coaxial illumination. The software characterized the shape of the reflection, which became distorted as the precorneal tear film evaporated; characterization was accomplished by fitting an ellipse to the reflection and measuring its projected surface area. Balanced salt solution Plus (BSS+) and a 2% hydroxypropylmethylcellulose viscoelastic were used as the test agents. The tear film evaporation rate was characterized and compared over a period of 20 minutes in 20 eyes from 10 New Zealand white rabbits.

RESULTS

The ellipse axes ratio and surface area were found to decrease initially after each application of either viscoelastic or BSS+ and then to increase linearly as the tear film began to evaporate (P < 0.001) for eyes treated with BSS+ only. Eyes treated with BSS+ required 7.5 ± 2.7 applications to maintain sufficient corneal hydration during the 20-minute test period, whereas eyes treated with viscoelastic required 1.4 ± 0.5 applications. The rates of evaporation differed significantly (P < 0.043) between viscoelastic and BSS+.

CONCLUSIONS

The shape and surface area of the corneal reflection are strongly correlated with the state of the tear film. Rabbits' corneas treated with viscoelastic remained hydrated significantly longer than corneas treated with BSS+.

Femtosecond laser-assisted astigmatic keratotomy for postoperative trabeculectomy-induced corneal astigmatism

PURPOSE

To describe a case of postoperative trabeculectomy-induced corneal astigmatism treated with femtosecond laser-assisted astigmatic keratotomy.

METHODS

After trabeculectomy, the patient demonstrated change in manifest refraction from -0.5 diopters preoperatively to mixed astigmatism of -3.5 + 5.25@100 postoperatively and a decrease in uncorrected distance visual acuity from 20/60 preoperatively to 20/200 at 1 month postoperatively. Because the patient was intolerant to spectacle use, she underwent femtosecond laser-assisted astigmatic keratotomy.

RESULTS

After astigmatic keratotomy there was improvement in corneal topographic astigmatism from 4.15 to 0.81 diopters with uncorrected distance visual acuity of 20/60(-2) and manifest refraction of -0.75 + 1.0@90 at 3 months postoperatively. There were no intraoperative or postoperative complications.

CONCLUSIONS

Femtosecond laser-assisted astigmatic keratotomy may be considered in eyes with postoperative trabeculectomy-induced mixed astigmatism.

Combinations of eight key mutations in the X/preC region and genomic activity of hepatitis B virus are associated with hepatocellular carcinoma

Accumulation of eight key mutations located in the X/preC regions of the hepatitis B virus (HBV) genome (G1613A, C1653T, T1753V, A1762T, G1764A, A1846T, G1896A and G1899A) is a risk marker for the development of hepatocellular carcinoma (HCC). In this study, we analysed the 8 key mutations in 442 serum samples collected from 310 non-HCC and 132 HCC patients to identify the combinations linked to HCC. After the patients were stratified according to the age groups and mutation combinations, clinical parameters were compared between the HCC and the non-HCC groups. Analyses were focused on patient ≥40 years of age infected by HBV genotype C with A1762T and G1764A mutations in the basal core promoter region (BCP double mutation). In patients with ≥6 mutations, the combination of [G1613A + C1653T + A1846T + G1896A] mutations was closely linked to HCC, whereas no specific single or double mutation combination was associated with HCC. In patients with ≤5 mutations, HBeAg and HBV DNA serum titres were lower in the HCC group than those in the non-HCC group. Unlike the number of mutations, no specific combination correlated with advanced clinical stage in HCC. Of the BCP double mutation-based HBV mutant types, combinations of ≥6 mutations that include G1613A + C1653T + A1846T + G1896A, and combinations of ≤5 mutations with reduced HBeAg production, may be more specific indicators of HCC risk than only the number of mutations or any specific combination(s).

The use of Bowman's layer vertical topographic thickness map in the diagnosis of keratoconus

PURPOSE

To evaluate the use of Bowman's layer (BL) vertical topographic thickness maps in diagnosing keratoconus (KC).

DESIGN

Prospective, case control, interventional case series.

PARTICIPANTS

A total of 42 eyes: 22 eyes of 15 normal subjects and 20 eyes of 15 patients with KC.

INTERVENTION

Bowman's layer 2-dimensional 9-mm vertical topographic thickness maps were created using custom-made ultra high-resolution optical coherence tomography.

MAIN OUTCOME MEASURES

Bowman's layer average and minimum thicknesses of the inferior half of the cornea, Bowman's ectasia index (BEI; defined as BL minimum thickness of the inferior half of the cornea divided by BL average thickness of the superior half of the cornea multiplied by 100), BEI-Max (defined as BL minimum thickness of the inferior half of the cornea divided by BL maximum thickness of the superior half of the cornea multiplied by 100), keratometric astigmatism (Ast-K) of patients with KC, and average keratometric (Avg-K) readings.

RESULTS

In patients with KC, BL vertical thickness maps disclosed localized relative inferior thinning of the BL. Inferior BL average thickness (normal = 15±2, KC = 12±3 μm), inferior BL minimum thickness (normal = 13±2, KC = 7±3 μm), BEI (normal = 91±7, KC = 48±14), and BEI-Max (normal = 75±8; KC = 40±13) all showed highly significant differences in KC compared with normal subjects (P< 0.001). Receiver operating characteristic (ROC) curve analysis showed excellent predictive accuracy for BEI and BEI-Max with 100% sensitivity and specificity (area under the curve [AUC] of 1) with cutoff values of 80 and 60, respectively. The AUC of inferior BL average thickness and minimum thickness were 0.87 and 0.96 with a sensitivity of 80% and 93%, respectively, and a specificity of 93% and 93%, respectively. Inferior BL average thickness, inferior BL minimum thickness, BEI, and BEI-Max correlated highly to Ast-K (R = -0.72, -0.82, -0.84, and -0.82, respectively; P< 0.001) and to Avg-K (R = -0.62, P< 0.001; R = -0.59, P = 0.001; R = -0.60, P< 0.001; and R = -0.59, P = 0.001, respectively).

CONCLUSIONS

Bowman's layer vertical topographic thickness maps of patients with KC disclose characteristic localized relative inferior thinning. Inferior BL average thickness, inferior BL minimum thickness, BEI, and BEI-Max are qualitative and quantitative indices for the diagnosis of KC that accurately correlate with the severity of KC. In our pilot study, BEI and BEI-Max showed excellent accuracy, sensitivity, and specificity in the diagnosis of KC.

Anterior and posterior corneal stroma elasticity after corneal collagen crosslinking treatment

The purpose of this project was to assess anterior and posterior corneal stromal elasticity after corneal collagen cross linking (CXL) treatment in human cadaver eyes using Atomic Force Microscopy (AFM) through indentation. Twenty four human cadaver eyes (12 pairs) were included in this study and divided into 2 groups (6 pairs per group). In both groups, the left eye (OS) served as a control (no riboflavin or CXL treatment was performed) and the right eye (OD) underwent CXL treatment (30 min of riboflavin pretreatment followed by 30 min of exposure to 3 mW/cm(2) of ultraviolet light). In group 1, the anterior stroma was exposed by manual delamination of approximately 50 μm of the corneal stroma including Bowman's membrane. In group 2, the posterior stroma was exposed by delamination of the anterior 50% of the corneal stroma including Bowman's membrane. Delamination was performed after crosslinking treatment in the case of the treated eyes. In all eyes, the stromal elasticity was quantified using AFM through indentation. Young's modulus of elasticity for the anterior cornea (group 1) was 245.9 ± 209.1 kPa (range: 82.3-530.8 kPa) for the untreated control eyes, and 467.8 ± 373.2 kPa (range: 157.4-1126 kPa) for the CXL treated eyes. Young's modulus for the posterior cornea (group 2) was 100.2 ± 61.9 kPa (range: 28.1-162.6 kPa) for the untreated control eyes and 66.0 ± 31.8 kPa (range: 31.3-101.7 kPa) for the CXL treated eyes. Young's modulus of the anterior stroma significantly increased after CXL treatment (p = 0.024), whereas the posterior stroma did not demonstrate a significant difference in Young's modulus after CXL treatment (p = 0.170). The anterior stroma was stiffer than the posterior stroma for both the control and CXL treatment groups (p = 0.077 and p = 0.023, respectively). Our findings demonstrate that stiffness of the anterior corneal stroma after CXL treatment seems to increase significantly, while the posterior stroma does not seem to be affected by CXL.

Management of pediatric keratoconus - evolving role of corneal collagen cross-linking: an update

Pediatric keratoconus demonstrates several distinctive management issues in comparison with adult keratoconus with respect to under-diagnosis, poor compliance and modifications in treatment patterns. The major concerns comprise of the accelerated progression of the disease in the pediatric age group and management of co-morbidities such as vernal keratoconjuntivitis. Visual impairment in pediatric patients may affect social and educational development and overall negatively impact their quality of life. The treatment algorithm between adults and pediatric keratoconus has been similar; comprising mainly of visual rehabilitation with spectacles, contacts lenses (soft or rigid) and keratoplasty (lamellar or penetrating) depending on the stage of the disease. There is a paradigm shift in the management of keratoconus, a new treatment modality, corneal collagen crosslinking (CXL), has been utilized in adult keratoconic patients halting the progression of the disease. CXL has been utilized for over a 10 year period and based on the evidence of efficacy and safety in the adult population; this treatment has been recently utilized in management of pediatric keratoconus. This article will present an update about current management of pediatric keratoconus with special focus on CXL in this age group.

Character comparison of abdomen-derived and eyelid-derived mesenchymal stem cells

OBJECTIVES

While most human adipose tissues, such as those located in the abdomen, hip and thigh, are of mesodermal origin, adipose tissues located in the face are of ectodermal origin. The present study has compared stem cell-related features of abdomen-derived adult stem cells (A-ASCs) with those of eyelid-derived adult stem cells (E-ASCs).

MATERIALS AND METHODS

Adipose tissue-derived cells were maintained in DMEM supplemented with 10% FBS. Before passage 6, cells were analysed using FACS, immunocytochemistry and quantitative real time PCR (qRT-PCR). To examine multi-differentiational potential, early passage ASCs were cultivated in each of a commercial Stempro(®) Differentiation kit.

RESULTS

Unlike fibroblast-like morphology of A-ASCs, E-ASCs had bipolar morphology. Both types of cell exhibited similar surface antigens, and neuronal cell-related genes and proteins. However, there were differences in mRNA expression levels of CD90 and CD146; neuron-specific enolase (NSE) and nuclear receptor-related protein 1 (Nurr1) were different between the two cell types. There was no difference in multi-differentiational potential between 3 E-ASCs lines, however, E-ASCs had higher expression levels of chondrocyte-related genes compared to A-ASCs. These cells underwent senescence and maintained normal karyotypes.

CONCLUSIONS

Although isolated from similar adipose tissues, both types of cells displayed many contrasting characteristics. Understanding defining phenotypes of such cells is useful for making suitable choices in differing clinical indications.

Complications of femtosecond laser-assisted re-treatment for residual refractive errors after LASIK

PURPOSE

To report complications of femtosecond laser-assisted re-treatment by the creation of side cuts within the old flaps for residual refractive error after primary LASIK in two patients.

METHODS

Case report.

RESULTS

Three eyes of two patients had complications with a circumferential sliver of stromal tissue displaced during surgery due to overlap of old and new side cuts. The displaced tissue was repositioned and corneal anatomy was restored. Two of three eyes demonstrated improvement in the uncorrected visual acuity, whereas one eye lost two lines of corrected visual acuity due to loss of tissue at side cut resulting from flap manipulation, which was done at 1 week.

CONCLUSIONS

These cases demonstrate a complication of femtosecond laser-enabled side-cut for LASIK enhancement and factors that may lead to this complication and precautions to avoid it.