Automatic segmentation and quantified analysis of meibomian glands from infrared images.

Purpose: An algorithm for automated segmentation of meibomian glands from infrared images obtained using a novel prototype infrared hand-held imager has been proposed in this study. Meibomian gland dysfunction (MGD) is quantified in terms of five clinically relevant metrics. A comparison of these metrics in patients with MGD has been presented against a sample of the normative healthy population. Methods: This is a prospective cross-sectional observational study. Patients presenting to the clinics were enrolled after written informed consent. The everted eyelids of 200 eyes of patients (of which 100 were healthy and 100 were diagnosed with MGD) were imaged using a prototype hand-held camera. The proposed algorithm was used to process the images using enhancement techniques and the glands were automatically segmented. A comparison of glands of normal eyes versus MGD-affected eyes is performed using five metrics presented in this study: (i) drop-out, (ii) length, (iii) width, (iv) the number of glands, and (v) the number of tortuous glands. Results: The 95% confidence interval for the metrics did not show any overlap between the two groups. In MGD patients, the drop-out ratio was higher than normal. The length and number of glands were significantly lesser than normal. A number of tortuous glands were more in the MGD group. The metrics for MGD versus healthy and cut-off ranges were computed in the results. Conclusion: The prototype infrared hand-held meibographer and the proposed automatic algorithm for gland segmentation and quantification are effective aids in MGD diagnosis. We present a set of five metrics, which are clinically relevant for guiding clinicians in the diagnosis of MGD.

Pupillodynamics and corneal spherical aberrations in a set of Indian cataract patients and its implications for aberrometric customisation of intraocular lenses.

PURPOSE: Assessment of pupil diameter in various light conditions and the corresponding corneal spherical aberrations in a cohort of Indian eyes with bilateral senile cataracts and the possible use of this data in aberrometric customization of intraocular lenses (IOLs). METHODS: In this prospective observational study done at a tertiary eye care centre in India, the selected patients were subjected to measurement of their pupil diameters in scotopic, mesopic, and photopic conditions as well as the corresponding corneal spherical aberrations, using the Sirius Topographer (Costruzione Strumenti Oftalmici, Florence, Italy). Shapiro-Wilk test, Independent t-test, ANOVA with Bonferroni correction on post-hoc testing were used for statistical analysis. RESULTS: 104 eyes of 52 patients were enrolled for the study. The mean age was 53 ± 11.88 years. The mean scotopic, mesopic, and photopic pupil sizes were 4.37 mm (4.11-4.63 mm), 3.92 mm (3.71 mm-4.15 mm), and 3.37 mm (3.18-3.67 mm), respectively. There was a statistically significant difference (P = <0.001) in the mean corneal spherical aberration measured at the 6 mm zone (0.23 ± 0.02 microns) and at the 4 mm zone (0.06 ± 0.01 microns). CONCLUSION: The mean corneal spherical aberration corresponding to the average mesopic pupil size of our patient population was substantially lower than that of the scotopic pupil size and also less than the amount corrected by most of the negative aspheric IOLs. This perhaps indicates the need for customising IOLs based on the spherical aberrations of cornea at the zone corresponding to the mesopic pupil diameter for optimal residual total postoperative spherical aberrations.

Foveal Layer Morphology Detected on Spectral Domain Optical Coherence Tomography and its Correlation with Visual Acuity in Asian Indian Premature Infants in their First Year of Life.

PURPOSE: To report foveal microanatomy imaged on handheld spectral domain optical coherence tomography (SDOCT) and correlate it with visual acuity in Asian Indian premature infants. METHODS: A retrospective analysis of 32 Asian Indian premature infants, 10 with Type 2 retinopathy of prematurity (ROP), were imaged between 3 and 12 months of corrected postmenstrual age (PMA) on the handheld SDOCT (Envisu 2300, Bioptigen, DNC, USA). The foveal findings on these images were correlated with visual acuity measured using Teller acuity cards. The study cohort was divided into three groups based on the corrected age, 3-<6 months, 6-<9 months, and 9-12 months. SDOCT images of the foveal center were analyzed for inner retinal layer (IRL) persistence or fusion and presence of the external limiting membrane (ELM), inner segment-outer segment or the ellipsoid zone (EZ), and the outer segment-retinal pigment epithelium (OS-RPE) layers. RESULTS: The mean visual acuity of the three groups was 1.60, 1.63, and 1.23 logMAR, respectively (p < 0.001). Visual acuity significantly correlated with all four layers (IRL fusion, ELM, EZ, and OS-RPE in the 3-<6-month group [p < 0.001], IRL fusion only in 6-<9-month group (p < 0.001), and IRL fusion and EZ in the 9-12-month group (p < 0.001 and p = 0.01, respectively). CONCLUSIONS: The study provides insights into our understanding of a premature infant's foveal maturation in the first year. Inner retinal fusion or maturation is the most important event that correlates with better visual acuity throughout the first year. In addition, between 9 and 12 months PMA, the completion of the EZ at the foveal center positively influenced visual acuity. The presence of ROP did not influence development of the layers, but the sample size was small for subgroup analysis.

Outcomes of a Management Strategy in Eyes with Corneal Irregularity and Cataract.

Purpose. To evaluate the outcomes of a management strategy in patients with irregular corneas and cataract. Methods. Six eyes of four patients presented for cataract surgery with irregular corneas following corneal refractive surgery. Topoguided ablation regularised the cornea, followed by phacoemulsification and intraocular lens implantation. Zonal keratometric coefficient of variation (ZKCV) measured structural changes and visual quality metrics measured functional improvement. Results. The mean duration after corneal refractive surgery was 7.83 ± 2.40 years. The logmar uncorrected distance visual acuity (0.67 ± 0.25) and the corrected distance visual acuity (0.38 ± 0.20) improved to 0.34 ± 0.14 and 0.18 ± 0.10, respectively. The changes in the standard deviations of the zonal keratometry values and the ZKCV were statistically significant in the 2, 3, and 4 mm zones. The changes in the Strehl ratio (ANOVA p = 0.043) were also statistically significant. Conclusions. Corneal regularisation followed by phacoemulsification resulted in lower residual refractive error with improved visual quality metrics. This strategy is a viable option in patients with symptomatic cataracts and irregular corneas.

Intra-Operative Cap Repositioning in Small Incision Lenticule Extraction (SMILE) for Enhanced Visual Recovery.

PURPOSE: To study the role of intra-operative cap repositioning in acute visual recovery after small incision lenticule extraction (SMILE). MATERIALS AND METHODS: Ninety-four eyes of 47 patients underwent the SMILE procedure for correction of myopic refractive error. Manifest refraction and visual quality parameters (optical quality analysis system) were evaluated before surgery. The Bowman's membrane was imaged using a handheld spectral domain optical coherence tomography device. All patients underwent an uneventful SMILE surgery by a single experienced surgeon. Intra-operative cap repositioning was done in the "right" eye of all patients (repositioned group) and the "left" eye of each patient served as controls (non-repositioned group). Visual acuity and optical quality were assessed 1 day and 1 week after surgery. RESULTS: Bowman's membrane microdistortions were found in 21.3% of eyes in the repositioned group and 59.57% of the eyes in the non-repositioned group (p = 0.003) on the first day after surgery. Comparison of optical quality parameters was carried out between eyes where repositioning was done and control eyes (with and without microdistortions). On the first day after surgery, the modulation transfer function (MTF) and Strehl's ratio (SR) were significantly better in the repositioned group when compared with the controls (p = 0.002 and p = 0.003, respectively). Refractive error and lenticule thickness in eyes with microdistortions were similar (p > 0.05) between the two groups indicating other contributors to acute optical quality postoperatively. CONCLUSIONS: Although the refractive error before surgery determines the extent of microdistortions, intra-operative cap repositioning can reduce them, thereby expediting acute visual recovery after SMILE.

Scleral fixation of a foldable intraocular lens with polytetrafluoroethylene sutures through a Hoffman pocket.

UNLABELLED: Scleral fixation of intraocular lenses (IOLs) is traditionally performed after conjunctival dissection and preparation of scleral flaps. The Hoffman pocket technique creates scleral pockets without conjunctival dissection. We describe a technique that uses a Hoffman pocket and 7-0 polytetrafluoroethylene (Gore-Tex) sutures for scleral fixation of a foldable posterior chamber IOL in patients with insufficient capsule support. The technique eliminates the need for conjunctival dissection, scleral cauterization, knot rotation, and sutured wound closure. The favorable properties of the suture material and the use of a small incision to insert a foldable IOL are additional advantages. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.

Microscope Integrated Intraoperative Spectral Domain Optical Coherence Tomography for Cataract Surgery: Uses and Applications.

AIM: To demonstrate the uses and applications of a microscope integrated intraoperative Optical Coherence Tomography in Micro Incision Cataract Surgery (MICS) and Femtosecond Laser Assisted Cataract Surgery (FLACS). METHODS: Intraoperative real time imaging using the RESCAN™ 700 (Carl Zeiss Meditec, Oberkochen, Germany) was done for patients undergoing MICS as well as FLACS. The OCT videos were reviewed at each step of the procedure and the findings were noted and analyzed. RESULTS: Microscope Integrated Intraoperative Optical Coherence Tomography was found to be beneficial during all the critical steps of cataract surgery. We were able to qualitatively assess wound morphology in clear corneal incisions, in terms of subclinical Descemet's detachments, tears in the inner or outer wound lips, wound gaping at the end of surgery and in identifying the adequacy of stromal hydration, for both FLACS as well as MICS. It also enabled us to segregate true posterior polar cataracts from suspected cases intraoperatively. Deciding the adequate depth of trenching was made simpler with direct visualization. The final position of the intraocular lens in the capsular bag and the lack of bioadhesivity of hydrophobic acrylic lenses were also observed. CONCLUSIONS: Even though Microscope Integrated Intraoperative Optical Coherence Tomography is in its early stages for its application in cataract surgery, this initial assessment does show a very promising role for this technology in the future for cataract surgery both in intraoperative decision making as well as for training purposes.

Structural and Function Correlation of Cone Packing Utilizing Adaptive Optics and Microperimetry.

AIM: To assess the functional aspects of cone mosaic and correlate cone packing with retinal sensitivity utilizing microperimetry in emmetropes at different eccentricities. METHODS: Twenty-four healthy volunteers underwent microperimetry (MAIA Centervue, Italy) and assessment of photoreceptors using adaptive optics retinal camera, rtx1 (Imagine Eyes, Orsay, France), at 2 and 3 degrees from the foveal centre in 4 quadrants: superior, inferior, temporal, and nasal. Data was analyzed using SPSS version 17 (IBM). Spearman's correlation tests were used to establish correlation between mean cone packing density and retinal sensitivity at different quadrants. RESULTS: Thirteen females and 11 males (age range 20-40 years) were included. The cone density was found to be significantly different among all quadrants (temporal = 25786.68/mm(2) ± 4367.07/mm(2), superior = 23009.35/mm(2) ± 5415.81/mm(2), nasal = 22838.09/mm(2) ± 4166.22/mm(2), and inferior = 21097.53/mm(2) ± 4235.84/mm(2)). A statistical significance (P < 0.008) was found between orthogonal meridians, that is, temporal, nasal (48624.77/mm(2))> superior, inferior (44106.88/mm(2)). A drop in retinal sensitivity was observed as the eccentricity increased (P < 0.05). It was also found that as cone packing density decreased retinal sensitivity also decreased (P < 0.05) in all quadrants. This was observed at both 2 and 3 degrees. CONCLUSION: It is of crucial importance to establish normative variations in cone structure-function correlation. This may help in detection of subtle pathology and its early intervention.

Repeatability and agreement of three Scheimpflug-based imaging systems for measuring anterior segment parameters in keratoconus.

PURPOSE: To assess the repeatability and agreement of three rotating Scheimpflug cameras, Pentacam, Galilei, and Sirius, in measuring the mean keratometry (Km), thinnest corneal thickness (TCT), anterior chamber depth (ACD), and mean posterior keratometry (pKm) in keratoconus patients in a prospective study. METHODS: Fifty-five eyes of 55 patients with keratoconus underwent three consecutive scans on each machine, performed by a single operator. Within-subject standard deviation (Sw), test-retest repeatability (TRT), and coefficient of variation (COV) for assessing repeatability and Bland-Altman plots for the agreement between the mean measurements of each machine were examined. RESULTS: The Sw of Km and pKm measurements with Pentacam (0.23 and 0.10 diopters [D], respectively) were significantly lower (better) than those of Galilei (0.60 and 0.17) and Sirius (0.23 and 0.36). The Sw of TCT measurements with Sirius (8.88 µm) was significantly lower than that of Galilei (11.64 µm). The COV ranged between 0.5 for the Km measurements of Pentacam and 2.8 for the TCT measurements of Galilei. Significant proportional bias in agreement was detected for the pKm measurements with all the three device pairs and for the ACD measurements between Pentacam and Galilei and between Galilei and Sirius. CONCLUSIONS: Though Pentacam, Galilei, and Sirius showed repeatable measurements for Km, TCT, ACD, and pKm, repeatabilities with Pentacam and Sirius were better than those with Galilei. There were significant differences in the measurements between the three devices; hence they cannot be used interchangeably for anterior segment measurements in keratoconus patients.

Keratoconus: a biomechanical perspective on loss of corneal stiffness.

Keratoconus (KC) is progressive disease of corneal thinning, steepening and collagen degradation. Biomechanics of the cornea is maintained by the intricate collagen network, which is responsible for its unique shape and function. With the disruption of this collagen network, the cornea loses its shape and function, resulting in progressive visual degradation. While KC is essentially a stromal disease, there is evidence that the epithelium undergoes significant thinning similar to the stroma. Several topographical approaches have been developed to detect KC early. However, it is now hypothesized that biomechanical destabilization of the cornea may precede topographic evidence of KC. Biomechanics of KC has been investigated only to a limited extent due to lack of in vivo measurement techniques and/or devices. In this review, we focus on recent work performed to characterize the biomechanical characteristics of KC.

Lens fiber orientation during phaco chop: clinical sign to identify appropriate nucleus depth.

UNLABELLED: Phaco chop is the preferred technique for many phaco surgeons. A critical step in chopping is the surgeon's ability to impale the nucleus in the middle of the core endonucleus, which can be challenging. We describe a clinical sign in the phaco chop technique to help surgeons identify the center of the endonucleus without estimating the nucleus thickness. This technique uses the morphological structure of the lens and the lens fiber orientation to precisely gauge the depth at which the surgeon should impale and hold the nucleus for effective chopping. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Toric implantable collamer lens for keratoconus.

Keratoconus is a progressive non-inflammatory thinning of the cornea that induces myopia and irregular astigmatism and decreases the quality of vision due to monocular diplopia, halos, or ghost images. Keratoconus patients unfit for corneal procedures and intolerant to refractive correction by spectacles or contact lenses have been implanted toric posterior chamber phakic intraocular lenses (PC pIOLs) alone or combined with other surgical procedures to correct the refractive errors associated with keratoconus as an off label procedure with special informed consent from the patients. Several reports attest to the safety and efficacy of the procedure, though the associated corneal higher order aberrations would have an impact on the final visual quality.