Retrospective assessment of accuracy of nine intraocular lens power calculation formulae in eyes with axial myopia.

PURPOSE: To compare the accuracy of nine conventional and newer-generation formulae in calculating intraocular lens power in eyes with axial myopia. SETTING: Tertiary eye care center, Bengaluru, India. DESIGN: Retrospective cross-sectional, comparative study conducted in India. METHODS: Patients undergoing uneventful phacoemulsification in eyes with axial length >26 mm were included. Preoperative biometry was done using Lenstar LS 900 (Haag-Streit AG, Switzerland). Single eye of patients undergoing bilateral implantation was randomly selected. Optimized lens constants were used to calculate the predicted postoperative refraction of each formula, which was then compared with the actual refractive outcomes to give the prediction errors, following which subgroup analysis was performed. The Kane formula, Barrett universal II, Emmetropia Verifying Optical (EVO) 2.0, Hill Radial Basis Function (Hill RBF) 3.0, Olsen formula, along with Wang Koch-adjusted four formulae, that is, Sanders Retzlaff Kraff/Theoretical (SRK/T), Holladay 1, Haigis, and Hoffer Q formula, were compared for intraocular lens power calculations. RESULTS: One hundred and sixty-five eyes that fulfilled all the inclusion criteria were studied. Hill RBF 3.0 had the lowest mean and median absolute prediction errors (0.355 and 0.275, respectively) compared to all formulas. In subgroup analysis (26-28, >28-30, and >30 mm), significant difference was seen only in extremely long eyes (>30 mm). The Hill RBF 3.0 formula generated the maximum percentage of eyes with refractive errors within ±0.25, ±0.5, ±0.75, and ±1 D (46%, 76.2%, 89.9%, and 95.8%, respectively). CONCLUSION: This is the first study evaluating all the formulas exclusively in the myopic eyes. Hill RBF 3 was found to be superior in accuracy to all other formulas.

3D visualization system and standard operating microscope for ease of visualization and surgeon comfort during phacoemulsification surgery.

PURPOSE: To compare the ease of visualization and comfort of the surgeon during phacoemulsification surgery using NGENUITY® 3D (NG) visualization system and standard operating microscope (SOM). METHODS: In this prospective, randomized, single-blind, single-center study, patients undergoing phacoemulsification surgery by one of the five surgeons were randomly assigned to two groups based on the visualization modality-NG and SOM. Ease of visualization and comfort of the surgeon was assessed using a 27-parameter in-house Surgeon Comfort Score questionnaire. RESULTS: A total of 224 phacoemulsification with intraocular lens implantations were performed in senile immature cataract (SIMC, n = 174) and mature cataract patients (MC, n = 50). Surgeon's ease of visualization (4.92-5.00) and hand-eye coordination score (4.97-5.00) were comparable between the NG- and SOM-groups. Postoperative neck discomfort was lower in both the groups, with a relatively lower discomfort in the NG-group (score: 1.04 vs 1.56). The Spearman rank correlation coefficient (r) between illumination of the operation theatre room and the surgical field revealed a weak negative correlation for most of the patients in the NG-group, and a positive correlation for patients in the SOM-group. No correlation was obtained between brightness of the surgical field and comfort with the surgical field brightness. CONCLUSIONS: Similar ease of visualization was experienced by the surgeons using NG- and SOM-system. Neck discomfort postsurgery was numerically lower in the NG-group, although not significant. Additionally, the NG-system permitted the safe performance of phacoemulsification using a lower surgical field illumination.

Management and prevention of corneal graft rejection.

The management of an episode of corneal graft rejection (CGR) is primarily by corticosteroids. Immunomodulators are useful for long-term immunosuppression and in dealing with cases of high-risk (HR) corneal grafts. The classical signs of CGR following penetrating keratoplasty (PKP) include rejection line, anterior chamber (AC) reaction, and graft edema. However, these signs may be absent or subtle in cases of endothelial keratoplasty (EK). Prevention of an episode of graft rejection is of utmost importance as it can reduce the need for donor cornea significantly. In our previous article (IJO_2866_22), we had discussed about the immunopathogenesis of CGR. In this review article, we aim to discuss the various clinical aspects and management of CGR.

Immunopathogenesis of corneal graft rejection.

The most common cause of corneal graft failure is corneal graft rejection (CGR). Although cornea is one of the immune-privileged sites, it can still get a rejection episode due to a breach in its natural protective mechanism. Both anatomical and structural properties of cornea and anterior chamber contribute toward its immune tolerance. Clinically, every layer of the transplanted cornea can get a rejection episode. A proper understanding of immunopathogenesis will help in understanding the various mechanism of CGR and the development of newer strategies for the prevention and management of such cases.

Repeatability of biometry measured by three devices and its impact on predicted intraocular lens power.

PURPOSE: To compare the repeatability of ocular biometry measured with the LENSTAR LS 900, IOLMaster 700, and Anterion and its impact on predicted intraocular lens (IOL) power. SETTING: Tertiary eye-care facility in South India. DESIGN: Prospective, observational, cross-sectional study. METHODS: Eyes diagnosed with cataract had 3 consecutive scans on each biometers. The repeatability was assessed using the within-subject standard deviation (Sw), test-retest repeatability, and coefficient of variation (CoV). The agreement was evaluated with the intraclass correlation (ICC). The IOL power was calculated with the Barrett Universal II formula. RESULTS: The study comprised 127 eyes of 76 patients. The repeatability of all parameters for a given device were excellent (ICC >0.9, low CoV and Sw). The agreement of the parameters between the biometers was very good (range from 0.93 to 0.99). The predicted IOL power differed statistically between the devices (P < .05), but the difference was clinically insignificant between the 3 biometers (ICC >0.99 for repeat calculation of IOL power). CONCLUSIONS: All the biometers included in the study had good to excellent repeatability of biometry parameters. The agreement of the predicted IOL power was excellent between the 3 optical biometers.

Simplifying and understanding various topographic indices for keratoconus using Scheimpflug based topographers.

Keratoconus (KC) is a progressive ectatic corneal disorder. There are multiple topographic devices and their varied indices used for diagnosis, detecting progression, and deciding management. It is important to understand the repeatablility, intra- test variabililty, and comparability amongst various topographic devices. The Scheimpflug camera-based devices, such as the Pentacam (Oculus, Wetzlar, Germany), Galilei (Ziemer, Biel, Switzerland), and Sirius (Costruzione Strumenti Oftalmici, Florence, Italy) are known to assist in the detection of early keratoconus and subclinical keratoconus. This article reviews the various Scheimpflug camera-based devices in depth, addressing their different indices, diagnostic accuracy, repeatability, and agreement and identifying the strongest parameter of each device. It will guide the practicing clinician by giving practical tips for decision making in the diagnosis and management of keratoconus.

Review of current status of refractive lens exchange and role of dysfunctional lens index as its new indication.

Advances in phacodynamics and intraocular lenses (IOLs) has given second life to clear lens extraction (CLE) or refractive lens exchange (RLE) in recent years for the treatment of patients with high degrees of myopia, hyperopia, and astigmatism who are unsuitable for laser surgery. Furthermore, presbyopia treatment with RLE supplemented with multifocal or accommodating IOLs gives the dual benefit of correcting refractive errors with eliminating the need for cataract surgery. RLE should be consistent and effective for a good refractive outcome along with safety during the surgical procedure and in the postoperative period. Therefore, proper patient selection and accurate preoperative protocols for IOL power calculations and selection are important along with an appropriate choice of surgical procedure. Dysfunctional lens index is a new objective tool that helps surgeon to aid in diagnosing, counseling, and educating patients with dysfunctional clear lens. In this article, we give a brief overview about the application of RLE for individuals with presbyopia and refractive errors like myopia, hyperopia, and astigmatism who are not suitable for laser correction.

Customized laser vision correction for irregular cornea post-refractive surgery.

Ablation-related complications following the refractive procedures are a major challenge for a refractive surgeon, considering the elective nature of the procedure. The use of topography-guided customized ablation has revolutionized the management of irregular corneas postrefractive surgery. This preferred practice highlights various hurdles encountered while managing cases of decentered ablation, small ablation zones, and planning a cataract surgery in patients with irregular corneas. It will give insight to the refractive surgeon on the planning of corneal regularization on various modern-day refractive platforms available, such as the WaveLight® EX-500 (Alcon Laboratories, Inc., Fort Worth, TX, USA), Schwind Amaris 1050 (Peramis; SCHWIND eye-tech-solutions, Kleinostheim, Germany), and Technolas Teneo 317 model 2 excimer laser (Bausch & Lomb, Rochester, NY, USA). The algorithmic approach outlined will enable the refractive surgeon to choose between the wavefront optomized and the topography-guided ablations.

Propensity and quantification of aerosol and droplet creation during phacoemulsification with high-speed shadowgraphy amid COVID-19 pandemic.

PURPOSE: To study propensity of aerosol and droplet generation during phacoemulsification using high-speed shadowgraphy and quantify its spread amid COVID-19 pandemic. SETTING: Aerosol and droplet quantification laboratory. DESIGN: Laboratory study. METHODS: In an experimental set-up, phacoemulsification was performed on enucleated goat eyes and cadaveric human corneoscleral rims mounted on an artificial anterior chamber. Standard settings for sculpt and quadrant removal mode were used on Visalis 100 (Carl Zeiss Meditec AG). Microincision and standard phacoemulsification were performed using titanium straight tips (2.2 mm and 2.8 mm in diameter). The main wound incisions were titrated equal to and larger than the sleeve size. High-speed shadowgraphy technique was used to detect the possible generation of any droplets and aerosols. The visualization and quantification of size of the aerosols and droplets along with calculation of their spread were the main outcome measures. RESULTS: In longitudinal phacoemulsification using a peristaltic pump device with a straight tip, no aerosol generation was seen in a closed chamber. In larger wounds, there was a slow leak at the main wound. The atomization of balanced salt solution was observed only when the phacoemulsification tip was completely exposed next to the ocular surface. Under this condition, the nominal size of the droplet was approximately 50 µm, and the maximum calculated spread was 1.3 m. CONCLUSIONS: There was no visible aerosol generation during microincision or standard phacoemulsification. Phacoemulsification is safe to perform in the COVID-19 era by taking adequate precautions against other modes of transmission.

Tele-consultations in the wake of COVID-19 - Suggested guidelines for clinical ophthalmology.

While telemedicine has been around for a few decades, it has taken great importance and prominence in recent times. With the fear of the virus being transmitted, patients and physicians across specialties are using consultation via a telephone call or video from the safety of their homes. Though tele-ophthalmology has been popular for screening, there are no clear guidelines on how to comprehensively manage patients seeking advice and treatment for a particular eye condition. Some major barriers to diagnosis and management are compromised detailed examination, no measurement of the visual acuity or intraocular pressure and a retinal evaluation not being feasible. Despite these limitations, we do need to help those patients who need immediate care or attention. Hence, this article has put together some guidelines to follow during such consultations. They are important and timely due to the medicolegal and financial implications.

Keratoconus Screening Indices and Their Diagnostic Ability to Distinguish Normal From Ectatic Corneas.

PURPOSE: To compare the diagnostic ability of 3 Scheimpflug devices in differentiating normal from ectatic corneas. DESIGN: Comparison of diagnostic instrument accuracy. METHODS: This study included 42 normal, 37 subclinical keratoconic, and 51 keratoconic eyes seen in a tertiary eye care institute. Keratoconus screening indices were evaluated using the Pentacam (Oculus, Wetzlar, Germany), Galilei (Ziemer, Biel, Switzerland), and Sirius (Costruzione Strumenti Oftalmici, Florence, Italy). Sensitivity, specificity, and area under receiver operating characteristic curve (AUC) were calculated. RESULTS: Highest sensitivity (100%) to diagnose keratoconus was seen for 6 parameters on Pentacam and 1 on Galilei. None of the indices in Sirius reached 100% sensitivity. For subclinical keratoconus, the highest sensitivity (100%) was seen for 2 parameters on Pentacam but for none of them on Galilei and Sirius. All parameters were strong enough to differentiate keratoconus (AUC > 0.9). On comparing the best parameters of all 3 machines, the AUC of the Belin/Ambrosio enhanced ectasia total derivation (BAD-D) and the inferior-superior value (ISV) of Pentacam were statistically similar to that of the keratoconus prediction index (KPI) and keratoconus probability (Kprob) of Galilei (P = .27) and 4.5 mm root mean square per unit area (RMS/A) back of Sirius (P = .55). When differentiating subclinical from normal corneas, BAD-D was similar to the surface regularity index (SRI) of Galilei (P = .78) but was significantly greater than the 8 mm RMS/A back of Sirius (P = .002). CONCLUSION: Keratoconus indices measured by all 3 machines can effectively differentiate keratoconus from normal corneas. However, new cutoff values might be needed to differentiate subclinical from normal corneas.

Effect of post crosslinking haze on the repeatability of Scheimpflug-based and slit-scanning imaging devices.

PURPOSE: The aim of this study was to analyze the effect of postcollagen crosslinking (CXL) haze on the measurement and repeatability of pachymetry and mean keratometry (Km) of four corneal topographers. MATERIALS AND METHODS: Sixty eyes of sixty patients with progressive keratoconus who had undergone accelerated CXL (ACXL) underwent imaging with a scanning slit imaging device (Orbscan II) and three Scheimpflug imaging devices (Pentacam HR, Sirius, and Galilei). Post-ACXL haze was measured using the densitometry software on the Pentacam HR. Readings of the thinnest corneal thickness (TCT) and Km from three scans of each device were analyzed. Effect of haze on the repeatability of TCT and Km measurements was evaluated using regression models. Repeatability was assessed by coefficient of variation. RESULTS: Corneal densitometry in different zones affected the repeatability of TCT measurement of Orbscan (P < 0.05) significantly but not the repeatability of TCT with Pentacam HR and Sirius (P = 0.03 and 0.05, respectively). Km values were affected by haze when measured with the Pentacam HR (P < 0.05). The repeatability of Km readings for all devices was unaffected by haze. In the anterior 0-2 mm and 2-6 mm zone, TCT (P = 0.43 and 0.45, respectively), Km values (P = 0.4 and 0.6, respectively), repeatability of TCT (P = 0.1 in both zones), and Km (P = 0.5 and 0.1, respectively) with Galilei were found to be the most reliable. CONCLUSION: Galilei measurements appear to be least affected by post-ACXL haze when compared with other devices. Hence, topography measurements in the presence of haze need to be interpreted with caution.

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.

The Role of Aberrometry in Accommodative Spasm After Myopic Photorefractive Keratectomy.

PURPOSE: To report the role of aberrometry in a case of accommodative spasm following myopic photorefractive keratectomy (PRK). METHODS: Observational case report. RESULTS: One month following myopic PRK, a 33-year-old healthy woman complained of seeing multiple images and headache that interfered with her daily activities. Her corrected distance visual acuity (CDVA) was 20/40 in the right eye and 20/25 in the left eye with a manifest refraction of -0.75 -0.50 × 165° in the right eye and plano -0.50 × 20° in the left eye. Cycloplegic refraction was plano -0.50 × 165° in the right eye and plano -0.5 × 20° in the left eye. Ray tracing aberrometry showed variable refraction with increase in internal defocus, which after cycloplegia reduced from 1.019 to 0.142 µm in the right eye and 0.366 to 0.230 µm in the left eye. Total ocular aberrations decreased by 53.16% in the right eye (range: 1.511 to 0.708 µm) and 18.77% (range: 0.671 to 0.545 µm) in the left eye; corresponding simulated Snellen visual acuity charts also showed improvement. The patient was treated with one drop of cyclopentolate 1% three times a day for 6 weeks, following which headache and ghosting of images completely resolved. CONCLUSIONS: Accommodative spasm should be considered in patients with visual disturbances of uncertain causes following myopic refractive surgery. Ray tracing aberrometry can serve as a diagnostic and educative tool in managing such patients.

Association Between Corneal Deformation and Ease of Lenticule Separation From Residual Stroma in Small Incision Lenticule Extraction.

PURPOSE: To study the association between corneal deformation (CD) and ease of lenticule separation from the stroma in small incision lenticule extraction. METHODS: Thirty-six myopic eyes of 36 patients underwent small incision lenticule extraction. Preoperative refraction, intraocular pressure, central corneal thickness, and CD were evaluated with Scheimpflug imaging and air-puff applanation. Fourier transform of CD waveform was also performed. The surgeon also graded the ease of separation of lenticule surfaces from the residual stroma intraoperatively as grades 1 (low effort), 2 (moderate effort), and 3 (high effort). All the procedures were performed by the same surgeon. CD values were concealed from the surgeon. Differences between the grades were assessed with 1-way analysis of variance and analysis of covariance. RESULTS: Mean preoperative refraction, intraocular pressure, central corneal thickness, lenticule thickness, and incision width were similar among the grades (P > 0.05). A total of 5 of the 10 analyzed CD variables were significantly different among the grades. Among them, deformation amplitude (1.20 vs. 1.13 vs. 1.07 mm in the order of increasing grades, P = 0.001), velocity of the corneal apex at the second applanation point (-0.47 vs. -0.43 vs. -0.40 m/s, P = 0.02), peak distance (5.33 vs. 5.25 vs. 5.07 mm, P = 0.006), area under the deformation amplitude (13.40 vs. 12.84 vs. 12.06, P = 0.04), and root mean square of Fourier coefficients (0.12 vs. 0.12 vs. 0.11 mm, P = 0.005) decreased from grades 1 to 3. CONCLUSIONS: CD was inversely correlated with the ease of lenticule separation from the residual stroma and may assist in customization of the energy parameters of the laser.

Current review and a simplified "five-point management algorithm" for keratoconus.

Keratoconus is a slowly progressive, noninflammatory ectatic corneal disease characterized by changes in corneal collagen structure and organization. Though the etiology remains unknown, novel techniques are continuously emerging for the diagnosis and management of the disease. Demographical parameters are known to affect the rate of progression of the disease. Common methods of vision correction for keratoconus range from spectacles and rigid gas-permeable contact lenses to other specialized lenses such as piggyback, Rose-K or Boston scleral lenses. Corneal collagen cross-linking is effective in stabilizing the progression of the disease. Intra-corneal ring segments can improve vision by flattening the cornea in patients with mild to moderate keratoconus. Topography-guided custom ablation treatment betters the quality of vision by correcting the refractive error and improving the contact lens fit. In advanced keratoconus with corneal scarring, lamellar or full thickness penetrating keratoplasty will be the treatment of choice. With such a wide spectrum of alternatives available, it is necessary to choose the best possible treatment option for each patient. Based on a brief review of the literature and our own studies we have designed a five-point management algorithm for the treatment of keratoconus.

Profile of microbial keratitis after corneal collagen cross-linking.

PURPOSE: To report the profile of microbial keratitis occurring after corneal collagen cross-linking (CXL) in keratoconus patients. METHODS: A retrospective analysis of 2350 patients (1715 conventional CXL, 310 transepithelial CXL, and 325 accelerated CXL) over 7 years (from January 2007 to January 2014) of progressive keratoconus, who underwent CXL at a tertiary eye care centre, was performed. Clinical findings, treatment, and course of disease of four eyes that developed postprocedural moxifloxacin resistant Staphylococcus aureus (MXRSA) infectious keratitis are highlighted. RESULTS: Four eyes that underwent CXL (0.0017%) had corneal infiltrates. All eyes that developed keratitis had conventional CXL. Corneal infiltrates were noted on the third postoperative day. Gram's stain as well as culture reported MXRSA as the causative agent in all cases. Polymerase chain reaction (PCR) in each case was positive for eubacterial genome. All patients were treated with fortified antibiotic eye drops, following which keratitis resolved over a 6-week period with scarring. All these patients were on long-term preoperative oral/topical steroids for chronic disorders (chronic vernal keratoconjunctivitis, bronchial asthma, and chronic eczema). CONCLUSION: The incidence of infectious keratitis after CXL is a rare complication (0.0017%). MXRSA is a potential organism for causing post-CXL keratitis and should be identified early and treated aggressively with fortified antibiotics.

Intrastromal fluid drainage with air tamponade: anterior segment optical coherence tomography guided technique for the management of acute corneal hydrops.

AIMS: To describe a new technique of corneal stab incision with intracameral air injection for management of patients with acute corneal hydrops. METHODS: Five patients with acute corneal hydrops with large Descemet's membrane (DM) detachment and multiple stromal clefts underwent the procedure. The technique entailed anterior segment optical coherence tomography guided intrastromal fluid drainage through multiple corneal stromal venting incisions along with anterior chamber air tamponade. The time taken for the DM to reattach, resolution of corneal oedema and the best-corrected visual acuity (BCVA) were assessed postoperatively. RESULTS: Five patients (age range, 10-25 years) with large DM detachment underwent the procedure. The presenting visual acuity varied from hand motions close to face to 1/60. No intraoperative complications were encountered. The DM attached on first postoperative day in four out of five cases. The corneal oedema resolved over 2-3 weeks in all cases. Repeat air injection was not required in any of the cases. All patients had a final BCVA of ≥3/60 with two of them achieving a BCVA of ≥6/24 at three months postoperatively. CONCLUSIONS: The technique of intrastromal drainage of fluid combined with air tamponade can be effectively used as a treatment modality for the management of severe cases of acute corneal hydrops.