Sean McCafferty

Pseudophakic cystoid macular edema prevention and risk factors; prospective study with adjunctive once daily topical nepafenac 0.3% versus placebo

BackgroundDefine the effectiveness of a topical non-steroidal anti-inflammatory drug (NSAID) added to topical steroid use after uncomplicated phacoemulsification for the prevention of pseudophakic cystoid macular edema (PCME) using a prospective, randomized, double-masked, placebo-controlled clinical study.MethodsEyes (1000) were randomized to placebo (497) or nepafenac 0.3% (503) used once daily, post-operatively for 5xa0weeks at two ophthalmology clinics. Diagnosis of PCME was made by clinical, ocular coherence tomography (OCT), and with fluorescein angiography confirmation. Correlation of PCME to NSAID use and the presence of pre-operative risk factors for PCME were assessed including, contralateral PCME, diabetic retinopathy, retinal vein occlusion, macular hole, epiretinal membrane, macular degeneration, retinal detachment repair, and prostaglandin use.ResultsPCME was the most common complication associated with routine cataract surgery (4.2% with PCME risk factors, 2.0% with risk factors excluded). Topical nepafenac 0.3% significantly reduces the incidence of PCME compared to placebo when used after routine cataract surgery (pu2009=u2009.0001). When patients with pre-operative risk factors are excluded, the incidence of PCME between treatment and placebo groups is equivalent (pu2009=u20090.31). PCME relative risk (RR) was most significant in contralateral PCME (RR 19.5), diabetic retinopathy (RR 13.1), retinal vein occlusion (RR 12.9), macular hole (RR 7.7), and epiretinal membrane (RR 5.7). Prostaglandin use and previous retinal detachment were not shown to increase risk.ConclusionPseudophakic cystoid macular edema is common after phacoemulsification cataract surgery. Topical nepafenac 0.3% reduces PCME in patients with pre-operative risk factors for PCME compared to placebo but shows no benefit in patients without pre-operative risk factors.Trial registrationNIH ClincalTrials.gov retrospectively registered January 15, 2017, NCT03025945.

Corneal Surface Asphericity, Roughness, and Transverse Contraction after Uniform Scanning Excimer Laser Ablation

PURPOSEnTo examine the interaction between the excimer laser and residual tissue.nnnMETHODSnTen cadaveric porcine eyes with exposed corneal stroma and plastic test spheres underwent uniform 6-mm ablation with a scanning excimer laser. Corneal profilometry of the central 3 mm was measured with submicrometer resolution optical interferometry, before and after uniform excimer ablation. Eleven surface-marked eyes were photomicrographed before and after excimer ablation. Images were superimposed, and mark positional changes were measured.nnnRESULTSnUniform scanning excimer laser ablation of the corneal stroma produces a significant central steepening and peripheral flattening in the central 3-mm of the diameter. The central 1-mm corneal curvature radius (r) decreased from r = 10.07 ± 0.44 (95% CI) to 7.22 ± 0.30 mm, and the central 2-mm radius decreased from r = 10.16 ± 0.44 to 8.10 ± 0.43 mm. Q values, measuring asphericity in the 2-mm radius of the central cornea, were significantly lower before than after ablation (-5.03 ± 4.01 vs. -52.4 ± 18.7). Surface roughness increased significantly from 0.65 ± 0.06 to 1.75 ± 0.32 μm after ablation. The central 2 mm of the stromal surface contracted by 2.21% ± 0.80% at a sustained temperature of 5°C. Ablation of plastic spheres produced no significant change.nnnCONCLUSIONSnThe excimer laser interacts with the nonablated residual stromal surface in a characteristic fashion not seen with isotropic, inorganic material. Increases in asphericity, surface roughness, surface contraction, and stromal morphologic changes are supportive of this interaction. The surface changes demonstrated may be indicative of temperature-induced transverse collagen fibril contraction and stress redistribution, or the ablation threshold of the stromal surface may be altered. This phenomenon may be of increased importance using lasers with increased thermal load.

Goldmann applanation tonometry error relative to true intracameral intraocular pressure in vitro and in vivo

BackgroundGoldmann applanation tonometryxa0(GAT) error relative to intracameral intraocular pressure (IOP) has not been examined comparativelyxa0in both human cadaver eyes and in live human eyes.xa0Futhermore, correlations to biomechanical corneal properties and positional changes have not been examined directly to intracameral IOP and GAT IOP.MethodsIntracameral IOP was measured via pressure transducer on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically on each patient alternately to 10, 20, and 40xa0mmHg. IOP was measured using a Perkins tonometer in the supine position on 58 eyes and upright on a subset of 8 eyes. Twenty one (21) fresh human cadaver globes were Intracamerally IOP adjusted and measured via pressure transducer. Intracameral IOP ranged between 5 and 60xa0mmHg. IOP was measured in the upright position with a Goldmann Applanation Tonometer (GAT) and supine position with a Perkins tonometer. Central corneal thickness (CCT) was also measured.ResultsThe Goldmann-type tonometer error measured on live human eyes was 5.2 +/−1.6xa0mmHg lower than intracameral IOP in the upright position and 7.9 +/− 2.3xa0mmHg lower in the supine position (pxa0<u2009.05). CCT also indicated a sloped correlation to error (correlation coeff.u2009=u20090.18). Cadaver eye IOP measurements were 3.1+/−2.5xa0mmHg lower than intracameral IOP in the upright position and 5.4+/− 3.1xa0mmHg in the supine position (pxa0<u2009.05).ConclusionGoldmann IOP measures significantly lower than true intracameral IOP by approximately 3xa0mmHg in vitro and 5xa0mmHg in vivo. The Goldmann IOP error is increased an additional 2.8xa0mmHg lower in the supine position. CCT appears to significantly affect the error by up to 4xa0mmHg over the sample size.

Goldmann tonometer error correcting prism: clinical evaluation

Purpose Clinically evaluate a modified applanating surface Goldmann tonometer prism designed to substantially negate errors due to patient variability in biomechanics. Methods A modified Goldmann prism with a correcting applanation tonometry surface (CATS) was mathematically optimized to minimize the intraocular pressure (IOP) measurement error due to patient variability in corneal thickness, stiffness, curvature, and tear film adhesion force. A comparative clinical study of 109 eyes measured IOP with CATS and Goldmann prisms. The IOP measurement differences between the CATS and Goldmann prisms were correlated to corneal thickness, hysteresis, and curvature. Results The CATS tonometer prism in correcting for Goldmann central corneal thickness (CCT) error demonstrated a reduction to <±2 mmHg in 97% of a standard CCT population. This compares to only 54% with CCT error <±2 mmHg using the Goldmann prism. Equal reductions of ~50% in errors due to corneal rigidity and curvature were also demonstrated. Conclusion The results validate the CATS prism’s improved accuracy and expected reduced sensitivity to Goldmann errors without IOP bias as predicted by mathematical modeling. The CATS replacement for the Goldmann prism does not change Goldmann measurement technique or interpretation.

Goldmann Tonometer Prism with an Optimized Error Correcting Applanation Surface

Purpose We evaluate solutions for an applanating surface modification to the Goldmann tonometer prism, which substantially negates the errors due to patient variability in biomechanics. Methods A modified Goldmann or correcting applanation tonometry surface (CATS) prism is presented which was optimized to minimize the intraocular pressure (IOP) error due to corneal thickness, stiffness, curvature, and tear film. Mathematical modeling with finite element analysis (FEA) and manometric IOP referenced cadaver eyes were used to optimize and validate the design. Results Mathematical modeling of the optimized CATS prism indicates an approximate 50% reduction in each of the corneal biomechanical and tear film errors. Manometric IOP referenced pressure in cadaveric eyes demonstrates substantial equivalence to GAT in nominal eyes with the CATS prism as predicted by modeling theory. Conclusion A CATS modified Goldmann prism is theoretically able to significantly improve the accuracy of IOP measurement without changing Goldmann measurement technique or interpretation. Clinical validation is needed but the analysis indicates a reduction in CCT error alone to less than ±2 mm Hg using the CATS prism in 100% of a standard population compared to only 54% less than ±2 mm Hg error with the present Goldmann prism. Translational Relevance This article presents an easily adopted novel approach and critical design parameters to improve the accuracy of a Goldmann applanating tonometer.

Goldmann tonometry tear film error and partial correction with a shaped applanation surface

Purpose The aim of the study was to quantify the isolated tear film adhesion error in a Goldmann applanation tonometer (GAT) prism and in a correcting applanation tonometry surface (CATS) prism. Methods The separation force of a tonometer prism adhered by a tear film to a simulated cornea was measured to quantify an isolated tear film adhesion force. Acrylic hemispheres (7.8 mm radius) used as corneas were lathed over the apical 3.06 mm diameter to simulate full applanation contact with the prism surface for both GAT and CATS prisms. Tear film separation measurements were completed with both an artificial tear and fluorescein solutions as a fluid bridge. The applanation mire thicknesses were measured and correlated with the tear film separation measurements. Human cadaver eyes were used to validate simulated cornea tear film separation measurement differences between the GAT and CATS prisms. Results The CATS prism tear film adhesion error (2.74±0.21 mmHg) was significantly less than the GAT prism (4.57±0.18 mmHg, p<0.001). Tear film adhesion error was independent of applanation mire thickness (R2=0.09, p=0.04). Fluorescein produces more tear film error than artificial tears (+0.51±0.04 mmHg; p<0.001). Cadaver eye validation indicated the CATS prism’s tear film adhesion error (1.40±0.51 mmHg) was significantly less than that of the GAT prism (3.30±0.38 mmHg; p=0.002). Conclusion Measured GAT tear film adhesion error is more than previously predicted. A CATS prism significantly reduced tear film adhesion error bŷ41%. Fluorescein solution increases the tear film adhesion compared to artificial tears, while mire thickness has a negligible effect.

Goldmann and error correcting tonometry prisms compared to intracameral pressure

BackgroundCompare Goldmann applanation tonometer (GAT) prism and correcting applanation tonometry surface (CATS) prism to intracameral intraocular pressure (IOP), in vivo and in vitro.MethodsPressure transducer intracameral IOP was measured on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically to 10, 20, and 40xa0mmHg. Simultaneously, IOP was measured using a Perkins tonometer with a standard GAT prism and a CATS prism at each of the intracameral pressures. Statistical comparison was made between true intracameral pressures and the two prism measurements. Differences between the two prism measurements were correlated to central corneal thickness (CCT) and corneal resistance factor (CRF). Human cadaver eyes were used to assess measurement repeatability.ResultsThe CATS tonometer prism measured closer to true intracameral IOP than the GAT prism by 1.7+/−2.7xa0mmHg across all pressures and corneal properties. The difference in CATS and GAT measurements was greater in thin CCT corneas (2.7+/−1.9xa0mmHg) and low resistance (CRF) corneas (2.8+/−2.1xa0mmHg). The difference in prisms was negligible at high CCT and CRF values. No difference was seen in measurement repeatability between the two prisms.ConclusionA CATS prism in Goldmann tonometer armatures significantly improve the accuracy of IOP measurement compared to true intracameral pressure across a physiologic range of IOP values. The CATS prism is significantly more accurate compared to the GAT prism in thin and less rigid corneas. The in vivo intracameral study validates mathematical models and clinical findings in IOP measurement between the GAT and CATS prisms.

Intraocular Pressure Measurement Accuracy and Repeatability of a Modified Goldmann Prism: Multicenter Randomized Clinical Trial

PURPOSEnTo clinically evaluate a modified surface Goldmann applanation tomometer (GAT) prism for intraocular pressure (IOP) accuracy, repeatability, and safety.nnnDESIGNnProspective, open-label, randomized, controlled, multicenter reference device reliability and validity analysis.nnnMETHODSnA GAT and a modified surface GAT prism measured IOP on 173 unique eyes. The study design and analysis complied with FDA 510(k) and ANSIZ80.10-2014 guidelines. All eyes were randomized to IOP measurement by 1 of 5 standard prisms or 5 modified prisms, each from a different manufacturing lot. Pressures were measured by 6 investigators, 2 times with each prism, for a total of 1384 IOP measurements. Analysis included Bland-Altman difference accuracy, intraoperator and interoperator IOP measurement, and manufactured lot repeatability.nnnRESULTSnBland-Altman indicated no IOP measurements pairs outside the ±5xa0mm Hg guidelines. Operator and manufactured lot repeatability F tests and 1-way ANOVAs indicated no statistical difference between the standard and modified prisms (all P > .10). The difference in IOP measurements of the standard and modified prisms correlated well to Dresdner central corneal thickness (CCT) correction (Pxa0= .01).nnnCONCLUSIONnA modified surface replacement prism is statistically equivalent to a flat-surfaced prism. The modified surface prism indicated statistically significant correction for CCT requiring further testing outside the ANSI standard limits (0.500xa0mm < CCT < 0.600xa0mm) to examine its full potential.

Tactile Eye Pressure Measurement Through the Eyelid

This article presents the early results from a 10-person human subject study evaluating the accuracy of a novel method of indirect estimation of intraocular pressure using tactile sensors. Manual digital palpation tonometery is an old method used to estimate the eye pressure through palpation with ones fingers. Based on this concept, we present an instrumented measurement method, where multiple tactile stiffness sensors are used to infer the intraocular pressure of the eye. The method is validated using experimental data gathered from human subjects with eye pressures from 15 to 22 mmHg and determined by Goldman applanation tonometry (GAT). Bland-Altman plots comparing the GAT measurements and the proposed through-the-eye-lid tonometry indicate a statistical error of 5.16 mmHg, within the 95% confidence interval, which compares favorably with the FDA-mandated error bound of 5 mmHg. Details on the unit operation and data filtering are also presented. Due to its indirect and non-invasive nature, the proposed new tactile tonometry method can be applied at home as a self-administered home tonometer for management of glaucoma.Copyright

Thermal load from a CO2 laser radiant energy source induces changes in corneal surface asphericity, roughness, and transverse contraction.

PURPOSEnWe examined corneal surface response to an isolated thermal load.nnnMETHODSnCadaveric porcine eyes were pressurized and stabilized for processing and imaging. A carbon dioxide (CO2) laser (1.75 W) delivered a uniform disk of continuous wave thermal radiant energy to the exposed corneal stromal surface without ablation. Thermal load was determined by measuring corneal surface temperature during CO2 laser irradiation. Corneal profilometry was measured with broad-band optical interferometry before and after CO2 laser irradiation. Photomicrographs of the stromal surface were taken before and after irradiation, and the images were superimposed to examine changes in positional marks, examining mechanical alterations in the stromal surface.nnnRESULTSnThermal load from uniform laser irradiation without ablation produces central corneal steepening and paracentral flattening in the central 3-mm diameter. Q values, measuring asphericity in the central 2 mm of the cornea increased significantly and it was correlated with the temperature rise (R2=0.767). Surface roughness increased significantly and also was correlated with temperature rise (R2=0.851). The central stromal surface contracted and underwent characteristic morphologic changes with the applied thermal load, which correlated well with the temperature rise (R2=0.818).nnnCONCLUSIONSnThe thermal load created by CO2 laser irradiation creates a characteristic spectrum of morphologic changes on the porcine corneal stromal surface that correlates to the temperature rise and is not seen with inorganic, isotropic material. The surface changes demonstrated with the CO2 laser likely are indicative of temperature-induced transverse collagen fibril contraction and stress redistribution. Refractive procedures that produce significant thermal load should be cognizant of these morphologic changes.