Clemens Vass

Partial coherence interferometry: a novel approach to biometry in cataract surgery

PURPOSE To compare biometry performed by an enhanced version of dual beam partial coherence interferometry and applanation ultrasound in a prospective study of 85 cataract eyes to improve refractive outcome of cataract surgery due to a more accurate calculation of intraocular lens power. METHODS The SRK II formula using ultrasound biometry data was employed. Three months after surgery, partial coherence interferometry biometry was repeated and refractive outcome was determined. Preoperative partial coherence interferometry biometry data were used to determine the refractive power of the intraocular lenses retrospectively and to calculate the possible refractive outcome. RESULTS Precision of partial coherence interferometry biometry was more than 10 times better than that of ultrasound. Therefore, the possible mean absolute error for postoperative refraction achieved with partial coherence interferometry biometry was 0.49 diopters (compared with 0.67 diopters with ultrasound biometry), resulting in an improvement of 27%. Axial eye length measured with the two techniques differed by a mean of 460 microm. The difference in lens thickness measured with partial coherence interferometry and ultrasound significantly correlated with cataract grade. A mean shortening of 120 microm of axial eye length following cataract surgery was also detected by partial coherence interferometry. CONCLUSIONS The enhanced version of partial coherence interferometry offers biometry with unprecedented precision (<10 microm) and resolution (approximately 12 microm), therefore improving the refractive outcome in cataract surgery. This noninvasive technique provides a high degree of comfort for the patient, with no need for local anesthesia or pupil dilation and minimized risk of corneal infection.

Assessment of optic disk blood flow in patients with open-angle glaucoma

PURPOSE To characterize optic disk blood flow in patients with open-angle glaucoma compared with age-matched healthy control subjects. METHODS In this prospective cross-sectional study, 90 eyes of 90 patients with open-angle glaucoma and 61 eyes of 61 age-matched healthy control subjects were evaluated. Flow in the optic disk cup and the neuroretinal rim were assessed with scanning laser Doppler flowmetry. Fundus pulsation amplitude in the cup and the macula were assessed with laser interferometry. Visual field mean deviation was measured with the Humphrey 30 to 2 program. RESULTS Flow in the neuroretinal rim (-18%, P =.002), and in the cup (-46%, P <.001) and fundus pulsation amplitude in the cup (-33%, P <.001) and in the macula (-24%, P <.001) were significantly lower in patients with open-angle glaucoma compared with healthy control subjects. A significant association between blood flow measurements in the cup and fundus pulsation amplitudes in the cup was observed in both study cohorts. A significant association was also observed between the mean defect from visual field testing and ocular hemodynamic parameters. CONCLUSIONS Reduced optic disk perfusion in patients with open-angle glaucoma is evidenced from two independent methods in the present study. Moreover, our data indicate that reduced ocular blood flow in these patients is linked to visual field changes. It remains to be established whether compromised optic disk and choroidal blood flow contributes to optic disk damage in glaucomatous eyes or is a secondary functional phenomenon.

Estimation of Ocular Rigidity Based on Measurement of Pulse Amplitude Using Pneumotonometry and Fundus Pulse Using Laser Interferometry in Glaucoma

PURPOSE There is evidence from theoretical models and animal studies that the biomechanical properties of the optic nerve head and the sclera play a role in the pathophysiology of glaucoma. There are, however, only a few data available that demonstrate such biomechanical alterations in vivo. In this study, the hypothesis was that patients with primary open-angle glaucoma (POAG) have an abnormal ocular structural stiffness based on measurements of intraocular pressure amplitude and ocular fundus pulsation amplitude (FPA). METHODS Seventy patients with POAG and 70 healthy control subjects matched for age, sex, intraocular pressure and systemic blood pressure were included. The ocular PA and pulsatile ocular blood flow were assessed with pneumotonometry. The FPA was measured by using laser interferometry. Based on the Friedenwald equation, a coefficient of ocular rigidity (E1) was calculated relating PA to FPA. RESULTS There was no difference in systemic blood pressure, intraocular pressure, and ocular perfusion pressure (OPP) between the patients with glaucoma and the healthy control subjects. Both, FPA and PA were lower in the patients with glaucoma than in the control subjects. The calculated factor E1 was significantly higher in the patients with POAG (0.0454 +/- 0.0085 AU) than in the control subjects (0.0427 +/- 0.0058 AU, P = 0.03). Multiple regression analysis revealed that E1 was independent of age and sex, and correlated only slightly with OPP. CONCLUSIONS The present study indicates increased ocular rigidity in patients with POAG. This is compatible with a number of previous animal experiments and supports the concepts that the biomechanical properties of ocular tissues play a role in the diseases process.

Accurate determination of effective lens position and lens-capsule distance with 4 intraocular lenses.

Purpose: To measure effective lens position (ELP) of 4 intraocular lenses (IOLs) using high precision and high resolution dual‐beam partial coherence interferometry (PCI) and to assess the tendency of these IOLs to produce a lens‐capsule distance (LCD), a possible risk factor for posterior capsule opacification. Setting: Department of Ophthalmology, Vienna General Hospital; Institute of Medical Physics, University of Vienna, Austria. Methods: In a retrospective study, PCI was used to measure ELP and LCD in 139 pseudophakic eyes of 110 patients with 4 IOLs: acrylic 3‐piece IOL (AcrySof MA60BM); silicone 3‐piece IOL without a capsular tension ring (PhacoFlex SI30) and with a capsular tension ring (PhacoFlex SI30 and Morcher Type 14); silicone plate‐haptic IOL (Staar AA4203VF); and a hydrogel plate‐haptic IOL (logel 1103). Results: The ELP and LCD were determined with a precision of approximately 3 to 4 &mgr;m. An LCD was detected in 21 % eyes with the AcrySof, 20% of eyes with the SI30 without a capsular tension ring, 10% of eyes with a capsular tension ring, 21 of eyes with the Staar, and 17% of eyes with the logel. The LCDs detected by PCI, but not by slitlamp examination, were significantly smaller than those detected by both. Conclusion: The amount of LCD detected by PCI was approximately the same with all IOL types (∼20%) except the PhacoFlex SI30 with a capsular tension ring (10%).

Capsular bag shrinkage after implantation of an open-loop silicone lens and a poly(methyl methacrylate) capsule tension ring

Purpose: To quantify the dynamics of capsular bag shrinkage after cataract surgery. Setting: University Eye Hospital, Vienna, Austria. Methods: Nineteen eyes in 13 patients had clear corneal cataract surgery with implantation of a foldable, open‐loop, silicone posterior chamber intraocular lens (IOL) (AMO SI‐30). At the same time, an open, poly(methyl methacrylate) capsule tension ring (Morcher type 14 or 14A) was inserted to allow measurement of capsular bag circumference and diameter. After surgery, capsular bag shrinkage was quantified by measuring anterior chamber depth (ACD), iris‐lens distance (ILD), and distance between the eyelets of the capsule tension ring using optical methods. Capsular bag circumference (CBC) was deduced from these measurements, which were taken 1 day (baseline), 1 week, and 1 and 3 months postoperatively. Results: Between 1 day and 3 months, all three parameters decreased significantly. During the first postoperative week, ACID and ILD did not change, while both parameters decreased between 1 week and 1 month. After 1 month, ACID did not decrease further; ILD continued to decrease. The CBC decreased during the entire postoperative period. Conclusion: Besides ACID and ILD, CBC significantly decreased during the first 3 months after cataract surgery with in‐the‐bag posterior chamber IOL implantation. The CBC can be calculated from the distance between the ends of the capsule tension ring, which can be measured gonioscopically. From this, the diameter of the capsular bag can be calculated in the living eye. The influence of the capsule tension ring itself on capsular bag shrinkage remains to be established.

Correlation between the early morphological appearance of filtering blebs and outcome of trabeculectomy with mitomycin C

PurposeTo correlate the morphologic appearance of filtering blebs in the early postoperative period with the outcome of trabeculectomy with mitomycin C (MMC) during the first postoperative year. Patients and MethodsIn a prospective study, the morphologic appearance of filtering blebs after primary trabeculectomy with adjunctive MMC (0.1 mg/ml for 5 minutes intra-operatively) was classified; 49 eyes of 49 patients were examined preoperatively, 1 and 3 days, 1 and 2 weeks, 1, 3, 6, and 12 months postoperatively. Status of filtering bleb, intraocular pressure (IOP), and number of medications were recorded. ResultsOne year after surgery all patients had IOP ≤ 21; 6 patients received antiglaucoma medication. One eye required needling of the filtering bleb because of encapsulation. During the first postoperative year, eyes with conjunctival subepithelial micro cysts, observed in the first and the second postoperative week, had significantly lower mean IOP, than eyes without (11.1 mm Hg vs. 13.9 mm Hg; p:0.0043, ANOVA). Eyes with corkscrew vessels, observed in the first and the second postoperative week, had significantly higher mean IOP, than eyes without during the first postoperative year (13.4 mm Hg vs. 11.7 mm Hg; p:0.0141, ANOVA). ConclusionClassification of filtering blebs after trabeculectomy with MMC may help to disclose patients with an increased failure risk.

High Resolution Spectral Domain Optical Coherence Tomography (SD-OCT) in Multiple Sclerosis: The First Follow Up Study over Two Years

Background “Non-invasive, faster and less expensive than MRI” and “the eye is a window to the brain” are recent slogans promoting optical coherence tomography (OCT) as a new surrogate marker in multiple sclerosis (MS). Indeed, OCT allows for the first time a non-invasive visualization of axons of the central nervous system (CNS). Reduction of retina nerve fibre layer (RNFL) thickness was suggested to correlate with disease activity and duration. However, several issues are unclear: Do a few million axons, which build up both optic nerves, really resemble billions of CNS neurons? Does global CNS damage really result in global RNFL reduction? And if so, does global RNFL reduction really exist in all MS patients, and follow a slowly but steadily ongoing pattern? How can these (hypothesized) subtle global RNFL changes be reliably measured and separated from the rather gross RNFL changes caused by optic neuritis? Before generally being accepted, this interpretation needs further critical and objective validation. Methodology We prospectively studied 37 MS patients with relapsing remitting (n = 27) and secondary progressive (n = 10) course on two occasions with a median interval of 22.4±0.5 months [range 19–27]. We used the high resolution spectral domain (SD-)OCT with the Spectralis 3.5 mm circle scan protocol with locked reference images and eye tracking mode. Patients with an attack of optic neuritis within 12 months prior to the onset of the study were excluded. Principal Findings Although the disease was highly active over the observation period in more than half of the included relapsing remitting MS patients (19 patients/32 relapses) and the initial RNFL pattern showed a broad range, from normal to markedly reduced thickness, no significant changes between baseline and follow-up examinations could be detected. Conclusions These results show that caution is required when using OCT for monitoring disease activity and global axonal injury in MS.

Effect of levodopa on the human pattern electroretinogram and pattern visual evoked potentials

Pattern electroretinograms (P-ERGs) and pattern visual evoked potentials (P-VEPs) were recorded at three luminance levels and five different check sizes in a group of 16 control subjects before and after the oral administration of levodopa. At the lower luminance levels, significant decrease in P-ERG and P-VEP latencies were found. For P-VEPs the latency changes occurred only at small check sizes. No changes were observed in control experiments without levodopa administration. Our results show that levodopa-induced changes even occur at the retinal level and support a dopaminergic involvement in light and dark adaptation. Our observations are in agreement with a VEP delay found in Parkinsons disease and with a VEP latency increase in rats after dopamine depletion.

Measuring retinal nerve fiber layer birefringence, retardation, and thickness using wide-field, high-speed polarization sensitive spectral domain OCT.

PURPOSE We presented a novel polarization sensitive optical coherence tomography (PS-OCT) system for measuring retinal nerve fiber layer (RNFL) birefringence, retardation, and thickness, and report on the repeatability of acquiring these quantities. METHODS A new PS-OCT system, measuring at 840 nm, was developed that supports scan angles of up to 40° × 40° with an A-scan rate of 70 kHz. To test the performance and reproducibility, we measured 10 eyes of 5 healthy human volunteers five times each. All volunteers were imaged further with scanning laser polarimetry (SLP). The obtained RNFL birefringence, retardation, and thickness maps were averaged, and standard deviation maps were calculated. For quantitative comparison between the new PS-OCT and SLP, a circumpapillary evaluation within 2 annular segments (superior and inferior to the optic disc) was performed. RESULTS High quality RNFL birefringence, retardation, and thickness maps were obtained. Within the superior and inferior segments, the mean retardation for individual eyes ranged from 20° to 28.9° and 17.2° to 28.2°, respectively. The quadrant precision over the 5 consecutive measurements for each subject, calculated for the average retardation obtained within the superior and inferior quadrants ranged from 0.16° to 0.69°. The mean birefringence ranged from 0.106°/μm to 0.141°/μm superior and 0.101°/μm to 0.135°/μm inferior, with a quadrant precision of 0.001°/μm to 0.007°/μm. The mean RNFL thickness varied from 114 to 150 μm superior, and 111 to 140.9 μm inferior (quadrant precision ranged from 3.6 to 11.9 μm). CONCLUSIONS The new PS-OCT system showed high image quality and reproducibility, and, therefore, might be a valuable tool for glaucoma diagnosis.

Effect of dorzolamide and timolol on ocular pressure: blood flow relationship in patients with primary open-angle glaucoma and ocular hypertension.

PURPOSE The authors have reported previously that a study population, consisting of patients with glaucoma and ocular hypertension, is characterized by an impaired association between ocular blood flow parameters and systemic blood pressure, indicative of abnormal autoregulation. Here they report on the effects of dorzolamide and timolol on ocular pressure/flow relationships to test the hypothesis that these drugs improve autoregulation. METHODS One hundred forty patients with primary open-angle glaucoma or ocular hypertension were included in a clinical trial in a controlled, randomized double-masked study in two parallel groups. Seventy patients were randomly assigned to receive timolol, and 70 patients were randomly assigned to receive dorzolamide for a 6-month period. Scanning laser Doppler flowmetry was used to measure blood flow in the temporal neuroretinal rim and the cup of the optic nerve head. Pulsatile choroidal blood flow was assessed using laser interferometric measurement of fundus pulsation amplitude. The association between blood flow parameters and systemic blood pressure was compared before and after the 6-month treatment period. RESULTS Before treatment a significant association was observed between ocular blood flow parameters and systemic blood pressure in both parallel groups (r = 0.23-0.42). All regression lines between ocular hemodynamic parameters and systemic blood pressure were less steep after treatment with either dorzolamide or timolol (r = 0.03-0.24). CONCLUSIONS The present study indicates that intraocular pressure reduction with timolol or dorzolamide is associated with normalization of the ocular pressure/flow relationship. Whether this is related to the beneficial effects of IOP-lowering therapy in glaucoma remains to be established. (ClinicalTrials.gov number, NCT00991822.).