Maria Jesus Giraldez

Accuracy and precision of EyeSys and Orbscan systems on calibrated spherical test surfaces.

Background: It is important to know how well the surface topography can be measured with current devices for corneal topographic analysis. There are several applications that need an accurate and precise method to measure corneal shape and variations, such as the effect of contact lens wear and the different refractive surgery techniques. Purpose: The aim of this study is to compare the accuracy and reproducibility of the measurement of the central curvature on calibrated steel balls using the EyeSys videokeratoscope and the Orbscan corneal topography system. Methods: The videokeratoscope (EyeSys Corneal Analysis System 2000, version 3.1) and the Orbscan corneal topography system (Orbscan II version 3.0) were used by four trained investigators to measure a series of five uniform and calibrated test surfaces with known radius of curvature ranging from 6.13 to 9.00 mm. Result: No statistically significant difference was found between the videokeratoscope and Orbscan systems in relation to accuracy or precision. The 95% confidence limits showed a close agreement between both instruments. The mean bias was less than ± 0.05 mm for both devices. The precision of the instruments was found to be similar. Conclusion: The EyeSys seems to measure more accurately, but the accuracy of the Orbscan was also acceptable, suggesting that both instruments are accurate and precise enough for research and clinical purposes. However, further studies of accuracy and repeatability of topographical measurements on human eyes generated by different topographers are necessary.

Contact Lens Hydrophobicity and Roughness Effects on Bacterial Adhesion

Purpose. This study was designed to assess whether hydrogel contact lens (CL) surface hydrophobicity and roughness affect Staphylococcus epidermidis adhesion. Methods. Bacterial adhesion experiments were performed on two unworn silicone hydrogel and three unworn conventional hydrogel CLs using the S.epidermidis strain CECT 4184. Microbial colonization was assessed by conducting counts expressed as colony-forming units. CL hydrophobicity was determined through water contact angle measurements and the roughness parameters such as mean surface roughness (Ra), kurtosis (Rku), and skewness (Rsk) were determined through atomic force microscopy in Tapping Mode. Results. The conventional CLs showed similar water contact angles (p > 0.05) and were classified as hydrophilic. The silicone hydrogel CLs yielded hydrophobic contact angles with no significant differences between them (p > 0.05). The lenses with the highest (nelfilcon A and ocufilcon B) or lowest (comfilcon A and omafilcon A) Ra values displayed a lesser or greater extent of spikiness of their surfaces, respectively. All lenses showed a predominance of peaks (Rsk > 0) over troughs. S. epidermidis adhered more to the hydrophobic CLs (p < 0.05). Omafilcon A and comfilcon A, which showed the lowest Ra values among the hydrophilic and hydrophobic lenses, respectively, returned the lowest bacterial adhesion scores (p < 0.05). Conclusions. Our results suggest that more hydrophobic CLs are more prone to S. epidermidis adhesion. Although the Ra appears to be related to S. epidermidis adhesion, the influence of Rku and Rsk on this variable remains unclear.

Soft Contact Lens Surface Profile by Atomic Force Microscopy

Purpose. This study was designed to qualitatively and quantitatively characterize the surface morphology of four unworn conventional hydrogel contact lenses (omafilcon, hioxifilcon, nelfilcon A, and ocufilcon B) and two silicone-hydrogel contact lenses (senofilcon A and comfilcon A) without surface treatment. Methods. Surface roughness was assessed using atomic force microscopy in Tapping ModeTM to determine the representative roughness parameters mean surface roughness (Ra), mean square roughness (Rms), kurtosis (Rku), and skewness (Rsk). To date, these last two parameters have not been used to characterize contact lens surfaces. Rku provides information on the distribution of spikes above and below the mean line, and Rsk provides information about the asymmetric roughness of surfaces. The surface topography of the lenses was also mapped in detail. Results. In all the lenses, higher Ra and Rms values were obtained when larger surface areas were examined. The daily replacement contact lenses (nelfilcon A and ocufilcon B) showed the highest Ra and Rms values but according to their Rku scores, their surface profiles were less spiky than the remaining lenses. On the contrary, the lowest Ra and Rms values were recorded for comfilcon A and omafilcon A, which also exhibited the spikiest surface profiles. All the materials except the hioxifilcon showed a predominance of peaks (Rsk >0) over troughs. Conclusions. The shape parameters Rku and Rsk are useful for characterizing contact lens surfaces, because they provide different yet complementary information to that offered by Ra and Rms. Precise knowledge of the shape profile of a contact lens surface will give an idea of its susceptibility to deposit formation or colonization by microorganisms.

Rigid gas permeable contact lens and corneal topography

We investigated the effect of high Dk daily wear rigid gas permeable contact lenses on corneal topography. Eight young myopic subjects wore hard contact lenses for 21 days. Corneal topography was monitored using the EyeSys system. It was measured every day during the next 21 days after the fitting. We recorded the corneal radius of curvature at 16 peripheral points approximately 1, 2, 3 and 4u2003mm along the four principal meridians (nasal, superior, inferior and temporal). Our study showed that daily wear RGP Forum 210 does not produce significant alterations of the corneal curvature as a function of time.

Clinical assessment of the lower tear meniscus height.

Purpose:u2002 Different values of the lower tear meniscus height (TMH) can be obtained depending on the method and technique of measurement employed. This study aimed to assess (1) differences between the absolute (TMH‐A), reflex (TMH‐R) and fluorescein (TMH‐F) lower tear meniscus heights, (2) differences between the central (TMH‐R), nasal (TMH‐RN) and temporal (TMH‐RT) reflex lower tear meniscus heights and (3) the amount of fluorescein present in the lower tear meniscus, 5u2003min after fluorescein instillation (TMH‐FV).

Further information on the knowledge of topographical corneal thickness.

Central and peripheral corneal thickness has been used increasingly to obtain information about physiologic and clinical conditions of the cornea. In this study, a new method based on ultrasonic pachometry for topographical corneal thickness measurement is described. Results suggest that the technique is reliable for clinical determination of global corneal thickness. Measurements taken by one observer on different sessions (intersession variation) and measurements taken by different observers (interobserver variation) are not significant different (p = 0.586 and 0.273, respectively). This new ultrasound topographical pachometric method can be considered a useful tool for determination of topographical corneal thickness. It has implications for the use of topographical ultrasonic pachometry in contact lenses research, refractive surgery, and management of different pathologic conditions.

Asfericidad corneal en una población de adultos jóvenes: Implicaciones clínicas

espanolObjetivos: Determinacion de la relevancia de diferentes componentes opticos oculares en el estado refractivo de adultos jovenes, con especial atencion a la topografia corneal representada por el valor de asfericidad. Sujetos y metodos: Las topografias corneales y biometrias ultrasonicas fueron obtenidas en 109 estudiantes universitarios con diversas formas de error refractivo (rango equivalente esferico: +3,25 D a -11,00 D). Se practica un estudio de regresion para establecer las relaciones entre la asfericidad corneal y el error refractivo, asi como otros componentes opticos oculares relacionados con el mecanismo de emetropizacion del ojo. Resultados: La asfericidad promedio fue -0,23 (DE 0,08, rango: -0,42 a -0,03). Todos los valores se corresponden con la descripcion matematica de la elipse prolata, la mas comunmente aceptada para la cornea humana normal. La correlacion estadistica entre la asfericidad y el error refractivo esferico equivalente no fue significativa, pero existia correlacion significativa de la asfericidad con respecto al radio de curvatura, a la profundidad de la camara vitrea y a la longitud axial. Conclusiones: 1) Los valores de asfericidad apoyan la morfologia generalizada de la cornea prolata como estandar. Se discuten las influencias de esta configuracion en la adaptacion de LC, en la cirugia refractiva o en la capacidad visual del ojo. 2) Los resultados sugieren que, si bien existe relacion entre la longitud axial y la topografia corneal, esta ultima probablemente no participe en los mecanismos de emetropizacion que determinan el estado refractivo del ojo adulto. EnglishPurpose: To determine the relevance of the different ocular optical components in the refractive state of young adults, paying special attention to the corneal topography represented by the asphericity value. Subjects and methods: Corneal topographies and ultrasonic biometries were obtained from 109 university students with different refractive errors (spherical equivalent range: +3.25 D to -11.00 D). A regression study was performed in order to establish the relationships between corneal asphericity and refractive error, as well as other ocular optical components related to the emmetropization mechanism of the eye. Results: The mean asphericity values were -0.23 (SD 0.08, range: -0.42 to -0.03). All the values correspond to the mathematical description of the prolate ellipse, most commonly accepted for the normal human cornea. The statistical correlation between asphericity and equivalent refractive error was not significant, but a significant correlation was found for the asphericity with respect to the radius of curvature, vitreous chamber depth and axial length. Conclusions: 1) The asphericity values support the generalised morphology of the prolate cornea as the standard. The influence of this configuration on the contact lens fit, refractive surgery or the visual performance of the eye are discussed. 2) Results suggest that, although a relationship between axial length and corneal topography actually exists, it is not likely that the latter has implications for the emmetropization mechanisms which determine the refractive state of the adult eye.

Accuracy and repeatability of a new tono-pachymeter for measuring central corneal thickness.

Objectives: The recently developed noncontact tonopachymeter Tonopachy NT-530 P provides intraocular pressure values corrected for central corneal thickness (CCT). The purpose of this study was to assess the accuracy and repeatability of its CCT measurements. Methods: The CCT measurements were obtained in 64 right eyes of 64 young healthy subjects using the Orbscan corneal topography system followed by the Tonopachy and then by ultrasound pachymetry (UP). Another sample of 31 subjects was used to test the repeatability of the tonopachy measurements in 2 separate sessions 1 week apart. To compare the tonometers and determine intersession repeatability for the tonopachymeter, differences in the readings provided by pairs of the instruments or obtained in the two sessions were plotted against mean differences. The hypothesis of zero bias was examined by a paired t-test. The coefficient of repeatability was calculated as the 95% limits of agreement (LoAs) of differences between the 2 sessions. Results: Measurements made using the three instruments were significantly correlated (P<0.001). Mean CCTs (±SD) measured using the Tonopachy, Orbscan (acoustic factor set at 0.92) and ultrasound pachymeter were 530.42±34.96, 526.73±39.53, and 550.69±37.26 &mgr;m, respectively. The differences between modalities (±95% LoAs) were −3.68±24.36 for Orbscan versus Tonopachy, 20.66±14.69 for UP versus Tonopachy, and 23.95±24.21 for UP versus Orbscan. The coefficient of repeatability for the tonopachymeter was ±15.11 &mgr;m. Conclusions: The Tonopachy offers similar CCT measurements to those provided by conventional pachymeters with good repeatability.

Efecto de la instilación del colicursi® anestésico doble (tetracaína 0,1% y oxibuprocaína 0,4%) sobre el espesor corneal central y paracentral

OBJECTIVE To study the effect of 1 drop of combined topical anaesthesia (tetracaine 0.1% and oxybuprocaine 0.4%) on central corneal thickness (CCT) values and at 2.5 mm from the corneal centre in nasal, temporal, superior and inferior hemi meridians, monitored by Orbscan over a period of 16 minutes. MATERIALS AND METHODS The corneal thickness of 12 right eyes of 12 young healthy men was determined using the Orbscan Topography System. Values were determined at the centre and paracentral regions 2.5 mm from the centre every 2 minutes for 16 minutes before and after the administration of 1 drop of double anaesthetic Colircusi which contains tetracaine 0.1% and oxybuprocaine 0.4%. RESULTS There was no obvious trend of central and paracentral corneal thickness value change before and after administration of Colircusi (paired ANOVA, p>0.05). Although corneal thickness variation was not statistically significant, higher differences were observed at the 6 minute time-point for CCT and at 8 minutes for nasal paracentral corneal thickness. CONCLUSIONS One drop of double anaesthetic Colircusi with tetracaine 0.1% and oxibuprocaine 0.4% does not produce any significant change in central corneal thickness or in paracentral regions 2.5 mm from the centre (nasal, temporal, superior and inferior hemi meridians).

Hyperacuity test to evaluate vision through dense cataracts: research preliminary to a clinical study in India

Using high luminance point-of-light stimuli, Vernier judgments can be made in the presence of markedly degraded retinal imagery. Without coaching, observers perform center-of-gravity assessments of relative locations of degraded point images. We seek to define, presurgery, individuals who will derive the most benefit from advanced cataract removal (a form of triage), and to determine which of two cataractous eyes has the better postsurgical visual prognosis. There are incredible and growing backlogs of patients with severe cataracts (and other dense media opacities) in the developing world, and generally, limited resources are available for provision of health care. Postcataract surgical failure rates for good visual function are often high, and only one eye is operated on in over 95% of indigent patients treated. Prior to initiating advanced studies in the developing world, at Berkeley we conducted preliminary research on Vernier acuity test techniques on normal adult subjects. We sought to determine the number of repeat trials necessary; to compare a two-point and a three-point Vernier display; to determine the shape of the measured response function at large gap separations between test points (required when testing advanced cataract patients); to assess the effect(s) of a broad range of uncorrected refractive errors on outcomes; and to consider means to minimize refraction-based errors. From these and prior data and analyses, we defined a protocol for use in the developing world. Using a newly designed and rugged precision instrument, these tests were repeated on an advanced cataract population at Aravind Eye Hospital in Madurai, India. Although we had much prior experience in India, the initial protocol required major revision on site. Necessary changes in test methods and analytical approaches were made, and next stages in this program were planned. And a new and simple gap «visual acuity» (gap «VA») test was added to the protocol, which greatly facilitated the outcome. The presented material is of interest for several reasons: The health care problems addressed are of considerable social and economic importance; it is valuable to compare the initial protocol and instrument defined in Berkeley and the resultant protocol and instrument designs that finally evolved in India; and the difficulties encountered when seeking to adapt what we thought were simple techniques to patient populations and technical personnel in a «small town setting» (ca. 1 million inhabitants in Madurai alone) in rural south India, are worthy of note. We point out that the Aravind Eye Hospital is an ophthalmological exemplar in the developing world