Impact of Defocus and High-Order Aberrations on Light Disturbance Measurements.

PURPOSE: To evaluate the impact of different levels of positive and negative defocus on light disturbance (LD) measures and to understand how high-order aberrations (HOAs) and topographic quality parameters may influence the perception of photic phenomena. METHODS: Thirty young healthy subjects (21 females and 9 males) attended this cross-sectional study. LD was evaluated with the light distortion analyzer (LDA) in natural accommodative and cycloplegic conditions with positive and negative induced defocus of 1.00D. HOAs were taken for a natural mesopic (without cycloplegia) and for fixed 5 mm (with cycloplegia) pupil size. The impact of corneal morphological parameters (SAI, SRI, and Q-value) in LD was also investigated. RESULTS: Positive and negative induced defocus of 1.00D significantly increased the size of LD (p < 0.010, Wilcoxon signed rank test) but not its irregularity index. Spherical-like HOAs were associated with the size of LD, while coma-like and total-like HOAs were associated with LD irregularity. Our results showed that SRI was significantly correlated with the size of the disturbance area (r=0.519, p=0.003, Spearman correlation) and SAI with both size (r=0.502, p=0.005, Spearman correlation) and irregularity (r=0.371, p=0.044, Spearman correlation). However, no correlation between the Q-value and LD parameters was found. CONCLUSIONS: The uncorrected positive and negative refractive errors might increase the size of the LD, such as the spherical-like HOAs, SAI, and SRI, instead of asphericity. Coma-like and total-like HOAs and SAI may influence the perception of irregularities in the LD shape. These results might have an impact on postrefractive surgery visual performance that should be investigated.

Light disturbance analysis in the controlled randomized clinical trial MiSight® Assessment Study Spain (MASS).

PURPOSE: To evaluate the perception of light disturbances (LD) in children wearing Dual Focus (DF) MiSight® contact lenses (CLs) for myopia control compared with children wearing single vision spectacles (SV). METHODS: This was a randomized, controlled clinical trial involving subjects aged 8-12 with myopia of -0.75 to -4.00D and astigmatism <1.00D allocated to MiSight® study CLs group or control group wearing SV. LD was determined at baseline, 12 and 24 months visit with a validated device, Light Disturbance Analyzer (LDA) to determine the shape, size and regularity of the LD phenomena with parameters of Light Disturbance Index (LDI) Best Fit Circle (BFC) and Standard Deviation between LD and BFC (BFCIrreg.SD). RESULTS: 74 children completed the study, 41 in the CL group and 33 in the SV group. SV group didn´t show any significant differences between monocular and binocular LD measurements throughout the study. Binocular BFCRadius was smaller at 24 months visit compared with 12 month visit (p < 0.05) and for BFCIrreg.SD was significantly smaller at 24 month visit compared with baseline (p < 0.05). In MiSight® group, binocular and monocular LDI, BFCRadius and BFCIrreg.SD measurements didn't show any significant change between 12 and 24 month visits (p > 0.05). However, monocular BFCIrreg. as well as monocular and binocular BFCIrreg.SD showed a significant decrease at 24 month visit compared with 12 month visit. CONCLUSIONS: DF lenses increase the monocular light disturbance perception compared with a single vision spectacle correction. However, this effect decreased over the follow-up time and presented a significant binocular attenuation effect.

Analysis of the application of the generalized monod kinetics model to describe the human corneal oxygen-consumption rate during soft contact lens wear.

This work is an analysis of the application of the generalized Monod kinetics model describing human corneal oxygen consumption during soft contact lens wear to models previously used by Chhabra et al. (J Biomed Mater Res B Appl Biomater, 2009a;90:202-209, Optom Vis Sci 2009b;86:454-466) and Larrea and Büchler (Invest Ophthalmol Vis Sci 2009;50:1076-1080). We use oxygen tension from in vivo estimations provided by Bonanno [Bonanno et al., Invest Ophthalmol Vis Sci 2002;43:371-376, and Bonanno et al 2009]. We consider four hydrogel and six silicone hydrogel lenses. The cornea is considered a single homogeneous layer, with constant oxygen permeability regardless of the type of lens worn. Our calculations yield different values for the maximum oxygen consumption rate Qc,max , whith differents oxygen tensions (high and low pc ) at the cornea-tears interface. Surprisingly, for both models, we observe an increase in oxygen consumption near an oxygen tension of 105 mmHg until a maximum is reached, then decreasing for higher levels of oxygen pressure. That is, when lowering the pressure of oxygen, the parameter Qc,max initially increases depending on the intensity of the change in pressure. Which, it could be related with the variation of the pH. Furthermore, it is also noted that to greater reductions in pressure, this parameter decreases, possibly due to changes in the concentration of glucose related to the anaerobic respiration. The averaged in vivo human corneal oxygen consumption rate of 1.47 × 10-4 cm3 of O2 /cm3 tissue s, with Monod kinetics model, considering all the lenses studied, is smaller than the average oxygen consumption rate value obtained using the Larrea and Büchler model. The impact that these calculations have on the oxygen partial pressure available at different depths in the corneal tissue is presented and discussed, taking into consideration previous models used in this study. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2269-2281, 2017.

Peripheral myopization and visual performance with experimental rigid gas permeable and soft contact lens design.

PURPOSE: To evaluate the performance of two experimental contact lenses (CL) designed to induce relative peripheral myopic defocus in myopic eyes. METHODS: Ten right eyes of 10 subjects were fitted with three different CL: a soft experimental lens (ExpSCL), a rigid gas permeable experimental lens (ExpRGP) and a standard RGP lens made of the same material (StdRGP). Central and peripheral refraction was measured using a Grand Seiko open-field autorefractometer across the central 60° of the horizontal visual field. Ocular aberrations were measured with a Hartman-Shack aberrometer, and monocular contrast sensitivity function (CSF) was measured with a VCTS6500 without and with the three contact lenses. RESULTS: Both experimental lenses were able to increase significantly the relative peripheral myopic defocus up to -0.50 D in the nasal field and -1.00 D in the temporal field (p<0.05). The ExpRGP induced a significantly higher myopic defocus in the temporal field compared to the ExpSCL. ExpSCL induced significantly lower levels of Spherical-like HOA than ExpRGP for the 5mm pupil size (p<0.05). Both experimental lenses kept CSF within normal limits without any statistically significant change from baseline (p>0.05). CONCLUSIONS: RGP lens design seems to be more effective to induce a significant myopic change in the relative peripheral refractive error. Both lenses preserve a good visual performance. The worsened optical quality observed in ExpRGP was due to an increased coma-like and spherical-like HOA. However, no impact on the visual quality as measured by CSF was observed.

Propiedades biomecánicas de la cornea con corvis ST y ocular response analyser después de diferentes procedimientos quirúrgicos en pacientes con queratocono / Corneal biomechanical properties with corvis ST and ocular response analyser in eyes with keratoconus which were submitted to different surgical procedures

Introducción. Las opciones quirúrgicas disponibles para el tratamiento del queratocono (QC) se han ampliado y mejorado. Nuestro objetivo es comparar las propiedades biomecánicas de la córnea con dos instrumentos de uso clínico en ojos con QC sin cirugía o intervenidos con diferentes tipos de cirugía corneal (cross-linking (CXL), segmentos intra-corneales (ICSR) y queratoplastia penetrante(QP)). Material e Métodos. Se analizaron 91 ojos de paciente con KC no operados, 22 ojos con ICSR, 16 ojos con QP y 6 ojos con CXL. Se analizó el espesor corneal central (ECC), presión intra-ocular y los parámetros obtenidos con ORA (clásicos, y análisis de señal) y Corvis. Resultados. Tanto los valores de presión intra-ocular (PIO) obtenidos directamente con ORA y Corvis como los valores de PIO corregidos por el ORA (PIOcc) fueron significativamente diferentes entre los distintos grupos. Hasta 9 de los parámetros resultantes del análisis de señal de medida del ORA (p1area, p2area, h2, dive2, path1, aplhf, p1area1, p2area1 y w11) mostraron diferencias estadísticamente significativas entre los grupos. En cuanto al Corvis, A1 Time, A2 Time y Peak Distance fueron significativamente diferentes entre los grupos considerados. Conclusiones. Las nuevas tecnologías de evaluación y análisis de datos de la respuesta biomecánica de la cornea permiten cuantificar y diferenciar el comportamiento biomecánico tras diferentes tipos de cirugía para la estabilización, regularización o substitución corneal en pacientes con queratocono (AU)

Background. Surgical options for the treatment of keratoconus (KC) have been expanded and improved. Our goal is to evaluate the changes in biomechanical properties of the cornea measured with two instruments for clinical use in KC eyes not operated or which undergoing different surgical procedures (cross-linking (CXL), intra-corneal ring segment (ICSR) and penetrating keratoplasty (QP)). Material and methods. The population consisted of 91 eyes with KC not operated, 22 eyes that underwent ICRS implant, 16 eyes that were submitted to PK and 6 eyes that underwent CXL. We analyzed corneal thickness, intraocular pressure and the parameters obtained with ORA (classic and signal analysis) and Corvis. Results. Both the values of intraocular pressure (IOP) obtained directly from ORA and Corvis, as IOP values corrected by the ORA (IOPcc) were significantly different between groups. For 9 of the parameters resulting from ORA analysis of signal (p1area, p2area, h2, Dive2, path1, aplhf, p1area1, p2area1 and w11) showed statistically significant differences between groups. Regarding Corvis, A1 Time, A2 Time and Peak Distance were significantly different between the groups. Conclusions. The new technology assessment and analysis of the biomechanical response of the cornea to quantify and differentiate the biomechanical behavior after different types of surgery for stabilization, regularization or corneal replacement in patients with keratoconus (AU)

Ocular dominance and visual function testing.

PURPOSE: To show the distribution of ocular dominance as measured with sensory and eye sighting methods and its potential relationship with high and low contrast LogMAR visual acuity in presbyopic subjects. METHOD: Forty-four presbyopes (48.5 ± 3.5 years) participated in this study. Ocular dominance was determined by eye sighting (hole-in-card) and sensorial (+1.50 D lens induced blur) methods. According to the dominance detected with each method (RE: right eye or LE: left eye), patients were classified in dominance type 1 (RE/RE), type 2 (RE/LE), type 3 (LE/RE) and type 4 (LE/LE). RESULTS: Baseline refractive error (MSE) was RE:-0.36 ± 1.67 D and LE:-0.35 ± 1.85 D (P = 0.930). RE was the dominant eye in 61.4% and 70.5% of times as obtained from sensorial and sighting methods, respectively. Most frequent dominance was of type 1 (52.3%), in this case the RE showed statistically significant better distance low contrast LogMAR VA (0.04 LogMAR units) compared to the LE (P < 0.05). CONCLUSIONS: The dominance was more frequent in RE in this sample. The eye sighting and sensorial methods to define ocular dominance agreed in more than half of cases. Amount of MSE was not significantly different between dominant and non-dominant eye. But in case of right dominance, the RE presented better distance low contrast VA compared to the LE.

Multi-site clinical assessment of Complete Revitalens MPDS in 2981 contact lens wearers across Europe and USA.

PURPOSE: To evaluate ocular response and subject acceptance of a new multipurpose disinfecting solution (MPDS), Complete Revitalens (RevitaLens OcuTec in the US Market), for soft contact lens care in a large "real practice" setting. METHOD: This is an international multi-center, open-label assessment carried out in 10 countries across Europe and in the USA. Up to 10 subjects who were currently wearing soft contact lenses for at least 1 year and using a MPS as a lens care system were included at each investigational site. RESULTS: Data were collected from 996 European and 1985 American wearers, 75% of those patients wore silicone hydrogel contact lenses. Approximately 94% found the new MPDS "somewhat more effective" to "much more effective" in keeping contact lenses feeling clean and 88% found the new MPDS to be somewhat more effective to much more effective in keeping their lenses feeling comfortable in the evening. Over 93% reported an improvement in vision clearness in the evening after approximately 1 month while using the new MPDS. Wearers with grade 2, 3 or 4 of severity decreased by 11.3, 6.4 and 9.8% over 1 month period for redness, burning and irritation, respectively. After approximately 1 month 83% of wearers declared that they would prefer to use the new MPDS. CONCLUSIONS: Over 88% felt their lenses were somewhat to much more comfortable at the end-of-day and 94% found the new MPDS to be somewhat to much more effective in keeping their lenses feeling clean compared to their previous care system.

Comparison of visual and refractive results of Toric Implantable Collamer Lens with bioptics for myopic astigmatism.

PURPOSE: To compare visual and refractive results of Toric Implantable Collamer Lens (TICL) and bioptics (ICL plus excimer corneal surgery) to treat myopic astigmatism. METHODS: Eighty-one eyes underwent TICL implantation and 83 eyes were treated with bioptics (corneal ablation was performed between 1.5 and 6 months after ICL implantation). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refraction, adverse events, safety, and efficacy were evaluated 12 months postoperatively. RESULTS: At 12 months postoperatively, the mean spherical equivalent was -0.15 ± 0.36 diopters (D) in the TICL group and -0.08 ± 0.26 D in the bioptics group (p = 0.099). Sixty-six (81.5 %) and 78 (94.0 %) eyes were within ±0.50 D for TICL and bioptics groups, respectively. The mean Snellen UDVA was not statistically different between both procedures (p = 0.909); 53 (65.4 %) and 54 (65.1 %) eyes achieved at least 20/25 or better in TICL and bioptics groups, respectively. No eye had lost more than two lines of CDVA, and 32.1 % of eyes (26/81) in the TICL group and 57.8 % of eyes (48/83) in the bioptics group had better postoperative UDVA than preoperative CDVA (p < 0.001). Safety was not statistically different between groups (p = 0.464) while efficacy was significantly higher in the bioptics group (p = 0.000). Two eyes with a TICL were treated to correct TICL decentration. CONCLUSIONS: Bioptics showed slightly better outcomes in some clinical measures such as uncorrected visual acuity, efficacy, and refractive predictability. TICL implantation shows reliable results similar to bioptics. A single procedure with TICL implantation might be preferred, eliminating the inherent risks of laser treatments and the risks of a second surgical procedure.

Long-term evaluation of the central vault after phakic Collamer® lens (ICL) implantation using OCT.

PURPOSE: The aim of this work is to evaluate the changes in the central vault after using implantable Collamer® lenses (ICL) to correct myopia. METHODS: This cohort study included 133 eyes; mean spherical equivalent -9.47 ± 3.71 diopters (D) (range: -2.75 to -22.25 D) who underwent ICL V4 implantation. Besides a complete ophthalmologic examination, the central vaulting was measured with Visante OCT and evaluated between different periods of follow-up (1 week, 1, 3, and 6 months, and yearly postoperatively). Post-operative time ranged from 6 to 73 months. RESULTS: Within the first 6 months, the mean central vaulting dropped from 510 ± 238 µm (range 100 to 940 µm) to 439 ± 231 µm (range 90 to 910) a significant decrease by 71 ± 58 µm (range -170 to 30 µm) (p = 0.028) with a trend to a lower reduction after this period. After 36 month from ICL implantation, this variation tends to be smaller with the majority of the eyes having a mean decrease smaller than 2 µm per month. Initial vault (Spearman Rho = -0.237, p = 0.006) was the factor more significantly associated with decrease in vault; eyes presenting a reduction in vault >100 µm had an average initial vault that was 141 µm and 184 µm higher than eyes with no change or with increase in vault over time, respectively. CONCLUSIONS: This study shows a continuous reduction of central vault over time. The reduction is highest during the first 6 months and tends to be lower and slow down over time. The decrease of vaulting was more pronounced in eyes with larger initial vaulting.

Comparison of the IOPen and iCare rebound tonometers with the Goldmann tonometer in a normal population.

This study proposes to evaluate the level of accuracy of intraocular pressure (IOP) measurements of a second generation rebound tonometer (IOPen, taking as references the Goldmann Applanation Tonometer (GAT) and the iCare rebound tonometer. The right eyes of 101 consecutive clinical patients were assessed with the three tonometers. The IOPen and iCare measurements were taken by two different optometrists and the GAT by an ophthalmologist. In this study, statistically significant differences were found when comparing the IOPen tonometer with the other two tonometers (p < 0.001). The IOPen underestimated the IOP value when compared to the GAT and the iCare (mean differences were 2.94 +/- 4.65 mmHg and 3.20 +/- 4.72 mmHg (mean +/- S.D.), respectively). The frequency distribution of differences demonstrated that in more than 55% of measurements the IOP readings differed by more than 3 mmHg between the IOPen and the GAT. Based on the present population study, these results suggest that IOPen measurements should be interpreted with caution.

Clinical evaluation of the IOPen® in a glaucomatous population.

The aim of this study was to evaluate the level of agreement of measurements of intraocular pressure (IOP) taken by a rebound tonometer (IOPen®), in comparison to a reference Goldmann applanation tonometer (GAT) in a glaucomatous population. Both eyes from 60 patients were assessed with the two tonometers, the induction tonometry was performed first by an experienced optometrist, and the GAT by an ophthalmologist. In this study, statistically significant differences were found when comparing the IOPen® tonometer with the GAT tonometer (p < 0.001), mean differences were -4.81 ± 4.31 and -4.76 ± 5.76 mmHg (mean ± S.D.) for the right eye and left eye respectively These values represent an underestimation in the present population by the IOPen® when compared with the GAT. Frequency distribution of differences demonstrated that in more than 71.6% of the measurements the IOP readings differed by more than 3 mmHg between the two tonometers. These results suggest that IOPen® should be used with great caution in the determination of IOP.

Surface AFM microscopy of unworn and worn samples of silicone hydrogel contact lenses.

PURPOSE: To evaluate the qualitative and quantitative topographic changes in the surface of worn contact lenses (CLs) of different materials using atomic force microscopy (AFM). METHODS: The topography of five different CL materials was evaluated with AFM over a surface of 25 microm(2) according to previously published experimental setup. Average roughness (R(a)) and root mean square (Rms) values were obtained for unworn and worn samples. RESULTS: The R(a) value increased for balafilcon A (11.62-13.68 nm for unworn and worn samples, respectively), lotrafilcon A (3.67-15.01 nm for unworn and worn samples, respectively), lotrafilcon B (4.08-8.42 nm for unworn and worn samples, respectively), galyfilcon A (2.81-14.6 nm for unworn and worn samples, respectively), and comfilcon A (2.87-4.63 nm for unworn and worn samples, respectively). Differences were statistically significant for all lenses except Rms and R(a) for comfilcon A, and R(a) parameter for balafilcon A (p > 0.05). The least relative increase was observed for some balafilcon A samples and for some of these samples the roughness decreased after the lenses had been worn. CONCLUSION: The changes in surface roughness between unworn and worn lenses are different for different silicone-hydrogel materials. Overall all CLs increased the degree of surface roughness after being worn, even for very short periods of time. However, for samples of balafilcon A, roughness increases at a lower extent or even can decrease as compared to unworn samples of the same material due to filling of the macropores.

Dynamic in vitro dehydration patterns of unworn and worn silicone hydrogel contact lenses.

PURPOSE: To evaluate the effect of wear on dynamic in vitro dehydration of silicone hydrogel (Si-Hi) contact lens (CL) using a previously described gravimetric procedure. METHODS: Five different silicone hydrogel (Si-Hi) contact lenses (CL) were evaluated after being worn by patients under daily wear conditions for 15 days to 1 month. Lenses were conditioned and disinfected with a multipurpose solution after each day of wear. Lenses were left to dehydrate in an analytical balance under controlled conditions of temperature and relative humidity and the results compared with data from new lens samples of the same power and material. Several quantitative parameters were obtained and compared between worn and unworn samples. RESULTS: The quantitative parameters derived from the dehydration curves showed statistically significant differences between worn and unworn lenses regarding the initial dehydration rate and ability to maintain their original hydration. Worn lenses showed shorter phase I duration (decreased by 30 to 60% compared to unworn samples), a significantly faster initial dehydration rate (increased by about 1%/minute), and lower water retention index (decreased by 10 to 20%) as derived from the initial cumulative dehydration. All the differences were statistically significant for all lenses (p < 0.05). CONCLUSION: The initial dehydration rates were significantly increased in all CL after wear. This could be of clinical interest because it represents the average initial dehydration rates during the first moments when the lens is left to dehydrate after a blink. This study suggests that even after the lenses had been equilibrated in saline solution for several days, the materials lose their ability to retain water.

Influence of fogging lenses and cycloplegia on open-field automatic refraction.

PURPOSE: To compare refractive values measured with and without cycloplegia, or with fogging lenses, using an open-field auto-refractor. METHODS: One hundred and forty-two young adults were enrolled from a university population; 96 were female (67.6%) and 46 were male (32.4%), the age range was 18-26 years (mean 22.3 +/- 3.7 years). The refraction measurement was obtained for the right eye of each subject with the Grand Seiko Auto Ref/Keratometer WAM-5500 (GS) under three conditions, always in this sequence: (1) without cycloplegia (GS), (2) without cycloplegia but using a + 2.00 D fogging lens (GS_2D) and (3) with cycloplegia (GS_cycl). RESULTS: When the average values of spherical equivalent were compared, both accommodation control strategies were almost equally successful: GS, M = -0.85 +/- 2.21 D; GC_2D, M = -0.53 +/- 2.10 D and GS_cycl, M = -0.57 +/- 2.24 D (Kruskal-Wallis test, p < 0.001). When the results were analysed separately for different refractive groups, emmetropes and hyperopes show statistically significant differences while myopes did not. When both accommodation strategies were compared there was a trend for more myopic subjects to display more negative values under cycloplegia, while low myopes, emmetropes and hyperopes tend to display more negative values with the +2.00 D fogging lenses, suggesting this was less effective for accommodation control. CONCLUSIONS: Over-refraction through +2.00 D fogging lenses is useful to achieve additional relaxation of the accommodative response in a similar way to cycloplegia when open-field autorefraction is performed in young adults.

[The relationships between ocular optical components and implications in the process of emmetropization]. / Relación entre los componentes ópticos oculares e implicaciones en el proceso de emetropización.

PURPOSE: To report the relationship between different optical ocular components and the influence of axial length on emmetropization. METHODS: 109 young university students, divided into five groups, were enrolled in this study: emmetropes, hyperopes, low myopes, moderate myopes and high myopes. Intraocular parameters and topographic corneal analyses were performed by ultrasonography and videokeratoscopy respectively. RESULTS: Anterior chamber depth and axial length were found to correlate significantly in eyes with axial lengths less than 24 mm (r = 0.441; p < 0.001) However this correlation was not found in eyes with longer axial lengths (r = 0.098; p = 0.527). Lens thickness showed an inverse correlation with axial length for shorter eyes (r = 0.391; p < 0.001), whereas any correlation in longer eyes was associated with moderate to high levels of myopia. Anterior corneal curvature only correlated, although weakly, with vitreous chamber depth for shorter eyes (r = 0.363; p < 0.003). CONCLUSION: Differences in optical parameters of the human eye displayed different associations in longer eyes. A lack of correlation was seen between ocular components in eyes with higher myopia, corresponding to myopia in excess of 2.00 D.

Technical note: a comparison of central and peripheral intraocular pressure using rebound tonometry.

PURPOSE: To compare central and peripheral intraocular pressure (IOP) readings obtained with rebound tonometry. METHODS: Intraocular pressure was measured on the right eye of 153 patients (65 males, 88 females), aged from 21 to 85 years (mean +/- S.D., 55.5 +/- 15.2 years) with the ICare rebound tonometer at centre, and 2 mm from the limbus (in the nasal and temporal regions along the 0-180 degrees corneal meridian). RESULTS: Intraocular pressure values obtained with the ICare were 14.9 +/- 2.8; 14.1 +/- 2.5 and 14.5 +/- 2.7 mmHg at centre, nasal and temporal corneal locations, respectively. On average, nasal and temporal IOP readings were 0.75 and 0.37 mmHg lower than the central reading (p < 0.05 and p > 0.05, respectively). A highly significant correlation was found between central and peripheral measurements in nasal (r(2) = 0.905; p < 0.001) and temporal (r(2) = 0.879; p < 0.001) regions along the horizontal meridian. Almost 80% of patients presented nasal IOP values within +/-1 mmHg of the central value. CONCLUSIONS: Intraocular pressure values measured with the ICare rebound tonometer on the nasal corneal region is slightly lower on average and highly correlated with IOP values recorded at corneal centre. Both nasal and temporal readings are in good agreement with central IOP, and could be used to obtain a reliable estimate of rebound IOP in corneas where central readings cannot be taken.

Technical note: Accuracy and repeatability of a new portable ultrasound pachymeter.

PURPOSE: To assess the accuracy and repeatability of central corneal thickness (CCT) measurements taken with a new portable ultrasound (US) pachymeter. METHODS: Central thickness measurements were taken with a portable pachymeter (SP-100 Handy; Tomey, Nagoya, Japan) and a conventional US pachymeter (Nidek UP-1000; Nidek Technologies, Gamagori, Japan) from 57 right corneas of 57 young adults (19 males, 38 females) aged 18-44 years (mean +/- S.D., 22.95 +/- 3.92). Three repeated measures were obtained and then compared to obtain the repeatability of each instrument and the agreement between the pachymeters. The three readings taken with the portable pachymeter were compared against each other in order to evaluate intra-session repeatability and bias of each individual measurement with respect to the mean of three. RESULTS: Mean values of CCT were 537 +/- 35 microm for conventional and 534 +/- 35 microm for the new portable pachymeter. A high agreement was found between the two instruments (mean difference = 2.58 microm; 95% CI 1.41-3.75 microm) with only two eyes presenting differences larger than +/-8.6 microm which represents 95% CI in the Bland-Altman plots which represents 1.6% of the mean CCT. The first reading taken showed the highest agreement with the mean value for the portable pachymeter. CONCLUSIONS: The instrument tested in this study is able to take reliable measurements of corneal thickness even if a single reading is considered. Intra-session repeatability was very high, as was also the agreement between the average of three readings taken with the two US pachymeters.