Accuracy of intraocular lens power formulas in eyes with keratoconus: Multi-center study in Japan.

PURPOSE: To assess the accuracy of intraocular lens (IOL) power formulas, namely, SRK/T, Haigis, Barrett Universal II, Barrett True-K for keratoconus, Kane formula, and Kane formula for keratoconus, for cataract with keratoconus in Japanese eyes. SETTING: Five surgical sites in Japan. DESIGN: A retrospective case series. METHODS: Eyes with keratoconus undergoing cataract surgery were included. Postoperative refraction was compared with the prediction by the formulas. Visual acuity, manifest spherical equivalent, prediction error (PE), and mean absolute errors (MAEs) were determined 1 month postoperatively. The PE within 0.50 diopter (D), 1.00 D, and 2.00 D were compared between IOL formulas. Subgroup analysis based on the steepest keratometry (stage 1, ≤ 48 D; stage 2, > 48 D and ≤ 53 D; and stage 3, > 53 D) was performed. The relationship between PE and preoperative biometric data were assessed. RESULTS: Fifty eyes were included. The MAE of the Barrett True-K for keratoconus, Kane keratoconus, and Kane formulas were significantly lower than that of Haigis. A statistically significant difference in the prediction accuracy within ± 0.50 D was found between Kane keratoconus and Haigis. The prediction accuracy of the Barrett True-K for keratoconus, SRK/T, and Kane within ± 1.00 D was statistically significant compared with that of Haigis. In stage 3, the Barrett True-K for keratoconus had a significantly lower MAE than SRK/T and Haigis. CONCLUSION: Keratoconus-specific formulas were more accurate than existing formulas in Japanese eyes. The Barrett True-K formula for keratoconus had higher prediction accuracy in severe keratoconus.

Lens thickness in atopic cataract: case-control study.

PURPOSE: To examine whether atopic cataracts are associated with thinner lenses. SETTING: Department of Ophthalmology, Jikei University Hospital, Tokyo, Japan. DESIGN: Retrospective matched case-control study. METHODS: 31 eyes with atopic cataracts, 62 with nonatopic cataracts, and 31 without cataracts were analyzed. Each group was matched for age (±4 years) and sex. RESULTS: The mean lens thickness (LT) was 3.76 ± 0.40 mm, 3.94 ± 0.49 mm, and 4.11 ± 0.40 mm in eyes with atopic cataracts, nonatopic cataracts, and normal lenses, respectively. Repeated-measures analysis of variance showed that the LT in the atopic cataract group was significantly thinner than that in the nonatopic cataract ( P = .036) and normal lens ( P < .001) groups. In multivariate logistic regression analysis, a thinner LT was negatively correlated with age (odds ratio [OR], 0.91; 95% CI, 0.86-0.96) and positively correlated with anterior subcapsular cataract (ASC) (OR, 5.61; 95% CI, 1.97-15.99). Atopy was not a significant factor. 24 (38.7%) of the 62 eyes with nonatopic cataracts and 24 (77.4%) of the 31 eyes with atopic cataracts had ASC. CONCLUSIONS: The lenses of eyes with atopic cataracts were thinner than those of controls. Atopic cataracts frequently present with anterior subcapsular opacity, which is associated with lens thinning.

Correlation between higher-order aberration and photophobia after cataract surgery.

Cataract surgery impinges on the spatial properties and wavelength distribution of retinal images, which changes the degree of light-induced visual discomfort/photophobia. However, no study has analyzed the alteration in photophobia before and after cataract surgery or the association between retinal spatial property and photophobia. Here, we measured the higher-order aberrations (HOAs) of the entire eye and the subjective photophobia score. This study investigated 71 eyes in 71 patients who received conventional cataract surgery. Scaling of photophobia was based on the following grading system: when the patient is outdoor on a sunny day, score of 0 and 10 points were assigned to the absence of photophobia and the presence of severe photophobia prevents eye-opening, respectively. We decomposed wavefront errors using Zernike polynomials for a 3-mm pupil diameter and analyzed the association between photophobia scores and HOAs with Spearman's rank sum correlation (rs). We classified patients into two groups: photophobia (PP) unconcerned included patients who selected 0 both preoperatively or postoperatively and PP concerned included the remaining patients. After cataract surgery, photophobia scores increased, remained unchanged (stable), and decreased in 3, 41, and 27 cases, respectively. In the stable group, 35 of 41 cases belonged to PP unconcerned. In PP concerned, there were significant correlations between photophobia score and postoperative root-mean-square values of total HOAs (rs = 0.52, p = 0.002), total coma (rs = 0.52, p = 0.002), total trefoil (rs = 0.47, p = 0.006), and third-order group (rs = 0.53, p = 0.002). In contrast, there was no significant correlation between photophobia scores and preoperative HOAs. Our results suggest that the spatial properties of retinal image modified by HOAs may affect the degree of photophobia. Scattering light due to cataracts could contribute to photophobia more than HOAs, which may mask the effect of HOAs for photophobia preoperatively.

Age-related visual outcomes in eyes with diffractive multifocal intraocular lenses.

BACKGROUND/OBJECTIVES: To assess the influence of patient age on visual outcomes in eyes with diffractive multifocal intraocular lenses (IOLs) SUBJECTS/METHODS: Based on age, we classified eyes with diffractive multifocal IOL into four groups: u50 (under 50 years old), 50s (50-59 years), 60s, and 70s. Corrected distance (CD), distance-corrected near (DCN) visual acuity (VA), and defocus curve were measured postoperatively. Using an "area-of-focus" metric, the distant, intermediate, and near area-of-focus (AoF) were also measured. These postoperative results were compared between the age groups. RESULTS: At 3 months after surgery, the CDVA in the u50, 50s, 60s, and 70s groups were -0.18, -0.16, -0.14, and -0.10 logMAR, respectively. The 70s CDVA was significantly worse than the u50 and 50s groups (P = 0.002, P = 0.049). The DCNVA in the u50, 50s, 60s, and 70s were 0.01, 0.03, 0.03, and 0.08 logMAR. DCNVA in the 70s group was significantly worse than that in the u50 and 60s groups (P = 0.008 and P = 0.019, respectively). The near AoF was smaller in the 70s than in the u50 and 50s groups (P = 0.040, P = 0.047). In both the intermediate and distant AoFs, there was no significant difference between the four age groups. A steep decline in near AoF was observed in patients over 60 years of age. CONCLUSIONS: The CDVA, DCNVA, and near AoF declined with patient age in eyes with diffractive multifocal IOL. The near AoF showed a drastic decline over 60 years.

Inspection of the lens thickness with preoperative biometric measurements prevents an erroneous interpretation of posterior capsule during FLACS.

Optical opacity reduces quality of biometry images, making it potentially difficult to find the correct location for irradiation during femtosecond laser-assisted cataract surgery (FLACS). After experiencing a case of posterior capsule (PC) rupture because of optical opacity, we started lens thickness (LT) inspection, which indicates comparison of between intra- and pre-operatively measured LT. We retrospectively investigated the effectiveness of the LT inspection. One observer reviewed all FLACS treatment summaries for 3 years by CATALYS in the Jikei University Hospital, Tokyo. Based on the lines defining the PC on intraoperative OCT images, all cases were classified into three groups: undescribed, appropriate and inappropriate PC. Among the 1070 cases, 1047 cases had appropriate PC. In 19 cases, the PC line was undescribed because of dense cataract. Among 474 cases with no inspection, 4 cases had an inappropriate PC. Whereas, in 596 cases with the LT inspection, there was no case of an inappropriate PC. LT inspection significantly reduced the cases with inappropriate PC. The safety margins normally work to prevent severe complications. However, rare outlier cases had a high risk of severe complications. We propose LT inspection could be the most practical and convenient way for safety surgery.

Posterior capsule rupture with FLACS due to erroneous interpretation of a high OCT intensity area in anterior vitreous.

PURPOSE: We describe a case of posterior capsule rupture during femtosecond laser-assisted cataract surgery (FLACS) due to direct exposure of the posterior capsule to the laser beam. OBSERVATIONS: A 47-year-old man underwent FLACS for anterior capsule opacity. The CATALYS® system automatically detected the posterior capsule from the optical coherence tomography (OCT) images, after which the operator manually adjusted the line of posterior capsule. Femtosecond laser irradiation was presumed to be completed successfully. However, upon insertion of a phaco-tip, the diced nucleus of the lens dropped into the vitreous chamber. Reviewing intraoperative OCT images of the treatment summary to check the area irradiated by laser, an arc-shaped high-intensity area was observed behind the posterior capsule. This high-intensity was misinterpreted as the posterior capsule, which led to error in application of laser beam during procedure. CONCLUSIONS AND IMPORTANCE: Comparison of data acquired using different imaging modalities could enable correct identification of the posterior capsule.

Blended Vision Achieved by Combining High and Low Addition Power Diffractive Intraocular Lenses with Micromonovision: A Clinical Outcome.

PURPOSE: To evaluate the clinical outcome of blended vision combined with micromonovision (MMBV) using a +4 diopter (D) addition power (add) diffractive intraocular lens (MIOL) and a +2.75D add MIOL with a myopic target of -0.5 D. METHODS: One hundred twenty eyes of 60 cases were enrolled. The +4 D add MIOLs were placed in the nondominant eye, the +2.75 D add MIOLs were placed in the dominant eye with a myopic target of -0.5 D in 30 cases (the MMBV group), and the +4 D add MIOLs were placed in both eyes in another 30 cases (controls). Postoperative clinical outcomes were compared between the two groups. RESULTS: Compared with the controls, binocular uncorrected intermediate vision at 70 cm was significantly better in the MMBV group (p=0.02). Contrast sensitivity at 12 cycles per degree and the 6% and 12.5% low-contrast visual acuities were also significantly better in the MMBV group compared with the controls (p values = 0.05, 0.05, and 0.04, respectively). Uncorrected and corrected distance and near VA did not differ significantly between the two groups. CONCLUSION: MMBV provided a better intermediate VA, contrast sensitivity, and low-contrast VA than bilateral implantation of the +4 D add MIOL, while preserving comparable near and distance vision.

Posture-related ocular cyclotorsion during cataract surgery with an ocular registration system.

Ocular cyclotorsion when a patient changes from seated to supine position in cataract surgery and factors predicting the amount of cyclotorsion were investigated using VERION system. Variables analyzed were age, gender, preoperative visual acuity, axial length, laterality of eyes, operative duration, and the direction and degree of cyclotorsion. The mean cyclotorsion of 107 eyes of 93 cataract patients was 0.98 ± 4.85 degrees (median, 1 degree; range, -11 to 12 degrees), and the median absolute value was 4 degrees (mean, 4.05 ± 2.82 degrees; range, 0 to 12 degrees). Cyclotorsion was ≥3 degrees in 68 (63.6%) eyes. Excyclotorsion occurred more frequently than incyclotorsion (50.5% vs. 43.0%). There was no cyclotorsion in seven (6.5%). Multiple regression analysis showed that gender was a significant predictive factor for the absolute value of cyclotorsion (ß = 1.06, P = 0.041); however, the other variables had no effect on cyclotorsion. The absolute value of cyclotorsion was significantly larger in female than in male patients [median, 4 degrees and 3 degrees, respectively; mean, 4.66 ± 3.02 degrees and 3.44 ± 2.52 degrees, respectively (P = 0.039)]. In conclusion, cataract patients had significant posture-related ocular cyclotorsion. The amount of cyclotorsion was larger for female than male patients.

Analysis of Symptom Development in Relation to Quantity of Rice stripe virus in Rice (Oryza sativa) to Simplify Evaluation of Resistance.

Rice stripe virus (RSV) is one of the most devastating pathogens of rice (Oryza sativa) in rice-growing regions of East Asia. We analyzed the increase in RSV accumulation in infected rice plants over time and evaluated the association between disease severity and RSV accumulation with the aim of establishing an experimental system for accurate and efficient evaluation of RSV resistance in rice. As an index of RSV accumulation in plants, relative concentration of RNA corresponding to the coat protein gene region was measured using reverse-transcription quantitative polymerase chain reaction. Actin and elongation factor 1a were used as the host reference genes. RSV concentrations tended to increase with time from 7 to 28 days after inoculation, and a strong positive correlation was observed between the log RSV concentrations in the midsections of the uppermost leaves and in the stems at the first leaf sheath position. We analyzed RSV concentrations at these two locations 21 days after inoculation with RSV and assessed severity of disease symptoms based on a commonly used scale (Washio's six-grade scale) rated as A (most severe), B, Bt, C, Cr, or D (mild symptoms). RSV concentrations at both locations were high in plants graded A, B, or Bt, with no significant difference in concentration of RSV among the three grades, but concentrations were significantly higher in the three grades compared with that in the plants in grade D. RSV concentrations were highly variable among plants in grades C and Cr. On the basis of these data, we propose a new formula to estimate the range of disease severities with greater ease and practical value. The values calculated by the new formula corresponded well to those based on Washio's six-grade scale.

Diffractive multifocal intraocular lens implantation in eyes with a small-diameter pupil.

Postoperative outcome of diffractive multifocal intraocular lens (MIOL) implantation in eyes with a small-diameter pupil was evaluated. This non randomized case series involved 23 eyes of 23 patients who underwent diffractive MIOL implantation and whose preoperative photopic pupil diameter was ≤3.0 mm [small-diameter pupil (SDP) group], and 79 eyes of 79 patients implanted with the same MIOL whose pupil diameter was >3.0 mm as controls (LDP group). Contrast sensitivity of high spatial frequency (12, and 18 cycle per degree) and both 12.5% and 6% low-contrast visual acuity (VA) were significantly worse in the SDP group than in the LDP group (P = 0.04, 0.05, 0.05, 0.03). However, no significant difference was found between eyes in the SDP group with a postoperative pupil diameter greater than 3.0 mm and LDP group eyes. No significant differences were found in uncorrected and corrected distance VA (UDVA, CDVA), uncorrected and corrected near VA (UNVA, CNVA), contrast sensitivity with low spatial frequency, and defocus curve between the two groups. In conclusion, in eyes implanted with a diffractive MIOL, a pupil diameter of ≤3.0 mm deteriorates contrast sensitivity. This effect was eliminated postoperatively when pupil size was enlarged to >3.0 mm during surgery.

Transcutaneous aponeurotic repair with small detachment of the levator aponeurosis for aponeurotic blepharoptosis in Japanese patients.

PURPOSE: To examine the surgical outcomes of a modified transcutaneous aponeurotic repair for aponeurotic blepharoptosis in a Japanese population. METHODS: This retrospective study included 75 eyelids of 45 patients with aponeurotic blepharoptosis who had undergone a modified transcutaneous aponeurotic repair. This procedure included a long skin incision for securing a wide surgical field, creation of a double eyelid crease, and a small extent of detachment of the levator aponeurosis from the tarsal surface. Functional success was defined as a postoperative margin reflex distance-1 of 2-5 mm without serious complications at 3 months postoperatively. Cosmetic success was judged by achieving a ≤ 1-mm laterality of eyelid height, a ≤ 2-mm laterality of pretarsal show, and symmetry of the eyelid contour at 3 months postoperatively. RESULTS: The functional success rate was 70.7% among all patients, with 84.4%, 86.7%, and 88.9% of patients showing cosmetic success regarding symmetry of eyelid height, pretarsal show, and eyelid contour, respectively. After applying functional and all 3 cosmetic criteria simultaneously, 28 patients (62.2%) were satisfied in this study. No serious complications occurred during the follow-up period. CONCLUSIONS: This modified procedure provided good functional and cosmetic outcomes for aponeurotic blepharoptosis, indicating an acceptable blepharoptosis repair for East Asian patients.

The Pharmacological Mydriatic Pupil-to-Limbal Diameter Ratio as an Intuitive Predictor for the Risk of Intraoperative Floppy Iris Syndrome.

PURPOSE: To predict development of intraoperative floppy iris syndrome (IFIS) using the preoperative pharmacologically dilated pupil-to-limbal diameter (PL) ratio. METHODS: The subjects were male patients treated by phacoemulsification who were or were not taking α1-adrenoceptor antagonists (ARAs). The PL ratio was calculated from the horizontal dilated pupil diameter and the horizontal corneal white-to-white distance measured by two observers in surgical videos. IFIS severity was graded using the criteria of Chang et al. We predicted the intuitive PL ratio to describe how precisely the experimenter can estimate the PL ratio without any tools. RESULTS: There were 36 eyes in the α1-ARA group and 48 eyes in the control group. The pupil diameter and PL ratio were both significantly smaller in the α1-ARA group compared to the control group (p < 0.001). All of pupil diameter, PL ratio, and intuitive PL ratio were negatively correlated with IFIS severity. The cutoff value for prediction of IFIS from the ROC curve was 7.20 mm for the pupil diameter, 58.7% for the PL ratio, and 62.5% for the intuitive PL ratio. The AUC for the ROC curve using the PL ratio (0.913) and intuitive PL ratio (0.892) did not perform substantially worse than that for the ROC curve based on the pupil diameter (0.875). CONCLUSIONS: The PL ratio is a simple and useful parameter for compensated prediction of IFIS development. Patients in whom this ratio is <60% are particularly likely to develop IFIS, and measures against onset of IFIS should be considered. This study is registered with UMIN000033012.

Conjunctival Chemosis Caused by Exposure of the Lacrimal Caruncle: A Case Report.

An 84-year-old woman presented with a 3-month history of conjunctival chemosis in the left eye. At the first examination, the chemosis neighbored the lacrimal caruncle and was localized in the inferomedial region of the conjunctiva. During eyelid closure, only the left lacrimal caruncle was exposed. One month later, the chemosis further extended to the inferolateral region. We debulked the lacrimal caruncle to prevent the exposure of the caruncle. One month after the surgery, conjunctival chemosis had resolved completely. At the postoperative 6-month follow-up, the patient showed no recurrence of chemosis.

Quantitative analysis of Rice stripe virus in a transovarial transmission cycle during the development and reproduction of its vector, Laodelphax striatellus.

The amount of Rice stripe virus (RSV) maintained through transovarial transmission was analyzed during the development and reproduction of its vector, Laodelphax striatellus. Reverse transcription quantitative PCR analysis was used to quantify RNA expressed from the RSV coat protein (CP) gene as an estimate of RSV content in nymphs and adults of L. striatellus at various developmental stages. The 18S ribosome RNA gene of L. striatellus was chosen as the reference for calculating RSV CP expression using the comparative Ct method. Based on the CP transcript levels, the amount of RSV did not differ significantly throughout the nymphal stage or between adult females of different ages; however, RSV content tended to increase slightly as males became older. The average RSV content in males was 1.30-2.49 times that in females. The amount of RSV in L. striatellus adults was compared between generations. The RSV content of female adults did not differ significantly between the parent and progeny populations three of three different females. L. striatellus grown to adults on a susceptible cultivar and five RSV-resistant cultivars were compared to analyze whether the amount of RSV varied among cultivars. Although the amount of RSV in L. striatellus adults differed significantly among the six rice cultivars evaluated, the difference seemed independent of whether resistance genes were present. In addition, the percentage of viruliferous insects was similar among cultivars.

Prewound assisted technique for hydrophobic foldable intraocular lens implantation.

PURPOSE: To describe a technique for intraocular lens (IOL) implantation that lessens the degree of surgical invasiveness by implanting a tightly rolled IOL through a small incision without touching the eye with the cartridge tip. METHODS: An IOL was inserted through an incision by first allowing the leading haptic to protrude slightly from the cartridge tip. It was then injected through the incision without allowing any part of the cartridge to touch the eye during IOL implantation. In one eye, the entire circumference of the beveled portion of the cartridge tip was inserted into the anterior chamber to implant the IOL, whereas in the other eye, the IOL was inserted through the incision by first allowing the leading haptic to protrude slightly from the cartridge tip. It was then injected through the incision without allowing any part of the cartridge to touch the eye during IOL implantation. We analyzed the incision width before and after IOL implantation and the degree of surgically induced astigmatism on the day after surgery and at 1 and 3 months after surgery. RESULTS: Using our technique, both the amount by which the wound was enlarged and the hydration rate were significantly lower compared with conventional IOL implantation. Our method enables IOL implantation to be carried out through a small incision at a width that was only previously possible with forcible insertion. CONCLUSIONS: Our IOL implantation technique can be performed using both hands with no need to immobilize the eyeball.

Seasonal Changes in the Percentage of Rice Stripe Virus Viruliferous Laodelphax striatellus (Hemiptera: Delphacidae) in Paddy Fields in Japan.

Rice stripe disease, which is caused by Rice stripe virus (RSV), is one of the most serious viral diseases of rice. RSV is transmitted in a persistent manner by Laodelphax striatellus (Fallén). The incidence of the disease can be estimated from the density of viruliferous vectors. Understanding seasonal changes of the percentage of viruliferous L. striatellus can facilitate forecasting and controlling the disease. In paddies, the percentage of viruliferous insects fluctuated in phase with the rate of detection of RSV-infected rice; it gradually increased from July to August, plateaued or temporarily declined in September, and increased sharply on ratoons in October. These findings indicate that horizontal transmission of RSV from diseased plants to vector insects occurred frequently, and the insects acquired RSV from the ratoons. However, the percentages of viruliferous insects overwintering in poaceous weeds, the main hosts for L. striatellus in winter, were lower than those in ratoons. Few L. striatellus that acquired RSV from ratoons seemed to move to overwintering sites and transmit the virus to the next generation. However, there was a tendency for the percentages of viruliferous overwintering insects to be higher on paddy ridges than in river levees. Insects could probably move from ratoons to poaceous weeds when the weeds were near a paddy. Although increasing percentage of viruliferous insects on ratoons seem to have relatively little impact on RSV dynamics in the next crop season, appropriate weed management around paddies is still needed to reduce the incidence of rice stripe disease.

Usefulness of Surgical Media Center as a Cataract Surgery Educational Tool.

Purpose. This study retrospectively analyzed cataract surgeries to examine the usefulness of Surgical Media Center (SMC) (Abbott Medical Optics Inc.), a new cataract surgery recording device, for training of cataract surgery. Methods. We studied five hundred cataract surgeries conducted with a phacoemulsification system connected to the SMC. After surgery, the surgical procedures were reviewed, with changes in aspiration rate, vacuum level, and phaco power displayed as graphs superimposed on the surgical video. We examined whether use of SMC is able to demonstrate the differences in technique between experienced and trainee operators, to identify inappropriate phacoemulsification techniques from analyzing the graphs, and to elucidate the cause of intraoperative complications. Results. Significant differences in the time taken to reach maximum vacuum and the speed of increase in vacuum during irrigation and aspiration were observed between experienced and trainee operators. Analysis of the graphs displayed by SMC detected inappropriate phacoemulsification techniques mostly in cases operated by trainee operators. Conclusions. Using SMC, it was possible to capture details of cataract surgery objectively. This recording device allows surgeons to review cataract surgery techniques and identify the cause of intraoperative complication and is a useful education tool for cataract surgery.

Trisection technique for the extraction of dislocated intraocular lenses through a small surgical incision.

UNLABELLED: We describe a trisection technique for extracting a dislocated IOL through a small surgical incision. The dislocated IOL is brought into the anterior chamber and cut into 3 equal segments, with a negligible risk for the segments falling into the vitreous cavity. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Usefulness of Implantation of Diffractive Multifocal Intraocular Lens in Eyes with Long Axial Lengths.

Purpose. This study retrospectively analyzed the postoperative visual functions of myopic eyes implanted with multifocal intraocular lens (IOL) to evaluate the efficacy of multifocal IOL in highly myopic eyes. Methods. We studied 61 patients (96 eyes) who were implanted with multifocal IOL ZMA00 or ZMB00 (Abbott Medical Optics). The patients were stratified into two groups by axial length: 26 mm or above (AL ≥ 26 group) and below 26 mm (AL < 26 group). Postoperative corrected and uncorrected distance (5 m) and near (30 cm) visual acuity (VA), contrast sensitivity, and depth of focus were compared between two groups. Results. In the AL ≥ 26 group and the AL < 26 group, the mean ± standard deviation uncorrected distance logMAR VA at 12-month postoperative follow-up was -0.04 ± 0.11 and -0.01 ± 0.14, respectively; and the corrected distance VA was -0.17 ± 0.08 and -0.14 ± 0.07, with no significant differences between two groups (p = 0.558 and 0.101; Mann-Whitney U test). For near VA, the corresponding uncorrected VA was 0.06 ± 0.08 and 0.05 ± 0.09; and distance-corrected VA was 0.01 ± 0.06 and 0.01 ± 0.02, with no significant differences between two groups (p = 0.572, and 0.157; Mann-Whitney U test). Conclusion. The present study demonstrates that it is possible to achieve good uncorrected near and distance VA following implantation of multifocal IOL in eyes with long axial lengths.

Prefilled syringes and usability of ophthalmic viscosurgical devices.

PURPOSE: To examine the influence of the configuration of prefilled syringes on the usability of ophthalmic viscosurgical devices (OVDs). SETTING: Department of Ophthalmology, Jikei University School of Medicine, Tokyo, Japan. DESIGN: Experimental study. METHODS: The maximum force needed to extrude the whole OVD (extrusion force) was compared among viscous cohesive OVDs (OPEGAN Hi(®) 0.85 mL and Healon(®) 0.85 mL) and very low viscosity dispersive OVDs (OPEGAN(®) 0.6 mL and OPEGAN(®) 1.1 mL). Additionally, to exclude the influence of any differences between syringes of viscous cohesive OVDs on the extrusion force, empty syringes of the same configuration were refilled with the same products. In addition, the syringe inner surface and that of the piston attached to the tip of the plunger were measured. RESULTS: The extrusion force of Healon 0.85 mL (3.28±0.19 kgf) was significantly (P<0.01) higher than that of OPEGAN Hi 0.85 mL (2.54±0.23 kgf). The inner syringe chamber for Healon 0.85 mL was vial shaped and had a built-in needle in the Luer tip, which was clearly different from OPEGAN Hi 0.85 mL. There were no significant differences in the extrusion force between refilled syringes. The extrusion force of OPEGAN 1.1 mL (3.44±0.12 kgf) was significantly (P<0.01) higher than that of OPEGAN 0.6 mL (1.63±0.06 kgf). The syringe of OPEGAN 1.1 mL was obviously bigger than that of OPEGAN 0.6 mL. CONCLUSION: It was confirmed that the configuration of the syringes is another determinant of the extrusion force and a factor related to the difference in usability among products that meet the same cohesive class.