The proper uses of ophthalmic and optical instruments play an important role in diagnosis and treatment of eye diseases. Precision and accuracy assessment are the major indicator for evaluation of instruments. The former consists of repeatability and reproducibility， while the agreement assessment decides its accuracy. There are so many studies focused on this field due to the rapid development of new techniques and instruments， followed by the arising of problems in method selection. This article introduces the main methods of precision and accuracy assessment. And we also provide the ideas of proper method selection in clinical practice and research with examples. Moreover， we discussed the influence of analytic approach with one eye or two， as well as sample size calculation.

Objective To assess the repeatability and agreement of Scheimpflug Noncontact Tonometry （Corvis ST） on normal subjects. Methods Forty-seven myopic subjects （right eye） were enrolled in this prospective study with Scheimpflug Noncontact Tonometry （Corvis ST）. The right eyes of 34 myopic subjects were measured by the Ocular Response Analyser （ORA）， non-contanct tonometer （NCT） and Pentacam. The repeatability of data was analyzed by intraclass correlation coefficient （ICC） and Cronbach′s Alpha coefficients， and the data were compared using a paired t test， the Pearson correlation test and Bland-Altman plot． Results The ICC and Cronbach′s Alpha coefficients of 1st A-time， 2nd A-time， Vout， HC-DA，IOPst and CCTst were more than 0.8， which showed high intraobserver repeatability. The Bland-Altman plots displayed relatively good agreement between IOPst and IOPg， IOPst and IOPcc， IOPst and IOPnct， and CCTst and CCTp. The 95% limits of agreement were -2.62 to 4.91 mmHg， -3.04 mmHg to 6.22 mmHg， -2.29 to 4.44 mmHg and -15.57 to 13.59 μm. A positive correlation was found between IOPst and IOPg， IOPst and IOPnct， and CCTst and CCTp （r=0.774， 0.791， 0.981， P＜0.05）. Significant differences were found between IOPst and IOPg， IOPcc， IOPnct （t=-3.464， -3.922， -3.661， P＜0.05）， but there was no significant difference between CCTst and CCTp （t=0.778， P＞0.05）. Pearson analysis showed a high correlation between 1st A-time， Vout， HC-DA and CRF， CH （r=0.721， 0.520， -0.545， -0.354， -0.596， -0.391， P＜0.05）. Conclusion In healthy eyes， the repeatability of some parameters using Scheimpflug Noncontact Tonometry （Corvis ST） is good. The agreement between Corvis ST and ORA and Pentacam was high.

Objective To analyze the effect of contact lens （CL） wear on corneal reinnervation after sub-Bowman keratomileusis （SBK） corneal subbasal nerve fibers （CSNFs） by in vivo confocal microscopy （IVCM） and to evaluate the clinical applications of IVCM on corneal reinnervation. Methods It was a prospective cohort study. Forty-three patients （86 eyes） were selected from May 2010 to June 2011 in Beijing Tongren Eye Center. The age was 18-35 years old， refractive error was -2.75--10.00 D. They were divided into 4 groups： group I， time of soft CL wearing ≤5 years （20 eyes）； group II， 5 years＜time of soft CL wearing≤10 years （12 eyes）； Group III， time of soft CL wearing ＞10 years （8 eyes）； group IV， without history of CL wearing （46 eyes）. The density， number， tortuosity and regenerated velocity of CSNFs of different group were evaluated by IVCM before and 1， 3， 6 months after SBK. Data were analyzed with independent t test， one-factor analysis of variance and chi-square test. Results There were no significant difference of density， number and tortuosity of central CSNFs among different groups preoperative （F=1.042， 1.947， 0.821， P＞0.05）， but the density and number of central CSNFs decreased and the tortuosity increased in group of CL wearing ＞10 years. The density and number of central CSNFs were significant lower， and the tortuosity was significant higher than that of pre-operation （t=6.150， -4.141， 9.709， P＜0.01）. The density， number and tortuosity of central CSNFs among different groups were not significant different （F=1.472， 0.318， 0.353， P＞0.05）， but the longer CL wearing， the lower density and number of central CSNFs and the higher tortuosity were. The velocity of CSNFs regeneration among different groups were not significant different （χ2=4.273， 8.806， 5.364， P＞0.05）， but the percentage of regenerated CSNFs deriving into the central 3 mm in group III was lower than other groups at 3 and 6 month after surgery. Conclusion The time of CL wearing has no significant effect on CSNFs reinnervation before and after SBK. But long time wearing would delay the reinnervation of CSNFs. IVCM was useful to quantitative evaluate the corneal reinnervation pre-SBK and post-SBK.

Objective To evaluate the role that confocal microscopy could play in post- laser in situ keratomileusis （LASIK） examinations. Methods Twenty-seven patients （54 eyes） who had LASIK surgery in Peking Union Medical College Hospital were included in this cross-sectional study. Patients were divided into 2 groups （6-month group and 1-year group） based on the post-LASIK follow-up. Confocal microscopy was used to observe the regeneration of corneal nerves that could then be analyzed by ACCMetrics software using quantitative parameters （e.g.， corneal nerve fiber length， density， nerve branch density， tortuosity and reflectivity of nerve fiber） before undergoing comparisons between the 2 groups. Confocal microscopy could also provide a general idea about the healing of the corneal flap and changes in keratocytes. The quantitative data of the 2 groups was compared using an independent samples t test. Results The values of corneal nerve fiber length， density， nerve branch density， and grading scores of nerve fiber tortuosity and reflectivity in patients from the 1-year group were all higher than those from the 6-month group （t=7.246， 5.335， 3.789， 3.808， 2.825， P<0.01）， and confocal microscopy revealed a clear-cut corneal flap edge in patients who had FS-LASIK surgery. For the 2 patients whose post-LASIK visual acuity did not reach 1.0， confocal microscopy also help to identify some abnormalities in corneal structure that might have contributed to the condition. Conclusion The use of confocal microscopy revealed that central corneal nerves were in a regenerative state within 1 year post-LASIK， with their density and morphological features undergoing significant changes. Besides， confocal microscopy could also assess corneal micro-structural changes at a cellular level， thus promoting the diagnosis and treatment of post-LASIK complications.

Objective To assess the agreement of keratometry and corneal astigmatism measurements by Orbscan II and Topolyzer. Methods In a prospective comparative study， 50 eyes of 50 healthy subjects were measured with the Orbscan II and Topolyzer. Data were analyzed using a paired sample t test and Bland-Altman plots. Results The mean differences of K1， K2， Km， J0 and J45 measured by Orbscan II and Topolyzer were -0.14±0.22 D， -0.18±0.29 D， -0.16±0.23 D， 0.03±0.12 D and -0.01±0.11 D， respectively. There were significant differences between the results of these 2 methods in K1 （t=-4.697， P<0.01）， K2 （t=-4.516， P<0.01） and Km （t=-5.144， P< 0.01）， but not for J0 （t=1.875， P>0.05） and J45 （t=-0.383， P>0.05）. A Bland-Altman analysis showed that the results for the 2 devices were not comparable results for K1， K2 and Km （The largest 95% LoAs were 0.57 D， 0.75 D and 0.61 D， respectively.）， but results were comparable for J0 and J45 （The largest 95% LoAs were 0.27 D and 0.22 D， respectively.）. Conclusion The corneal astigmatism values obtained with Orbscan II were correlated very well with those of the Topolyzer. However， it is important to note in clinical practice that corneal power values acquired by these 2 devices are not directly interchangeable.

Objective To investigate the relationship between central corneal thickness （CCT） measured by optical coherence tomography （OCT） and age， spherical equivalent（SE）， axial length， gender， and right vs. left eye in myopic juveniles. Methods This was a cross-sectional study. One hundred and forty-three juveniles （age range， 7~18 years） underwent ophthalmic examination. CCT was measured by a Stratus OCT on one randomly selected eye of each subject. Axial length was measured by A-scan ultrasound. SE was measured after cycloplegia. The effects of several factors （age， SE， axial length， gender， and right vs. left eye） on CCT were investigated in univariate regression analyses and multivariate stepwise regression analyses. Results The mean CCT was 549.3±35.7 μm . In univariate regression analysis， no correlation was found between CCT and age （r=0.065， P>0.05）， gender （r=0.059， P>0.05）， refractive status （r=0.125， P>0.05）， or axial length （r=0.146， P>0.05）. There was a significant positive correlation between CCT and SE （r=0.250， P<0.01）. The regression equation was ■=561.458+4.514X （F=9.417， P<0.01）. In multivariate stepwise regression analysis， there was also a significant positive correlation between CCT and SE （r=0.247， P<0.01）. The regression equation was ■=561.096+4.465X （F=8.813， P<0.01）. And the following parameters were not significantly associated with CCT： age， gender， right vs. left eye， or axial length. Conclusion The Stratus OCT is a good instrument to measure children′s CCT. Among Chinese myopic juveniles， CCT did not correlate with axial length， age， gender or right vs. left eye， but showed a direct correlation with SE.

Objective The aim of this study is to investigate the influence of pterygium on corneal biomechanical properties by comparing the corneal hysteresis （CH） and the corneal resistance factor （CRF） measured by an ocular response analyzer （ORA） in normal and pterygium eyes. Methods In a case control study， 40 patients with monocular nasal simple pterygiums were randomly selected. The contralateral eyes were used for comparison. CH，CRF， IOPg and IOPcc were measured with an ORA and corneal curvature were measured with an corneal curvemeter. A paired t test， linear correlation and regression analysis were used in this study. Results Both the mean CH and CRF in pterygium eyes were both lower than in normal eyes and the differences were statistically significant （t=2.637， 2.415， P<0.05）. Both the mean horizontal corneal curvature and vertical curvature in pterygium eyes were lower than in normal eyes and the differences were statistically significant （t=12.447， P<0.01； t=2.578， P<0.05）. In linear correlation and regression analysis， the D-values of CH and CRF between normal and pterygium eyes were both positively correlated with that of corneal horizontal curvature （r=0.622， 0.678， P<0.01）， and corneal astigmatism （r=0.525， 0.515， P<0.01）. Conclusion The CH and CRF were significantly lower in pterygium eyes than in normal eyes， and the D-values of CH and CRF between normal and pterygium eyes were correlated with horizontal corneal curvature. Using the measurements of CH， CRF and corneal curvature is helpful to assess the severity of pterygium′s influence on the cornea.

Objective To investigate the amblyopia status of preschool children in the Yangpu district of Shanghai， and to analyze the incidence and distribution of amblyopia based on a new diagnostic standard. Methods Using a cross-sectional investigation method， 13 288 children aged 3 to 6 years who were enrolled in 96 kindergardens in the Yangpu District of Shanghai were included in this investigation. Visual acuity and refractive status were examined， and the incidence of amblyopia was evaluated using a new diagnostic criteria. Subsequently， the distribution of amblyopia was evaluated by a chi-square test and trend chi-square test. Results The incidence of amblyopia was much higher when using the old criterion compared to the new one （63.52% and 0.91%， respectively， P<0.01）. In this cohort study of amblyopia， refractive error amblyopia accounted for 72.7%， anisometropic amblyopia accounted for 14.5%， strabismic amblyopia accounted for 9.1%， and deprivation amblyopia accounted for 3.6%. The incidence of amblyopia was much higher in 4-5 year olds （χ2=27.52， P<0.01）， but there was no difference in the incidence of amblyopia between genders（χ2=0.41， P>0.05）. Conclusion The main reasons for amblyopia in preschool children in the Yangpu District were refractive error， anisometropia， strabismus and deprivation amblyopia. Taking into account the importance of visual development patterns in the diagnosis of amblyopia in children， age was considered as a factor in the diagnosis of amblyopia based on the new diagnostic criterion. This avoided a higher number of amblyopia diagnoses and excessive treatment.

Objective To observe axial length， refraction and morphology in formdeprivation myopia （FDM） with genetransferred tissue inhibitors of metalloproteinase （TIMP2） in guinea pigs. Methods Sixty fourweekold guinea pigs in this experimental study were randomly divided into 4 groups： TIMP2 group， empty plasmid group， saline group and control group. A FDM model was established in the right eye by using a translucent plastic occluder. The left eye of the TIMP2 group was considered as the selfcontrol group. Genetransferred liposome， empty plasmidtransferred liposome and saline were injected in the first 3 groups， respectively， on the 15th day of deprivation. Refraction， axial length and the scleral structure were observed on 2， 7 and 14 days after injection. Data were analyzed using twoway analysis of variance. Results On 2， 7 and 14 days after injection， the average amounts of myopia in the TIMP2 group were -0.4±0.5 D， 0.9±0.6 D and 1.2±0.6 D. The differences for the day 14 were statistically significant compared to the other 3 groups （q=5.78， 5.34， 6.07， P<0.05）. Compared with the control group， the differences of day 2， 7， 14 were statistrcally significant （q=13.09， 9.72， 6.93， P<0.05）. On 2， 7 and 14 days after injection， the axial lengths of the experimental group were 7.78±0.04 mm， 7.69±0.03 mm and 7.65±0.03 mm. The differences on days 7 and 14 were statistically significant compared to the control groups （q7=5.51， 4.43, 4.82， q14=5.36， 4.78， 5.16； P<0.05）. The collagen fibrillar diameters of the sclera in the posterior segment of FDM eyes were found to be distinctly bigger and the space between the fibers was smaller than that of the control eyes. The average diameters of the fiber in the TIMP2 group were 49.7±6.8 nm， 71.3±6.0 nm and 97.8±10.4 nm， respectively， 2， 7 and 14 days after injection. The differences on day 7 and 14 were statistically significant compared to the the other 3 groups （q7=30.70， 12.30， 12.20， q14=21.80， 21.50， 21.20； P<0.05）. Compared with the control group， the differences of day 2 were statistically significant （q=14.40， P<0.05）. Conclusion The ectogenic gene of TIMP2 has an inhibitory effect on the changes in the biology and morphology in formdeprivation myopia of guinea pigs.

Objective To investigate the changes in accommodative responses at 33 cm of children with mixed astigmatism with and without wearing full corrective spectacles. Methods The right eyes of 54 5-7 year old children with mixed astigmatism were investigated in this cross-sectional study. They were given full corrective spectacles according to the results of optometric testing using 1% atropine eye ointment. An infrared autorefractor （Shin-Nippon Ophthalmic Instruments） was used to measure the accommodative responses of children with and without wearing full corrective spectacles at 33 cm （reading distance）. A paired t test was used for analysis. Results The results demonstrated that with glasses or unaided vision the accommodative lag at 33 cm was 0.64±0.67 D and 0.09±0.59 D， respectively， and the difference was statistically significant （t=5.262， P<0.01）. The data were then divided by spherical equivalent refraction （SER） into 3 groups， SER>0.00 D， SER=0.00 D， SER<0.00 D. The respective accommodative lags at 33 cm with or without glasses were 0.52±0.51 D and 0.17±0.53 D （t=2.680， P<0.05）， 0.75±0.57 D and 0.08±0.74 D （t=4.746， P<0.01）， and 0.73±0.96 D and -0.07±0.52 D （t=3.011， P<0.01）. Conclusion The near accommodative lag might lead to hyperopic retinal blur during near viewing and drive myopia progression.

Objective To compare visual quality after using an iTrace Aberrometer or Pentacam system to guide personalized aspheric intraocular lenses （IOLs） implantations； to discuss the feasibility of using the 2 instruments to guide IOL implantation or whole eye spherical aberrations About +0.1 μm. Methods This was a prospective clinical study. One day before phacoemulsification and aspheric IOL implantation surgery， a Pentacam or iTrace aberrometer was used to measure corneal spherical aberrations （Z40） under a 6 mm pupil diameter of patients with age-related cataract. Fifty-five patients （58 eyes were divided into an iTrace group （31 eyes） and a Pentacam group （27 eyes）. Tecnis IOLs， AcrySof IQ IOLs or ADAPT-AO IOLs were implanted in these patients based on the measurement results so that the patient′s predictive value of the whole eye spherical aberration was in the range of 0.05-0.15 μm after surgery. After 3 months， uncorrected visual acuity （UCVA）， best corrected visual acuity （BCVA）， modulation transfer function （MTF） for less than a 6 mm pupil diameter， spherical aberrations of the whole and inside eye were measured. The relevant data were analyzed using a paired t test and independent samples t test. Results ① After surgery， the UCVA and BCVA were compared for the 2 groups. The differences were not statistically significant （UCVA： t=0.83， P>0.05； BCVA： t=0.37， P>0.05）. ②All predicted preoperative whole eye spherical aberrations under a 6 mm pupil diameter were compared to +0.1 μm for the 2 groups. The differences were not statistically significant （iTrace group： t=- 1.70， P>0.05； Pentacam group： t=0.64， P>0.05）. After surgery， the actual spherical aberrations of the 2 groups under a 6 mm pupil diameter were compared to +0.1 μm. The difference for the iTrace group was not statistically significant （t=0.58， P>0.05）， but there was a statistically significant difference for the Pentacam group （t=2.33， P<0.05）. ③The difference in the predicted values of the preoperative spherical aberrations of the whole eye and the actual values after surgery were not statistically significant （iTrace group： t=-1.55， P>0.05； Pentacam group： t=-2.04， P>0.05）. The actual spherical aberrations of the inside eye after surgery vs. spherical aberrations of IOLs and the differences were not statistically significant （iTrace group： t=-1.55， P>0.05； Pentacam group t=0.73， P>0.05）. The difference between the 2 groups′actual values of the spherical aberrations of the whole eye was not statistically significant （t=1.52， P>0.05）. ④After surgery， under a 6 mm pupil diameter at 5， 10， 15， 20， 25 and 30 cycles per degree （c/d） spatial frequencies， the differences in the values of the MTFs of higher-order aberration between the 2 groups were not statistically significant （t=0.88， 0.47， 0.34， 0.02， -0.57， -0.23， P>0.05） and the differences in the values of the MTFs of spherical aberration for the 2 groups were not statistically significant （t=-0.37， -0.46， -0.43， -0.39， -0.68， -1.08， P>0.05）. Conclusion The 2 groups that underwent 2 different instrument-guided aspheric IOL implantations can achieve satisfactory targets for spherical aberrations. The iTrace group′s predictive value is closer to the actual value than the Pentacam group′s. Aspheric IOL implantation surgery guided with either instrument can achieve good postoperative visual quality.

Objective To construct an optical bench that can measure the wavefront aberrations of the intraocular lenses （IOLs）. Methods This was an experimental study. An optical path was constructed to measure the wavefront aberrations of IOLs based on the HartmannShack principle. The optical bench was composed of 2 parts： an eye model and optical components. The eye model was a combination of a spherical photographic lens with a 28 mm focal length， a water cell containing the IOLs （diopters： +10， +15， +20， +25， +30 D） and a chargecoupled device （CCD）. The optical components were composed of a light source， filters （peak wavelengths： 436.0， 486.0， 525.0， 546.1， 589.0， 660.0， 710.0 nm）， a microlens array with a 15 mm focal length and an achromatic doublet lens with a 100 mm focal length. The images received by the CCD were analyzed with Matlab software. IOL Zernik polynomials and wavefront aberration parameters such as modulation transfer function and point spread function were also obtained. Results By changing the filters or IOLs on the optical bench， the wavefront aberrations of each IOL were measured at different wavelengths of 436.0-710.0 nm， so the spherical aberrations and higher order aberrations of the IOLs could be compared. Conclusion Wavefront aberrations of IOLs can be measured in this optical path， therefore the optical properties of the IOLs can be evaluated objectively.

Objective To explore the combined surgical method for treatment of fracture of the orbital maxillary zygomatic and eyeball atrophy， and evaluate its effect. Methods A retrospective clinical study was performed on 12 patients with fracture of the orbital maxillary zygomatic and eyeball atrophy who were treated at Tianjin Medical University General Hospital between September 2009 and November 2011. Surgical effects were followed up such as facial appearance， exophthalmos and activity of the ocular prosthesis， mouth opening and jaw relationship. Results Patients were followed up for 6.8±2.6 months with a range of 3-12 months. All patients had facial symmetry and did not develop secondary infection or rejection. Ten patients wearing an ocular prosthesis had good appearance， six patients with limited mouth opening preoperatively recovered movement and the jaw relationship returned to normal postoperatively. Six patients with facial and upper lid numbness preoperatively regained feeling in 6 months postoperatively. Conclusion The combined surgery is a valuable treatment option for fracture of the orbital maxillary zygomatic and eyeball atrophy. A single surgery can eliminate the limitation of mouth opening and improve facial appearance， which results in a good surgical outcome.

The proper uses of ophthalmic and optical instruments play an important role in diagnosis and treatment of eye diseases. Precision and accuracy assessment are the major indicator for evaluation of instruments. The former consists of repeatability and reproducibility， while the agreement assessment decides its accuracy. There are so many studies focused on this field due to the rapid development of new techniques and instruments， followed by the arising of problems in method selection. This article introduces the main methods of precision and accuracy assessment. And we also provide the ideas of proper method selection in clinical practice and research with examples. Moreover， we discussed the influence of analytic approach with one eye or two， as well as sample size calculation.

The three-dimensional simulation technology refers to the technology which can use the computer technology to generate a realistic virtual environment with visual， hearing， touch， taste， and other perception. Users can have interaction with entity in the virtual environment. With its very vivid virtual reality （VR） technology， 3D simulation technology has gained more and more attention and provided a new development platform for ophthalmology and optometry teaching. This paper mainly introduced teaching the present development situation and the specific application of the 3D simulation model， 3D animation technology， virtual reality technology in optometry and ophthalmology.