Comparison of keratometric and topographic cylinder and axis measurements on normal corneas with low astigmatism

PURPOSE: To evaluate agreement in measurements of astigmatic axis power and location between keratometry and computer assisted videokeratography (corneal topography) on normal corneas with less than 1.50 D of idiopathic astigmatism. METHODS: Keratometric readings with the 10 SL/O Zeiss ophthalmometer and corneal topographic maps with the TMS-1 were obtained by two independent examiners on 32 normal corneas. Measurement agreement between the two instruments was evaluated in regard to steep and flat meridian power and location, and in astigmatism magnitude (D). RESULTS: The limits of agreement (d-2 SD to d+2 SD) between the two instruments were found to be broad for clinical purposes in measuring the steep meridian power (-0.16 to -1.20 D), flat meridian power (0.43 to -1.25 D), and astigmatism (0.60 to -1.12 D). A constant bias of the TMS-1 towards the 10 SL/O Zeiss ophthalmometer was found, in measuring steeper both principal meridians and higher amount of astigmatism. Mean location difference was 19 degrees (+/-190) for the steep meridian and 17 degrees (+/-20 degrees) for the flat meridian. CONCLUSIONS: Despite the differences seen in measurements between the 10 SL/O ophthalmometer and the TMS-1, these differences may be clinically small enough for the methods to be used interchangeably in measuring only the magnitude of astigmatism on normal corneas. However, the disagreement in astigmatism axes is too great to be ignored.     

The effect of head tilt on keratometric measurement using the IOLMaster

Purpose

To investigate the effect of head tilt on keratometric measurement using the IOLMaster.

Methods

Twenty-seven right eyes of 27 volunteers were examined using a manual keratometer (MK), automated keratometer (AK), and an IOLMaster. MK and AK measurements were performed in the upright head position, whereas IOLMaster measurements were performed in five different head positions (upright, 5° or 15° clockwise head tilt, and 5° or 15° counter-clockwise head tilt). The repeatability of IOLMaster was compared with MK and AK. The keratometric measurements (mean keratometric power, magnitude of astigmatism, and steep meridian) in different head positions were compared.

Results

The IOLMaster showed good repeatability of keratometric measurement comparable to MK or AK. 15° and 5° clockwise head tilt resulted in 12.09±9.51 (mean±SD) (P<0.001 vs upright) and 5.51±5.97 (mean±SD) degrees (P<0.001) of clockwise rotation of steep meridian, respectively. 15° and 5° counter-clockwise head tilt resulted in 12.49±7.07 (mean±SD) (P<0.001) and 6.08±5.09 (mean±SD) degrees (P<0.001) of counter-clockwise rotation of steep meridian, respectively.

Conclusions

The patient''s head tilt (5° or 15°, clockwise or counter-clockwise) significantly changed the steep meridian of astigmatism measured using IOLMaster and the steep meridian generally shifted to the direction of head tilt. The importance of maintaining the upright head posture during IOLMaster measurement is demonstrated.     

Reliable keratometry with a new hand held surgical keratometer: calibration of the keratoscopic astigmatic ruler

AIM—Some surgeons consider hand held surgical keratometers unreliable. This may be due to incorrect use through not realising that the distance that the keratometer is held from the cornea influences the shape of the image. When a keratometer is held closer to the astigmatic cornea, the elliptical image will appear more circular, particularly for larger degrees of astigmatism. However, the keratoscopic astigmatic ruler (KAR) has design features that correct the hitherto unrecognised problems with the use of a hand held keratometer. This study assesses the reliability and accuracy of measurement of astigmatism using the KAR.
METHODS—The KAR and the Bausch & Lomb keratometer (B&L) were compared using six back surface toric cut contact lens blanks representing 1 to 6 dioptres of astigmatism. Two observers (one experienced in the use of the keratometers, the other a novice) took eight randomly repeated "masked" measurements of each lens blank with the KAR and four measurements with the B&L in a similar fashion.
RESULTS—There was no difference between the measurements with either instrument by each of the observers (p=0.95, ANOVA). The standard error of measurement for the KAR was 0.59 D, for the B&L, 0.31 D. The intraclass correlation coefficient of reliability for the KAR was 0.90 and for the B&L it was 0.97. The coefficient of repeatability for the KAR was plus or minus 0.83 D, and for the B&L plus or minus 0.77 D. The interobserver reliability for the KAR was 0.898, and for the B&L, 0.975.
CONCLUSION—These results suggest that the KAR has good reliability and reproducibility and compares favourably with the B&L keratometer. Inexperience with use does not affect reliability.

     

自动角膜曲率计与角膜地形图仪测量儿童角膜屈光力的比较研究

目的 比较KR-8100自动角膜曲率计与TMs-4角膜地形图仪测量屈光不正儿童角膜屈光力及散光轴向的差异,并对两种测量方法进行一致性评价.方法 采用KR-8100自动角膜曲率计及TMS-4角膜地形图仪对53例(106只眼)屈光不正儿童进行测量,应用配对t检验对两种方法测量的陡峭 子午线角膜屈光力(Ks)、平坦子午线角膜屈光力(Kf)、角膜散光Ks-Kf大小及轴向进行比较,并应用Bland-Altmann分析对两种测量方法进行一致性评价.结果 角膜地形图仪测量的Ks、Kf、Ks-Kf值均高于角膜曲率计的测量值(P<0.01);角膜地形图仪与角膜曲率计的散光轴向测量值差异有统计学意义(P<0.01).两种仪器测量Ks的差值的均数为1.72D,测量Kf的差值的均数为1.37D,这种测量差别临床上不能接受,说明两种仪器测量角膜屈光力的一致性较差.结论 KR-8100自动角膜曲率计与TMS-4角膜地形图两种测量方法在临床上不能替代使用.     

VERION数字导航系统测量角膜曲率和散光的可重复性及其与iTrace、Lenstar LS900、手动角膜曲率计检测结果的一致性研究

目的 分析VERION数字导航系统测量角膜曲率和散光的可重复性及其与iTrace、Lenstar LS900、手动角膜曲率计检测结果的一致性.方法 对62名年龄相关性白内障患者分别用上述四种仪器进行角膜生物测量,记录并分析陡峭轴角膜曲率(steep keratometry,Ks)、平坦轴角膜曲率(flat keratometry,Kf)、散光幅度、散光轴位、矢量参数J0和J45.分析VERION测量的可重复性,并比较VERION与其他三种仪器测量结果的一致性.结果 用组内相关系数(intraclass correlation coefficient,ICC)和克隆巴赫系数(Cronbach's alpha,α)分别对Ks、Kf、散光幅度、散光轴位、J0以及J45做出分析,结果均大于0.9(均为P＜0.001),提示VERION测量角膜曲率及散光的可重复性极好.VERION测量的Ks、散光幅度均高于iTrace(均为P＜0.05),其余指标的差异无统计学意义(均为P＞0.05).Bland-Altman分析显示J0、J45及散光轴位的95％ LOA分别为(-0.31 ～0.35)D、(-0.25～0.31)D、-13.5°～12.3°.二者测量的散光轴位差小于10°者占总体的77％ (48/62),在合并角膜散光大于1D的患者中占91％ (42/46).VERION与Lenstar LS900测量结果仅J45差异有统计学意义(P＜0.05),其余指标差异无统计学意义(均为P＞0.05).Bland-Altman分析发现J0、J45及散光轴位的95％ LOA分别为(-0.25 ～0.31)D、(-0.27 ～0.36)D、-13.5°～11.0°.二者测量的散光轴位差小于10°者占总体的85％(53/62),在合并角膜散光大于1D的患者中占93％(43/46).VERION与手动角膜曲率计检测的Kf、散光幅度差异有统计学意义(均为P＜0.05),其余指标差异无统计学意义(均为P＞0.05).Bland-Altman分析显示J0、J45及散光轴位的95％ LOA分别为(-0.38 ～0.35)D、(-0.41 ～0.42)D、-12.6° ～16.4°.二者测量的散光轴位差小于10°者占总体的81％ (50/62),在合并角膜散光大于1D的患者中占91％(42/46).结论 VERION在测量角膜曲率及散光方面具有良好的可重复性.其与iTrace、Lenstar LS900和手动角膜曲率计在角膜曲率、散光幅度的测量方面一致性较好,但对散光轴位的测量差别较大.     

Comparing IOLM700 TK,Berdahl and Hardten astigmatism fix calculator and Barrett Rx formula in managing residual astigmatism due to toric intraocular lens misalignment

Purpose:To compare the accuracy in astigmatism reduction by using IOLM 700 steep total keratometry (TK) axis, Berdahl and Hardten astigmatism fix, and Barrett Rx formula following misaligned toric intraocular lens (IOL).Methods:Ten patients with residual refractive astigmatism due to misalignment following toric IOL implantation were included in this retrospective study. They were analyzed at days 4, 7/8, and 10/11 following primary cataract surgery on the platform of Berdahl and Hardten astigmatism fix, Barrett Rx formula, and IOLM 700 to determine the optimum axis of repositioning, and underwent IOL realignment on the steep TK axis of IOLM 700 assisted by the Callisto eye. The final outcome parameters were subjective refraction and orientation of toric IOL assessed 22 ± 1 days following repositioning surgery. These parameters were fed in the Barrett Rx formula and its vector analysis graph was utilized to determine the predicted ideal axis with the least residual astigmatism and the estimated residual astigmatism if the toric IOL was realigned according to the axis suggested by Berdahl and Hardten astigmatism fix and Barrett Rx formula.Results:Realigning the toric IOL on IOLM 700 steep TK axis along with the Callisto eye reduces the residual refractive astigmatism significantly (P = 0.003) from 2.00 ± 0.78 D to 0.18 ± 0.12 D (90.5 ± 7.6%) in comparison to the estimated 0.57 ± 0.31 D (68.4 ± 21.9%) by Berdahl and Hardten astigmatism fix and 0.61 ± 0.33 D (66.4 ± 23.5%) by Barrett Rx formula.Conclusion:Realigning the misaligned toric IOL on the IOLM 700 steep TK axis gives a better reduction in the residual refractive astigmatism in comparison to Berdahl and Hardten astigmatism fix and Barrett Rx formula.     

Interobserver and intraobserver reliability of a classification scheme for corneal topographic patterns

AIMS—To determine the interobserver and the intraobserver reliability of a published classification scheme for corneal topography in normal subjects using the absolute scale.
METHOD—A prospective observational study was done in which 195 TMS-1 corneal topography maps in the absolute scale were independently classified twice by three classifiers—a cornea fellow, an ophthalmic technician, and an optometrist. From these observations the interobserver reliability for each category and the intraobserver reliability for each observer were determined in terms of the median weighted kappa statistic for each category and for each observer.
RESULTS—For interobserver reliability, the median weighted kappa statistic for each category varied from 0.72 to 0.97 and for intraobserver reliability the range was 0.79 to 0.98.
CONCLUSION—This classification scheme is extremely robust and even in the hands of less experienced observers with minimal training it can be relied upon to provide consistent results.

     

Measurement of corneal curvature after corneal transplantation and radial keratotomy using standard and automated keratometry

Keratometry readings obtained with a standard Bausch & Lomb keratometer were compared to readings obtained with a Humphrey automated keratometer in 50 eyes that had undergone radial keratotomy and 40 eyes that had undergone corneal transplantation. Both instruments recorded similar results for the flat, steep, and mean keratometry meridians, but they produced significantly different results in determination of keratometry-measured astigmatism and axis of astigmatism. Differences in readings were greater (with the automated keratometer recording more astigmatism than the Bausch & Lomb keratometer) following corneal transplantation than radial keratotomy. It is suggested that only one or the other instrument be used for a clinical study because of the potential differences that can occur when measuring postsurgical astigmatism.     

Agreement between Two Swept-Source Optical Coherence Tomography Biometers and a Partial Coherence Interferometer

PurposeTo evaluate the level of agreement between ANTERION (Heidelberg Engineering, Heidelberg, Germany), OA-2000 (Tomey, Nagoya, Japan), and IOLMaster 500 (Carl Zeiss AG, Jena, Germany).MethodsFifty-one eyes of 51 patients were included in the study. Flat keratometry (K) and steep K, vector component of astigmatism (Jackson cross-cylinder at 0° and 90° [J₀] and Jackson cross-cylinder at 45° and 135° [J₄₅]), anterior chamber depth, and axial length were compared using the three devices. Repeated measures analysis of variance was conducted to compare the mean values of the biometrics. Pearson correlation test was conducted to analyze the correlations of the measured values, and a Bland-Altman plot was used to assess the agreement between the three devices. The predicted intraocular lens power of each device was compared to the others using the SRK/T, Haigis, Barrett Universal II, and Kane formulas.ResultsAll K values measured using ANTERION were flatter than those of other instruments. However, good agreement was observed for flat K (ANTERION - OA-2000; 95% limits of agreement [LoA], 0.86 diopters [D]) and steep K (ANTERION - OA-2000; 95% LoA, 0.93 D) and OA-2000 - IOLMaster 500 (95% LoA, 0.93 D). J₀ and J₄₅ vector components of astigmatism were not statistically different; however, the agreements were poor between the devices (95% LoA ≥1.97 D). Anterior chamber depth values of ANTERION and OA-2000 were interchangeable (95% LoA, 0.15 mm). The axial length showed a high agreement (95% LoA ≤0.17 mm) among the three devices. The predicted intraocular lens powers of the three devices were not interchangeable regardless of formulas (95% LoA ≥1.04 D).ConclusionsSignificant differences in ocular biometrics were observed between ANTERION and the other two devices. This study demonstrated that only axial length showed good agreement among devices.     

Postmortale Evaluation des kornealen Astigmatismus nach Astigmatismus-orientierter perforierender Keratoplastik (AOpKP)

Background. Reduction of astigmatism following penetrating keratoplasty can be achieved if the graft is oriented according to astigmatism parameters in donor and host (AOPKP). Postmortem evaluation of these parameters is therefore essential. The aim of our investigation was to compare postmortem measurements using a hand-held keratometer with those of the living donor's astigmatism. Method. The 72-year-old female patient had underrgone AOPKP on her right eye. After death the astigmatism in the right eye was evaluated 4.5 h postmortem using a hand-held keratometer. After explantation, the eyeball was examined by computer-assisted topography (TMS-1). Results/Conclusion. We could show that hand keratometry in situ is reliable for evaluating astigmatism in donor eyes after death. As far as our AOPKP study is concerned, these results are of great interest. Reduction of postoperative astigmatism following penetrating keratoplasty is only possible if data on astigmatism of the donor and host corneas are available.     

Corneal topography for residual astigmatism prediction in computer-assisted rigid contact lens fitting

Residual astigmatism often limits the use of rigid gas permeable (RGP) contact lenses in the correction of certain ametropias. The ability of the Topographic Modeling System (TMS-1, Computed Anatomy, Inc.) Contact Lens Program to predict residual astigmatism was evaluated. An examination, including manifest refraction, central keratometry, and computerized corneal topography was performed on 62 eyes of 31 patients. Initial RGP parameters were ordered exactly as chosen by the TMS-1 for Boston RXD default lens settings. Calculated residual astigmatism (CRA) was determined by subtracting, in minus cylinder form, the corneal toricity (difference between the keratometer readings of the two principal meridians), from the spectacle astigmatism. CRA was significantly different from that predicted by the computer (p < 0.0001) and the clinically measured residual astigmatism (MRA) (p < 0.0001). Comparison of TMS-1 predicted residual astigmatism (PRA) to the MRA yielded no correlation (r² = 0.0229). Eleven eyes (18%) were predicted to have residual astigmatismm by the computer, but in no case was it manifest clinically. Conversely, eight eyes (13%) had MRA that was not predicted by the software. However, the differences between the PRA and MRA were not significant (Student t-test; p = 0.7247). Clinically, the TMS-1 is a poor predictor of residual astigmatism. However, corneal topography is a better predictor of residual astigmatism than is the traditional method of calculation.     

Oxygen free radical damage in the cornea after excimer laser therapy

AIMS/BACKGROUND—To evaluate the extent of oxygen radical damage in the cornea after excimer laser ablation.
METHODS—The 193 nm argon fluoride excimer laser was programmed for an average fluence of 150 mJ/cm², with a firing rate of 5 Hz and an ablation zone diameter of 6 mm. Phototherapeutic keratectomy was performed to remove 30 µm of epithelium and 50 µm of stroma from the corneas of New Zealand white rabbits. Oxidative tissue damage after laser was determined by measuring oxidised lipids (conjugated dienes and ketodienes) in corneal lipid extracts, and by fast blue B staining to localise the lipid peroxide in the tissue.
RESULTS—Conjugated diene levels were 3.73 (SD 0.56) nmol per hemicornea in ablated corneas and 1.99 (0.33) nmol per hemicornea in normal corneas (p = 0.0044). Ketodiene levels were 2.72 (0.38) nmol per hemicornea in treated corneas and 0.91 (0.12) nmol per hemicornea in normal corneas (p < 0.001). Fast blue B staining disclosed that the tissue damage occurred primarily on the surface of the ablated cornea.
CONCLUSION—The presence of lipid peroxidation in the superficial corneal stroma in excimer laser treated corneas was demonstrated. This lipid peroxidation could be from oxygen free radicals generated by the infiltrating polymorphonuclear cells at the site of tissue damage.

     

[Online First]Agreement between IOLMaster® 500 and Pentacam® HR for keratometry assessment in type 2 diabetic and non-diabetic patients

AIM: To evaluate inter-device agreement of anterior keratometry obtained by the IOLMaster® 500 and Pentacam® HR in type 2 diabetic and non-diabetic patients.METHODS: Corneal measurements were sequentially performed in 60 diabetic (DM) and 48 age and sex-matched controls undergoing cataract surgery. Variables recorded included flat and steep keratometry (K), mean keratometry (Km), astigmatism magnitude, axis location, J0 and J45 components. Bland-Altman plots and intraclass correlation coefficients were used for examination of agreement. Subgroup analyses were performed for astigmatism magnitude, diabetes duration, HbA1c levels and diabetic retinopathy (DR) stage.RESULTS: Agreement for Km and astigmatism magnitude were considered good and moderate, with 95% limits of agreement (LoA) of -1.09 to +1.23 diopters (D) and -0.83 to +0.86D in DM group, respectively; and -0.59 to +0.72D and -0.98 to +0.75D in non-DM group, respectively. In contrast, the 95% LoA for corneal axis exceeded the clinically relevant margins in both groups. In the total sample, only 41 eyes (38%) had a smaller than 5-degree difference. Diabetes duration, HbA1c levels and DR stage were not found to significantly affect agreement. Logistic regression showed that higher corneal power (P=0.021) and astigmatism magnitude (P=0.011) were associated with a decreased risk of having a difference in axis location greater than 10-degrees.CONCLUSION: In both groups, IOLMaster and Pentacam agree well for corneal power and moderately for astigmatism. However, axis location disagreement is frequent in eyes with flatter corneas and small amounts of astigmatism.     

Blind spot size depends on the optic disc topography: a study using SLO controlled scotometry and the Heidelberg retina tomograph

AIMS—To find out whether the size of the blind spot area, determined by static perimetry, depends on the surface topography of the optic disc and its surrounding area.
METHODS—Ten eyes were examined; all had a parapapillary atrophy adjacent to the temporal side of the disc. Microperimetry was performed under direct fundus control using a Rodenstock scanning laser ophthalmoscope. The horizontal meridian of the optic discs was examined in 0.5° steps using five stimulus sizes (Goldmann I to V), each with 10 different degrees of brightness. Optic disc topography was measured with the Heidelberg retina tomograph (HRT).
RESULTS—Stimuli with a high luminance level (Goldmann IV, 4 dB), presented on the horizontal meridian, were seen up to 0.75° centrally (that is, towards the optic disc centre) from the temporal edge of the parapapillary atrophy but up to 1.85° centrally from the nasal optic disc border (p<0.01). Horizontal HRT section profiles of the optic disc consistently showed prominent nasal disc borders contrasting with a shallow excavation within the temporal parapapillary atrophy.
CONCLUSIONS—The size of scotomas depends on the surface topography of the tested area. The prominent nasal part of the optic disc appears less `blind' than the shallow temporal part, probably because of more intensive light scattering by the prominent nasal part of the disc. These considerations should also apply to other scotomas.

     

Comparing keratometry readings with manual separation of lids and wire speculum in children under general anesthesia

Purpose:Keratometry (K) readings are crucial for intraocular lens power calculation in cataract surgery. In children who do not cooperate, the keratometry is done under general anesthesia with a handheld autokeratometer. However, there is little consensus regarding the method for the measurement of K readings. The lids can be separated either by fingers or a wire speculum may be placed to separate the lids for measurement.Methods:The children selected for the study were patients cooperative for keratometry reading. Nidek KM-500 handheld keratometer was used first in the awake period. Then under general anesthesia, readings were taken first by separating the lids manually with fingers and then after putting a wire speculum in both the eyes.Results:The average keratometry reading for participants in the OPD, anesthetized with lids manually opened and with lids separated with speculum was 44.7 ± 1.7 D, 44.4 ± 1.9 D, and 44.7 ± 1.7 D, respectively.Conclusion:No significant change was observed in keratometry values in children with manual separation of eyelids or with wire speculum.     

Intraoperative PAR corneal topography system (CTS): comparison of its keratometric readings to manual keratometer, auto-keratometer, EyeSys Corneal Analysis system, and slit lamp PAR CTS in healthy eyes.

PURPOSE: To compare the keratometric readings obtained from Intraoperative PAR Corneal Topography System (IOPAR) to those produced by manual keratometer (Mnl-Km), autokeratometer (Auto-Km), EyeSys CAS (EyeSys Corneal Analysis System) and slit lamp PAR CTS in healthy eyes. METHODS: All instruments were calibrated prior to use and only data from the best image obtained was used for statistical analysis. Simulated keratometry readings obtained from the central 3-mm zone of the corneas by IOPAR, including flat (K1) and steep (K2) keratometry readings, average keratometric power (AK), astigmatism (As) (difference between steep and flat keratometry readings) and the axis of the steep meridian (Ax) were compared to those from four other units. The latter units were also compared among themselves. Statistical analysis was done for right and left eyes separately. For each variable, average differences between the measurements taken from pairs of instruments were estimated, with corresponding 95% confidence intervals. The degree of agreement between pairs of instruments on individual measurements was additionally assessed, via the use of "Bland-Altman"-type plots, and estimates of the proportion of cases achieving satisfactory agreement. Additionally, for every variable, the average of the measurements taken from the different instruments were compared. RESULTS: Forty-five (22 right and 23 left) normal corneas of 26 volunteers were examined. On the average, IOPAR tended to measure K1 higher than slit lamp PAR CTS system. Because K2 measurements taken by the IOPAR were higher than that of all other instruments, the As measurements, on the average, were also higher than that of others, with the exception of the PAR CTS. For the same reasons, the IOPAR produced average AK readings that were higher than those taken by EyeSys CAS and PAR CTS. When the individual measurements taken by the IOPAR were compared with each of the other units, according to the arbitrary designation of satisfactory agreement within +/-0.5 D (for K1, K2, AK, and As) and +/-20 degrees (for Ax), for almost all parameters, proportion of differences that were within the agreement range varied from 0.33 to 0.82, with wide confidence intervals (confidence interval lower limits ranging from 0.20 to 0.61 and upper limits ranging from 0.62 to 0.94). CONCLUSIONS: IOPAR is a clinically useful topographic system, producing qualitative and quantitative data in the operating environment that, in normal corneas, on the average, matches those produced by the other units in the clinic. When individually analyzed, its keratometric measurements may show greater variations with respect to other units. Further studies with multiple examiners, in corneas with high or irregular astigmatism are required to establish its reproducibility and efficacy.     

Influence of topical human epidermal growth factor on postkeratoplasty re-epithelialisation

AIM—To test the efficacy and safety of recombinant human epidermal growth factor (hEGF) on corneal re-epithelialisation following penetrating keratoplasty.
METHODS—A prospective, randomised, placebo controlled study was carried out in which patients were matched for diagnosis and received either hEGF ophthalmic solution (30 µg/ml or 100 µg/ml) or placebo in a double masked fashion. Matched pairs of patients received donor corneas from the same donor and were operated by the same surgeon on the same day. At the end of surgery all donor epithelium was removed mechanically. Patients were examined twice daily and fluorescein stained photographs were taken until the epithelium had closed. The area of the defect was measured by planimetry of the fluorescein stained defect on the photographs.
RESULTS—There were no significant differences in re-epithelialisation of the donor cornea between the placebo group and the group treated with 30 µg/ml hEGF. Time until complete closure was slightly longer with 100 µg/ml hEGF compared with 30 µg/ml hEGF and with placebo. Mean healing rate of the epithelial defect with 100 µg/ml hEGF was significantly slower than in the other groups.
CONCLUSION—No significant acceleration of corneal re-epithelialisation was demonstrated with the use of recombinant hEGF after penetrating keratoplasty in humans.

     

Minimizing surgically induced astigmatism in non-phaco manual small incision cataract surgery by U-shaped modification of scleral incision

Purpose:To evaluate the amount and type of surgically induced astigmatism (SIA) in manual small incision cataract surgery (SICS) with a 4.5 mm U-shaped scleral incision.Methods:A prospective cross-sectional study was done on a total of 61 patients above 40 years of age with senile cataract. All patients underwent complete examination including preoperative uncorrected visual acuity (UCVA), refraction, best-corrected visual acuity (BCVA), and keratometry using a manual keratometer (Bausch and Lomb). All 61 patients underwent manual SICS with a 4.5 mm U-shaped scleral incision within the astigmatic neutral incisional funnel. Patients were thoroughly examined on immediate postoperative day 1 and findings of UCVA, BCVA, refraction, and keratometry were noted at the end of the 1^st week, 4^th week, and 6^th week follow-up visits. SIA was calculated for all the follow-ups using the SIA calculator version 2.1, a free software program. The changes in the amount and type of postoperative SIA were tested for statistical significance using Fischer''s exact test. Variance was tested using intraclass score effect. The threshold for statistical significance was set to P < 0.001.Results:Postoperatively, the average SIA was 0.43 ± 0.13 D at the end of 1^st week, 0.29 ± 0.20 D at the end of the 4^th week, and remained the same 0.29 ± 0.21 D at the end of 6^th week. The type of astigmatism shifted more towards against-the-rule (ATR) type in 45.9% of cases during the final postoperative follow-up.Conclusion:In our study, we conclude that the incision within the funnel of astigmatic neutralization is one of the major determinants of SIA in manual SICS. We were able to achieve phacocomparable SIA in our study mainly because of our type of incision.     

Local hypothermia protects the retina from ischaemic injury in vitrectomy

AIMS—Hypothermic irrigating solutions were used during vitrectomy in pressure induced ischaemic eyes so that their effects on retinal function and histological changes could be investigated.
METHODS—After anaesthetised albino rabbits underwent closed vitrectomy, their vitreous cavities were continuously irrigated for 30 minutes at a perfusion pressure of 140 mm Hg. The rabbits were divided into three groups according to their intraocular perfusion temperatures—8°C, 22°C, and 38°C. Electroretinograms were taken before and after irrigation. Glutamate levels in the vitreous were examined after irrigation. Eyes were enucleated on the seventh postoperative day and examined histologically.
RESULTS—On the seventh postoperative day, the recovery rate of a-wave amplitudes was significantly lower in the 38°C group than in the 8°C group, and that of b-wave amplitudes was significantly lower in the 38°C group than in either the 8°C or 22°C group. Retinal damage in the 38°C group revealed more severe histological impairment than in either the 8°C or 22°C group. Oedema of the inner retinal layer was significant in both the 22°C and 38°C groups. Glutamates reached peak values 30 minutes after the end of ischaemia in the 38°C group. However, no significant glutamate increases were detected 15 to 60 minutes after ischaemia in either the 8°C or 22°C group.
CONCLUSION—Local hypothermia during vitrectomy in acute ischaemic eyes appears to decrease retinal damage.

     

Automatic full field analysis of perfusion images gained by scanning laser Doppler flowmetry

BACKGROUND—Scanning laser Doppler flowmetry (SLDF) enables the measurement of the laser Doppler frequency shift in retinal tissue. This process allows the quantification of retinal and optic nerve head perfusion in an area of 2.7 mm × 0.7 mm within 2 seconds and with a spatial resolution of 10 µm × 10 µm. Owing to the local heterogeneity of the retinal microcirculation itself and to heart associated pulsation the capillary retinal blood flow depends on location and time. Because of technical limitations measurements of flow are only valid in retinal points with adequate brightness and focus, and away from big vessels. To include the heart beat associated pulsation and the spatial heterogeneity of retinal blood flow into the evaluation of blood flow an algorithm was developed examining automatically the whole SLDF perfusion image.
AIM—To report intraobserver reliability and interobserver reliability of a new method for analysing automatically full field perfusion images.
METHOD—The base of blood flow calculation by the automatic full field perfusion image analyser (AFFPIA) was 16 384 intensity time curves of all pixels of the whole perfusion image gained by the SLDF. AFFPIA calculates the Doppler frequency shift and the haemodynamic variables flow, volume, and velocity of each pixel. The resulting perfusion image was processed with respect to (1) underexposed and overexposed pixels, (2) saccades, and (3) the retinal vessel tree. The rim area and the saccades were marked interactively by the operator. The capillaries and vessels of the retinal vessel tree were identified automatically by pattern analysis. Retinal vessels with a diameter greater than 30 µm, underexposed or overexposed areas, and saccades were excluded automatically. Based on the whole perfusion image total mean flow, total mean volume, total mean velocity, standard deviation, cumulative distribution curve of flow, and the capillary pulsation index were calculated automatically. Heart beat associated pulsation of capillary blood flow was estimated by plotting the mean capillary flow of each horizontal line against time. Intraobserver reliability was estimated by measuring 10 eyes of 10 subjects on five different days by one observer. Interobserver reliability of AFFPIA was evaluated by analysing 10 perfusion maps by five different operators. To find a baseline of retinal blood flow, perfusion maps of 67 eyes of normal subjects with a mean age of 40.4 (SD 15) years were evaluated by AFFPIA.
RESULTS—The coefficient of reliability of the intraobserver reproducibility of flow was 0.74. The coefficient of reliability of the interobserver reproducibility was 0.95. The juxtapapillary retinal capillary flow was temporally 484 (SD 125), nasally 450 (117); the rim area capillary flow was 443 (110). The mean capillary pulsation index of retinal flow was 0.56 (0.14).
CONCLUSION—Retinal blood flow evaluation by the AFFPIA increases significantly the interobserver reliability compared with conventional evaluation of 100 µm × 100 µm areas in SLDF images with the original Heidelberg retina flowmeter software. The intraobserver reliability of AFFPIA was in the same range as conventional evaluation.

Keywords: retinal blood flow; optic nerve head blood flow; scanning laser Doppler flowmetry