In VivoValidation of the New Tonopen AVIA Tonometer using Manometers placed in the Anterior chamber and the Vitreous Cavity under Various Vitreous Conditions

Central anterior chamber depth correlated with white-to-white distance in normal, long, and short eyes

PURPOSE

To explore the associations between central anterior chamber depth (CACD) and other anterior segment biometric parameters and to determine the possible determinants of CACD in short, normal, and long eyes.

METHODS

The biometric data of pre-operation patients aged 50-80 years with coexisting cataract and primary angle-closure disease or senile cataract were reviewed. Axial length (AL), CACD, lens thickness (LT), central corneal thickness (CCT), and white-to-white distance (WTW) were measured by Lenstar optical biometry (Lenstar 900). The data of 100 normal eyes (AL = 22 to 26 mm), 100 short eyes (AL ≤ 22 mm), and 100 long eyes (AL ≥ 26 mm) were consecutively collected for subsequent analyses.

RESULTS

The mean age of the subjects was 66.60 ± 7.85 years, with 25.7% of the sample being men. Both CACD and WTW were found to be smallest in short eyes and were smaller in normal eyes than in long eyes (F = 126.524, P < 0.001; F = 28.458, P < 0.001). The mean LT was significantly thicker in short eyes than in normal and long eyes (4.66 mm versus 4.49 mm versus 4.40 mm; F = 18.099, P < 0.001). No significant differences were observed in CCT between the three AL groups (F = 2.135, P = 0.120). Stepwise regression analysis highlighted AL, LT, and WTW as three independent factors associated with CACD in the normal AL group. In the short AL group and long AL group, LT and WTW were independent factors associated with CACD.

CONCLUSIONS

CACD increases as AL elongates and reaches a peak when AL exceeds 26 mm. Furthermore, CACD showed inverse correlation with LT and positive correlation with WTW. A relatively small WTW results in an anteriorly positioned lens, and thus, a decrease in CACD.

Comparison of Tono-Pen Avia and Handheld Applanation Tonometry in Primary Congenital Glaucoma

PRCIS

Tono-Pen AVIA (TPA) intraocular pressure (IOP) values are different from those taken with handheld Goldmann applanation tonometer (GAT) in primary congenital glaucoma (PCG). These differences indicate both tonometers cannot be used interchangeably for measuring IOP in PCG.

PURPOSE

The aim was to compare IOP measurements obtained using TPA and a handheld version of GAT in children with PCG.

MATERIALS AND METHODS

Forty-two eyes from 23 patients were evaluated for central corneal thickness (CCT), axial length, biomicroscopy and IOP measurement with TPA and a handheld GAT under inhalation anesthesia. After 1 eye from each patient was randomized, paired the Student t-test and the Pearson correlation were used for analysis. Generalized linear mixed model was used to estimate the difference between tonometers.

RESULTS

Mean age of children was 28.3±20.5 months. Mean axial length was 24.89±3.33 mm and mean CCT was 605.9±81.0 µm. Mean IOP was 22.1±9.6 for TPA and 14.0±4.5 mm Hg for GAT. There was a significant difference of 8.1±6.9 mm Hg between TPA IOP and GAT IOP (P<0.001). Each 6 months increase in age was associated with 1.32 mm Hg reduction in the difference between tonometers (P=0.002) and each 1 mm Hg higher of mean GAT IOP was associated with -0.73 mm Hg in the difference between TPA and GAT (P=0.002). Also, for every 20 µm increase in CCT an increase of 1.16 mm Hg in the difference between both devices was expected (P=0.003), after adjustment for potentially confounding variables.

CONCLUSION

There is a significant difference between TPA IOP and GAT IOP in PCG. The difference between TPA and GAT in PCG is influenced by CCT, age and GAT IOP value.

In vivo intraocular pressure monitoring during microincision vitrectomy with and without active control of infusion pressure

PURPOSE

To evaluate intraocular pressure (IOP) fluctuation during vitrectomy, we directly monitored IOP in vivo using 2 vitrectomy machines with or without constant infusion pressure monitoring and control.

METHODS

Among 61 eyes of 61 consecutive patients, 32 were assigned to the Accurus system (group 1) and 29 were assigned to the Constellation system (group 2) in this prospective case series. The IOP fluctuations were evaluated during routine vitrectomy procedures.

RESULTS

The initial IOP before vitrectomy was 20.3 ± 2.4 mm Hg in group 1 using a conventional vented gas forced infusion system and 20.0 ± 0.0 mm Hg in group 2 using active IOP control at 20 mm Hg (p = 0.532). However, the average IOP change during core vitrectomy was -8.6 ± 4.3 mm Hg in group 1 and -0.8 ± 1.1 in group 2 (p<00.001). Maximum IOP was significantly decreased in group 1 (-17.0 ± 2.6 mm Hg) compared with that in group 2 (-4.1 ± 2.2 mm Hg) (p<00.001). Partial ocular collapse was observed during vitrectomy only in group 1 (78.1%). Peak IOP significantly increased during scleral compression and gas and fluid injection but was not significantly different between the groups (all p≥0.147). The IOP fluctuation range was 50-70 mm Hg in both groups.

CONCLUSIONS

The IOP fluctuated significantly during routine vitrectomy using both systems. Hypotony and partial ocular collapse were more frequently observed during vitrectomy with the Accurus system than with the Constellation system. Both systems were vulnerable to IOP surge during indentation and intravitreal injection.

Prospective Comparative Analysis of 4 Different Intraocular Pressure Measurement Techniques and Their Effects on Pressure Readings

PURPOSE

To compare intraocular pressure (IOP) measurement using the Goldmann applanation tonometry (GAT) without fluorescein, with fluorescein strips, with fluorescein droplets, and IOP measurement with Tono-Pen Avia (TPA).

PATIENTS AND METHODS

This was a prospective comparative clinical analysis. It was performed in clinical practice. The study population consisted of 40 volunteer patients, 1 eye per patient. All patients who were 18 years and older having routine ophthalmological examination were eligible to participate. Active corneal abrasions and/or ulcers, previous glaucoma surgery, or prostheses interfering with GAT measurement were excluded. GAT IOP was measured first without fluorescein, then with fluorescein strip, then with fluorescein droplet, and finally with the TPA device. The main outcome measure was central corneal IOP.

RESULTS

Mean±SD IOP measurements for GAT without fluorescein, with fluorescein strip, with fluorescein droplet, and for TPA groups were 12.65±3.01, 14.70±2.82, 15.78±2.64, and 16.33±3.08 mm Hg, respectively. Repeated-measures analysis of variance corrected with the Greenhouse-Geisser estimate ([Latin Small Letter Open E]=0.732) showed that measuring technique had a significant effect on IOP measurements (F2.20,85.59=34.66, P<0.001). The pairwise post hoc testing showed statistically significant mean differences (P≤0.001) between all techniques except when GAT with fluorescein droplet was compared with TPA (P=0.222). The Bland-Altman analyses showed 95% limits of agreement maximum potential discrepancies in measurement ranging from 5.89 mm Hg in the GAT with fluorescein strip versus droplet compared with 11.83 mm Hg in the GAT with fluorescein strip versus TPA comparison.

CONCLUSIONS

IOP measurement technique significantly impacted the values obtained. The ophthalmologist should ensure consistent measurement technique to minimize variability when following patients.

Comparison of intra-ocular pressure changes with liquid or flat applanation interfaces in a femtosecond laser platform

Cataract surgery is the most common surgical procedure and femtosecond laser assisted cataract surgery (FLACS) has gained increased popularity. FLACS requires the application of a suction device to stabilize the laser head and focus the laser beam accurately. This may cause a significant escalation in intra-ocular pressure (IOP), which poses potential risks for patients undergoing cataract surgery. In this study we aimed to assess the effect of the Ziemer LDV Z8 femtosecond cataract machine on IOP. We demonstrated through a porcine model that IOP was significantly higher with a flat interface but could be abrogated by reducing surgical compression and vacuum. Pressure was lower with a liquid interface, and further altering angulation of the laser arm could reduce the IOP to 36 mmHg. A pilot series in patients showed comparable pressure rises with the porcine model (30 mmHg). These strategies may improve the safety profile in patients vulnerable to high pressure when employing FLACS with the Ziemer LDV Z8.

Utility of the Tono-Pen in Measuring Intraocular Pressure in Trinidad: A Cross-sectional Study

AIM

To determine the sensitivity and specificity of the Reichert™ Tono-Pen AVIA® when used by novice medical students in an ethnically diverse population in Trinidad.

SUBJECTS AND METHOD

Participants were residents of Trinidad between the ages of 20 and 90 years attending the Ophthalmology Clinic at the Eric Williams Medical Sciences Complex (EWMSC). Intraocular pressure (IOP) was measured using the Goldmann applanation tonometer (the gold standard) for ophthalmology clinic patients as part of their routine care. Intraocular pressure measurements were then taken using the Tono-Pen.

RESULTS

One hundred persons participated, consisting of Indo-Trinidadians (55%), Afro-Trinidadians (36%), Mixed (8%) and 1% of Caucasian descent. Fourteen per cent reported a diagnosis of glaucoma, with 70.6% of these being of African descent. One hundred and ninety-eight readings of IOP were taken. At a cut-off point of 21 mmHg, there were nine true positives, four false positives, seven false negatives and 178 true negatives. The sensitivity and specificity were found to be 56.3% (95% CI 33.2, 76.9) and 97.8% (95% CI 94.5, 99.1), respectively. The positive predictive value was calculated as 69.2% (95% CI 42.4, 87.3) while the negative predictive value was 96.2% (95% CI 92.4, 98.2). The prevalence of elevated IOP in this population was 8.1% (95% CI 4.8, 13.0). The likelihood ratio of a positive result was calculated to be 25.6 (95% CI 8.6, 73.9).

CONCLUSION

The high specificity and negative predictive value suggests that the Tono-Pen can be used with minimal training, and can prove beneficial at the primary care level in the exclusion of increased IOP in an ethnically diverse high-risk Caribbean population.

Intraocular pressure profiles during femtosecond laser-assisted cataract surgery

PURPOSE

To document the intraocular pressure (IOP) profiles during femtosecond laser-assisted cataract surgery.

SETTING

Refractive cataract surgery center.

DESIGN

Prospective case series.

METHODS

Intraocular pressure was measured using a handheld portable applanation tonometer (Tono-Pen Avia) during femtosecond laser-assisted cataract surgery using the Victus platform.

RESULTS

Forty-one eyes of 35 patients were recruited. The mean age of the patients was 70.5 years ± 8.2 (SD) (range 51 to 85 years). The mean IOP before, during, and after suction was 17.2 ± 3.2 mm Hg (range 10 to 23 mm Hg), 42.1 ± 10.8 mm Hg (range 20 to 55 mm Hg), and 13.8 ± 3.4 mm Hg (range 9 to 25 mm Hg), respectively. The mean difference between IOP before and during suction was 25.0 ± 11.3 mm Hg (range 5 to 43 mm Hg) (P<.01, Wilcoxon signed-rank test). The mean difference between IOP during and after suction was -28.7 ± 10.8 mm Hg (range -45 to -10 mm Hg) (P<.01, Wilcoxon signed-rank test). The mean suction duration was 216 ± 15 seconds (range 180 to 245 seconds).

CONCLUSIONS

The increase in IOP during the suction phase of femtosecond laser-assisted cataract surgery was statistically significant compared with the baseline IOP. Caution should be taken in patients with ocular conditions that are vulnerable to IOP fluctuation.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.