Correlation between corneal and scleral pneumatonometry: an alternative method for intraocular pressure measurement

Outcomes of Boston Keratoprosthesis Type I Implantation in Poland: A Retrospective Study on 118 Patients

Background: Boston Keratoprosthesis Type I (BI-KPro I) is a synthetic cornea that can be used to restore vision in patients with corneal blindness. This retrospective study evaluated the outcomes of BI-KPro implantation in 118 patients. Material: The mean age of the patients was 56.76 ± 14.24 years. Indications for keratoprosthesis implantation were as follows: graft failure, 47 (39.83%); ocular burn, 38 (32.20%); neurotrophic keratopathy, 11 (9.32%), mucous membrane pemphigoid 9 (7.67%); autoimmune, 6 (5.08%); Stevens-Johnson syndrome, 4 (3.39%); and aniridia (2.54%). Methods: The surgeries were performed between March 2019 and June 2022 at a single clinical center in two locations. The postoperative visual acuity, complications, and need for additional surgical procedures were analyzed. Results: The Best Corrected Visual Acuity before surgery was 0.01 ± 0.006. After one year (V1), it was 0.30 ± 0.27; at two years (V2), it was 0.27 ± 0.26; and at three years (V3), it was 0.21 ± 0.23. The percentage of patients with visual acuity better than 0.1 on the Snellen chart was 37.29% after 1 year, 49.35% after 2 years, and 46.81% after 3 years of follow up. The most common complications were glaucoma (78 patients; 66.1%), corneal melting (22 patients; 18.6%), and retroprosthetic membranes (20 patients; 17.0%). Conclusions: The BI-KPro can significantly improve visual acuity. The worst long-term results were obtained in the group of patients with autoimmune diseases; therefore, careful consideration should be given to implanting BI-KPro in this group. The high incidence of de novo glaucoma or the progression of pre-existing glaucoma suggests the need for careful monitoring.

Advancements in Wearable and Implantable Intraocular Pressure Biosensors for Ophthalmology: A Comprehensive Review

Glaucoma, marked by its intricate association with intraocular pressure (IOP), stands as a predominant cause of non-reversible vision loss. In this review, the physiological relevance of IOP is detailed, alongside its potential pathological consequences. The review further delves into innovative engineering solutions for IOP monitoring, highlighting the latest advancements in wearable and implantable sensors and their potential in enhancing glaucoma management. These technological innovations are interwoven with clinical practice, underscoring their real-world applications, patient-centered strategies, and the prospects for future development in IOP control. By synthesizing theoretical concepts, technological innovations, and practical clinical insights, this review contributes a cohesive and comprehensive perspective on the IOP biosensor's role in glaucoma, serving as a reference for ophthalmological researchers, clinicians, and professionals.

Assessment by Optical Coherence Tomography of Short-Term Changes in IOP-Related Structures Caused by Wearing Scleral Lenses

BACKGROUND

The mechanism that could increase intraocular pressure (IOP) during scleral lens (SL) wear is not fully understood, although it may be related to compression of the landing zone on structures involved in aqueous humor drainage.

METHODS

Thirty healthy subjects were fitted with two SLs of different sizes (L1 = 15.8 mm, L2 = 16.8 mm) for 2 h in the right eye and left eye as a control. Central corneal thickness (CCT), parameters of iridocorneal angle (ICA), Schlemm's canal (SC), and optic nerve head were measured before and after wearing both SLs. IOP was measured with a Perkins applanation tonometer before and after lens removal and with a transpalpebral tonometer before, during (0 h, 1 h, and 2 h), and after lens wear.

RESULTS

CCT increased after wearing L1 (8.10 ± 4.21 µm; p < 0.01) and L2 (9.17 ± 4.41 µm; p < 0.01). After L1 removal, the ICA parameters decreased significantly (p < 0.05). With L2 removal, nasal and temporal SC area and length were reduced (p < 0.05). An increased IOP with transpalpebral tonometry was observed at 2 h of wearing L1 (2.55 ± 2.04 mmHg; p < 0.01) and L2 (2.53 ± 2.22 mmHg; p < 0.01), as well as an increased IOP with Perkins applanation tonometry after wearing L1 (0.43 ± 1.07 mmHg; p = 0.02).

CONCLUSIONS

In the short term, SL resulted in a slight increase in IOP in addition to small changes in ICA and SC parameters, although it did not seem to be clinically relevant in healthy subjects.

Anatomical and physiological considerations in scleral lens wear: Intraocular pressure

Intraocular pressure (IOP) is maintained through complex and interrelated systems which control aqueous production and drainage, and it has been suggested that scleral lens (SL) wear may disrupt these vital homeostatic processes. This review provides an overview of anatomical and physiological processes that control IOP, identifies potential effects of SLs on these regulatory mechanisms, and examines studies that have attempted to quantify the effect of SLs on IOP. Lack of access to the cornea during SL wear makes accurate assessment of IOP challenging; therefore, a range of different assessment techniques and instruments have been employed to quantify IOP during and following SL wear. Some studies have evaluated IOP using standard techniques prior to lens application and following lens removal, or through a large central fenestration. Other studies have utilised instruments that facilitate assessment of IOP on the peripheral cornea or conjunctiva overlying the sclera (e.g. Schiotz, transpalpebral, and pneumatonometry). Two studies have recently evaluated changes in optic nerve structure during SL wear. Conflicting results have been reported on this topic, much of which examines changes in IOP in healthy subjects over limited periods of time. Currently, only a few studies have reported on long-term effects of SL wear on IOP in habitual SL wearers (after lens removal). Future research in this area must not only consider the fact that ocular conditions treated with SLs may potentially alter corneal biomechanical properties which can influence IOP, but also that these properties may be further altered by SL wear. Monitoring other risk factors for glaucoma (permanent alterations in optic nerve physiology, visual field defects) could provide a more comprehensive assessment of potentially increased risk of glaucomatous optic neuropathy due to SL wear. Ongoing clinical assessment of optic nerve structure and function is advisable in patients at risk for glaucoma who require SLs.

Comparison of Pneumatonometry and Transpalpebral Tonometry Measurements of Intraocular Pressure during Scleral Lens Wear

SIGNIFICANCE

As scleral lens wear becomes more common, understanding the impact of these lenses upon ocular physiology is critically important. Studies on the effect of scleral lens wear upon intraocular pressure (IOP) have used different instruments and have reported conflicting results.

PURPOSE

The purpose of this study was to compare assessment of IOP during scleral lens wear using pneumatonometry and transpalpebral tonometry.

METHODS

Twenty healthy subjects wore a small-diameter (15.2 mm) and a large-diameter (18.0 mm) scleral lens on the right eye, each for 1 hour in randomized order. IOP was assessed with pneumatonometry and transpalpebral tonometry on both eyes before lens application, immediately after lens application, after 1 hour of lens wear, and immediately after lens removal. Paired t test compared mean IOP in the study eye to the control eye. Repeated-measures ANOVA was performed to take instrumentation, lens diameter, and their interaction into account in an analysis of the change in IOP in the study eye.

RESULTS

Mean peripheral IOP measured with pneumatonometry was not significantly different from baseline at any subsequent measurement. Measurements with transpalpebral tonometry, however, were significantly different during scleral lens wear immediately after application and after 1 hour of wear with both diameter lenses (P < .005), but were not significantly different after either sized lens was removed. Repeated-measures ANOVA revealed that the instrument used to measure IOP was a significant factor in IOP changes found during lens wear (P ≤ .001).

CONCLUSIONS

Assessment of IOP during scleral lens wear varies based upon the instrument that is used. Although further studies are clearly needed to further elucidate this issue, clinicians should continue to monitor optic nerve structure and function in scleral lens wearers, as they do in all patients.

[Intraocular pressure with miniscleral contact lenses]

According to literature data, some experts do not exclude the possibility that scleral lens wear could influence intraocular pressure.

PURPOSE

To evaluate the influence of rigid gas permeable miniscleral contact lenses on intraocular pressure (IOP), keratometry readings and corneal thickness, and to study the correlation between scleral (IOPs) and corneal (IOPc) intraocular pressure using the Icare ic100 tonometer (model TAO11, Icare Finland Oy).

MATERIAL AND METHODS

The study included 99 volunteers without history of ocular diseases. The first group consisted of 66 participants (122 eyes) aged 22.3±2.2 years - IOPc and IOPs were measured by the Icare ic100 tonometer in order to determine the correlation. The second group (33 participants, aged 22.7±1.7 years) - day 1, diurnal IOPc and IOPs fluctuations were measured; on day 2, a miniscleral lens (diameter 14.9 mm) was placed on the study eye and was worn for 6 hours, the paired eye served as control. IOP was measured before, after lens placement, after 2 hours of lens wear, and before and after lens removal. Corneal topography was evaluated before and after lens removal.

RESULTS

In the first group, there was a weak but significant correlation between IOPc and IOPs (Spearman correlation coefficient 0.285, p=0.001). In the second group, IOPc in the study eye before lens placement (14.8±3.8 mm Hg) and IOPc after its removal (13.6±3.9 mm Hg) were not different from those in the control eye. There were also no statistically significant changes in IOPs before, during lens wear, and after lens removal. The central corneal thickness increased by 2.9% (p<0.001) after 6 hours of lens wear.

CONCLUSION

In young individuals without history of ocular diseases, wearing the miniscleral lens for 6 hours does not have significant influence on IOP and does not cause clinically significant corneal edema.

Estimation of Goldmann applanation tonometer intraocular pressure (IOP) from scleral Schiotz IOP values in eyes with type-1 keratoprostheses

PURPOSE

To validate estimation of Goldmann applanation tonometer (GAT) intraocular pressure (IOP) from scleral Schiotz IOP measurements using a regression model in normal eyes and eyes with type-1 keratoprostheses.

METHODS

In this prospective cross-sectional study, cohort-1 had 253 normal anterior segment eyes, and cohort-2 had 100 eyes with type-1 keratoprostheses. Scleral Schiotz IOP measurements were used (in a non-linear model) to predict GAT IOP values for these eyes. Accuracy of predicted GAT IOP values was assessed using actual GAT IOP values for normal eyes, while for type-1 keratoprosthetic eyes, finger tension (FT) IOP assessments by an experienced glaucoma specialist were used. Primary outcome was agreement between FT IOP (assessed by an experienced glaucoma specialist) and predicted GAT IOP-derived clusters.

RESULTS

The actual values of GAT IOP measurements in normal eyes (n=253; mean age ±SD, 51.35±15.56 years) ranged between 6 mm Hg and 62 mm Hg (mean=22±10.05 mm Hg). Estimated and actual GAT IOP values for normal eyes were very similar (mean difference=0.05 mm Hg with limits of agreement: -5.39 to 5.5 by Bland-Altman plot). Of the 100 eyes with type-1 keratoprostheses, 68 were classified as having digitally normal IOP, 28 as borderline and 4 as high. The agreement between classification by FT assessment and model-predicted GAT IOP values was substantial (Kappa=0.81, 95% CI 0.69 to 0.93). The accuracy of the model in assessing IOP was found to be 91% (95% CI 0.84 to 0.96).

CONCLUSION

Scleral Schiotz IOP values along with our predictive model can be an alternative objective method to FT IOP in assessing IOP in eyes with type-1 keratoprostheses.

COMPARISON OF VISUAL AND ANATOMICAL OUTCOMES OF EYES UNDERGOING TYPE I BOSTON KERATOPROSTHESIS WITH COMBINATION PARS PLANA VITRECTOMY WITH EYES WITHOUT COMBINATION VITRECTOMY

PURPOSE

To determine whether 1-year visual and anatomical results after surgery combining pars plana vitrectomy, Boston keratoprosthesis, and a glaucoma drainage device as needed are similar, better, or worse than Boston keratoprosthesis initial implantation alone.

METHODS

We performed a retrospective review of adult patients undergoing Boston keratoprosthesis at our institution. Visual acuity outcomes, anatomical results, and complication rates of patients undergoing combination surgery (including pars plana vitrectomy and a posterior glaucoma drainage device) were compared with those undergoing keratoprosthesis placement alone.

RESULTS

There were 70 eyes in the keratoprosthesis alone group and 55 eyes in the keratoprosthesis with pars plana vitrectomy group. Mean follow-up durations were 54.67 months in the keratoprosthesis alone group and 48.41 months in the combination group. Baseline mean Snellen equivalent visual acuities were worse for the combination group compared with the keratoprosthesis alone group (P = 0.027). Visual acuities improved postoperatively by 1 month after keratoprosthesis implantation for both groups and improved three or more lines of Snellen acuity in the majority of eyes for both groups (≥72% by 12 months). Eyes undergoing pars plana vitrectomy had lower rates of de novo (P = 0.015) and significantly lower rates of secondary procedures (P = 0.002) at 1 year. One year complications rates for retroprosthetic membrane formation, retinal detachment, hypotony, cystoid macular edema, epiretinal membrane formation, endophthalmitis, and corneal melting were similar for both groups.

CONCLUSION

Compared with keratoprosthesis alone, combining keratoprosthesis with pars plana vitrectomy and a glaucoma drainage device as needed, resulted in lower rates of de novo glaucoma, lower rates of additional surgical procedures, similar visual acuity outcomes at 1 year, and did not result in higher complication rates.

Assessment of Glaucomatous Damage After Boston Keratoprosthesis Implantation Based on Digital Planimetric Quantification of Visual Fields and Optic Nerve Head Imaging

PURPOSE

To investigate glaucomatous damage in Boston keratoprosthesis type I (KPro) patients through structural analysis of the optic nerve head and digital planimetric quantification of Goldmann visual fields, a novel method of monitoring perimetric changes in KPro patients.

METHODS

Records of patients undergoing KPro implantation from 2007 to 2015 at a single institution were reviewed. Parameters related to glaucoma status and KPro outcomes were analyzed.

RESULTS

Twenty-two eyes from 21 patients met inclusion criteria, with mean follow-up of 49.4 months (range 15-90). Mean results for the following parameters before KPro implantation and at last follow-up were (pre-KPro; at last follow-up): best-corrected visual acuity (2.07; 0.70 logMAR), number of glaucoma medications (1.14; 1.05), intraocular pressure (IOP) (18.4; 18.4 mm Hg), vertical cup-to-disc ratio (C/D) (0.48; 0.50), and horizontal C/D (0.52; 0.52). IOP-lowering procedures were performed pre-KPro (5/22), concurrently with KPro (10/22), post-KPro (6/22), or never (6/22). An increase in C/D ≥0.1 and loss of V4e isopter area >30% occurred in 22.7% and 12.5%, respectively. Development of post-KPro glaucoma, progression of preexisting or post-KPro glaucoma, and no glaucoma development as evidenced by an objective assessment of structural and functional parameters were seen in 2/22 (9.1%), 7/22 (31.8%), and 6/22 (27.3%) eyes, respectively.

CONCLUSIONS

Clinicians should strive to vigilantly monitor for glaucoma despite the inherent difficulties in tonometry, optic nerve visualization and imaging, and visual field testing in KPro patients. Meticulous glaucoma surveillance with structural and functional testing combined with earlier IOP-lowering surgical intervention may result in decreased rates of glaucomatous vision loss in KPro patients.

Limbal rebound tonometry: clinical comparisons and applications

PURPOSE

The accuracy of contact tonometry may be compromised in cases with disorders affecting central corneal bio-mechanical properties. This study examined the reliability of rebound tonometry (RT) on the area of corneo-scleral limbus, instead of the conventional central corneal area, and the correlation of findings with ocular biometric parameters.

METHODS

This is a prospective cross-sectional study performed at the Department of Ophthalmology of the University Hospital of Heraklion, in Crete, Greece. Consecutive cataract surgery candidates without concomitant ocular pathology, apart from cataract, were included. RT was performed on the central cornea (central RT, CRT) as well as on the limbus and scleral spur area (limbal RT, LRT). Findings were correlated with Goldmann applanation tonometry (GAT) as well as axial length (AL), central corneal thickness (CCT), and corneal curvature (CC) measurements.

RESULTS

LRT readings were significantly correlated with central CRT as well as with GAT readings, whereas respective correlations with other parameters examined were not statistically significant.

CONCLUSIONS

LRT may be used as an alternative tool in clinical practice to determine intraocular pressure when conventional devices and techniques might be inadequate or unreliable.

Intraocular Pressure After 2 Hours of Small-Diameter Scleral Lens Wear

OBJECTIVES

Compression of episcleral veins or deformation of tissue in the Schlemm's canal beneath the landing zone of scleral lenses could elevate intraocular pressure (IOP). We examined the effect of 2 hr of small-diameter scleral lens wear on IOP.

METHODS

Twenty-nine participants, 29 ± 6 years old (mean ± SD) who experienced no history of eye disease or scleral lens wear, were included in the study. Each participant was fitted with a 15-mm Jupiter scleral lens on one eye (study eye). Intraocular pressure was measured in both eyes by pneumatonometry centrally on the cornea and peripherally on the sclera. The lens was then placed on one eye and was worn for 2 hr. Intraocular pressure was remeasured immediately after lens placement, at 1 and 2 hr of lens wear, and immediately after lens removal. Intraocular pressure after removal of the scleral lens was compared with IOP before placing the lens and to IOP in the control eye using paired t tests.

RESULTS

Immediately after removing the scleral lens, mean central IOP in the study eye (13.9 ± 3.1 mm Hg) was not different from mean central IOP in the control eye (13.5 ± 2.2 mm Hg, P = 0.4) or in the same eye before lens wear (13.6 ± 1.9 mm Hg, P = 0.6). There were also no differences in IOP measured peripherally at 2 hr of lens wear (P = 0.8).

CONCLUSIONS

Neophyte scleral lens wear of a 15-mm scleral lens for 2 hr does not increase IOP in healthy eyes.

Innovative approaches to glaucoma management of Boston keratoprosthesis type 1

Glaucoma remains a prevalent disorder and visual limiting factor after Boston keratoprosthesis type 1 implantation. Patients with glaucoma have worse initial and late visual acuity outcomes after otherwise successful keratoprosthesis implantation. Management of glaucoma in the setting of a keratoprosthesis is challenging because of relatively rapid progression and an inability to accurately measure intraocular pressure (IOP). In addition, there are no standard guidelines for glaucoma surveillance and monitoring after keratoprosthesis surgery. This report provides a review of the current literature and offers innovative strategies that will overcome the challenges in managing glaucoma in the setting of a Boston keratoprosthesis type 1 implant. The topics that will be discussed in this section include alternative methods for IOP measurement, rationales and surgical techniques for a pars plana tube placement for glaucoma drainage device, effective medical and laser treatment, the risk for IOP elevations after YAG laser, and practical guides to glaucoma surveillance and monitoring.

Correlation of Serial Scleral and Corneal Pneumatonometry

PURPOSE

To evaluate the usefulness of scleral pneumatonometry as an alternative for corneal measurements of intraocular pressure (IOP) over a broad range of IOPs.

DESIGN

Prospective, observational cohort study.

PARTICIPANTS

The study was conducted in the University of California, San Francisco, Retina Clinic between August and November 2013 in 33 adult patients (age range, 34-94 years; mean ± standard deviation, 74.1±13.4 years) receiving anti-vascular endothelial growth factor intravitreal injections, which transiently increase IOP.

METHODS

Corneal pachymetry and serial corneal and temporal scleral pneumatonometry (baseline, immediately after, and 10, 20, and 30 minutes after injection) were collected. One-time baseline corneal and scleral pneumatonometry readings were obtained in the noninjected eye.

MAIN OUTCOME MEASURES

Correlation analysis and a Bland-Altman plot were used to evaluate reliability and agreement between scleral and corneal measurements of IOP. A linear mixed model was used to determine the relationship between measurements and to perform covariate analyses.

RESULTS

Scleral and corneal pneumatonometry showed nearly 1:1 linear correlation, although scleral pneumatonometry was biased toward higher values (r = 0.94; P < 0.001). Scleral pneumatonometry averaged 9.0 mmHg higher than corneal pneumatonometry (95% limits of agreement, -1.5 to 19.5 mmHg). A linear mixed model resulted in the following equation: corneal IOP = 1.04 × scleral IOP - 10.37. Age, central corneal thickness, laterality, and glaucoma and lens status did not impact this relationship. The difference between corneal and scleral pneumotonometry was correlated between the two eyes of individual patients (r = 0.75; P < 0.001).

CONCLUSIONS

Differences between serial scleral measurements reflect differences between serial corneal measurements. Scleral pneumatonometry should be considered as an alternative to corneal pneumatonometry for following patients in whom corneal measurements are unreliable or unobtainable.