Schiotz Scleral Intraocular Pressure Readings Predict Goldmann Applanation Readings Better Than Rebound Tonometry

Variation of Bruch's membrane opening in response to intraocular pressure change during scleral lens wear, in a population with keratoconus

PURPOSE

The present study aimed to determine the potential impact of scleral lenses on intraocular pressure (IOP) by analysing the Bruch's membrane opening-minimum rim width (BMO-MRW) while the lenses are worn, in a population with keratoconus.

METHODS

Participants were required to have keratoconus and be successfully fitted with scleral lenses for at least 3 months. A new pair of optimised scleral lenses was provided before the study. During the first session, corneal biomechanics was assessed using an air tonometer, coupling Scheimpflug technology. Then, a scan of the optic nerve was carried out using optical coherence tomography (OCT) at 2 h intervals for 6 h. Particular attention was paid to identifying the BMO-MRW, which represents the smallest distance between the BMO and the internal limiting membrane. These tests were repeated, respecting the time at which the initial measurements were taken, while the scleral lens was worn. Results from only one eye were analysed.

RESULTS

A statistically significant change of 10.5 ± 3.6 μm (95% CI [241.3-473.1]; p = 0.02) in BMO-MRW was observed after 6 h of scleral lens wear, compared to measurements without lenses (4.8 ± 3.4 μm; 95% CI [285.1-439.7]; p = 0.18). The fluctuation was greater in participants with keratoconus than found in a previous study of regular corneas.

CONCLUSION

BMO-MRW became significantly thinner after 6 h of scleral lens wear compared with measurements without lenses. These variations may be associated with a rise in IOP during lens wear. Close monitoring for optic head changes should be carried out for patients at risk. These results should be compared with future longer-term studies including a larger cohort of patients.

Intermediate-Term Outcomes and Complications of Ahmed Glaucoma Valve in Type 1 Keratoprostheses

PURPOSE

To evaluate intermediate-term outcomes and complications associated with Ahmed glaucoma valve (AGV) implantation in eyes with type 1 keratoprosthesis (KPro).

METHODS

We retrospectively reviewed records of 43 eyes of 43 Indian patients with type 1 KPro and AGV from 2009 to 2021 with a minimum of 6-months of follow-up. Five eyes that had AGV before KPro were excluded, leaving 38 eyes for analysis. Primary outcome measure was postoperative complications. Secondary outcome measure was stability of glaucoma, assessed by Humphrey visual fields, intraocular pressure, and best-corrected visual acuity (BCVA). Sight-threatening complications, implant removal, or repeat glaucoma surgery was considered failure.

RESULTS

Median age (interquartile range) at AGV implantation was 36.5 (23-49) years, with median post-AGV follow-up of 30.5 (6.5-53) months. Preoperative logarithm of minimal angle of resolution median BCVA was 0.6 (0.4-1). Post-AGV, median intraocular pressure as measured by scleral Schiotz reduced significantly from 30.4 (20.6-30.4) to 13.5(12.2-14.8) mm Hg (P < 0.0001), and the mean number of antiglaucoma medications significantly decreased from 3.4 to 1.7 (P < 0.0001). Mean BCVA (P = 0.24) remained stable. Humphrey visual fields mean deviation progressed from -13.5 dB (-25, -9) to -26 dB (-30, -13) at final follow-up (P = 0.05) and progression occurred in 10 eyes. Seven eyes (18.4%) had postoperative complications needing surgical intervention, including tube block [5 eyes (13.1%)] and tube exposure [2 eyes (5%)]. One failed AGV needed additional glaucoma surgery after 8 years. None had implant extrusion/explanation or endophthalmitis.

CONCLUSIONS

Ahmed glaucoma valve implantation offered promising results in managing glaucoma in eyes with type 1 KPro, particularly in relatively young Indian population. However, close monitoring for tube-related complications and glaucoma progression is warranted.

Agreement of intraocular pressure measurement by scleral Schiotz and Goldmann applanation tonometer

Aim & background : Intraocular pressure (IOP) measured through the sclera has some advantages over IOP measured through cornea. This study aimed to determine the agreement between IOP as estimated by scleral Schiotz (SS) tonometer and Goldmann applanation tonometer (GAT).

METHODS

In this cross-sectional observational study, IOP was measured by GAT on the cornea and Schiotz tonometer on the temporal sclera. Axial length and central corneal thickness (CCT) were noted. IOP was then estimated from SS IOP as eGAT using a predictive formula. Agreement of IOP corrected for CCT (cGAT) with eGAT and SS IOP were assessed. The effects of age, axial length, refraction, CCT, gender, and ocular and systemic comorbidity on measured IOP were also assessed.

RESULTS

The study included 155 patients with a mean age of 54.27 ± 10.02 years. Mean IOP measured by GAT and scleral Schiotz were 16.58 ± 2.76 mm Hg and 16.10 ± 2.96 mm Hg, respectively. The mean IOP by cGAT and eGAT were 16.70 ± 2.80 mm Hg and 17.07 ± 3.10 mm Hg, respectively. Both eGAT & SS IOP had good agreement with cGAT on the Bland-Altmann plot (p = 0.96 & 0.51, respectively). Further, SS IOP showed good agreement even with GAT IOP (p = 0.78). Age, axial length, refraction, central corneal thickness, gender, and ocular and systemic comorbidity did not show significant correlation with IOP measurement.

CONCLUSION

Estimated GAT IOP showed good agreement with measured GAT values. SS IOP also agreed well with GAT IOP. Clinical significance IOP measurement on the sclera using Schiotz can be used as an alternative to GAT.

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.

[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.