Schiotz Tonometry Accurately Measures Intraocular Pressure in Boston Type 1 Keratoprosthesis Eyes

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.

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.

Reliability of Several Glaucoma Tests in Patients With Boston Type 1 Keratoprosthesis

PURPOSE

Managing glaucoma after Boston type 1 keratoprosthesis (KPro) surgery remains challenging. We herein assessed the fitness of commonly used clinical tests to evaluate glaucoma in KPro eyes versus eyes with penetrating keratoplasty (PK) as controls.

METHODS

Sixteen patients with KPro and 14 patients with PK tested in an identical manner. After the 10-2 visual field with size V stimulus, intraocular pressure (IOP) was estimated with palpation by the first observer. Then, retinal nerve fiber layer (RNFL) thickness analysis was performed twice using optical coherence tomography by an ophthalmic photographer, before and after a short break. After the second observer estimated the IOP, the visual field was repeated. Finally, color photographs of the optic disk were captured by an ophthalmic photographer. The cup-to-disk ratio was assessed by 2 masked observers, at 2 different time points, in a random manner. Agreements between and within observers and reliability of repeated measurements were evaluated using the intraclass correlation coefficient (ICC) and Bland-Altman plots.

RESULTS

Inter-rater agreement of palpation IOP estimate was moderate for eyes with KPro (ICC = 0.47) and fair for eyes with PK (ICC = 0.27). Visual field and RNFL thickness showed high test-retest reliability in both KPro and PK eyes (ICC > 0.80 for both). Inter-rater agreement of cup-to-disk ratio assessments was substantial in eyes with both KPro (ICC = 0.62) and PK (ICC = 0.70).

CONCLUSIONS

The 10-2 visual field and RNFL thickness seem sufficiently repeatable and might allow the detection of glaucoma progression in KPro eyes. Such testing is important, given limited inter-rater agreement regarding the palpation IOP estimate.

Challenges of Glaucoma Management in Patients with Type I Boston Keratoprosthesis

Type I Boston keratoprosthesis is implanted in patients with severely diseased eyes who are considered poor candidates for traditional keratoplasty. Glaucoma is considered a major visual comorbidity following the implantation of type I Boston keratoprosthesis (KPro). Eyes that receive a Boston KPro are at high risk of progression of pre-existing glaucoma and the development of de novo glaucoma. Both complications can limit best-corrected visual acuity postoperatively. Diagnosis and surveillance for glaucoma in KPro eyes are fundamental to mitigate the risk of visual morbidity. However, managing these patients presents several challenges. The diagnosis of glaucoma after KPro implantation is usually hindered by inaccurate intraocular pressure (IOP) measurements and unreliable ophthalmic investigations such as visual field testing and optical coherence tomography (OCT) of the retinal nerve fiber layer (RNFL). In these eyes, medical management of glaucoma with topical medications is usually insufficient, and glaucoma surgery is usually warranted either prior to or during KPro implantation. Options for glaucoma surgery include glaucoma drainage device (GDD) and cyclodestructive procedures. The aim of this article is to highlight the incidence, pathophysiology, diagnosis, and management options of glaucoma in eyes that have undergone type I Boston keratoprosthesis.

Effects of Medetomidine, Dexmedetomidine and their combination with Acepromazine on the intraocular pressure (IOP), tear secretion and pupil diameter in dogs

Background

A great number of sedatives and anaesthetics have been used to perform surgeries or routine ophthalmologic examinations in animals and sometimes the combination of these medicines has more suitable effects than each one alone.

Objectives

This paper aims to explore the main effects of Medetomidine + Acepromazine, Dexmedetomidine + Acepromazine on intraocular pressure, tear secretion and pupil diameter.

Methods

To accomplish the aforementioned aim, 32 adult dogs (aged one‐to‐three‐years‐old) were clinically examined. Dogs were divided into four groups consisting of group DA, Dexmedetomidine (5 µg/kg) + Acepromazine (0.05 mg/kg); Group D, Dexmedetomidine (5 µg/kg); Group M, Medetomidine (10 µg/kg); Group MA, Medetomidine (10 µg/kg) + Acepromazine (0.05 mg/kg). The ocular factors including tear production, pupil diameter and intraocular pressure of both right and left eyes were first measured and then recorded in each dog at time T₀ (−15 min). Afterwards, the drugs were administered intramuscularly, based on which the ocular factors were re‐measured at T₁ (+5 min), T₂ (+15 min) and T₃ (+20 min). All four groups showed a reduction in intraocular pressure, which was significant in DA, D and M groups.

Results

Furthermore, there was a fluctuation in the amount of tear secretion in DA and D groups (increase and then decrease), as well as a significant reduction in M and MA groups. Decreasing in pupil diameter also occurred in all four groups, but the reduction was significant only in DA and MA groups.

Conclusion

According to the results obtained, as the changes caused by the systemic administration of the above drug compounds did not exceed the physiological range, it can be concluded that these combinations could be utilized as suitable sedatives or pre‐anaesthetic compounds in the eye surgeries.

Boston Type 1 Keratoprosthesis: Updated Perspectives

The use of Boston type 1 keratoprosthesis (BKPro) has significantly increased worldwide. It is no longer considered a procedure of last resort but a reasonable option for patients with otherwise poor prognosis for a traditional penetrating keratoplasty. BKPro was approved by the Food and Drug Administration in 1992 for bilateral severe corneal blindness due to multiple corneal transplant failure. Over the years, indications have extended beyond recurrent immunologic rejection to include other conditions such as chemical injury and other causes of bilateral limbal stem cell deficiency, extensive corneal neovascularization, neurotrophic corneas and hypotony, among others. Numerous advances in the design of the BKPro, improvement of preoperative, intraoperative and postoperative management have resulted in favorable outcomes and a reduction in postoperative complications. Accordingly, many studies have shown that implantation of this device is highly effective in restoring vision with very good short-term outcomes. However, due to the lifetime risk of sight-threatening complications after BKPro implantation, a longer follow-up period should provide outcomes that are more realistic. In this review, the authors examined only the results of publications with an average of at least 2 years of follow-up. The overall intermediate to long-term visual outcomes and retention rate in BKPro seem to be favorable. However, autoimmune diseases and cicatrizing conditions continue to show a higher incidence of postoperative complications that require further management.

Comparison of Intraocular Pressure Measurement with Schiotz Tonometer and Tono-Pen Vet Tonometer in Healthy Dogs

Introduction

Measurement of intraocular pressure (IOP) in dogs has high diagnostic value because of the possibility of detecting ocular and systemic diseases. Various types of tonometers are available for this measurement in small animal practice. The aim of the study was to compare the IOP values measured with Schiotz and Tono-Pen Vet tonometers in healthy dogs. Clinical diagnostic usefulness of both models was also evaluated.

Material and Methods

The examination was performed in 62 eyes in 31 clinically healthy dogs of different races, gender, and ages.

Results

The values for intraocular pressure obtained with Schiotz tonometer were in the range of 12 to 24 mmHg, with the mean of 16.3 ± 2.1 mmHg. The intraocular pressure measured with Tono-Pen Vet tonometer was in the range of 11–25 mmHg, with a mean of 18.1 ± 3.8 mmHg. The mean results of measurements taken using the two tonometers differed statistically significantly, the difference being 1.79 mmHg and the higher values being read from the Tono-Pen Vet tonometer.

Conclusion

Correlation coefficients calculated for the results obtained in the right and left eyes using two tonometers indicated highly correlative relationships between the results. The study shows that both tonometers can be advantageously used in clinical practice to measure intraocular pressure in dogs.

INTRAOPERATIVE OCULAR MANOMETRY IN SILICONE OIL-FILLED EYES WITH A BOSTON TYPE 1 KERATOPROSTHESIS

PURPOSE

To demonstrate a novel technique to measure the intraocular pressure in silicone oil (SO)-filled eyes with Boston Type 1 keratoprosthesis (KPro) during intraocular surgery.

METHODS

In this retrospective case series, an ocular manometer that is predicated on a continuous fluid column between a pressure sensor and interior of the eye was designed and used to directly measure intraocular pressure during intraocular surgery in SO-filled eyes with KPro.

RESULTS

Six eyes of six patients were included in the study. The indications for SO injection with ocular manometry were hypotony in five patients, and endophthalmitis and complex retinal detachment with proliferative vitreoretinopathy in one patient. All patients had a successful reinflation of their globes without any evidence of SO underfill, without evidence of SO overfill, and without progression of glaucomatous optic neuropathy. Visual acuity increased in five eyes and was maintained in one eye.

CONCLUSION

Intraoperative ocular manometry is a safe and effective technique in determining intraocular pressure in SO-filled eyes with KPro.

Repeatability, reproducibility and agreement of intraocular pressure measurement in rabbits by the TonoVet and Tono-Pen

Tono-Pen and TonoVet have been used in rabbits to measure intraocular pressure (IOP) and investigate the effect of IOP lowering therapies. Therefore, their reliability and accuracy are very important and deserve careful evaluation. Our results showed that the with-subject deviation (S_w) and intraclass correlation coefficient (ICC) of the TonoVet and Tono-Pen were 0.61 mmHg/0.83 mmHg and 0.97/0.94, respectively for intrasession repeatability. For intersession reproducibility, the Sw and ICC of TonoVet and Tono-Pen were 1.42 mmHg/1.66 mmHg and 0.73/0.67, respectively. For interoperator reproducibility, the S_w and ICC of the TonoVet and Tono-Pen were 0.72 mmHg/1.11 mmHg and 0.91/0.82 respectively. Both TonoVet and Tono-Pen underestimated the IOP measured by manometry. The regression function was: y = 0.8249x + 0.1011 and y =0.6881x + 2.2290 for TonoVet and Tono-Pen, respectively. Our study suggests that both TonoVet and Tono-Pen had excellent intrasession repeatability and inter-operator reproducibility, but good intersession reproducibility. Both TonoVet and Tono-Pen correlated well with manometry, but underestimated the manometric IOP with presence of fixed and proportional biases. These factors should be considered when measuring IOP with Tono-Pen or TonoVet in rabbit eyes.