Owner Obtained Intraocular Pressure Measurements in Canine Primary Angle Closure Glaucoma: A Pilot Study in 14 Dogs

ABSTRACT

Purpose

To explore the clinical value of intraocular pressure (IOP) measurements obtained by owners in dogs predisposed to primary angle closure glaucoma (PACG).

Materials and Methods

Owners of 14 dogs with eyes predisposed to developing PACG obtained IOP measurements with a TonoVet Plus from the time of diagnosis of PACG until they developed clinical PACG or were lost to follow up.

Results

Owners measured IOP values in 14 dogs. In nine dogs, IOP was measured until they developed overt glaucoma with marked IOP elevations. Four dogs were lost to follow‐up, and IOP continues to be monitored in one dog. In seven of the nine dogs that developed overt glaucoma, onset of glaucoma was associated with a sudden rise in IOP > 50 mmHg that was not preceded by an obvious gradual rise in average IOP readings or prior smaller rises in IOP. Dogs that were treated with latanoprost following the onset of overt glaucoma continued to have sporadic rises in IOP.

Conclusion

Owner obtained, at home IOP measurements can provide information that may be useful in the management of canine PACG.

1. Introduction

Canine primary angle closure glaucoma (PACG) is a neurodegenerative disease of the retina and optic nerve associated with elevations in intraocular pressure (IOP) [1]. These elevations in IOP result in damage to the retina through alterations in perfusion and deformation of the lamina cribrosa [1]. The pathogenesis of the IOP rises has not been fully elucidated, but they can be sudden and severe [2]. Moreover, though these rises in IOP lead to retinal damage, they initially don't result in dramatic clinical signs that owners would interpret as requiring immediate attention [2]. This results in many eyes losing vision before care is sought. This is particularly true of the first eye affected by PACG. Owners simply don't realize the urgency of the clinical signs they see [1]. Even though they are primed and alert to notice clinical signs in the second eye, the rises in IOP can be sudden and severe enough to lead to blindness anyway.

Tonometry is readily available in veterinary practices and is the cornerstone of glaucoma management used by ophthalmologists. However, tonometry can only be reasonably performed by veterinarians infrequently and during office hours. It is not practical for an owner to bring their dog to a veterinary hospital for tonometry daily or even weekly. Moreover, the likelihood of capturing an elevated IOP at one of these sporadic visits is low [3]. Increasing the frequency of tonometry substantially increases the likelihood of detecting an abnormal IOP [3].

If owners could reliably and safely measure intraocular pressure at home, they could substantially increase the likelihood of detecting these pressure rises. Early detection of elevated IOP could lead to early treatment and prevention of permanent retinal damage and vision loss. Thus, this study aimed at exploring the data obtained by owners measuring IOP with a rebound tonometer in dogs with a confirmed diagnosis of PACG to determine whether the data obtained might be useful in the clinical management of PACG.

2. Materials and Methods

This was an exploratory pilot study to evaluate the clinical value of IOP data obtained by owners of dogs with eyes predisposed to PACG. Owners of dogs participating in a separate study involving serial imaging (goniophotography, high‐resolution ultrasound of the ciliary cleft, optical coherence tomography of the optic nerve head, and quantitative pupillometry) of eyes predisposed to PACG were offered the option of taking a rebound tonometer (TonoVet Plus) home and measuring IOP. They were asked to measure IOP twice daily if possible (around the time they were administering ophthalmic medications) and record the readings including the date and time at which the recording took place. All dogs included in the study had PACG confirmed by the presence of elevated IOP in the first eye (> 35 mmHg), presence of characteristic pectinate ligament changes in the fellow eye, characteristic ciliary cleft morphology on high resolution ultrasound in the fellow eye, and the absence of any disease process known to cause secondary glaucoma in either eye. Goniophotographs (RetCam II, Clarity Medical Systems) of the eye predisposed to developing PACG obtained at the time at which the owners started measuring IOP were graded using the modified ZibWest system as previously described [4]. Histologic examination of enucleated eyes consistent with primary glaucoma supported the clinical diagnosis in cases 2,3,6,8,10,11, and 12. Histologic examination was not available for the remaining cases because either the eye was enucleated at a referring veterinarian's practice and histologic examination was not pursued, an evisceration with intrascleral prosthesis was performed, or no eyes were enucleated.

All owners were taught how to use the tonometer by the same board‐certified veterinary ophthalmologist. The instruction consisted of a one‐on‐one in person overview of how the tonometer estimates IOP, factors that could result in spuriously high results, and a demonstration of how to use the tonometer on their dog and how to appropriately restrain their dog during IOP measurement. Factors such as neck pressure, eyelid pressure, and changes in head position were discussed. Following a demonstration by the board‐certified ophthalmologist and an opportunity to ask any clarifying questions, the owners were asked to demonstrate use of the instrument. They were first asked to practice using the instrument on the tip of their index finger, and once they were able to obtain a reading they then practiced on their own dog's eye. The ophthalmologist corrected any mistakes in technique and offered additional instruction until owners could consistently obtain intraocular pressures that were within 2 mmHg of that obtained by the ophthalmologist. All tonometers were set to the dog setting and owners were instructed to not change this setting. Owners were instructed to call if IOP readings were greater than 35 mmHg or if they noted any changes in vision or the appearance of the eye. When any of these were encountered, the owners were instructed to bring their dog in for a complete ophthalmic exam. Treatment recommendations were then made based on the findings of this exam and considering the owner obtained IOP readings. All eyes predisposed to PACG were treated with twice daily combination therapy of topical ophthalmic dorzolamide 2%/timolol 0.5%. All dogs underwent the ocular imaging modalities listed above as well as a complete ophthalmic examination approximately every 3 months by a board‐certified veterinary ophthalmologist. During each of these exams, the owner obtained IOP readings were evaluated by the ophthalmologist and incorporated into any treatment recommendations. The recommendations varied based on the owners' treatment goals and financial constraints. But in general, if IOP values greater than 35 mmHg were repeatedly obtained by owners, and/or historical and clinical signs associated with elevated pressure were reported or noted during an office visit, or IOP greater than 25 mmHg was recorded during that visit by the ophthalmologist, then addition of latanoprost to the medical therapy was recommended. If the same occurred while being treated with the combination of dorzolamide, timolol, and latanoprost, then surgical intervention with an aqueous humor shunt was recommended. This study was approved by the Institutional Animal Care and Use Committee (Protocol # 23–311).

The IOP measurements and the time at which these measurements were obtained by the owners were entered into a Microsoft Excel spreadsheet. Then the date of the first measurement was subtracted from the rest of the measurement time points so that measurements were labeled as starting on day and time zero. Then a scatterplot for the measurements from each eye was created with the time on the X‐axis and the corresponding IOP measurement on the Y‐axis (bioRender Graph, www.biorender.com).

3. Results

There were 13 owners who agreed to measure and record IOP in their dog's eye predisposed to developing PACG. One owner had two dogs, so there were 14 dogs in which IOP was measured at home by the owners. The breed, sex, age, gonioscopic ZibWest score, and initial IOP measured at the first office visit prior to at‐home IOP measurements starting are listed in Table 1. The figure in which the scatterplot corresponding to each case can be found and the outcome for each is also listed in the last two columns of Table 1.

TABLE 1.

The case number, breed, age, sex, initial iridocorneal angle ZibWest score, and initial IOP reading in office of the dogs at the beginning of the study are listed in the first six columns of this table.

Case	Breed	Age	Sex	ZibWest score	Initial IOP	Figure	Outcome
1	Cocker Spaniel	12	F/S	0.1	10	1a	Lost to follow‐up
2	Dandie Dinmont	10.4	F/S	0.1	12	1b	Lost to follow‐up
3	Siberian Husky	8.9	M/N	0.06	14	1c	Lost to follow‐up
4	Cocker Spaniel	12.5	F/S	0.13	15	1d	Lost to follow‐up
5	Golden Retriever	1.4	F/S	0.08	13	1e	Continues monitoring
6	Basset hound	6.7	F/S	0.07	16	2a	Glaucoma, enucleated
7	Cocker Spaniel	9.2	F/S	0.14	5	2b	Glaucoma, shunt surgery
8	Miniature dachshund	5.1	F/S	0.10	10	2c	Glaucoma, enucleated
9	Miniature dachshund	5.0	M/N	0.11	13	2d, 3a	Glaucoma, enucleated
10	Cocker Spaniel	5.5	F/S	0.08	18	2e, 3b	Glaucoma, shunt surgery
11	Australian shepherd	7.5	F/S	0.09	13	2i	Glaucoma, shunt surgery
12	Standard poodle	4.4	F/S	0.09	14	2 g	Glaucoma, enucleated
13	Cocker Spaniel	10.3	F/S	0.24	10	2 h	Glaucoma, shunt surgery
14	Siberian Husky	7.9	M/N	0.09	10	2f	Glaucoma, enucleated

Note: The figure in which the scatterplot corresponding to each case can be found and the outcome for each is listed in the last two columns.

Although the owners that were trained to obtain IOP measurements did not report other household members obtaining IOP measurements, owners were not asked whether the same person restrained the dog every time for each measurement. Some owners reported that with positive reinforcement their dog permitted unrestrained IOP measurement and would come and sit in place to receive the ocular medications and have the IOP measured, allowing owners to measure the IOP without even touching their dog with their hands during measurement.

There were five dogs (Cases 1–5, Figure 1) that did not develop overt clinical glaucoma during the period in which IOP was measured. Cases 1,2, and 4 were euthanized due to unrelated disease. Case 3 moved away from the area and opted to stop measuring IOP. Case 5 continues to be monitored, and the owner continues to measure IOP as of the writing of this report. There were nine dogs (Cases 6–14, Figure 2) that developed overt clinical glaucoma during the time IOP was measured. Cases 6, 7, 8, 10, 12, 13 received additional medical therapy consisting of topical ophthalmic latanoprost administered twice daily (shown as a teal‐colored overlay in Figure 2) until either they lost vision, and the eye was enucleated, or an Ahmed shunt was placed. The decision to place an Ahmed shunt was based on an assessment of the likelihood for vision and the owner's ability or desire to pursue surgical intervention. Cases 6, 8, 9,12, and 14 were enucleated due to vision loss and continued IOP elevation while cases 7,10, 11, and 13 received surgical intervention with an Ahmed aqueous humor shunt. Case 9 had an opposite eye that had already developed overt glaucoma associated rises in IOP and was still visual that was being treated with twice daily topical ophthalmic latanoprost and dorzolamide2%/timolol 0.5%. The owner also obtained measurements from this eye (Figure 3a). The owner of case 10 asked to continue to measure IOP after an Ahmed shunt was placed (Figure 3b). This owner continues to measure IOP in this eye 4.5 years after placement of the shunt as of the time of this report.

FIGURE 1.

Scatterplots of the owner obtained IOP (TonoVet Plus) values of the five dogs predisposed to PACG (Cases 1–5, panels a–e, respectively) that did not develop clinical glaucoma during the study period. All dogs received twice daily topical ophthalmic dorzolamide 2%/timolol 0.5%. The time in days is on the x‐axis and the IOP measurement obtained by the owner using the TonoVet Plus is on the y‐axis. Note the x‐axis scale is different in panels (c–e) to accommodate the extended time during which IOP was measured in these cases.

FIGURE 2.

Scatterplots of the owner obtained IOP (TonoVet Plus) values of the nine dogs predisposed to PACG (Cases 6–14, panels a–i, respectively) that developed clinical glaucoma during the study period. The time in days is on the x‐axis and the IOP measurement obtained by the owner using the TonoVet Plus is on the y‐axis. All dogs received twice daily topical ophthalmic dorzolamide 2%/timolol 0.5% throughout the entire period. The time during which twice daily topical ophthalmic latanoprost was used is noted as a teal‐colored overlay in each panel. Note the x‐axis scale in panel (i) is different to accommodate the extended time in which IOP was measured in this case.

FIGURE 3.

(a) Scatterplot of the owner obtained IOP values of the opposite of eye from case 9 that had already developed overt glaucoma that was being treated with twice daily topical ophthalmic latanoprost (teal‐colored overlay) and twice daily topical ophthalmic dorzolamide 2%/timolol 0.5%. (b) Scatterplot of the owner obtained IOP values from Case 10 after an Ahmed shunt was placed. The pink‐colored overlay represents the time during which once daily topical ophthalmic 1% prednisolone acetate was being administered.

A reading greater than 35 mmHg was only recorded in one dog on a single occasion within the dogs that did not develop clinical glaucoma within the period IOP was being measured (Cases 1–5). This occurred in Case 5 on Day 854. As of the time of this report, approximately 1.5 years after this reading was obtained, the dog has not developed clinical glaucoma. Six ophthalmic examinations by a board‐certified veterinary ophthalmologist have not detected any signs of clinical glaucoma. An obvious upward trend within the group of dogs that did not develop glaucoma (Cases 1–5) is only noted in the measurements from Case 3 (Figure 1c). There is also an apparent increase in the variability of IOP measurements obtained toward the end of the measurement period. Unfortunately, this owner left the area, and the dog was lost to follow‐up.

In the dogs that developed clinical glaucoma during the study period, readings > 35 mmHg were obtained in one dog prior to the onset of clinical glaucoma. That is, an IOP > 35 mmHg that was not associated with any noticeable changes in appearance of the eye or vision noticed by the owner or during a follow‐up exam by a board‐certified ophthalmologist. Case 7 had two transient elevations in IOP > 35 mmHg not associated with any noticeable signs. In the rest of the cases, except for case 13, the first IOP greater than > 35 mmHg recorded by the owner was associated with clinical signs (e.g., cloudiness, pupillary dilation, redness, signs of discomfort, or decreased vision). In all these cases IOP was > 50 mmHg. Case 13 was the only case that showed a slow rise in IOP over time. In this case, when IOPs were consistently measured to be over 25 mmHg, the decision to increase medical therapy to include latanoprost was made even though no other clinical signs were apparent.

In the six dogs that were treated with latanoprost prior to enucleation or placement of an Ahmed shunt, a noticeable decrease in the average measured IOP was only observed in three of the cases (Cases 7, 12, and 13; Figure 2b,g,h) after starting latanoprost treatment. In the remaining three cases, the average IOP appears to remain unchanged (Cases 6, 8, and 10; Figure 2a,c,e). In four of the six dogs treated with latanoprost, additional IOP readings > 50 mmHg were recorded within 21 days of starting latanoprost (Cases 7, 8, 10, and 12). In Case 6 an elevation > 50 mmHg was recorded 82 days after starting latanoprost. In Case 13, readings > 50 mmHg were not recorded after starting latanoprost. However, multiple IOP readings > 35 mmHg noted by the owner approximately 30 days after starting latanoprost resulted in a recommendation to intervene surgically by placing an Ahmed shunt.

The owner of Case 9 also measured IOP in the eye that had already developed clinical glaucoma and was being treated with topical ophthalmic latanoprost and dorzolamide 2%/timolol 0.5% twice daily. During the approximately 9 months IOP was measured in that eye, an IOP > 35 mmHg was measured 39 times and an IOP > 50 mmHg was measured twice (Figure 3a). A wide variation in IOP measurements is also evident. The owner of Case 9 did not want to pursue placement of an Ahmed shunt and opted to enucleate the eye once vision was lost. The owner of Case 10 requested to continue measuring IOP after placement of an Ahmed shunt. Figure 3b represents intraocular pressures immediately after placement of the shunt. After discontinuation of the medications used in the postoperative period, topical prednisolone acetate was continued once daily. The time during which once daily topical 1% prednisolone acetate was being administered is noted with a pink overlay in Figure 3b. Remarkably stable measurements with a downward trend are apparent during the time the topical ophthalmic 1% prednisolone acetate was being administered. Due to worsening corneal lipid degeneration, topical prednisolone was discontinued. Within 2 weeks of discontinuation, a rise in IOP was seen. Intra‐bleb injection of 5‐fluorouracil was performed, and the topical prednisolone was resumed. Following this, IOP returned to the values obtained prior to discontinuation of the topical prednisolone and this eye remains visual with stable IOP values (all measured values between 15 and 17 mmHg) 3 years after topical steroid administration was resumed.

Based on a discussion with the owners and their goals or financial limitations, the owners of cases 6, 8, 9, 12, and 14 had decided to not pursue placement of a glaucoma shunt when IOP became uncontrolled by medical therapy and had decided to enucleate whenever vision was lost. In case 7, the owner obtained measurements that led to a recommendation of surgical intervention. There were intermittent IOP elevations that would resolve with latanoprost administration but would recur approximately 12 h after latanoprost was given. Abnormal IOPs were not recorded at any office visit. In case 10, multiple large elevations recorded by the owner contributed to solidifying a recommendation for surgical intervention along with elevated IOPs measured at office visits (24, 34, and 44 mmHg). In case 11, a measurement by the owner of 78 mmHg prompted by abnormal behavior by the dog led to emergency examination. At the time of emergency examination approximately 1 h later, IOP was 48 mmHg and 1 h after that, 15 mmHg. This led to a recommendation for surgical intervention. In case 13, the owner obtained IOP measurements that led to surgical intervention. In office IOP measurements did not exceed 14 mmHg. However, the owner measured slowly rising IOP values with at‐home measurements consistently exceeding 30 mmHg and occasionally reaching 40 mmHg despite treatment with latanoprost.

The frequency of measurement varied substantially among owners and can be seen depicted in Figures 1 and 2. Some consistently measured IOP 2 times a day, and more frequently if they obtained suspicious values. Others measured only daily, and others sporadically. Some owners recorded the time and the relationship to this time with when ophthalmic glaucoma medications were given, while others only recorded the date and whether it was morning or evening. The owner of cases 8 and 9 stopped measuring IOP in case 9 for approximately 60 days until loss of vision prompted them to measure IOP. Owners were asked to call when they obtained IOP readings of greater than 35 mmHg. All did except for one owner. The owner of Case 14 only called when vision loss was noted following an unrelated surgical procedure, even though they had measured IOP values in the 50–70 mmHg range the week prior.

4. Discussion

The goal of this study was to explore whether the IOP values obtained at home by owners could provide any information on when eyes predisposed to glaucoma would develop overt clinical glaucoma or help in the clinical management of PACG. The results of this study suggest owner‐obtained IOP measurements can provide useful information in the clinical management of canine PACG. The current study also highlights important characteristics of PACG disease progression in dogs which have a direct impact on management of this disease. Namely that on most occasions, IOP rises occur suddenly and without any warning. Because the IOP values between these rises are within the normal range, it is extremely unlikely these rises would be captured had the owners not been able to measure IOP at home. Once these marked rises begin to occur, they can continue to occur with increasing severity and frequency despite increasing medical therapy.

The owners that participated in this study were highly motivated owners and perhaps do not represent the average population of owners. These owners had already agreed to participate in another clinical trial evaluating glaucoma progression and had been referred by other veterinary ophthalmologists in the area and traveled to participate in the study. The results show there was a big variation in consistency in how often owners measured intraocular pressure potentially leading to valuable information not being collected. It is possible that due to the gaps in measurement, subtle rises or occasional spikes were missed, leading to a false sense of security that IOP was controlled. Thus, although valuable information was obtained in this study, and in some cases, the measurements obtained by the owners helped guide treatment, it cannot be assumed that this is a useful tool for all owners. This was highlighted by the owner that recorded all measurements yet failed to report the extremely high values, resulting in vision loss despite faithfully measuring IOP. Ideally, IOP would be continuously monitored and reported telemetrically immediately to the ophthalmologist. This may be possible in the future with technologies currently under development [5].

The authors of the current study are of the opinion that owner obtained IOP measurements were influential in a recommendation for surgical intervention in the cases in which owners had decided surgical intervention was something they would pursue. However, this begs the question as to whether the same recommendation would have been reached without having the owner obtained measurements. Or whether the recommendation for surgery might have occurred later during the disease without the owners' measurements and whether that delay would have resulted in poorer visual outcomes. It is also the authors' opinion that had the owners that had declined placement of a shunt been willing to pursue it, the data they obtained would have influenced the timing of the recommendation for surgical intervention in some cases. However, all these questions are unanswerable from the data. A large, randomized study would be needed to answer these questions. Nevertheless, the authors would much rather have owner obtained IOP values, as imperfect as they might be, than not have them when making clinical decisions on when to intervene surgically or increase medical therapy.

The accuracy of IOP measurements obtained by owners can be questioned. All owners used the same rebound tonometer model (TonoVet Plus). Rebound tonometers have been shown to quickly result in reliable readings in novice operators [6]. A recent report showed that owners who received a short tutorial on how to perform tonometry obtained readings that were within 3 mmHg of an experienced operator 90% of the time using the TonoVet Pet [7]. Another recent report compared experienced users to novices who were provided with the user manual for the TonoVet Plus and a single demonstration on the use of the device [8]. In that report, there were no significant differences in measured IOPs between novices and experienced users over the first seven measurement attempts. The mean difference in IOP between novices and experienced users was 0.6 mmHg [8]. In the current study, there are a variety of “internal controls” that suggest readings obtained by these owners were reliable. In nearly all cases, abnormal readings were obtained only after owners had obtained many normal values. The measurements in Figures 2,c,d and 3a were performed by the same owner. It could be argued that the extreme variability seen in Figure 3a represents user error. However, the measurements concurrently obtained from the opposite eye (Figure 2d) suggest the measurements obtained in Figure 3a represent true IOP variation since the measurements in Figure 2d do not display the same variability. Since owners inconsistently reported when they obtained IOP measurements and those that did consistently report the timing did not obtain IOP readings at the same time each day, some of the variation seen within dogs might be due to normal diurnal variation [9]. Moreover, it has been shown that IOP values obtained in the home setting are systematically lower than in the clinic [10].

The cutoff of 35 mmHg was arbitrarily chosen by the authors of this study as the threshold IOP at which owners should call the hospital and be evaluated by an ophthalmologist. It was based on the clinical experience that dogs with PACG usually experience rises in IOP that are greater than this and to decrease the number of unneeded calls from owners. Owners in this study were using the TonoVet Plus with the original software implementing a calibration curve that resulted in higher estimated IOP readings [11]. This cutoff value resulted in a small number of events that were not associated with clinical glaucoma. This cutoff value is likely not appropriate for all situations or tonometers and those wishing to institute an at‐home measurement program should consider what cutoff value is best suited for the situation. For example, if owners are measuring IOP at home in dogs that have received an Ahmed shunt, the cutoff value should likely be lower, since these implants should maintain an IOP of < 15 mmHg [12, 13]. Detection of IOP values greater than this likely represents a need for intervention.

In seven of the nine cases that developed glaucoma during the time owners were measuring IOP, the first IOP value > 35 corresponded to the onset of clinical glaucoma. In these seven cases, the IOP value recorded was > 50 mmHg and was accompanied by clinical signs noticeable by the owner. In the remaining two cases, one (Case 7) had occasional elevations in IOP > 35 mmHg that occurred within 70 days of the onset of clinical glaucoma and the other (Case 13) had a noticeable slow rise in IOP with average values exceeding 25 mmHg. One could argue that owner obtained measurements were only useful in predicting the onset of glaucoma in these last two cases. In Case 7, the IOP values > 35 mmHg not associated with clinical signs could be interpreted as indicative of greater pressure rises to come and in Case 8 the slow rise would likely have not been apparent with occasional measurements taken by an ophthalmologist. However, it is the opinion of the authors of the current study that there is great value in having owners be able to confirm IOP elevation at home at the time clinical signs are noted. The initial rises in IOP seen in all cases, except for Case 13, were temporary. And it is possible that by the time owners arrived at the hospital, IOP values would be normal again and there would be doubt as to whether the clinical signs seen were truly due to IOP elevation and whether additional intervention was truly necessary. Thus, in these cases, the fact there was documentation of an elevation in IOP was helpful in determining the most appropriate therapy.

The continued IOP spikes noted by owners in some dogs following an initial spike, despite starting treatment with latanoprost, have several important implications. The first is that it provides a reason for continued vision loss in PACG despite apparently controlled IOP. Progressive vision loss in PACG has been attributed to the initiation of an apoptotic cascade caused by the initial IOP spike [14, 15]. And it is likely this mechanism does contribute to this vision loss. However, the IOP spikes documented after the initial spike, even while latanoprost was being administered, suggest the IOP spikes themselves could continue to inflict damage on the retina and explain the vision loss noted even when occasional measurements show an IOP reading within the target range. The second implication is that if the IOP spikes continue even in the face of aggressive medical therapy, and these IOP spikes are resulting in vision loss, surgical treatment should be pursued as soon as one IOP spike is documented. Alternatively, the cases in which there wasn't an obvious decrease in IOP readings and that continued to have large rises in IOP might have been controlled with an increased frequency of administration [16] or could be considered “non‐responders” to latanoprost and might have been controlled with an alternate medication, such as bimatoprost [17, 18]. Regardless, if owners had not been measuring IOP at home, these IOP spikes would not have been noted.

Long term topical ophthalmic steroid or NSAID administration has been previously advocated to decrease the amount of scarring around the footplate of an Ahmed aqueous humor shunt [19, 20]. The authors of the current study had prior anecdotal evidence suggesting discontinuation of topical steroid administration would result in pressure rises following Ahmed aqueous humor shunt placement. Although this may not be true in all cases, it is clearly documented in Figure 3b. This data reinforces that discontinuing topical steroid administration can result in decreased aqueous humor flow through the shunt bleb and result in IOP rises. Additionally, it reinforces the utility of having owners measure intraocular pressure at home following placement of a glaucoma shunt. This rise in IOP might not have been captured in a timely fashion had the owner not been measuring IOP and it is possible this might have resulted in vision loss prior to intervention. The highest reported success rate following glaucoma shunt placement involved owners in the home measurement of IOP values following surgery [20].

There are several limitations to this study. The first has already been discussed but remains a possible weakness. The accuracy of the measurements obtained by owners was not evaluated. It is possible that all the abnormal measurements obtained were due to operator error. Ideally, owners would have been asked to obtain an IOP measurement with the tonometer they had been using during each of the 3‐month office visits. Immediately after the owner obtained that reading, the ophthalmologist would obtain an IOP reading and the correlation between the two could be used to validate the owner's ability to measure an accurate IOP over the entire study period. Unfortunately, that data was not collected during this study, so a correlation analysis cannot be performed on the data from this study since there was a significant time difference between when the owner last obtained an IOP reading and when the ophthalmologist did during each 3‐month visit. Future studies should consider obtaining this data to validate the accuracy of owner‐obtained measurements. The second limitation is the likely inconsistency in restraint of the dogs, which could likely introduce variability into the owner‐obtained measurements. The third is the lack of a control group. It would have been ideal for owners to not only measure the pressure of dogs predisposed to PACG but also dogs not predisposed to PACG. If similar spikes in IOP were recorded in normal dogs, the significance of these measurements would be easily discounted. And third, the data represents a small number of dogs. It is possible the IOP profiles recorded in this study are not broadly representative of the typical disease progression in eyes predisposed to PACG. However, the fact this type of IOP profile was recorded means that it is possible and, though it may not occur in all cases, it should be considered as a possibility.

Taken together, the findings of this study suggest there is value in having highly motivated owners measure IOP at home in their dogs predisposed to PACG. Home IOP monitoring can help corroborate clinical signs are caused by IOP elevation, which can be useful in determining an appropriate treatment plan for dogs with PACG. The findings of this study also hint at the possibility that in some cases, continued transient rises in IOP occur despite aggressive medical therapy and may be responsible for continued vision loss in dogs with PACG. In these cases, early surgical intervention may be indicated to avoid the continued vision loss caused by these IOP elevations. Further studies evaluating owner‐obtained IOP measurements in a larger cohort of dogs are needed to further define the validity and utility of these measurements.

Funding

This study was funded in its entirety by a grant from the Vision for Animals Foundation (VAFGL‐2017).

Disclosure

Artificial Intelligence Statement: The authors have not used AI to generate any part of the manuscript.

Ethics Statement

The procedures described in this study were approved by the North Carolina State University College of Veterinary Medicine Institutional Animal Care and Use Committee (Protocol #17‐160) and informed consent and approval were obtained from all owners.

Conflicts of Interest

The authors declare no conflicts of interest.

Westermeyer H. D. and Salmon J. H., “Owner Obtained Intraocular Pressure Measurements in Canine Primary Angle Closure Glaucoma: A Pilot Study in 14 Dogs,” Veterinary Ophthalmology 29, no. 2 (2026): e70156, 10.1111/vop.70156.

Data Availability Statement

The data supporting the findings of this study are available on request from the corresponding author.