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 Table of Contents    
Year : 2023  |  Volume : 16  |  Issue : 1  |  Page : 82-87  

Transpalpebral intraocular pressure measured by Diaton tonometer before, 1 week, and 1 month after transepithelial photorefractive keratectomy in young myopic Saudi patients and its determinants

Department of Ophthalmology, College of Medicine, Qassim University, Buraidah, Saudi Arabia

Date of Submission19-Jul-2022
Date of Decision07-Nov-2022
Date of Acceptance28-Dec-2022
Date of Web Publication21-Feb-2023

Correspondence Address:
Sultan Alzuhairy
Department of Ophthalmology, College of Medicine, Qassim University, Buraidah
Saudi Arabia
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ojo.ojo_215_22

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PURPOSE: To present changes in transpalpebral intraocular pressure (tpIOP) in eyes after transepithelial photorefractive keratectomy (TPRK) in myopic Saudi patients and its determinants.
METHODS: This one-armed cohort included the myopic eyes of Saudi adolescents treated with TPRK in 2020–2021. The difference in tpIOP before surgery, 1 week after surgery, and 1 month after surgery using Diaton was the main outcome. Central corneal thickness (CCT), myopia grade, gender, age, and corneal epithelial thickness before surgery were independent factors. Matched-pair analysis was conducted. The determinants of tpIOP post-TPRK were studied.
RESULTS: Our cohort included 193 eyes of 97 participants (25.6 ± 5.8 years). Mild, moderate, and severe myopia were present in 93, 79, and 21 eyes, respectively. tpIOP was 22 mmHg or more in 5 and 8 eyes at 1-week and 1-month follow-up, respectively. The change in tpIOP ranged from − 7.00 to + 11.0 mmHg at 1 week and − 8.0 to + 26.0 mmHg at 1 month. The median change of CCT at 1 month was 59 μ. Change in tpIOP was not correlated with change in CCT at 1 month (r = −0.107, Pearson P = 0.14). Change of tpIOP was significantly correlated to spherical equivalent (SE) before surgery (matched-pair P < 0.001). SE (Mann–Whitney U P = 0.02) and tpIOP (Mann–Whitney U P = 0.02) before TPRK were significantly correlated to tpIOP >22 mmHg after TPRK.
CONCLUSION: The changes in tpIOP following refractive surgery correlate to the refractive status of the eye and tpIOP before surgery.

Keywords: Glaucoma, myopia, refractive surgery, transepithelial photorefractive keratectomy, transpalpebral intraocular pressure

How to cite this article:
Alzuhairy S. Transpalpebral intraocular pressure measured by Diaton tonometer before, 1 week, and 1 month after transepithelial photorefractive keratectomy in young myopic Saudi patients and its determinants. Oman J Ophthalmol 2023;16:82-7

How to cite this URL:
Alzuhairy S. Transpalpebral intraocular pressure measured by Diaton tonometer before, 1 week, and 1 month after transepithelial photorefractive keratectomy in young myopic Saudi patients and its determinants. Oman J Ophthalmol [serial online] 2023 [cited 2023 Mar 31];16:82-7. Available from: https://www.ojoonline.org/text.asp?2023/16/1/82/370038

   Introduction Top

Measuring intraocular pressure (IOP) before planning a refractive surgery is crucial for better outcomes. In addition, postrefractive surgery monitoring IOP using conventional methods is a challenge.[1] The presence of fluid between the flap and stromal bed following laser in situ keratomileusis (LASIK) gives false results of transient steroid-induced IOP rise when a conventional Goldmann applanation tonometer (GAT) is used.[2] Newer technologies of measuring IOP through the transscleral route have been shown to be less influenced by altered corneal properties following pathology or corneal surgeries than GAT.[3]

Diaton, a transpalpebral IOP (tpIOP) measuring tonometer, is an acceptable screening tool, especially for young healthy people. It is accurate, patient friendly, and can be used without corneal anesthesia.[3],[4]

Juvenile-onset open-angle glaucoma (JOAG) is a known entity linked to myopia and is a prevalent subset of primary open-angle glaucoma.[5] Its prevalence is as high as 3.9% in Nigeria but was reported to be 1.3% in Saudi Arabia.[6],[7] Thus, it is vital to evaluate the IOP of the adolescent population with a high risk of JOAG before and after refractive surgery where steroids are used to minimize postoperative inflammation.

Among secondary school Saudi students, myopia prevalence is reported to be 55%.[8] The compliance of spectacle wearing is 75%.[9] Thus, uptake of refractive surgery in Saudi adolescents is likely to be high in coming years. Cornea surgeons, therefore, will have to be vigilant in screening for glaucoma when selecting patients for refractive surgery. Few publications on newer IOP-measuring modalities such as the transpalpebral route exist among populations undergoing refractive surgeries.[10],[11],[12] To the best of our knowledge, experience of tpIOP measurement using Diaton in patients undergoing transepithelial photorefractive keratectomy (TPRK) has not yet been studied in the Arab population.

We present tpIOP measurements before TPRK and 1 week and 1 month after TPRK as well as the determinants of high IOP after TPRK.

   Methods Top

Our hospital's ethical and research committee approved this study. This one-armed cohort study was held at our hospital, and patients managed by TPRK between January 2020 and December 2021 were included. Informed written consent was obtained. Tenets of the Helsinki declaration were strictly followed.

To calculate the sample size for our study, we assumed that increased IOP post-TPRK would be in 7.6% of patients, as reported by Kim et al.[13] For a study with 1000 annual refractive surgeries done in our hospital with a 95% confidence interval (CI) and an acceptable error margin of 5%, we needed to study 98 myopic patients. We used OpenEpi software to calculate the sample size for this study.[14]

One refractive and glaucoma surgeon served as a field investigator. The patients' ages at surgery, gender, and the eye operated on were documented. Myopia status was determined based on spherical and cylindrical refraction in diopters. The spherical equivalent (SE) of myopia was calculated using the following formula: spherical + (cylinder/2). Myopia was further graded as “mild” if SE was <−3.0 D, “moderate” if SE was between − 3.0 and − 6.0 D, and “severe” if SE was >6.0 D.[15] The IOP of each eye was measured using a Diaton tonometer (Bicom Inc., NY, USA) with both eyelids closed and the patient in a seated position. The steps to measure IOP in healthy adults using a Diaton tonometer are described in detail by Da Silva and Lira.[3] The patient was asked to look down so that the probe would be located at the superior region of the sclera above the limbus. Central corneal thickness (CCT) and corneal epithelial thickness were measured with the help of anterior optical coherent tomography (Pentacam AXL, Oculus, Germany).[16] The participants were further grouped based on CCT. Grade I comprised CCTs <530 μm, Grade II had CCTs between 530 and 560 μm, and those with CCTs >560 μm were in Grade III.[17]

We used SCHWIND AMARIS 1050RS (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany) for transepithelial laser ablation with a speed of 1.3 s per diopter and created aspheric ablation profiles of each eye by applying a SmartPulse allocation. This technique included applying a topical anesthetic and then directing the laser's aim to the eyes without removing the epithelium by blade. Further details are given in the literature.[18],[19]

After TPRK, patients were treated with topical steroid eye drops every 4 h for 1 week, then four times, three times, twice, and once a day for 3 months, respectively. tpIOP was measured at follow-up visits 1 week and 1 month after surgery. CCT was measured at the week 1 visit.

tpIOP was further graded as high IOP if it was ≥22 mmHg. Eyes with IOPs <22 mmHg were considered having normal tpIOP. If IOP was high at week 1 and subsequently declined due to a change of steroid that is compliant with glaucoma treatment, it was considered steroid-induced increased pressure. Cases with high IOP after 1 week were treated by withdrawal of steroid, and other nonsteroidal anti-inflammatory eye drops were instilled. If required, oral and topical antiglaucoma were initiated to protect eyes from the effects of high pressure.

The data were collected from hospital records using Microsoft XL®. The data were cleaned, and information on the eye as a unit was compiled. Then, the data were transferred into the Statistical Package for Social Studies (SPSS 25) (IBM, NY, USA). Both univariate and multivariate analyses were carried out. The qualitative data were presented as numbers and percentage proportions. The quantitative data, if distributed normally, were presented as mean and standard deviations. If the distribution was skewed, data were presented as median and interquartile range values. The difference of IOP pre- and post-TPRK was termed as change in tpIOP, and preoperative factors were associated/correlated with change in tpIOP using a nonparametric method. Validation was carried out using Mann–Whitney U P for two subgroups of an independent variable, and the Kruskal–Wallis P value was used for three or more subgroups of an independent variable. The presence or absence of high tpIOP post-TPRK was associated/correlated with preoperative variables using univariate analysis. For qualitative variables, the odds ratio, 95% CI, and two-sided P value were estimated. For quantitative variables, Mann–Whitney U P values were calculated using a nonparametric method. Binary regression analysis was performed to determine predictors of high tpIOP postoperatively. Step-out methods were used to remove independent variables that did not have significant association/correlation with the outcome variable. P < 0.05 was considered statistically significant.

   Results Top

The cohort included 193 eyes (96 right eyes and 97 left eyes) of 97 patients with myopia. Their mean age was 25.6 ± 5.8 years (minimum–maximum: 18–42 years). Of the participants, 45 were male and 52 were female.

Prior to TPRK, ocular parameters were evaluated. The mean SE was − 3.37 ± 1.79 D (minimum–maximum: −8.0 to −0.5). Mild, moderate, and severe myopia were found in 93 (48.2%), 79 (40.9%), and 21 (10.9%) eyes, respectively. The mean CCT before TPRK was 544.8 ± 38.3 μm (minimum–maximum: 455–669 μm). CCTs of Grade I (<530 μm), Grade II (530–560 μm), and Grade III (>560 μm) were found in 65 (33.7%), 68 (35.2%), and 60 (31.1%) eyes, respectively. The mean corneal epithelial thickness was 56.5 ± 7.7 μm (minimum–maximum: 15–79 μm).

Ocular parameters before TPRK and 1 week and 1 month after TPRK are given in [Table 1]. There were significant differences in the mean tpIOPs, CCTs, and corneal epithelial thicknesses of the eyes before and after TPRK.
Table 1: Comparison of ocular parameters at different follow-up visits after transepithelial photorefractive keratectomy for myopia

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Among our cohort, 5 eyes at week 1 and 8 eyes at month 1 had IOPs ≥22 mmHg. In 4 eyes, tpIOP became <22 mmHg between week 1 and month 1. One eye continued to have high IOP. Seven new eyes developed high IOPs after week 1. The incidence of IOP >22 mmHg post-TPRK was 6.2% (95% CI: 2.8, 9.6).

The pre-TPRK ocular parameters in eyes with and without high IOP after TPRK are given in [Table 2]. None of the qualitative variables were significantly associated with post-TPRK IOP >22 mmHg. However, myopia (SE) and tpIOP before TPRK were significantly correlated to tpIOP >22 mmHg after TPRK.
Table 2: Comparison of ocular parameters in eyes with and without high intraocular pressure after transepithelial photorefractive keratectomy for myopia

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Binary logistic regression analysis suggested that tpIOP before TPRK (Mann–Whitney U P = 0.03) and SE myopia before TPRK (Mann–Whitney U P = 0.03) were independent predictors of IOP >22 mmHg after TPRK.

The changes in tpIOP at 1 month compared to before surgery were validated using matched-pair analysis, as shown in [Table 3]. At 1 week after TPRK, tpIOP declined in 67 eyes (34.7%), remained stable in 30 eyes (15.5%), and increased in 96 eyes (49.7%). At 1 month after TPRK, tpIOP declined in 82 eyes (42.5%), remained stable in 19 eyes (9.8%), and increased in 92 eyes (42.7%). The change in tpIOP was significantly more in women compared to men (Mann–Whitney U P = 0.05). Age was not significantly correlated with changes in tpIOP (R = −0.07, Pearson P = 0.304). Preoperative CCT grades were not significantly associated with changes in tpIOP (Kruskal–Wallis P = 0.15). Myopia grade before TPRK was not significantly associated with changes in tpIOP (Kruskal–Wallis P = 0.237).
Table 3: Changes in parameters after transepithelial photorefractive keratectomy for myopia compared to before surgery

Click here to view

   Discussion Top

tpIOP measurement was useful and promising for screening young populations with myopia undergoing refractive surgery. It also helped caregivers to monitor IOP changes following TPRK. One in 16 myopic eyes managed by TPRK showed high IOP after surgery. Although none of the eyes had glaucoma before surgery, eyes with IOP >22 mmHg post-TPRK were significantly associated with tpIOP >15 mmHg before surgery and a mild grade of myopia prior to TPRK. Changes in tpIOP after TPRK were independent of factors noted before surgery.

TPRK is a widely practiced refractive surgery for treating myopia. Conventional GAT has limitations for use in eyes after cornea surgeries. Our study demonstrated the usefulness of Diaton as a screening tool for reviewing the IOP status of myopic eyes before selecting patients for TPRK. Monitoring IOP after surgery was also useful. To the best of our knowledge, predictors of high IOP after TPRK are presented for the first time in our study.

Measuring tpIOP with Diaton was possible in all eyes of our cohort. Because none of the eyes had IOP >22 mmHg before surgery and none were being treated for glaucoma, we can safely say that screening IOP using Diaton was feasible. This was also suggested by Li et al.[4] and Rozhdestvenskaya et al.[10] One week after TPRK, we could also measure the IOP of all eyes using Diaton. We could monitor changes of 1 mmHg of IOP. At 1 week, change of IOP ranged from −7 to +11 mmHg, and at 1 month, it ranged from −8 to +26 mmHg. On this basis, raised IOP was managed. Thus, Diaton was useful for monitoring IOP changes post-TPRK. It will be interesting to study how far this variation of tpIOP matches with IOP measured by GAT or other methods of IOP measurement in the postoperative period.

In our study, eyes with high IOP postoperatively had a significantly less myopic refractive error (−2.25 D vs. −3.25 D). A sample with an adequate subgroup size and suitable study design is recommended to confirm this finding. Han et al.[20] had noted that although CCT did not significantly correlate to the grade of myopia, the stress–strain index, a parameter to demonstrate corneal biomechanical properties, was significantly higher in eyes with myopia >−3.0 D compared to eyes with myopia <−3.0 D. Thus, corneal factors in addition to CCT could be responsible for correlation of tpIOP and myopia grade.

tpIOP before TPRK was a predictor of high IOP after TPRK in our study. Higher baseline IOP was a risk factor for IOP >5 mmHg after TPRK in a study using a CorVis Scheimpflug Technology tonometer.[21] Eye health-care providers should note the importance of baseline IOP in selecting patients for refractive surgery and counsel them about the risk of high postoperative IOP and the need for more frequent follow-up visits to monitor and manage high IOP if needed. The trend of using topical steroids postoperatively is responsible for rise in IOP compared to the baseline.[22] The change in IOP also depends on the type of eye drops used.[23] tpIOP post-TPRK similar to baseline tpIOP is logical; however, it is difficult to explain the decline in tpIOP in nearly one-third of the cohort in our study, which requires further explanation. When different tonometers were used to measure IOP post-TPRK, Chow and Yeung[24] noted that GAT-measured IOP was much lower than the baseline, which was due to the influence of changes in CCT and other corneal biomechanical properties.

In our study, the incidence of high IOP as measured with Diaton was 6.2%. This was much less than the 38% reported at 3–6-month follow-ups of eyes treated with TPRK and 0.1% fluorometholone to address corneal haze.[13] Cacho et al.[11] used Diaton before and 1 month after LASIK refractive surgery and found a decline in IOP with none of the 57 myopic eyes having IOP more than 22 mmHg. We urge to compare this outcome to other studies with a caution as mentioned studies were with different follow-up period and refractive surgery. The use of steroids after refractive surgery poses a risk of glaucoma in steroid responders.[1] The route of administration and the formulation of the steroid medication have a role in penetration in ocular tissues, resulting in high IOP; hence, selection of steroid eye drops with less lipophilic preparation is recommended.[25] A study with long-term follow-up of our cohort is suggested to review long-term steroid-induced increases in IOP.

Our study has few limitations. The number of cases with high IOP was few. Hence, our comparison of those with high IOP to those with normal IOP post-TPRK only shows trends and requires further confirmation with a larger sample of cases with high IOP. There was a large gap between the postoperative evaluations at 1 week and 1 month after surgery. Therefore, it is difficult to discern when the change in IOP occurred between these two visits. All tpIOPs were measured with the patient in a seated position and in the upper region of the sclera adjoining the limbus in our study. Because the location of IOP measurement influences the result, with IOP being the greatest in the inferotemporal region of the sclera, a further study is recommended measuring tpIOP at different locations around the limbus after TPRK.[3]

[TAG:2]Conclusion [/TAG:2]

Managing IOP before and after TPRK requires the teamwork of the cornea surgeon, glaucoma specialist, mid-level eye care professionals, and patients. Although Diaton is useful and practical for baseline IOP screening, variations noted after TPRK in our study point to the necessity of a more vigilant follow-up. High IOP noted using Diaton also needs to be correlated to clinical evidence of glaucoma. Young patients may wish to have spectacle-free functional vision, but postoperative care needs to be closely monitored to avoid the negative effects of high IOP on the ocular tissues. Proper selection of anti-inflammatory topical medications postoperatively and close monitoring is recommended in cases with baseline predictors such as a tpIOP of more than 15 mmHg and a mild grade of myopia. Myopic patients with these risk factors of high IOP post-TPRK should also be counseled while discussing possible complications of refractive surgery.

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Conflicts of interest

There are no conflicts of interest.

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  [Table 1], [Table 2], [Table 3]


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