Angle-closure glaucoma is one of the sight-threatening diseases and is a major cause of worldwide blindness (6).
The reversible attachment of the trabecular meshwork to the periphery of the iris is defined as appositional angle-closure. It occurs due to physiological movement of the pupil and can lead to transient IOP increase in narrow angled eyes. If it became chronic, angle configuration will show permanent changes that will lead to increases in IOP and finally will cause PACG (7).
A relationship was found between the configuration of the anterior chamber and primary angle-closure (PAC) (8) it was proved that shallow anterior chamber and narrow-angle were significant risk factors for PACG, so, measurement of IOP and evaluation of anterior chamber angle are important for the prevention and early treatment of PACG (9).
Anterior chamber assessment can be done by multiple methods as Van Herrick technique, gonioscopy, ultrasound biomicroscopy (UBM), and AS-OCT and Scheimpflug photography (8).
As regarding the Van Herrick technique, it is simple and doesn’t need direct contact with the ocular surface, but it is highly subjective (9). Gonioscopy is considered the standard method for angle examination, but it has some problems that limit its use in assessing anterior chamber angle status. Firstly, it requires a certain degree of skill and experience to give trustable results. Secondly, any increase in illumination or pressure on the lens can change the findings. Lastly, it is considered to some degree a subjective technique (10).
Unfortunately, although UBM is very helpful in examination of anterior chamber angle, it has some difficulties as the need to place the patient in the supine position and to apply a topical anaesthetic and an ocular cup to the eye also,it requires skill and is equipment dependent, thus, it is not suitable for screening for narrow angled eyes (11). Now, AS-OCT allows cross-sectional imaging of the anterior chamber and the angle with high-resolution. Also, it doesn’t require contact with the eye and provides rapid examination. Another advantage is that the patients are examined while they are sitting. Also, it has good repeatability and reproducibility (12).
Recently, the Pentacam-Scheimpflug camera has been started to be used in the imaging of the anterior chamber angle. It is a non-contact method and gives high-resolution images. It creates 3-dimensional images of the anterior eye segment. The Pentacam parameters that are useful in glaucoma are ACD, ACV, corneal thickness (apical), and ACA, as well as inbuilt IOP correction formulae. Despite these advantages, it is not efficient as anterior segment OCT in the evaluation of the anterior chamber angle due to the inability to visualize the sclera spur. However, it is better than AS-OCT in giving more quantitative data of the anterior chamber, due to measuring peripheral ACD and ACV. Therefore, it has a promising future as a screening method for detecting narrow angled eyes (13).
This present study was conducted in Minia University Hospital Ophthalmology Department between April 2019 and December 2019, on forty PACS patients. We had chosen patients between twenty and seventy years age group who were either hyperopes, with a positive family history of angle-closure glaucoma, with shallow AC, or with gonioscopy, 180 degrees of their trabecular meshwork could not be seen, provided that their IOP is less than 21mmHg, no optic neuropathy and their visual field test was normal.
Patients who gave history of intraocular surgery or laser procedures to the eye, who gave a history of trauma, those with corneal opacity or anterior segment pathology or had any cause of 2dry glaucoma as angle neovascularization were excluded from this study.
In all patients, we examined different parameters of the anterior chamber using both AS-OCT and Pentacam before and after installation of one drop of combination of 5mg cyclopentolate HCL and 500mg phenylephrine HCL by 30 minutes.
AS regarding AS-OCT we measured ACA (TIA750), AOD750, and TISA750 in superior, inferior, nasal and temporal quadrants. After the mydriatic test, we noticed a decrease in all parameters measured, some decreased significantly while others did not. A significant decrease was noticed in ACA (TIA750) in all quadrants (P-value < 0.001in nasal, 0.001in superior &temporal, 0.003in inferior) and in TISA750 in the nasal quadrant only (P-value 0.004). AOD750 and TISA750 in the remaining quadrants also decreased but not significantly as ACA.
As regarding Pentacam, we measured ACA, ACD, and ACV before and after the mydriatic test. All parameters were noticed to be decreased after the mydriatic test. ACA (P-value < 0.001) and ACD (P-value 0.004) showed significant statistical decrease but ACV showed statistically non-significant decrease (P-value 0.558).
The results we had obtained, revealed a decrease in all parameters of the anterior chamber measured by both AS-OCT&Pentacam after the mydriatic test was done.
We also measured IOP before and after the mydriatic test. There was a significant increase in its measurements after pupillary dilatation (P-value < 0.001).
These changes that occurred in the parameters of anterior chamber and IOP after the mydriatic test are mostly attributed to the effect of the mydriatic agent which induces appositional angle-closure by one of these mechanisms of PACG:
(1) Pupillary block type: when the pupil becomes mid dilated the iris becomes crowded in the angle, (this is because the resulting block of the pupil causes the aqueous in the posterior chamber to push the iris towards the cornea so that, the angle is narrowed and the aqueous drainage is hindered and IOP becomes elevated). This effect is exaggerated in susceptible eyes (with narrow angles).
(2) Plateau iris type: when the pupil dilates in the eyes in which the iris is plateau shaped the iris becomes crowded in the angle causing trabecular meshwork occlusion.
(3) Lens factors: the cycloplegic agent present in the cyclopherine ED produces relaxation of ciliary muscle making the lens more spherical causing some decrease in ACD (14).
In this study, the main mechanism of angle narrowing in PACS eyes is mostly the pupillary block one
In a study done by Aptel et al (15)., with shifting from light to dark(i.e. with physiologic mydriasis), angle opening distance (AOD) at 500 µm decreased significantly more in fellow eyes of acute angle-closure patients than in PACS while the mean iris volume increased significantly in the fellow eyes of these patients and decreased significantly in most PACS eye, and in all open-angle eyes. Unlike our study, they used physiologic dilatation instead of pharmacologic one. It matches ours in that AOD500 decreased in PACS after physiologic mydriasis. (But in ours theAOD750 decrease is insignificant).
In a study done by Yamada et al (7) on seventy eyes of seventy consecutive patients with primary angle-closure suspect, primary angle-closure, or primary angle-closure glaucoma (based on gonioscopy), AS-OCT and IOP measurement was done for all those patients after the mydriatic provocative test (MPT) and the dark room prone provocative test (DRPPT), their results revealed that ACD and AOD 500 of the positive group(with a significant increase in IOP after the two tests), using the MPT, were significantly less than those of the negative group (with an insignificant increase in IOP). The trabecular-iris space area 500 of the positive group was significantly less than the negative group, using both the MPT and the DRPPT. This agrees with our study in the significant IOP elevation in PACS group after mydriatic test and in the decrease of both AOD &TISA after mydriatic test, but we differ from them in measuring AOD &TISA at 750Mm from the scleral spur not at 500 Mm and the decrease in both of them in our study is insignificant. We also differ from them in measuring ACD with Pentacam (not with AS-OCT), but both studies showed a significant decrease in ACD after the mydriatic test.
In another study done also by Aptel et al (16) included the fellow eyes of patients who suffered from a previous acute attack of primary angle-closure glaucoma and eyes of control subjects with open angles. All patients were imaged by AS-OCT after phenylephrine10% instillation and another time after tropicamide 1%instillation. The axial length and depth of anterior chamber did not change significantly after mydriasis. Also, in the eyes of the control group, the mean AOD 500 and TISA 500 did not change significantly after pupil dilation, while both of them were about 2 to 3 times smaller after mydriasis in the eyes of the case group, regardless of the mydriatic agent used. These results are consistent with our study which showed a decrease in AOD750 and TISA750 after mydriatic installation (but the decrease in ours is insignificant). We differ from them in measuring ACD with Pentacam not by AS-OCT and our study showed significant decrease in its value after mydriasis, unlike this study which showed non-significant change.
There is a study done by Hirose et al (17) showed that in the angle-closure group in each of the four quadrants, the iris thickness (IT) increased significantly in the dark, and the AOD500 and TISA500 decreased significantly in the dark. This is mostly due to physiologic dilatation of the pupil in the darkness which induces relative pupillary block and thickening of the iris periphery leading to narrowing in the angle of the anterior chamber, therefore decrease in AOD and TISA. This decrease in AOD and TISA after physiologic mydriasis is consistent with our study which revealed a decrease in these two parameters after pharmacologic mydriasis (but our decrease was insignificant in four quadrants except TISA in nasal quadrant).
Similarly, in a study done by Masoodi et al, ACA and AOD500 in the nasal and temporal quadrants were significantly greater in light compared to dark (all with p = 0.000). This is also consistent with our study (18).
Also, an old previous study was done by Ishikawa et al (19), under light conditions and with using UBM all eyes tested showed open angles. On the other hand, on darkroom provocation, the angles of 55.6% of the eyes were occluded and those of 44.4% of the eyes were not. In the dark, evidence of appositional angle-closure was found in the angles in 99 patients (55.6%) during testing. The eyes in which the angles were occluded showed decrease in ARA and AOD500 in the dark (this is consistent also with our study).
Another idea was done by Kobayashia et al (20), who studied the effect of miosis (using pilocarpine) on anterior chamber in narrow angled patients. After pilocarpine instillation, the whole narrow angled eyes showed an increase in the TIA, AOD250, and AOD500. Also, they noticed that pilocarpine induced a decrease in ACD which was more in eyes with narrow angles than in those with wide angles. (This is consistent with our study in the effect over TIA and AOD but does not match ours in the effect on ACD).
Another study consistent with ours, the one done with Friedman et al (21). it revealed that in both angle-closure cases and controls the AOD500&750 and the angle-recess area showed significant decrease in the dark using UBM (the decrease was more in cases than in controls).(This is consistent with our study). With Scheimpflug Camera there was noticed decrease (of borderline statistical significance) in the average angle width in the dark, (it was more in cases than in controls). (This also agrees with our study in a decrease of ACD and ACV post mydriatic). On the other hand, with instillation of pilocarpine, both cases and controls showed a significant increase in AOD 500 & 750 µm and angle-recess area with UBM. (This increase was less in cases than in controls) (These results agree with our study).
Leung et al (22), K woo et al (23) ,Jouzdani et al(24), and Ming Young et al(25)., also found the same results in the dark.
In another study done by Razeghinejad et al, (26) revealed that both mydriatic test and water drinking test performed in PACS patients caused a significant increase in IOP. This agrees with our study in significant IOP elevation after the mydriatic test.
Lavanya et al (27) also, agreed with us in post mydriatic increase in IOP in narrow-angle patients.
The results in all the studies that agree with us in the decrease in parameters of AC and increase in IOP after mydriasis (physiologic or pharmacologic) are mostly attributed to the same mechanisms of PACG we mentioned before (especially the pupillary block).
On the other hand, a study was done by Jing- Min Guo et al (28), found that iris thickness at 750 µm, in addition to depth and volume of the anterior chamber had increased significantly after pharmacologic mydriasis, while iris curve, cross-sectional area and volume had decreased significantly in both PACS and normal controls. This study differs from ours in that post mydriatic the AOD500 increased none significantly while in ours AOD750 decreased none significantly. Also, the significant increase in ACD and ACV in PACS after mydriasis does not match with our study which revealed a significant decrease in ACD and a non-significant decrease in ACV after mydriasis.
Also, another study was done by Razeghinejad et al (29) showed that the mydriatic test didn’t cause a significant difference in intraocular pressure or parameters of anterior chamber except the anterior chamber volume, which increased after the mydriatic test. Our study differs from this one in many aspects, firstly, in ours, there was a significant increase in IOP measurements after mydriasis, secondly, this study revealed a significant increase in ACV post mydriatic while ours showed a non-significant decrease in ACV post mydriatic
The difference in techniques and ethnicities of persons included in the previous studies can explain the discrepancies in their results.
Our study had some limitations. First, its results cannot be generalized to larger populations because it wasn’t a population-based study but a hospital-based one. Also, we did not use UBM for the precise diagnosis of plateau iris configuration. Although some studies used AS-OCT to detect plateau iris configuration, its definitive diagnosis should be done with UBM.