|Year : 2019 | Volume
| Issue : 3 | Page : 212-216
A comparative analysis of ocular biometry in acute and chronic presentations of primary angle-closure glaucoma
Saritha Valsala Krishnankutty, Gargi Sathish, Padmasree Kamalakshy Madhavan, Vijayamma Narayani
Department of Ophthalmology, Government Medical College, Kottayam, Kerala, India
|Date of Web Publication||31-Dec-2019|
Dr. Gargi Sathish
Department of Ophthalmology, Government Medical College, Kottayam, Kerala
Source of Support: None, Conflict of Interest: None
Purpose: Primary angle-closure glaucoma is the predominant form of glaucoma in the Asian population and is a leading cause of blindness. The objective of the study was to compare ocular biometric parameters among acute and chronic presentations of the disease. Materials and Methods: Sixty eyes of sixty patients diagnosed as having either acute (Group A) or chronic presentation (Group B) were studied. Those patients with a history of uniocular pain, headache, defective vision, along with high intraocular pressure (IOP 35 mmHg), shallow AC, and mid-dilated nonreactive pupil were classified as the acute variety. Chronic form was diagnosed in eyes with peripheral anterior synechiae of >180° with a chronically elevated IOP with disc and field changes. Patients with history of intraocular surgeries or trauma, secondary angle closure, active keratitis, or corneal opacities were excluded from the study. Contact ultrasonic biometry was used for measuring axial length, AC depth, and lens thickness. Lens-axial length factor (LAF) and relative lens position (RLP) were calculated. Statistical Analysis: Chi-square test and Independent sample t-test as applicable. Results: Group B patients were significantly older with a male predominance as compared to Group A. Lens thickness and LAF were significantly higher in Group A whereas axial length and AC depth were significantly lower in Group A (P < 0.001). RLP, keratometry, pachymetry, best-corrected visual acuity, and spherical equivalents were comparable in both groups. Conclusion: It is concluded that the mechanism of acute form of primary angle-closure disease can be explained by the ocular biometric parameters alone with possibility of some additional mechanism for the chronic presentation.
Keywords: Acute, chronic, ocular biometry, primary angle-closure glaucoma
|How to cite this article:|
Krishnankutty SV, Sathish G, Madhavan PK, Narayani V. A comparative analysis of ocular biometry in acute and chronic presentations of primary angle-closure glaucoma. Kerala J Ophthalmol 2019;31:212-6
|How to cite this URL:|
Krishnankutty SV, Sathish G, Madhavan PK, Narayani V. A comparative analysis of ocular biometry in acute and chronic presentations of primary angle-closure glaucoma. Kerala J Ophthalmol [serial online] 2019 [cited 2020 Jan 27];31:212-6. Available from: http://www.kjophthal.com/text.asp?2019/31/3/212/274588
| Introduction|| |
Primary angle-closure glaucoma (PACG) is the predominant form of glaucoma in the Asian population and is a leading cause of blindness. It is estimated that blindness from PACG is two-to-five times more common than that due to primary open-angle glaucoma.
Although the reasons for the relatively high prevalence of angle closure remain unclear, it is documented that the eyes of these patients have shorter axial length, shallower anterior chamber, and thicker lens.,,,, The thicker and anteriorly positioned lens usually results in shallower anterior chambers, and the gradual and progressive increase in lens thickness with aging results in exaggerated shallowing of the anterior chamber.
PACG generally has two types of presentations – those with acute onset of symptoms and those presenting in a relatively asymptomatic form. The prevalence of these two presentations varies in different races. In the Asian population, the prevalence of acute form is more compared to the chronic form, and the reverse is true in Blacks. The asymptomatic chronic form often presents late with advanced optic neuropathy in one eye which is a major cause of blindness in the Asian population.
The objective of the present study was to compare the ocular biometry among these presentations which might explain the mechanisms behind the two forms.
| Materials and Methods|| |
This study was conducted at the glaucoma clinic of a tertiary care teaching institute over a period of 2 years after obtaining clearance from the Institutional Ethical Committee and informed consent from the patients. Sixty eyes of sixty patients diagnosed as having either acute (Group A) or chronic presentations (Group B) were studied.
Patients were selected according to the type of presentation. Those patients presented with history of acute symptoms such as uniocular pain, headache, defective vision, colored halos, along with high intraocular pressure (IOP ≥35 mmHg), shallow anterior chamber, and mid-dilated nonreactive pupil were classified as the acute variety (acute primary angle closure) and constituted Group A. Chronic form was diagnosed in eyes with peripheral anterior synechiae (PAS) of >180° with a chronically elevated IOP with optic disc and visual field changes, who could remain asymptomatic (creeping angle closure) or present with occasional headaches (chronic PACG). These patients formed Group B.
For the diagnosed cases, Nd-Yag laser peripheral iridotomy was performed once the corneal edema got subsided. A thorough ophthalmologic evaluation, including biometry, was performed 3 weeks following the procedure.
Patients with previous history of intraocular surgeries or trauma, cases with secondary angle closure, active keratitis, or corneal opacities, in whom gonioscopy and fundus examination could not be performed, were excluded from the study.
A complete ophthalmological evaluation was done by an ophthalmologist. Best-corrected visual acuity (BCVA), automated refraction and keratometry, slit-lamp examination using a Haag–Streit 900 slit lamp, applanation tonometry, and corneal diameter were assessed. Corneal thickness was measured using optical pachymeter. Measurements of corneal diameters were taken with Castroviejo calipers, and average readings were calculated. Contact ultrasonic biometry (Sonomed model EZ Scan AB5500+) was used for measuring ocular biometric parameters such as axial length, anterior chamber depth, and lens thickness by placing the probe over the central cornea. Average value of five measurements (with a standard deviation of <0.05 mm) was calculated for statistical analysis. The measured parameters were used to calculate lens-axial length factor (LAF = LT/AL × 10) and relative lens position (RLP = [ACD + ½LT]/AL × 10)., Gonioscopic evaluation of angle was done using a Goldmann two-mirror gonioprism under standard testing conditions, and indentation gonioscopy was performed with Sussman four mirror lens. The optic disc evaluation was done using a 78D lens. Visual field testing (SITA Standard) was done by Humphrey Automated Perimetry.
Chi-square test was used to compare the categorical variables. Independent sample t-test was used to compare the continuous variables by group. Statistical analyses were conducted using SPSS version 20.0 for Windows (IBM Corporation Armonk, NY, USA).
| Results|| |
Sixty eyes of sixty patients were included in the study with equal number of patients in each group. While comparing the mean age in both groups, it was found that patients in Group A were significantly younger than patients in Group B [52.47 ± 9.10 vs. 58.70 ± 11.11, P = 0.021, [Table 1]. Comparison of the distribution of gender among the groups revealed that majority of patients were females in Group A (96.7%), whereas males predominated (60%) in Group B, which was statistically significant [P < 0.001, [Table 1].
While comparing the ocular biometric parameters among the two groups, it was found that patients in Group A had a significantly short axial length when compared Group B (21.62 ± 0.75 vs. 22.64 ± 0.51, P < 0.001). Comparison of AC depth revealed a similar trend in Group A and B (2.34 ± 0.31 vs. 2.69 ± 0.19, P < 0.001). Group A patients had a thicker lens compared to group B, and the values were statistically significant (4.83 ± 0.34 vs. 4.47 ± 0.25, P < 0.001). Lens thickness axial length factor when analyzed showed that Group A had significantly higher and group B had lower values (0.20 ± 0.01 vs. 0.17 ± 0.02, P < 0.001). Keratometry values did not show any statistically significant difference between the two groups (44.48 ± 1.96 vs. 44.28 ± 1.42, P = 0.639). Mean corneal diameter was comparable in both groups (11.55 ± 0.62 mm vs. 11.66 ± 0.67 mm, P = 0.499). Pachymetry was also comparable in both groups (514.70 ± 24.12 mm vs. 513.30 ± 28.95 mm, P = 0.839). RLP values were comparable in the two groups (2.20 ± 0.11 vs. 2.18 ± 0.13, P = 0.431) without any statistical significance [Table 2].
While BCVA was compared among the groups, it was found that 20% of patients in Group A and 43.3% of patients in Group B had BCVA of ≤6/60 which was comparable in both groups (P = 0.096). Analysis of spherical equivalents showed hyperopic refractive error in all patients. Twenty-five patients in the Group A showed hyperopic refractive error of 1–2 diopters and 5 patients showed hypermetropia of >2 diopters, while all the patients in Group B showed hypermetropia of 1–2 diopters, but the difference was not statistically significant [P = 0.052, [Table 3].
|Table 3: Comparison of best-corrected visual acuity and spherical equivalent|
Click here to view
| Discussion|| |
Ocular biometric studies have shown that PACG eyes have shorter axial length, thicker cornea with steep corneal curvature, shallower anterior chamber, and thicker lens with anterior lens position compared to normal eyes. However, biometric differences between eyes with acute and chronic presentations have not been widely studied.
In the present study, while comparing the two study groups, it was seen that the acute form presented at a significantly younger age compared to the chronic presentation [52.47 ± 9.10 vs. 58.70 ± 11.11, P = 0.021, [Table 1]. Patients with small eyes have short axial length, anterior chamber depth, and filtration angle width along with a comparatively large lens, thereby predisposing them to a high risk of developing primary angle closure at a younger age. In eyes which escape an acute attack, an increase in lens thickness secondary to aging process might lead to gradual closure of the angles with formation of PAS. This being a slow process might lead to chronic angle-closure disease explaining the older age of presentation.
It is well documented that angle-closure disease has a gender predisposition with females being more susceptible than males. But in our study, it was observed that 96.7% of patients in the acute presentation were females, whereas males predominated (60%) in the chronic group which was statistically significant [P < 0.001, [Table 1]. The male predominance in the chronic presentation observed in our study could not be supported by previous literature. This could be partly because gender influence on presentation of the chronic form was not specifically looked for in many published data. Existing data mainly focus on the anatomical differences in male and female eyes. However, other factors such as physiological changes, mainly due to hormonal effects in females, were not taken into account as these factors could also influence the acute presentation.
Axial length analysis showed a statistically significant difference between the two groups with the acute form having a shorter axial length in conformity with other studies. The shallower anterior chamber depth in acute angle closure is suggested to be secondary to a thicker and more anterior position of the crystalline lens. Similar observation was made in our study as well. Lens thickness analysis of the two groups also showed a statistically significant difference with the acute form having the maximum lens thickness (4.83 ± 0.34 vs. 4.47 ± 0.25, P < 0.001). Hence, it can be inferred that a thick lens leads to shallow anterior chamber, thereby producing angle closure.
The importance of lens thickness/axial length factor in primary angleclosure disease was evaluated by Lan et al., and the ratio was high for the angle-closure spectrum of disease. It indicates the relative size of the lens. In our study, eyes with acute presentation had a statistically significant higher lens thickness/axial length factor compared to the chronic presentation. A study by Markowitz and Morin also showed that in angle-closure disease lens thickness/axial length factor was age dependent and greater than normal in most of the age groups.
Regarding RLP, our study showed no statistically significant difference between the two study groups. Literature review shows that there have been conflicting reports on the importance of RLP in angle closure.,,, Pachymetry values were normal and comparable in the two groups in our study (514.70 ± 24.12 mm vs. 513.30 ± 28.95 mm). However, in a similar study by Sihota, values obtained were 572.7 ± 35.6 versus 524.2 ± 30.8 mm. The differences in pachymetry could be partly due to differences in timing of measurement after acute attack as well as due to the technique used.
Our study showed that corneal curvature was more in the eyes in the acute form as compared to chronic presentation, but there was no statistical significance. Regarding corneal diameter eyes in the acute variety had smaller corneal diameter compared to chronic form without any statistical significance. These observations made in our study were in agreement with a study by Sihota.
Regarding BCVA, 20% of eyes in the acute presentation had a BCVA ≤6/60, whereas 43.3% of eyes in the chronic form had the same. Literature review also supports this finding since chronic angle-closure glaucoma presents in a late stage with poorer visual acuity due to its relatively asymptomatic clinical course. However, the results obtained had no statistical significance. Similarly, regarding spherical equivalent, 83.3% of eyes in the acute and 100% eyes in the chronic presentation showed 1–2 D of hypermetropia. Five percent of eyes in the acute group had hypermetropia of >2.0 D but none in the chronic group. None of the eyes in either group were myopic or emmetropic in refraction. Although in the present study, it was found that chronic cases were more hypermetropic with poorer visual acuity at presentation, statistical analysis revealed no significance. This may be due to the small sample size of the groups studied.
Our study demonstrated that eyes with acute angle-closure disease were characterized by more crowded anterior segment as compared to eyes with chronic presentation. Hence, it can be presumed that there may be some other mechanism other than the ocular biometric parameters for the development of chronic angle closure. Recent developments such as ultrasound biomicroscopy, anterior segment optical coherence tomography, and Scheimpflug video imaging may throw light into the ultrastructural features and dynamic changes of the anterior ocular structures. Hence, let us hope that future studies may reveal the mechanisms other than the biometric parameters in the primary angle-closure spectrum of disease.
Limitations of the current study include performing biometry after laser peripheral iridotomy, absence of a control group, and the inherent errors that can occur when patients are selected from a hospital setting. There are reports which reveal that iridotomy deepens the peripheral anterior chamber without any effect on central anterior chamber depth. Hence, its values before and after Yag laser iridotomy could be considered comparable.
| Conclusion|| |
It is concluded that the mechanism of acute form of primary angle-closure disease can be explained by the ocular biometric parameters alone. However, there exists the possibility of some other unexplored additional mechanism which could contribute for the chronic presentation.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]