FP1012 : To Compare the Prevalence of Primary Angle Closure Disease with Vanherick, Gonioscopy & Asoct in OPD

Dr.Rajat Kapoor, K16899, Dr. Bhavatharini M, Dr.Amjad Salman, Dr. Sathyan Parthasarathy

INTRODUCTION

The word glaucoma came from the Greek word ‘glaukos’ which meant ‘clouded with a blue-green hue’. In the Hippocratic Aphorisms the term glaucoma was used to describe blindness coming on in advancing years associated with a glazed appearance of the pupil. The Hippocratic writings make no clear distinction between cataract and glaucoma.

Glaucoma

Glaucoma is a group of acute and chronic, progressive, multifactorial optic neuropathies in which intraocular pressure among other contributing factors are responsible for a characteristic acquired loss of retinal ganglion cell axons leading to atrophy of the optic nerve with demonstrable visual field defects.

Two major forms of glaucoma exist –

  1. Open angle glaucoma (OAG) in which aqueous humour has free access to the trabecular meshwork
  2. Angle closure glaucoma (ACG) in which access of the aqueous humour to the trabecular meshwork is restricted

The National Programme for Control of Blindness in India has listed glaucoma as the 3rd major cause for blindness in India, contributing to 5.8% of the total blind cases.1 The World Health Organization (WHO) lists glaucoma as the 2nd major cause for blindness worldwide, contributing to 8% of the total blind cases.2

Of the estimated 8.9 million blind in India, 12.8% are due to glaucoma. The problem is expected to reach alarming proportions by the turn of the century.3In the Indian population, the prevalence (95% CI) of POAG, PACG, and ocular hypertension were 4.1 (0.08-8.1), 43.2 (30.14-56.3), and 30.8 (19.8-41.9) per 1,000, respectively. All the PACG cases detected were of the chronic type. Hitherto unavailable community-based information on primary glaucoma in our study population indicates that PACG is about five times as common as POAG.4

The epidemiological studies in Asian population indicate a higher prevalence of primary open angle glaucoma (POAG) in comparison with primary angle closure glaucoma (PACG). However, the visual impairment in patients with PACG is 2 to 3 times more than POAG as it is an aggressive and visually destructive type of glaucoma.5

Primary angle closure (PAC) is an anatomic disorder. It is characterized by an abnormal relationship between anterior segment structures.6,7  The mechanism of angle closure can be explained by one or a combination of the following: (1) abnormalities of the size or position of anterior segment structures; (2) abnormal forces in the posterior segment that alter the anatomy of the anterior segment.4,8,9

Classification of individuals with narrow angles based on the results of ophthalmic evaluation, including gonioscopy and other clinical findings, is important in the management of their glaucoma. One system classifies individuals with Primary angle closure disease as being a primary angle-closure suspect (PACS) or as having primary angle closure (PAC) or primary angle closure glaucoma (PACG).

Classification as a PACS is defined by iridotrabecular contact of 180 degree or more without the presence of IOP elevation or peripheral anterior synechiae (PAS). Individuals with PAC have, in addition to iridotrabecular contact, IOP elevation, PAS, or both with no secondary cause, whereas those with PACG also have glaucomatous optic neuropathy.

Primary angle closure glaucoma (PACG) is a very destructive and aggressive type of glaucoma.6-8 It is caused by the appositioning of the peripheral iris against the trabecular meshwork, resulting in the obstruction of aqueous outflow.10 Shorter axial length, thickening of the lens in old adults, plateau iris, narrow anterior chamber angle (ACA), shallow anterior chamber depth (ACD) and shorter corneal diameter are considered as the major risk factors in the development of PACG.11

Assessment of the drainage angle is mandatory for all people suspected of having glaucoma. The high prevalence of occludable drainage angles and primary angle closure glaucoma in people of east Asian descent suggests that this should be considered in all adult Asians attending for an ophthalmological assessment.6, 12-14A large proportion of the PACG in the Indian population is undiagnosed and untreated. Because visual loss resulting from PACG is potentially preventable if peripheral iridotomy or iridectomy is performed in the early stage, strategies for early detection of PACG could reduce the high risk of blindness resulting from PACG seen in this urban population in India.

Goldmann gonioscopy is the gold standard in assessment of the anterior chamber angle and one of its most popular classifications was introduced by Shaffer. The Shaffer system16 grades the angle on how much of the angle is open in terms of the geometric measurement in degrees of the angle formed between the insertion of the iris into the wall of the eye and the trabecular meshwork.

Despite gonioscopy is regarded as the standard tool for determining angle status, it has some limitations for assessing anterior chamber angle status. It demands considerable skill, experience and knowledge to achieve a stable, focused image at the proper viewing angle. Also, gonioscopic findings can be affected by inadvertent pressure on the gonioscope lens and by increased illumination. Furthermore, gonioscopy is a semi subjective technique, so some studies report that even experienced cross-trained examiners achieve only moderate agreement in determining angle width using gonioscopy17, 18 The above mentioned limitations of gonioscopy, prevent it from being an effective screening tool in anterior chamber angle assessment.

Estimation of the limbal chamber depth was suggested as a non-invasive alternative to gonioscopy. A four point grading scheme given by Van Herick was shown to give results comparable with a five point gonioscopic grading scheme in estimation of the angular width of the peripheral anterior chamber.19

The Van Herrick method for the estimation of the chamber angle used in slit lamp examination does not require much time. Moreover, the performance of this test does not represent additional stress to the patient. Thus, the Van Herick method is suitable for a quick and easy assessment of the chamber angle. However, it is also semi subjective and affected by increased illumination.19, 20

The association between a shallow anterior chamber and primary angle-closure glaucoma (PACG) is well documented.21-24 The measurement of axial anterior chamber depth (ACD) may have potential in screening for PACG.23, 25, 26

Anterior segment OCT (AS-OCT) was designed based on low coherence interferometry, with a super luminescent diode having a wavelength of 1310 nm27-29This allows a deeper penetration and cross-sectional imaging of the anterior chamber (AC) and visualization of the angle.29

OCT was initially developed only for retinal imaging; in 1994 Izatt et al. (Izatt et al., 1994) for the first time used it also for imaging the anterior chamber (anterior segment OCT, ASOCT). Since then, AS-OCT has rapidly become popular for ACA assessment.

AS-OCT is a technique more rapid, more easily practiced by a technician. Also without the need to position a scanning probe close to the globe, better control of eye accommodation and pupil size is attainable with AS-OCT.

These characteristics compare favorably with the current gold standard, gonioscopy, which requires highly trained personnel. Although direct imaging of the ACA is possible with ASOCT, it has a few limitations, such as the inability of ASOCT to visualize structures posterior to the iris including the ciliary body, peripheral lens and the lens zonules and also the difficulty in localization of the Scleral Spur in some circumstances.

If AS-OCT were to provide an accurate assessment of angle anatomy, it could provide a rapid diagnostic and screening tool for the detection of angle closure.

  The need for public health initiatives to combat PACG was highlighted by an estimate that half of the 67 million people suffering from primary glaucoma globally have PACG. It has been calculated that 6.7 million people worldwide have been irreversibly blinded as a consequence of glaucoma. Half of these are Asian, majority Chinese.A means of detecting those at risk (people with occludable drainage angles) is a prerequisite of a prevention program. If an effective test can be identified, PACG may meet the criteria for viable population screening.30 

Thus we intend to find the degree of agreement between the Van Herick technique of anterior chamber angle assessment and the AS-OCT while keeping the gonioscopic grading of angle by Schaffer’s system as the gold standard.

MATERIALS AND METHODS

The study was an Analytical, Cross sectional study performed over a period of nine months (January 2014 to September 2014) in a tertiary eye care center in South India. A total of 300 eyes of 150 randomized patients who presented to the general OPD of the hospital were included in the study.

  • Inclusion Criteria
  • Consecutive patients coming to OPD of Sankara eye hospital.
  • Age between 40 years and 80 years.
  • Either gender
  • Spherical refraction values between -3.0 D to +3.0 D.
  • Exclusion criteria
    • Patients less than 40 years and more than 80 years of age.
    • Patients with history of prior laser or intra-ocular surgery.
    • Patients with history of prior ocular trauma.
    • Patients with mature / hypermature cataract.
    • Patients with severe corneal pathology which interferes with gonioscopy.
    • Patients with dilated pupil due to any cause.
    • Refractive errors i.e Myopia / Hypermetropia of >3.0 D.
  • Material and Methodology
  • The study was started after getting approval from the Scientific and Ethical Committee.
  • The study was carried out in accordance with the World Medical Association’s Declaration of Helsinki.
  • Written informed consent was obtained from all the patients.
  • They underwent an ophthalmic examination as follows-
  • Visual acuity for distance by Snellen’s chart.
  • Detailed history.
  • Slit lamp bio microscopy (Topcon SL 1E, Topcon Corp., Japan)
  • Fundus examination using slit lamp and +90D lens (Volk, USA)
  • Goldmannapplanation tonometry (OPTILASA S.I., Spain)
  • Central corneal thickness using contact ultrasound pachymetry (TOMEY SP-2000, Japan)
  • Gonioscopy using Goldmann 3 mirror gonioscopy lens, (Ocular Instruments Inc. Bellevue, WA, U.S.A) was done by the same examiner in all the patients.
  • Non contact Tonometry (Topcon CT.80, Topcon Corp,Japan) was done for measuring the intraocular pressure.
  • Anterior segment Optical Coherence Tomography (Topcon 3D OCT-1 Maestro, Topcon Corp, Japan)
  • The findings observed in the patients were recorded in a Proforma (Annexure).
  • General examination was carried out by a physician and detailed history was taken. Blood pressure was recorded using a mercury sphygmomanometer; an average of 3 readings was taken. Blood glucose (fasting and post prandial) values were measured.
  • Hypertension was defined using the guidelines given in the Indian Hypertension Guidelines II.39
  • Diabetes mellitus was defined using the guidelines given in the API-ICP guidelines on diabetes 2007.40

 INTRODUCTION

The word glaucoma came from the Greek word ‘glaukos’ which meant ‘clouded with a blue-green hue’. In the Hippocratic Aphorisms the term glaucoma was used to describe blindness coming on in advancing years associated with a glazed appearance of the pupil. The Hippocratic writings make no clear distinction between cataract and glaucoma.

Glaucoma

Glaucoma is a group of acute and chronic, progressive, multifactorial optic neuropathies in which intraocular pressure among other contributing factors are responsible for a characteristic acquired loss of retinal ganglion cell axons leading to atrophy of the optic nerve with demonstrable visual field defects.

Two major forms of glaucoma exist –

  1. Open angle glaucoma (OAG) in which aqueous humour has free access to the trabecular meshwork
  2. Angle closure glaucoma (ACG) in which access of the aqueous humour to the trabecular meshwork is restricted

The National Programme for Control of Blindness in India has listed glaucoma as the 3rd major cause for blindness in India, contributing to 5.8% of the total blind cases.1 The World Health Organization (WHO) lists glaucoma as the 2nd major cause for blindness worldwide, contributing to 8% of the total blind cases.2

Of the estimated 8.9 million blind in India, 12.8% are due to glaucoma. The problem is expected to reach alarming proportions by the turn of the century.3In the Indian population, the prevalence (95% CI) of POAG, PACG, and ocular hypertension were 4.1 (0.08-8.1), 43.2 (30.14-56.3), and 30.8 (19.8-41.9) per 1,000, respectively. All the PACG cases detected were of the chronic type. Hitherto unavailable community-based information on primary glaucoma in our study population indicates that PACG is about five times as common as POAG.4

The epidemiological studies in Asian population indicate a higher prevalence of primary open angle glaucoma (POAG) in comparison with primary angle closure glaucoma (PACG). However, the visual impairment in patients with PACG is 2 to 3 times more than POAG as it is an aggressive and visually destructive type of glaucoma.5

Primary angle closure (PAC) is an anatomic disorder. It is characterized by an abnormal relationship between anterior segment structures.6,7  The mechanism of angle closure can be explained by one or a combination of the following: (1) abnormalities of the size or position of anterior segment structures; (2) abnormal forces in the posterior segment that alter the anatomy of the anterior segment.4,8,9

Classification of individuals with narrow angles based on the results of ophthalmic evaluation, including gonioscopy and other clinical findings, is important in the management of their glaucoma. One system classifies individuals with Primary angle closure disease as being a primary angle-closure suspect (PACS) or as having primary angle closure (PAC) or primary angle closure glaucoma (PACG).

Classification as a PACS is defined by iridotrabecular contact of 180 degree or more without the presence of IOP elevation or peripheral anterior synechiae (PAS). Individuals with PAC have, in addition to iridotrabecular contact, IOP elevation, PAS, or both with no secondary cause, whereas those with PACG also have glaucomatous optic neuropathy.

Primary angle closure glaucoma (PACG) is a very destructive and aggressive type of glaucoma.6-8 It is caused by the appositioning of the peripheral iris against the trabecular meshwork, resulting in the obstruction of aqueous outflow.10 Shorter axial length, thickening of the lens in old adults, plateau iris, narrow anterior chamber angle (ACA), shallow anterior chamber depth (ACD) and shorter corneal diameter are considered as the major risk factors in the development of PACG.11

Assessment of the drainage angle is mandatory for all people suspected of having glaucoma. The high prevalence of occludable drainage angles and primary angle closure glaucoma in people of east Asian descent suggests that this should be considered in all adult Asians attending for an ophthalmological assessment.6, 12-14A large proportion of the PACG in the Indian population is undiagnosed and untreated. Because visual loss resulting from PACG is potentially preventable if peripheral iridotomy or iridectomy is performed in the early stage, strategies for early detection of PACG could reduce the high risk of blindness resulting from PACG seen in this urban population in India.

Goldmanngonioscopy is the gold standard in assessment of the anterior chamber angle and one of its most popular classifications was introduced by Shaffer. The Shaffer system16 grades the angle on how much of the angle is open in terms of the geometric measurement in degrees of the angle formed between the insertion of the iris into the wall of the eye and the trabecular meshwork.

Despite gonioscopy is regarded as the standard tool for determining angle status, it has some limitations for assessing anterior chamber angle status. It demands considerable skill, experience and knowledge to achieve a stable, focused image at the proper viewing angle. Also, gonioscopic findings can be affected by inadvertent pressure on the gonioscopic lens and by increased illumination. Furthermore, gonioscopy is a semisubjective technique, so some studies report that even experienced cross-trained examiners achieve only moderate agreement in determining angle width using gonioscopy17, 18 The above mentioned limitations of gonioscopy, prevent it from being an effective screening tool in anterior chamber angle assessment.

Estimation of the limbal chamber depth was suggested as a non-invasive alternative to gonioscopy. A four point grading scheme given by Van Herick was shown to give results comparable with a five point gonioscopic grading scheme in estimation of the angular width of the peripheral anterior chamber.19

The Van Herick method for the estimation of the chamber angle used in slit lamp examination does not require much time. Moreover, the performance of this test does not represent additional stress to the patient. Thus, the Van Herick method is suitable for a quick and easy assessment of the chamber angle. However, it is also semisubjective and affected by increased illumination.19, 20

The association between a shallow anterior chamber and primary angle-closure glaucoma (PACG) is well documented.21-24 The measurement of axial anterior chamber depth (ACD) may have potential in screening for PACG.23, 25, 26

Anterior segment OCT (AS-OCT) was designed based on low coherence interferometry, with a superluminescent diode having a wavelengthof 1310 nm27-29This allowes a deeper penetration and cross-sectional imaging of the anterior chamber (AC) and visualization of the angle.29

OCT was initially developed only for retinal imaging; in 1994 Izatt et al. (Izatt et al., 1994) for the first time used it also for imaging the anterior chamber (anterior segment OCT, ASOCT). Since then, AS-OCT has rapidly become popular for ACA assessment.

AS-OCT is a technique more rapid, more easily practiced by a technician. Also without the need to position a scanning probe close to the globe, better control of eye accommodation and pupil size is attainable with AS-OCT.

These characteristics compare favourably with the current gold standard, gonioscopy, which requires highly trained personnel. Although direct imaging of the ACA is possible with ASOCT, it has a few limitations, such as the inability of ASOCT to visualize structures posterior to the iris including the ciliary body, peripheral lens and the lens zonules and also the difficulty in localization of the Scleral Spur in some circumstances.

If AS-OCT were to provide an accurate assessment of angle anatomy, it could provide a rapid diagnostic and screening tool for the detection of angle closure.

 The need for public health initiatives to combat PACG was highlighted by an estimate that half of the 67 million people suffering from primary glaucoma globally have PACG. It has been calculated that 6.7 million people worldwide have been irreversibly blinded as a consequence of glaucoma. Half of these are Asian, majority Chinese.A means of detecting those at risk (people with occludable drainage angles) is a prerequisite of a prevention program. If an effective test can be identified, PACG may meet the criteria for viable population screening.30 

Thus we intend to find the degree of agreement between the Van Herick technique of anterior chamber angle assessment and the AS-OCT while keeping the gonioscopic grading of angle by Schaffer’s system as the gold standard.

MATERIALS AND METHODS

The study was an Analytical, Cross sectional study performed over a period of nine months (January 2014 to September 2014) in a tertiary eye care center in South India. A total of 300 eyes of 150 randomized patients who presented to the general OPD of the hospital were included in the study.

  • Inclusion Criteria
  • Consecutive patients coming to OPD of Sankara eye hospital.
  • Age between 40 years and 80 years.
  • Either gender
  • Spherical refraction values between -3.0 D to +3.0 D.
  • Exclusion criteria
    • Patients less than 40 years and more than 80 years of age.
    • Patients with history of prior laser or intra-ocular surgery.
    • Patients with history of prior ocular trauma.
    • Patients with mature / hypermature cataract.
    • Patients with severe corneal pathology which interferes with gonioscopy.
    • Patients with dilated pupil due to any cause.
    • Refractive errors i.e Myopia / Hypermetropia of >3.0 D.
  • Material and Methodology
  • The study was started after getting approval from the Scientific and Ethical Committee.
  • The study was carried out in accordance with the World Medical Association’s Declaration of Helsinki.
  • Written informed consent was obtained from all the patients.
  • They underwent an ophthalmic examination as follows
  • Visual acuity for distance by Snellen’s chart.
  • Detailed history.
  • Slit lamp bio microscopy
  • Fundus examination using slit lamp and +90D lens
  • Goldmannapplanation tonometry
  • Central corneal thickness using contact ultrasound pachymetry
  • Gonioscopy using Goldmann 3 mirror gonioscopy lens, was done by the same examiner in all the patients.
  • Non contact Tonometry was done for measuring the intraocular pressure.
  • Anterior segment Optical Coherence Tomography 
  • The findings observed in the patients were recorded in a Proforma (Annexure).
  • General examination was carried out by a physician and detailed history was taken. Blood pressure was recorded using a mercury sphygmomanometer; an average of 3 readings was taken. Blood glucose (fasting and post prandial) values were measured.
  • Hypertension was defined using the guidelines given in the Indian Hypertension Guidelines II.39
  • Diabetes mellitus was defined using the guidelines given in the API-ICP guidelines on diabetes 2007.40
  • Van Herick’s method19
  • Technique :
    • A narrow slit of light is projected onto the peripheral nasal or temporal cornea at an angle of 60° as near as possible to the limbus.
    • This results in a slit image on the surface of the cornea the width of which is compared with the peripheral anterior chamber depth (“black space”). A four-point scale is then used, with each grade indicating the probability of angle closure.
    • Grade 4 the anterior chamber depth (ACD) is ≥100% corneal thickness and the angle is wide open
    • Grade 3 it is > 25 to 50% and the angle is incapable of closure
    • Grade 2 it is 25% and the angle closure is possible;
    • Grade 1 is < 25% and angle closure is likely.
Grade Relation between corneal slit image and anterior chamber depth Interpretation
4 1 : 1 or higher Angle closure very unlikely; chamber angle approx 35o to 45o.
3 1 : ½ Angle closure unlikely; chamber angle approx 20o to 35o.
2 1 : ¼ Angle closure possible; chamber angle approx 20o.
1 1 : < 1/4 Angle closure likely; chamber angle approx 10o.
0 Closed Angle closure; chamber angle 0o

Table A. Van Herick grading of the anterior chamber angle

Technique :an Herick’s method19

  • A narrow slit of light is projected onto the peripheral nasal or temporal cornea at an angle of 60° as near as possible to the limbus.
    • This results in a slit image on the surface of the cornea the width of which is compared with the peripheral anterior chamber depth (“black space”). A four-point scale is then used, with each grade indicating the probability of angle closure.
    • Grade 4 the anterior chamber depth (ACD) is ≥100% corneal thickness and the angle is wide open
    • Grade 3 it is > 25 to 50% and the angle is incapable of closure
    • Grade 2 it is 25% and the angle closure is possible;
    • Grade 1 is < 25% and angle closure is likely.
Grade Relation between corneal slit image and anterior chamber depth Interpretation
4 1 : 1 or higher Angle closure very unlikely; chamber angle approx 35o to 45o.
3 1 : ½ Angle closure unlikely; chamber angle approx 20o to 35o.
2 1 : ¼ Angle closure possible; chamber angle approx 20o.
1 1 : < 1/4 Angle closure likely; chamber angle approx 10o.
0 Closed Angle closure; chamber angle 0o

Table A. Van Herick grading of the anterior chamber angle

Figure 2: Slit lamp grading of the peripheral anterior chamberdepth – The Van Herick method.

Figure 3: Grade 4 Van Herick, with anterior chamber depth more than the size of the corneal slit image.

  • Gonioscopy grading was done for recording the angle width. This investigation is considered as the gold standard technique for assessing the anterior chamber angle.
  • The examination of all subjects was carried out at a low level of ambient illumination with a Goldmann 3-mirror lens. A 1-mm beam of light was reduced to a very narrow slit. The vertical beam was offset horizontally for assessing superior and inferior angles, and a vertically offset horizontal beam was used for nasal and temporal angles. Care was taken to avoid light falling on the pupil during gonioscopy. The assessment was carried out at (x16) magnification.
  • All 4 quadrants were assessed with the eye in the primary position of gaze for measurement of angle width. Minimum adjustment of the lens or eye was allowed to enable a view over the hill of a steep iris while avoiding excessive eye movement and manipulation so as to gain an undistorted view of the angle.

 The Shaffer grading system 16

  • This is based on an estimate of the width of the angle in degrees and the angle structures which can be seen.
  • Grade 0 (0°) is a closed angle with irido-corneal touch, and no visible structures.
  • Grade 4 (35-45°) is a wide open angle with all structures to the ciliary body band being visible.
  • Grades 1-3 lie in between these two grades and relate to increasing width and visibility of angle structures.
  • The clinical relevance of the grading is that Grades 3 and 4 are thought to be incapable of closing, Grade 2 is a possible risk of closure, and Grade 1 is a high risk for closure.
  • With a closed angle (Grade 0), it is important to distinguish between appositional closure and synechial closure. To do this, indentation gonioscopy is used. With appositional closure, the angle will open and the iris will fall back away from the cornea, whereas with synechial closure, the iris remains stuck to the cornea and the angle will not open.

Table B: Shaffer grading system on Gonioscopy

Figure 4a, 4b, 4c: Showing technique of placement of Goldmann three mirrorGonioscopic lens

Figure 5: Normal angle structures as seen on Gonioscopy.

  • Anterior segment Optical Coherence Tomography
    • Performed with Topcon 3D OCT-1 Maestro, Topcon Corp, Japan.
  • Originally anterior and posterior segment imaging used the same wavelength (830 nm). Subsequently a longer wavelength of 1310 nm was preferred for AS-OCT. This increases the depth of penetration by reducing the amount of light scattered by the sclera and limbus, allowing for visualization of the ACA morphology in greater detail. In addition, the 1310 nm light incident on the cornea is strongly absorbed by water in the ocular media, with only 10% reaching the retina. This enables the AS-OCT to utilize higher power, enhancing imaging speed and eliminating motion artifacts.41
  • The scanning speed of this new system is 40 times faster than previous anterior segment OCT systems, enabling real-time imaging.
  • AS-OCT is a technique more rapid, more easily practiced by a technician, better tolerated because requires no contact. A limitation of AS-OCT is that it doesn’t allow visualizing the ciliary body and the supra-choroidal space.
    • Imaging was performed in dark conditions so as to prevent any external light source to cause pupillary constriction and thus artificial opening of the anterior chamber angle.
  • For the comparison with gonioscopy and the Van Herick method, only nasal and temporal angle images obtained with AS-OCT were used.
  • A single examiner analyzed all images qualitatively and measured the quantitative ASOCT parameters such as AOD500 and AOD750.
  • AS-OCT angle classification hinges on accurate localization of the scleral spur, as it is used as the reference point for all the other quantitative measurements. The sclera spur can be defined as the point where there is a change in curvature of the inner surface of the angle wall, often appearing as an inward protrusion of the sclera. One of the limitations of using the ASOCT is that there may be a difficulty in locating the Scleral Spur in all patients.35

Figure 6: Anterior segment OCT image of nasal and temporal angle showing an open angle

Figure 7: Anterior segment OCT image of nasal and temporal angle showing an angle closure

Figure 8: Anterior segment OCT image showing a closed anterior chamber angle with contact between the iris and angle wall
anterior to the Scleral Spur.

Figure 9: Anterior segment OCT image showing image of anterior chamber angle with a marking showing Scleral Spur.

Figure 10: Angle opening distance at 500 mm anterior to the scleral spur (AOD500), defined as the distance from the corneal endothelium to the anterior iris perpendicular to a line drawn
along the trabecular meshwork, at 500 mm from the scleral spur.

Definitions:

  • Gonioscopy: It is considered to be the gold standard technique to assess the angle structures. In gonioscopy, the angle closure was determined when the posterior pigmented trabecular meshwork (TM) was not visible on non-indentation gonioscopy. To compare with the Van Herick method, only temporal and nasal area measurements of gonioscopy and AS-OCT were used in this study analogus to the study done by Park et al.33 In the definition a narrow angle, either 180 or 270 degree of invisible TM is used as the cutoff point. It is either half or two-thirds of the total 360degree in an angle. In our study, we wanted to compare only the nasal and temporal angles, so an eye was defined as having a ‘narrow angle quadrant’ by gonioscopy if the posterior pigmented TM was not visible on non-indentation gonioscopy for at least 60degree (two-thirds of quadrant) both with and without PAS at either the nasal or temporal quadrant.33
  • Van Herick’s method:Angle closure was defined as a peripheral ACD of less than one-fourth of the corneal thickness that is grade I and grade O, in which the chamber angle is less than or equal to 10 degree.19, 33

 AS-OCT:The angle was defined as closed on an AS-OCT image if contact was visible between the peripheral iris and any part of the angle wall anterior to the scleral spur.33, 35 For the purpose of this study, only a qualitative analysis was done. The measurements of quantitative parameters such as AOD500 and AOD750 have been noted, but the assessment of this data is beyond the purview of this study.

  • In this study, we intend to find the degree of agreement between the Van Herick method with gonioscopy and also the ASOCT with gonioscopy while keeping the gonioscopic grading by Shaffer’s system as the gold standard technique in the assessment of the anterior chamber angle.
  • Statistical Methods
  • After data collection, data entry was done in Microsoft Excel 2007.
  • Data analysis was done with the help of SPSS Software version 15 and Open Epi Software.
  • Quantitave data is presented with the help of Mean, Standard deviation, Median and Inter Quartile Range(IQR).
  • Qualitative data is presented with the help of Frequency and Percentage table,
  • Agreement among different test modalities is assessed with Kappa statistics.
  • Kappa statistic value:
    • Good agreement – Kappa >0.60
    • Fair agreement – Kappa 0.40 – 0.59
    • Poor agreement – Kappa <0.39
  • P value less than 0.05 is taken as significant.
  • Data analysis is shown as Pie charts and vertical Bar diagrams.

 OBSERVATIONS AND RESULTS

          The present investigation was a prospective, analytical cross sectional study on patients who presented to the Outpatient department over a period of 9 months. (January 2014 to September 2014). Patients were registered and investigated after obtaining their consent on the same day. No follow up of these patients was observed. The data obtained was analyzed subsequently.

One hundred and fifty patients randomly selected from the outpatient department, who met the inclusion criteria and who consented, were enrolled for the study.

  1. Demographic Data

Distribution of study group as per,

  • Eye: Three hundred eyes of 150 patients were included in the study. Equal number of right and left eye (150 eyes) were present in the study sample.
  • This is also demonstrated in Table 1/Chart 1.

 Table 1: Distribution of sample population with respect to EYE

Eye Frequency Percent
LE 150 50.00%
RE 150 50.00%
Total 300 100.00%

Chart 1: Distribution of sample population with respect to EYE

  • Sex: Among the patients enrolled in the study, 54 patients (36%) were Males whereas 96 patients (64%) were females. This is shown in Table 2/Chart 2.

Table 2: Gender distribution of the study population

Sex Frequency Percent
Male 55 36.18%
Female 97 63.82%
Total 152 100.00%

Chart 2: Gender distribution of the study population

The study compares the Van Herick technique of angle grading and ASOCT with the gonioscopic grading of anterior chamber angle which was considered the gold standard investigation. All three investigations were carried out in all 300 eyes.

  1. Investigation data: Distribution of study group as per angle status (Open/Close) with each investigation.
  • Van Herick’sgrading :30 eyes(10%) showed closed angle and 270 eyes(90%) have an open angle. (Table 3/Chart 3)

Table No 3: Angle status (Open/Close) with Van Herick’s grading

Van Herick (O/C) Frequency Percent
Close 30 10.0
Open 270 90.0
Total 300 100.0

Chart 3: Angle status (Open/Close) with Van Herick’s grading

  • Gonioscopy: 12 eyes(4%) had angle closure whereas 288 eyes(96%) had an open angle.(Table 4/Chart 4)
  • Table 4: Angle status (Open/Close) with Gonioscopy (Shaffer’s grading)
    Gonio (O/C) Frequency Percent
    Close 13 4.33%
    Open 287 95.67%
    Total 300 100.00%

Chart 4: Angle status (Open/Close) with Gonioscopy (Shaffer’s grading)

  • Anterior segment Optical Segment Tomography: 10 eyes(3.33%) had a closed angle. On the other hand 290 eyes(96.67%) had an open angle.(Table 5/Chart 5)

 Table 5: Angle status (Open/Close) with ASOCT

ASOCT (O/C) Frequency Percent
Close 10 3.33%
Open 290 96.67%
Total 300 100.00%

Chart 5: Angle status (Open/Close) with ASOCT

3.Frequency Distribution: Quantitative data additionally obtained during the patient examination which includes GoldmannApplanation tonometry, Pachymetry and quantitative ASOCT parameters such as AOD500 and AOD750 is indicated in Table 6.

Table 6: Quantitaive data Frequency distribution

N Mean Std. Dev Median IQR Minimum Maximum
GAT(corrected) 300 18.12 4.32 17.00 4.00 10.00 44.00
Pachymetry 300 511.87 34.79 512.00 44.00 385.00 617.00
AOD500 300 512.52 218.91 461.00 252.75 160.00 1,438.00
AOD750 300 687.56 260.23 637.50 300.75 216.00 1,757.00
  • The Goldmannapplanation tonometry was done in all 300 eyes, the mean GAT value of the study group was 18.12 mmHg with a minimum and maximum value of 10 mmHg and 44 mmHg.
  • Pachymetry values were also obtained with a mean pachmetry value of 511.87.
  • Quantitaive data was obtained with ASOCT, which included parameters like AOD500 and AOD750.
  • The mean AOD500 value was 512.52 and the mean AOD750 value was 687.56.

4.Comparison among study groups: Ancillary investigations like Van Herick’s grading and ASOCT were compared with Gonioscopy which was considered to be the gold standard investigation to assess the status of the anterior chamber angle.

The comparison was done with the help of Kappa statistic value which gives the degree of agreement between the two investigations and checking if this agreement was statistically significant (p < 0.05).

The other data obtained after statistical analysis was the Sensitivity, Specificity, Positive predictive value, Negative predictive Value and the Diagnostic accuracy.

  • Van Herick (O/C) VsGonioscopy (O/C) :

Thirty eyes were found to be having a closed angle with the Van Herick’s grading, however among these 30 eyes, 12 eyes were actually found to be having a closed angle by Gonioscopy. The 270 eyes found to having an open angle with Van Hericks grading were all found to be having an open angle with Gonioscopy also. (Table 7/Chart 6)

The measure of agreement using the Kappa statistic was found to be 0.545 with a P value of <0.0001

The values of Sensitivity, Specificity, Positive predictive value, Negative predictive Value and the Diagnostic accuracy of the Van Herick’s technique when compared with the gold standard investigation Gonioscopy were 100%, 93.75%, 40%, 100% and 94% respectively.(Table 8/Chart 7).

 Table 7: Comparison of Van Hericks grading and Gonioscopy (Open/Close angle)

Van Herick (O/C) Gonio (O/C) Total
Close Open
Close Count 12 18 30
Percent 40.0% 60.0% 100.0%
Open Count 0 270 270
Percent 0.0% 100.0% 100.0%
Total Count 12 288 300
Percent 4.0% 96.0% 100.0%
Symmetric Measures Value P Value
Measure of Agreement Kappa 0.545 0.000

Using the asymptotic standard error assuming the null hypothesis

 

Chart 6: Comparison of Van Hericks grading and Gonioscopy (Open/Close angle)

Table 8: Assessment of Van Herick’s grading with Gonioscopy as the reference

Measure Estimate 95% Confidence Intervals
Lower Upper
Sensitivity 100.00% 75 100
Specificity 93.75% 90 1
PPV 40.00% 24 68
NPV 100.00% 98 100
Diagnostic Accuracy 94% 90 17

Chart 7: Assessment of Van Herick’s grading with Gonioscopy as the reference

  • ASOCT (O/C) VsGonio (O/C) :

Ten eyes were found to be having a closed angle with the ASOCT, however among these 10 eyes, gonioscopy confirmed 4 eyes to be actually having angle closure. Among the 290 eyes found to having an open angle with ASOCT, not all were found to be having an open angle with Gonioscopy. Two hundered and eighty two eyes among this group were actually confirmed to be having an open angle whereas 8 eyes were found to have angle closure on gonioscopy. (Table 9/Chart 8)

The measure of agreement using the Kappa statistic was found to be 0.340 with a P value of <0.0001

The values of Sensitivity, Specificity, Positive predictive value, Negative predictive Value and the Diagnostic accuracy of the ASOCT when compared with the gold standard investigation Gonioscopy were 33.33%%, 97.92%, 40%, 97.24% and 95% respectively.(Table 10/Chart 9)

 Table 9: Comparison of ASOCT and Gonioscopy (Open/Close angle)

ASOCT (O/C) Gonio (O/C) Total
Close Open
Close Count 4 6 10
Percent 40.0% 60.0% 100.0%
Open Count 8 282 290
Percent 2.8% 97.2% 100.0%
Total Count 12 288 300
Percent 4.0% 96.0% 100.0%
Symmetric Measures Value P Value
Measure of Agreement Kappa 0.340 0.000

Using the asymptotic standard error assuming the null hypothesis.

Chart

Comparison of ASOCT and Gonioscopy (Open/Close angle)

Table 10: Assessment of ASOCT with Gonioscopy as the reference

Measure Estimate 95% Confidence Intervals
Lower Upper
Sensitivity 33.33% 13 94
Specificity 97.92% 95 4
PPV 40.00% 16 73
NPV 97.24% 94 6
Diagnostic Accuracy 95% 92 2

Chart 9: Assessment of ASOCT with Gonioscopy as the reference

 Van Herick (O/C) Vs ASOCT (O/C) Crosstabulation:

Among the eyes found to have open angle with the Van Herick’s grading (270 eyes), 2 eyes were found to have angle closure with ASOCT. On the other hand out of the 290 eyes having open angle with ASOCT, 22 eyes were found to have closed angle with Van Herick’s technique. (Table 11/Chart 10)

The measure of agreement using the Kappa statistic was found to be 0.368 with a P value of <0.0001

The values of Sensitivity, Specificity, Positive predictive value, Negative predictive Value and the Diagnostic accuracy could not be calculated as none of these tests are considered to be the gold standard.

 Table 11: Comparison of Van Hericks grading and ASOCT (Open/Close angle)

Van Herick (O/C) ASOCT (O/C) Total
Close Open
Close Count 8 22 30
Percent 26.7% 73.3% 100.0%
Open Count 2 268 270
Percent 0.7% 99.3% 100.0%
Total Count 10 290 300
Percent 3.3% 96.7% 100.0%
Symmetric Measures Value P Value
Measure of Agreement Kappa 0.368 0.000

Using the asymptotic standard error assuming the null hypothesis.

DISCUSSION

Angle-closure glaucoma is a sight-threatening condition that can result in profound visual loss.42 In the early stages and in predisposed eyes the disease is curable by a non-invasive laser iridotomy.43 The prevalence of angle closure varies in different populations. Thus it is very important to detect the angle closure as soon as possible to enable early treatment.

This study aims to compare the prevalence of primary angle closure disease with Van Herick’s method, Gonioscopy and AS-OCT in randomly selected Outpatient department patients. As per current literature, Gonioscopy is considered as the gold standard investigation in assessment of anterior chamber angle status. We intend to compare other modalities such as the Van Herick’s grading of anterior chamber angle and ASOCT with Gonioscopy with respect to their sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy and also to study the degree of agreement between either of these two investigations using the Kappa statistic and finding out its significance.

In this study, 4% of the study population showed angle closure with gonioscopy. Angle closure was noticed in 10% of the eyes with Van Herick’s grading and 3.33% by ASOCT. Other similar studies like the one by Nolan et al35 found, 50% eyes to be having a closed angle. In the same population ASOCT found angle closure in 74% of the eyes. However unlike our study, this study was carried in a select population of pre diagnosed glaucoma patients.

The Van Herick’s grading diagnosed maximum number of closed angles (30) in our study group than gonioscopy (12) and ASOCT (10) in the current study. Nolan et al35 and Lisandro M. Sakata et al38 found that ASOCT diagnosed more number of closed angles than Gonioscopy. However, the study by Nolan et al35 was carried out in a subset of patients which were previously diagnosed of glaucoma.

Van Herick’s grading vsGonioscopy

The comparison of Van Herick’s grading and Gonioscopy revealed a fair agreement between the two (Kappa statistic of 0.545) in the current study. Our study presented with the diagnostic accuracy value of 94% with Van Herick’s technique when compared with Gonioscopy. SeongBae Park et al33 found good agreement between the same set of investigations with a Kappa statistic of 0.80 in the nasal quadrant and 0.82 in the temporal quadrant, but in this study the ASOCT was taken as the reference standard.

Sensitivity and specificity values of the Van Herick’s grading with keeping Gonioscopy as the reference standard came as 100% and 93.75%, thus vindicating its value as a good screening test. Also the negative predictive value of 100% indicates that Van Herick’s grading can be useful in ruling out a case of angle closure with accuracy. Similar good sensitivity (84%) and specificity (86%) values were obtained in a study by and Foster PJ et al.18  Another study conducted in a similar population of South India by Ravi Thomas et al31 shows a low sensitivity (61.9%) and high specificity (89.3%). Contradictory findings were published by Congdonet al26 who stated that, peripheral slit beam tests like Van Herick does not correlate well with Gonioscopy.

ASOCT vsGonioscopy

The current study showed poor agreement between ASOCT and gonioscopy (Kappa value 0.340). This finding was in line with another study by Lisandro M. Sakata et al38(Kappa value of 0.40) andSeongBae Park et al33(Kappa value of 0.15 and 0.16 in nasal and temporal quadrants respectively). However in the study by SeongBae Park et al33, the ASOCT was taken as the reference standard.  The diagnostic accuracy of ASOCT in our study was found to be 95%.

A high specificity value (97.92%) obtained in our study indicates that ASOCT could possibly used as a confirmatory and diagnostic test to detect angle closure. However, the screening potential of ASOCT was not proven as it had a low sensitivity of 33.33%. Radhakrishnanet al37observed similar high specificity values of 100% and low sensitivity value of 62.5%. Nolan et al35 reported dissimilar findings, he found that the ASOCT sensitivity was 98% and specificity was 55.4%. Wirbelauer C et al44 found both high sensitivity and specificity of 85% and 90% respectively. Hence, considering the high cost of the machine and also the low sensitivity provided by ASOCT, it is safe to say that ASOCT is not a very effective screening tool in the assessment of anterior chamber angle with respect to the Indian population.

Van Herick’s grading vs ASOCT

This study finds that a poor agreement exists between these two investigations (Kappa statistic of 0.368). SeongBae Park et al33 also observed a similar low agreement (Kappa value of 0.11 in nasal and 0.019 in the temporal quadrant). However in the study being talked about, ASOCT was considered to be the reference standard.

Our study results indicate that the agreement of detecting angle closure using gonioscopy and the Van Herick method was fairly good (kappa = 0.545). However, the agreement between AS-OCT and the other two techniques was poor in the detection of angle closure (gonioscopy vs. AS-OCT: kappa = 0.340; Van Herick method vs. AS-OCT: kappa = 0.368).

The reason for good agreement between gonioscopy and the Van Herick method could be explained in that both methods have some common features. Gonioscopy and the Van Herick method are performed under slit lamp examination, and both are semi-subjective and semi-quantitative. Another reason for good agreement between these two techniques is that both observe the wide area (quadrant) for detection of angle closure.

Since current AS-OCT, on the other hand, does not provide a continuous profile of the whole angle, angle closure by AS-OCT images is defined by a single axis scan of the angle, and thus it may vary depending on the scanned axis.27 It is also possible, that the discrepant findings between gonioscopy and AS OCT may be the result of the different anatomic landmarks and levels of iridoangle contact used to define a closed angle.38We also agree with previous suggestions that inadvertent pressure and subsequent distortions of the cornea by a gonioscopic lens may change the AC configuration and contribute to poor agreement between gonioscopy and AS-OCT.35, 45

Since gonioscopy and the Van Herick technique have some inherent limitations, which can show different results between examiners and difficulty in quantitative assessment, we have displayed interest in AS-OCT AC angle parameters. AS-OCT is an objective and quantitative technology, and it is reported that cross trained examiners achieve excellent reproducibility in determining angle width.28, 29

Hence, our study results are in line with previous similar publications.33, 35, 38 However, exactly similar comparison with respect to the investigations done and the statistical parameters analysed, does not exist in present literature to the best of our knowledge. The quantitative parameters obtained in the ASOCT like the AOD500 and AOD750, the values of which were obtained by us but not statistically analysed yet are the new area of interest. Thus, the defining of cutoff measurements for narrow angles on AS-OCT will be the subject of further data analyses.

 CONCLUSION

The assessment of angle structures in a general population by Van Herick grading and Gonioscopy showed fairly good agreement but both these techniques revealed a poor agreement with ASOCT. The Van Herick method, because of its high sensitivity and high negative predictive value can be used as a screening tool in detecting angle closure. ASOCT on the other hand, having a high specificity can be used to confirm angle closure and detect the mechanism of closure to some extent. At present, Gonioscopy is a mandatory tool in the evaluation of anterior chamber angle assessment and none of the above mentioned investigations can replace it.

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