Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques

doi:10.4236/ijcm.2013.412095

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International Journal of Clinical Medicine, 2013, 4, 548-555

Published Online December 2013 (http://www.scirp.org/journal/ijcm)

http://dx.doi.org/10.4236/ijcm.2013.412095

Open Access IJCM

Evaluation of Nasal and Temporal Anterior Chamber

Angle with Four Different Techniques

Fredrik P. Källmark, Mezghan Sakhi

Unit of Optometry, Section of Ophthalmology and Vision, Department of Clinical Neurosience, Karolinska Instetutet, Stockholm,

Sweden.

Email: [email protected]

Received October 8th, 2013; revised November 5th, 2013; accepted December 2nd, 2013

tribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is prop-

erly cited.

ABSTRACT

Background: Anterior chamber angle (ACA) can be measured by many different techniques. In order for a technique

to be a part of the routine eye examination, it has to be quick and easy in good agreement with gonioscopy both nasally

and temporally. Aim: To investigate variation in ACA measurement between gonioscopy, van Herick technique, ante-

rior segment optical coherence tomography (AS-OCT) and Sirius Scheimpflug-Camera both nasally and temporally.

Method: The ACA of 50 eyes of 25 healthy subjects was measured with gonioscopy, van Herick technique, AS-OCT

and Sirius Scheimpflug-Camera. The angle was measured both nasally and temporally. Results: No statistically sig-

nificant difference could be found between gonioscopy, van Herick technique and AS-OCT either nasally or temporally.

The Sirius Scheimpflug-Camera on the other hand showed statistically significant difference to gonioscopy (p < 0.0001),

van Herick technique (p < 0.0001) and AS-OCT (p < 0.0001) both nasally (p = 0.03, p = 0.001, p < 0.0001) and tempo-

rally (p = 0.0002, p = 0.001, p < 0.0001). Conclusion: This study showed good agreement between three of the four

techniques. ACA measurements obtained by the Sirius Scheimpflug-Camera should therefore not be considered inter-

changeable with those obtained by the remaining three methods.

Keywords: Anterior Chamber Angle (ACA); Gonioscopy; Van Herick Technique; Sirius Scheimpflug Camera;

AS-OCT; Angle Closure Glaucoma

1. Introduction

Angle Closure Glaucoma (ACG), a sight threatening eye

disease, is a major cause of blindness throughout the

world [1].

ACG is caused by the abnormal positioning of the pe-

ripheral iris towards the trabecular meshwork which

hinders the aqueous outflow resulting in an increased

intraocular pressure (IOP), eventually leading to glauco-

matous optic neuropathy and irreversible blindness [2-4].

Eyes with narrow angles and at risk of ACG can be

prevented from the disease if they are identified prior to

the disease’s onset [5]. It is therefore very important to

measure and evaluate the anterior chamber angle (ACA),

Figure 1, of all the patients in a routine eye examination.

One should also evaluate the ACA of elderly patients as

the prevalence of ACG increases with age due to the

gradual increase of the crystalline lens [1,2,6]. Evalua-

tion of ACA should also be performed at patients who

take medication that can cause pupil dilation [7]. For

ACA evaluation in a routine eye examination, a quick

and easy method is needed.

ACA can be measured by many different methods: e.g.

gonioscopy, ultra sound biomicroscopy (UBM), van He-

rick technique, Scheimpflug photography, anterior seg-

ment optical coherence tomography (AS-OCT) and the

Sirius Scheimpflug-Camera [1].

1.1. Gonioscopy

Gonioscopy, the current gold standard method, makes

use of a slit lamp and a contact lens (gonioscopy lens) to

view the ACA structures. When describing the angle

with gonioscopy, several systems have been developed

as Scheie, Shaffer, Becker and Spaeth [8,10,11]. Pressure

on the gonioscopy lens and illumination used during the

examination can alter the angle configuration. Further-

more, it is a time consuming subjective method that re-

Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques 549

Figure 1. Diagram of the anatomical structures forming the

iridocorneal angle.

quires considerable skill, knowledge and experience in

order to achieve reliable measurements [1,3,4,12]. These

limitations make gonioscopy less suitable as a quick

evaluation method for ACA in a routine eye examination.

1.2. Van Herick

Van Herick technique, Sirius Scheimpflug-Camera and

AS-OCT on the other hand can be part of a routine eye

checkup as they all are quick and easy to perform and do

not contact the cornea [1,7].

The van Herick technique uses a slit lamp to subjec-

tively estimate the ACA whilst Sirius Scheimpflug-

Camera and AS-OCT provide objective measurement of

the ACA.

1.3. AS-OCT

AS-OCT is a tomographic and biomicroscopic device of

high resolution designed for imaging and measuring the

anterior segment of the eye [3]. Measurement of the

ACA by the AS-OCT takes less than a second. The AS-

OCT takes cross sectional images of the anterior segment

that are analyzed by a semiautomatic software program

that is connected to the device. The examiner marks the

apex of the angle, the posterior surface of the cornea and

the anterior surface of the iris and the software calculates

the ACA in degrees [3,13].

1.4. Sirius Scheimpflug-Camera

Sirius Scheimpflug-Camera is a combination of a 3D

rotating Scheimpflug camera with a placido disc topog-

rapher that gives a detailed evaluation of the entire ante-

rior eye segment including ACA. The scanning process

takes less than one second and acquires about 25 Sch-

eimpflug images, which are analyzed by the computer

software program that is connected to the device and the

ACA is presented in degrees [14].

2. Previous Comparisons

Good agreement between gonioscopy and the van Herick

technique is reported in a study by Kashiwagi et al. and

in another study by Foster et al. [15,16]. Conversely, in a

study by Thomas et al. the van Herick technique is said

to be in disagreement with gonioscopy because it meas-

ures the angle wider than gonioscopy [17]. AS-OCT is

reported to detect more closed ACAs than gonioscopy in

a study by Sakata et al. [18]. Patients with narrow angle

and those at risk of ACG can be missed if the angle is

measured wider than its real size. If the angle on the

other hand is measured narrower than its actual size, ad-

ditional evaluation by gonioscopy is required, which will

incur unnecessarily costs to the health care system. A

quick and accurate ACA evaluation method is therefore

necessary.

Since the Sirius Scheimpflug-Camera is a recently de-

veloped device, limited number of studies has been per-

formed on it. High repeatability for the anterior segment

measurement by the Sirius Scheimpflug-Camera is re-

ported in a study by Savini et al. [19]. However, the

study does not state anything about the repeatability of

the ACA measurement by the device. In addition, to the

best of our knowledge, no study comparing the Sirius

Scheimpflug-Camera to gonioscopy, the van Herick tech-

nique and the AS-OCT has yet been performed.

Most of the previous studies compare the temporal

ACA findings of van Herick technique to that of gonio-

scopy [5,12,13]. In a study by Pettersson and Källmark

and in another study by Friedman et al. significant dif-

ference between temporal and nasal ACA is reported

[1,20]. For an accurate comparison of ACA measuring

techniques, the angle should therefore be measured both

nasally and temporally as the techniques can be in

agreement nasally but in disagreement temporally or vice

versa.

Aims

The aim of this study was to investigate variation in

ACA measurement between gonioscopy, van Herick

technique, AS-OCT and Sirius Scheimpflug-Camera

both nasally and temporally

3. Methods and Material

3.1. Patients and Clinical Investigation

ACA of both eyes of 25 randomly selected subjects

(mean age 24.28 ± 3.77) were measured with all the four

methods (i.e. gonioscopy, van Herick technique, Sirius

Scheimpflug-Camera and AS-OCT). The study was per-

formed at S:t Erik Eye hospital and in accordance with

the declaration of Helsinki. Informed consent was ob-

tained from all the participants after they were well in-

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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques

550

formed of the study’s nature. The ACA measurement

obtained with van Herick technique and gonioscopy was

carried out by an experienced optometrist masked to the

test results obtained by the Sirius Scheimpflug-Camera

and the AS-OCT. The Sirius Scheimpflug-Camera and

the AS-OCT measurements were performed by another

optometrist who was unaware of the gonioscopy and the

van Herick results. On the day the angle measures were

carried out, subjects had been free from contact lens

wear.

3.2. Van Herick Technique

ACA was measured both nasally and temporally with the

slit lamp using van Herick technique. The ACA was es-

timated by comparing the limbal anterior chamber depth

(LACD) (which was observed as an empty space be-

tween the corneal endothelium and the anterior iris) to

the corneal thickness. ACA was graded according to the

van Herick’s grading system which is illustrated in Table

1 [1,3,7,21].

3.3. Gonioscopy

Gonioscopy was performed using a Goldman 3-mirror

lens. The cornea was anesthetized using one drop of

0.4% oxybuprocaine hydrochloride. Two drops of 2%

methylcellulose were used as a coupling medium for the

gonioscopy lens. Care was taken to avoid accidental in-

dentation of the angle by direct illumination of the pupil

during the examination. Slight tilting of the lens was al-

lowed to gain view over the convexity of the iris. The

ACA was graded using Shaffer grading system which is

illustrated in Table 2 [1,4,6,13,22].

3.4. AC-OCT

The AS-OCT used in this study was Visante OCT manu-

factured by Carl Zeiss Meditec. The nasal and temporal

ACA can be measured simultaneously by the AS-OCT.

Images of the ACA were acquired with the subject seated

and fixating an internal fixation target. The subject was

instructed to blink and open his/her eye widely before

Table 1. ACA grading system as described by van Herik.

Width of the empty space

(LACD*) as compared to the

corneal thickness

van Herick

Grade Angle status

No black space observed 0 Closed

<1/4 Corneal thickness 1 Extremely narrow

1/4 of corneal thickness 2 Narrow

>1/4 to 1/2 of corneal thickness 3 Open

≥1 of corneal thickness 4 Wide open

*LACD = Limbal Anterior Chamber Depth.

Table 2. ACA grading system as described by Shaffer.

ACA*

in degrees ACA gradeAngle status Visible structures

0 0 Closed No structures visible

≤10 1 Extremely narrow Schwalbe’s line

11 - 19 2 Narrow Trabecular meshwork

20 - 34 3 Open Scleral spur

35 - 45 4 Wide open Ciliary body

*ACA = Anterior Chamber Angle.

each measurement. Acquired images were then analysed

using the semi-automated software programme provided

by the device.

3.5. Sirius Scheimpflug-Camera

The Sirius Scheimpflug-Camera gives values of both the

nasal and the temporal ACA in a single measurement.

The central fixation target of the device was used to align

the subject’s eye along the visual axis and to bring the

device into focus. The subject was instructed to blink and

open his/her eye widely before each measurement. Three

consecutive measurements were carried out per eye and a

mean value of the ACA was calculated which was taken

as the single measured value that was compared to the

values obtained by the other methods. Phoenix Software-

Suite was used by the device in this study to analyse the

obtained Scheimpflug images.

3.6. Angle Conversion

As stated before, both the AS-OCT and the Sirius

Scheimpflug-Camera measure the ACA in degrees and

can therefore not be directly compared to the van Herick

technique and gonioscopy. Hence the ACA values ob-

tained with these two devices were converted to the van

Herick’s grading system using Shaffer’s anterior cham-

ber angle grading system (illustrated in Table 2). Never-

theless, both AS-OCT and the Sirius Scheimpflug-

Camera measure the ACA in degrees so comparisons

between them were performed in degrees.

3.7. Statistical Analysis

The Graph pad Instat for windows (Version 3.10) was

used for statistical analysis. The Friedman test with post-

test was used for comparison between two different me-

thods. The Wilcoxon matched pair test was used for ei-

ther nasal or temporal data comparison between two me-

thods. A p value less than 0.05 (p < 0.05) was considered

statistically significant and indicated a difference be-

tween the measurements.

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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques 551

4. Results

The descriptive statistics for nasal and temporal measure-

ments is shown in Table 3.

The mean ACA measured by gonioscopy and the van

Herick technique differed by 0.12 nasally and by 0.04

temporally. No statistically significant difference could

be found between these two methods (p = 0.45) either

nasally (p = 0.20) or temporally (p = 0.68). Figure 1

compares measurements obtained by gonioscopy to that

obtained by van Herick technique.

On comparison of the mean ACA values obtained by

gonioscopy to that obtained by the AS-OCT a difference

of 0.14 was observed nasally and a difference of 0.08

was observed temporally. But no statistically significant

difference could be found between the two methods (p =

0.09) neither nasally (p = 0.15) nor temporally (p = 0.36).

A comparison of AS-OCT findings to that of gonioscopy

is shown in Figure 2.

When the mean ACA value obtained by gonioscopy is

compared to that obtained by the Sirius Scheimpflug-

Camera a difference of 0.18 was seen between nasal val-

ues and a difference of 0.30 was seen between temporal

11132132

6244

GN2GN3GN4GT2GT3 GT4

Number of eyes

VH1 VH2 VH3 VH4

Figure 2. Compares the measured ACA grading’s obtained

by gonioscopy to that obtained by van Herick technique.

Numbers over the bars; show the number of eyes, GN2 (go-

nioscopy nasal grade 2), GN3 (gonioscopy nasal grade 3),

GN4 (gonioscopy nasal grade 4), GT2 (gonioscopy temporal

grade 2), GT3 (gonioscopy temporal grade 3), GT4 (gonio-

scopy temporal grade 4), VH1, 2, 3 and 4 (van Herick grade

1, 2, 3 and 4).

Table 3. Descriptive statistics for nasal and temporal meas-

urements.

Gonio-scopy van Herick AS-OCT* Sirius**

Mean 3.66/3.66 3.54/3.62 3.52/3.58 3.84/3.96

SD*** 0.56/0.56 0.79/0.78 0.50/0.50 0.37/0.20

95%

confidence

interval

0.159/0.159 0.224/0.222 0.144/0.142 0.105/0.056

Range 2 - 4 1 - 4 3 - 4 3 - 4

*Anterior segment optical coherence tomography. **Sirius scheimpflug-

Camera. ***Standard deviation.

values. A statistically significant difference was found

between these two methods (p < 0.0001) both nasally (p

= 0.03) and temporally (p = 0.0002). Values obtained by

Sirius Scheimpflug-Camera are compared to that ob-

tained by gonioscopy in Figure 3.

A difference of 0.02 between the mean nasal meas-

urements and a difference of 0.04 between the mean

temporal measurements of the van Herick technique and

the AS-OCT was found. No statistically significant dif-

ference was found to exist between the two methods (p =

0.39) either nasally (p = 0.86) or temporally (p = 0.71).

Figure 4 shows a comparison of these two methods.

The mean ACA value obtained nasally by the van

Herick technique and the Sirius Scheimpflug-Camera

differed by 0.30 whilst that obtained temporally differed

by 0.34. The two methods were found to be significantly

different from each other (p < 0.0001) both nasally (p =

0.001) and temporally (p = 0.001). A comparison be-

tween these two methods.

The mean ACA value obtained nasally by the van

AS-OCTN3AS-OCTN4 AS-OCTT3AS-OCTT4

Number of eyes

G2 G3 G4

Figure 3. Compares the measured ACA grading’s obtained

by AS-OCT to that obtained by gonioscopy. Numbers over

the bars, show the number of eyes AS-OCTN3 (AS-OCT

nasal grade 3) AS-OCTN4 (AS-OCT nasal grade 4) AS-

OCTT3 (AS-OCT temporal grade 3) AS-OCTT4 (AS-OCT

temporal grade 4) G2, 3 and 4 (gonioscopy grade 2, 3 and 4).

11 2

582

33 35

SN3 SN4 ST3ST4

Number of eyes

G2 G3 G4

Figure 4. Compares the measured ACA grading obtained by

Sirius Scheimpflug-Camera to that obtained-by gonioscopy.

Numbers over the bars, show the number of eyesSN3 (Sirius

Scheimpflug-Camera nasal grade 3) SN4 (Sirius Scheimp-

flug-Camera nasal grade 4) ST3 (Sirius Scheimpflug-Cam-

era temporal grade 3) ST4 (Sirius Scheimpflug-Camera tem-

poral grade 4.

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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques

552

Herick technique and the Sirius Scheimpflug-Camera

differed by 0.30 whilst that obtained temporally differed

by 0.34. The two methods were found to be significantly

different from each other (p < 0.0001) both nasally (p =

0.001) and temporally (p = 0.001). A comparison be-

tween these two methods is illustrated in Figure 5.

Table 4 shows the descriptive statistic in degrees for

nasal and temporal measurements obtained by the AS-

OCT and the Sirius Scheimpflug-Camera. When com-

paring the mean ACA value obtained by the AS-OCT to

that obtained by the Sirius Scheimpflug-Camera a dif-

ference of 7.840 was observed nasally and a difference of

10.880 was observed temporally. Thus a statistically sig-

nificant difference was found to exist between these two

methods (p < 0.0001) both nasally (p < 0.0001) and tem-

porally (p < 0.0001). Values obtained by these two

methods are compared to each other in Figure 6.

5. Discussion

To decrease the risk for irreversible blindness due to

ACG, a quick and easy ACA evaluation method is

needed that should be a part of the routine eye examina-

tion.

AS-

OCTN3 AS -

OCTN4 AS -

OCTT3 AS-

OCTT4

Number o f eyes

VH1 VH2 VH3 VH4

Figure 5. Compares the measured ACA grading’s obtained

by the AS-OCT to that obtained by van Herick technique.

Numbers on the bars, show the number of eyes. AS-OCTN3

(AS-OCT nasal grade 3) AS-OCTN 4 (AS-OCT nasal grade

4) AS-OCTT3 (AS-OCT temporal grade 3) AS-OCTT4

(AS-OCT temporal grade 4) VH1, 2, 3 and 4 (van Herick

grade 1, 2, 3 and 4).

Table 4. ACA measurement in degrees obtained by AS-

OCT and the Sirius Scheimpflug-came r a.

AS-OCT*

nasal

(in degrees)

Sirius**

nasal

(in degrees)

AS-OCT*

temporal

(in degrees)

Sirius** temporal

(in degrees)

Mean 35.86 43.70 37.66 48.53

SD*** 7.059 5.819 5.793 7.042

95%

confidence

interval

1.66 2.01 2.00 1.64

Range 26 - 49.2 30 - 61.67 27 - 53.3 34 - 65

3324444

35 39

SN3 SN4ST3ST4

Number of eyes

VH1 VH2VH3 VH4

Figure 6. Compares the measured ACA grading’s obtained

by Sirius Scheimpflug-Camera to that obtained by van

Herick technique. Numbers on the bars, show the number of

eyes. SN3 (Sirius Scheimpflug-Camera nasal grade 3) SN4

(Sirius Scheimpflug-Camera nasal grade 4) ST3 (Sirius Sch-

eimpflug-Camera temporal grade 3) ST4 (Sirius Scheimp-

flug-Camera temporal grade 4) VH1, 2, 3 and 4 (van Herick

grade 1, 2, 3 and 4).

The van Herick technique, AS-OCT and Sirius Sch-

eimpflug-Camera can be used for this purpose as they all

are quick and easy to perform. But we need to know

which one of these is the most accurate one to be used.

To answer this question they have to be compared to

gonioscopy which is the current reference standard for

ACA measurement. This study was therefore carried out

to investigate variation between these four different

methods in measuring the ACA.

Our study showed good agreement between gonio-

scopy and the van Herick technique since no statistically

significant difference could be found between the two

methods (p = 0.45) either nasally (p = 0.20) or tempo-

rally (p = 0.68). Best agreement was shown for angles

that had grade 4 since the majority of the eyes graded as

4 by gonioscopy were also graded as 4 by van Herick

technique both nasally and temporally (Figure 1). This

finding is in good agreement with the results of the study

by Foster et al. where they also show good agreement

between gonioscopy and van Herick technique especially

for eyes having grade 4 [15].

Good agreement between gonioscopy and van Herick

technique is also reported in a study by Park et al. and in

another study by Kashiwagi et al. and in one other study

by Foster et al. [3,15,16]. However, the result of our

study disagrees with that of the study by Thomas et al.

where poor agreement between gonioscopy and van

Herick technique is reported. Difference in the study

population between the two studies may explain this

disagreement. Most of the subjects enrolled in their study

had narrow angles whilst most of the subjects enrolled in

our study had normal angles.

Both gonioscopy and the van Herick technique make

use of the slit lamp to measure the ACA and both are

subjective methods. These similarities can be the reason

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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques 553

for good agreement between the two methods.

Our findings suggest poor agreement between gonio-

scopy and the Sirius Scheimpflug-Camera (p < 0.0001)

both nasally (p = 0.03) and temporally (p = 0.0002). No

studies comparing Sirius Scheimpflug-Camera to gonio-

scopy has been performed before. Though, in a study by

Friedman et al., the ACA measured by Scheimpflug

camera is compared to the measurements obtained by

gonioscopy and poor agreement between the two is re-

ported [23].

Statistically significant difference between the results

obtained by the Sirius Scheimpflug-Camera and the van

Herick technique exists according to this study, indicat-

ing poor agreement between the two methods (p <

0.0001) both nasally (p = 0.001) and temporally (p =

0.001).

Sirius Scheimpflug-Camera is in disagreement with

gonioscopy and the van Herick technique may be be-

cause of its different nature compared to the other two

methods. Both gonioscopy and the van Herick technique

are subjective methods whilst the Sirius Scheimpflug-

Camera gives an objective measurement of the ACA. As

stated before, both gonioscopy and the van Herick tech-

nique make use of the slit lamp whilst the Sirius Sch-

eimpflug-Camera uses the 3D rotating Scheimpflug ca-

mera and bases its measurement results on the pictures

obtained by that camera. In addition, the illumination

used by the topographic rings and the fixation target of

the Sirius Scheimpflug-Camera is a bit bright. This

brightness can cause pupil constriction, which increases

the angle width and there by a wider angle measure is

given.

This study also showed good agreement between the

results obtained by gonioscopy and the AS-OCT (p =

0.09) for both nasal (p = 0.15) and temporal data (p =

0.36). In a study by Sakata et al. poor agreement between

gonioscopy and AS-OCT is reported for superior and

inferior angles, but the agreement for nasal and temporal

angle is reported to be good [18]. They also stated that

AS-OCT tends to detect more closed ACAs than gonio-

scopy which can partly be seen in our study too. When

comparing the mean ACA values obtained by gonio-

scopy to that obtained by AS-OCT, it can be seen that

AS-OCT measures the angle 0.14 nasally and 0.08 tem-

porally narrower than gonioscopy.

Our study showed good agreement between the AS-

OCT and the van Herick technique (p = 0.39) both na-

sally (p = 0.86) and temporally (p = 0.71). However,

AS-OCT is reported to be in disagreement with gonio-

scopy and van Herick technique in a study by Park et al.

[3]. Eyes with narrow angles were used in their study

whilst eyes with normal angles were used in our study.

This difference in the selection of eyes in the two studies

might be the reason for the disagreement between them.

AS-OCT also measures the ACA objectively but

unlike Sirius Scheimpflug-Camera, it is in good agree-

ment with both gonioscopy and the van Herick technique.

This can partly be explained by the fact that both gonio-

scopy and the AS-OCT make a direct view of the ACA

configuration to measure it. Also the AS-OCT makes use

of an internal fixation target of low illumination to com-

pensate for the subject’s refractive error as well as pre-

vent pupil constriction. Compensation of the refractive

error is essential for prevention of the pupil constriction

and lens disposition which normally occurs as a result of

accommodation [24].

According to this study the results obtained by the

AS-OCT differ significantly from those obtained by the

Sirius Scheimpflug-Camera (p < 0.0001) both nasally (p

< 0.0001) and temporally (p < 0.0001) showing dis-

agreement between the two devices.

The Sirius Scheimpflug-Camera makes use of visible

light to measure the angle and can thus alter the angle

configuration whilst the AS-OCT makes use of infrared

light for its angle measurement. Besides, the Sirius

Scheimpflug-Camera does not make any adjustment for

the subject’s refractive error and makes use of quite

bright illumination in its fixation target and in its topog-

raphic rings. The AS-OCT on the other hand takes all of

these factors in to account, which may thus explain the

existence of poor agreement between the two devices.

To state which one of the three methods (i.e. van

Herick technique, AS-OCT and Sirius Scheimpflug-

Camera) is the most accurate one to be used, is difficult

because all of these methods have their own strengths

and weaknesses. For instance, although the van Herick

technique is a quick method that makes use of a slit lamp

(which is available to all the optometrists and does not

cost very much), it requires experience and good meas-

uring skill to get reliable measurements [1]. Furthermore,

it is a subjective method that gives an estimation of the

angle as well as affected by the corneal thickness [4].

In contrast, measuring the ACA with the AS-OCT and

Sirius Scheimpflug-Camera is not only quick but also

easy to perform. In addition, they do not require much of

experience and measuring skill and are objective meth-

ods. Nevertheless, the weakness of these devices is their

high cost.

This study did have limitations. The illumination of

the room which plays a vital role on the pupil constric-

tion and dilation was not controlled in this study. At

times the ACA was measured in a totally dark room and

at times it was measured in a dimly illuminated room.

This should, however, not affect the results enormously

since light falling directly on the pupil affects its size

more than the room illumination. And the light directly

falling on the pupil was from the illumination used by the

slit lamp and the fixation target used by the Sirius

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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques

554

Scheimpflug-Camera and the AS-OCT. The measure-

ments by gonioscopy and the van Herick technique were

carried out by the same examiner which might have pro-

duced systemic bias. The number of subjects used in this

study was not very big, so in order to get more reliable

results the study should be performed on a larger group

of people. In spite of these limitations, this study to the

best of our knowledge is the first one to compare the

Sirius Scheimpflug-Camera with gonioscopy, the van

Herick technique and the AS-OCT.

6. Conclusion

In summary, this study showed good agreement between

gonioscopy, the van Herick technique and the AS-OCT.

The agreement between the Sirius Scheimpflug-Camera

and the other three methods (i.e. gonioscopy, van Herick

technique and AS-OCT) on the other hand was poor. It

should therefore be noted that the ACA measurements

obtained by the Sirius Scheimpflug-Camera, which can-

not be considered interchangeable with those obtained by

gonioscopy, the van Herick technique and the AS-OCT.

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