Reliability of Modified Hertels Exophthalmometer as an Intraoperative Tool for Assessment of Relative Globe Position in Orbital/Zygomatic Fracture.

INTRODUCTION: Axial globe position assessment is commonly carried out with Hertels Exophthalmometer. Hertels requires an intact lateral orbital rim for its placement, which is often fractured in zygomatic fractures. Hence, to overcome this problem, we have modified the instrument for its application in zygomatic/orbital fractures. Reliability of this Modified Hertels Exopthalmometer has been already validated in normal healthy patients. Therefore, the aim of this study is to assess the efficacy of the Modified Hertels Exophthalmometer in pateints with zygomatic/orbital fracture.
MATERIALS AND METHODS: This is a prospective study carried out between April 2015 and October 2017, including 20 patients with a mean age of 34 years. Enophthalmos was measured using Modified Hertels in patients with unilateral orbital/zygomatic fracture indicated for surgical intervention by a single observer. The data was collected and statistically analyzed. Paired sample t-test was done to compare the preoperative exophthalmometer reading with readings at different time points.
RESULTS: A statistically significant difference was noted (P = 0.031) among the variables of Modified Hertels. We believe this instrument to be of practical use in the assessment of enophthalmos/exophthalmos in patients with lateral orbital trauma, surgery or disease and also precludes the use of rim-based exophthalmometry and other modifications of same. Copyright:

INTRODUCTION

Orbital floor and medial wall fractures often manifest as periorbital edema and ecchymosis, subconjunctival hemorrhage, epistaxis, diplopia in horizontal gaze, hypoglobus, and enophthalmos.[1] Catone et al. stated that 7% to 10% of blowout fracture cases managed conservatively suffered persistent enophthalmos.[2]

Globe structure assessment and function is essential in evaluating a patient of orbital trauma. Clinically, axial position of the globe assessment is carried out with a device known as exophthalmometer. Hertels Exophthalmometer is the most commonly used exophthalmometer since its development in 1905 [Figure 1]. It aids in assessing symmetry between two eyes, which is referred to as “relative exopthalmometry” measured by the distance between the lateral orbital rim to orbital apex.[3]

Figure 1

Hertels exopthalmometer

One of the major drawbacks of standard Hertels is that it cannot be used in cases of zygomatic fractures as an intact lateral orbital rim is required for Hertels placement. However, when there is a displacement or fracture of all orbital rims, it becomes problematic to use the instrument. Many modifications have been developed which use other reference points such as superior, inferior orbital rim, and external auditory canal but none are found to be useful in zygomatic fractures. In order to circumvent the shortcoming of placement of Hertels on an intact lateral orbital rim, a modification was made in the conventional Hertels Exophthamometer by attaching a 360 degree spirit level with screws to the center of standard Hertels [Figure 2]. In the Modified Hertels, the footplate is rested on one of the rims and the three dimensional (3D) spirit level is used to make it parallel to the horizontal and anteroposterior plane. The superior or inferior plane cannot be assessed for a patient in this position. This is a highly reproducible position and the readings are done in a similar manner in the other side.[4] Reliability of Modified Hertels has been already validated in normal healthy patients.[5] Hence, the aim of this study is to assess the efficacy of the Modified Hertels Exophthalmometer in patients with zygomatic/orbital fracture.

Figure 2

Hertels exopthalmometer with spirit level attached

MATERIALS AND METHODS

Study design

This is a prospective case-control study performed at the Department of Oral and Maxillofacial Surgery, Faculty of Dental Sciences at Sri Ramachandra University between April 2015 and October 2017 on patients exhibiting enophthalmos following unilateral orbital/zygomatic fracture indicated for surgical intervention. The study comprised of a sample size of 20 patients comprising 19 males and 1 female. The age group ranged from 18 to 50 years, with a mean range of 34 years.

The study is approved by the Institutional Ethical Committee and informed consent was taken from all included patients who participated in our study.

The protocol for this study included measurement of enophthalmos pre, intra and postoperatively in 20 patients diagnosed with zygomatic/orbital fractures using Modified Hertels Exophthalmometer. Among 20 patients, 4 had right and 12 had left zygomatico maxillary complex fracture, 2 had right and 2 had left orbital floor fractures. Preoperatively, enophthalmos measurement in patients was done using Modified Hertels. The enophthalmos values of affected eye were then measured. Intraoperatively, Modified Hertels helps in verifying the anteroposterior position of the orbit after reduction of fractures. The data was assessed postoperatively on day 7, 1st month, 2nd, and 3rd month after the surgery. The preoperative and postoperative values were compared at all intervals.

RESULTS

The Modified Hertels value taken intraoperatively showed a reduction in enophthalmos level of <3 mm. At postoperative 1st week and 1st month period, the enophthalmos level was maintained at <3 mm. At postoperative 2nd month period the enophthalmos level was increased by 1–2 mm which could be due to atrophy of fat in the retrobulbar region. At postoperative 3rd month period, the enophthalmos level was reduced to normal compared to the unaffected orbit. This explains the gradual deposition of fat behind the eye during the postoperative period [Tables 1 and 2].

Table 1

Exophthalmometer readings of control and affected eye at all intervals and their difference

Serial number of patients	Control eye exophthalmometer reading	Affected eye exophthalmometer reading and difference
		Preoperative	Intraoperative	Postoperative
				1st week	1st month	2nd month	3rd month
1	20	17/−3	19/−1	20/0	20/0	19/−1	20/0
2	20	17/−3	18/−2	18/−2	18/−2	19/−1	20/0
3	22	18/−4	20/−2	20/−2	20/−2	20/−2	20/−2
4	21	18/−3	20/−1	19/−2	19/−2	20/−1	21/0
5	21	18/−3	20/−1	19/−2	19/−2	19/−2	21/0
6	21	17/−4	19/−2	19/−2	19/−2	19/−2	20/−1
7	18	15/−3	17/−1	17/−1	17/−1	18/0	18/0
8	21	18/−3	20/−1	20/−1	20/−1	19/−2	20/−1
9	22	18/−4	20/−2	20/−2	20/−2	19/−3	21/−1
10	21	18/−3	19/−2	19/−2	19/−2	20/−1	20/−1
11	22	18/−4	20/−2	20/−2	20/−2	19/−3	22/0
12	20	17/−3	20/0	19/−1	19/−1	18/−2	20/0
13	21	18/−3	20/−1	20/−1	20/−1	21/0	21/0
14	21	18/−3	21/0	19/−2	19/−2	20/−1	21/0
15	21	17/−4	20/−1	20/−1	20/−1	20/−1	20/− 1
16	22	18/−4	22/−1	21/−1	21/−1	22/0	22/0
17	20	17/−3	19/−2	18/−2	18/−2	19/−1	19/−1
18	20	17/−3	18/−2	18/−2	18/−2	19/−1	20/0
19	20	17/−3	19/−1	18/−2	18/−2	19/−1	20/0
20	21	18/−3	20/−1	20/−1	20/−1	19/−2	20/−1

Table 2

The exophthalmometer reading difference in the affected and unaffected orbit of the patient at all intervals

Serial number of patients	Preoperative	Intraoperative	Postoperative
			1st week	1st month	2nd month	3rd month
1	−3	−1	0	−1	−1	0
2	−3	−2	−2	−1	−1	0
3	−4	−2	−2	−2	−2	−2
4	−3	−1	−2	−2	−1	0
5	−3	−1	−2	−2	−2	0
6	−4	−2	−2	−3	−2	−1
7	−3	−1	−1	0	0	0
8	−3	−1	−1	−2	−2	−1
9	−4	−2	−2	−2	−3	−1
10	−3	−2	−2	−2	−1	−1
11	−4	−2	−2	−3	−3	0
12	−3	0	−1	−2	−2	0
13	−3	−1	−1	−2	0	0
14	−3	0	−2	−2	−1	0
15	−4	−1	−1	−1	−1	−1
16	−4	0	−1	−4	0	0
17	−3	−1	−2	−2	−1	−1
18	−3	−2	−2	−1	−1	0
19	−3	−1	−2	−2	−1	0
20	−3	−1	−1	−3	−2	−1

The difference between the readings is gradually decreased from intraoperative to postoperative 3rd month indicating the correction of enophthalmos done

Paired sample t-test was done to compare the preoperative Exophthalmometer reading with readings at different time points and the P values of the readings were statistically significant [Table 3].

Table 3

Paired sample t-test to compare the preoperative exophthalmometer reading with readings at different time points and the P values of the readings are statistically significant

Exophthalmometer reading difference	Paired difference mean±SD	t	Degrees of freedom	Significance level (P)
Preoperative versus intra operative	−2.100±0.718	−13.077	19	0.000*
Preoperative versus postoperative 1st week	−1.750±0.716	−10.925	19	0.000*
Preoperative versus postoperative 1st month	−1.350±0.813	−7.429	19	0.000*
Preoperative versus postoperative 2nd month	−1.950±0/826	−10.563	19	0.000*
Preoperative versus postoperative 3rd month	−2.850±0.587	−21.708	19	0.000*
Intra operative versus postoperative 1st week	0.350±0.671	2.333	19	0.031*
Intra operative versus postoperative 1st month	0.750±1.209	2.775	19	0.012*
Intra operative versus postoperative 2nd month	0.150±0.875	0.767	19	0.453
Intra operative versus postoperative 3rd month	−0.750±0.716	−4.682	19	0.000*
Postoperative 1stwk versus postoperative 1st month	0.400±0.995	1.798	19	0.98
Postoperative 1st month versus postoperative 2nd month	−0.600±1.046	−4.723	19	0.000*
Postoperative 2nd month versus postoperative 3rd month	−1.100±0.788	−6.242	19	0.000*
Postoperative 1st month versus postoperative3rd month	−0.500±1.000	−6.708	19	0.000*

SD: Standard deviation, p value <0.005*

Thus the results of this study showed that Modified Hertels Exophthalmometer is reliable for assessment of axial position of globe in patients with zygomatico-orbital fractures.

DISCUSSION

Enophthalmos is considered as the commonly encountered consequence of defects of the floor of orbit or medial wall fractures. A successful outcome of surgery necessitates adequate reduction, effective fixation of zygomatic and orbital fracture in order to avoid secondary complications like enophthalmos, hypoglobus and restriction of extraocular movements. Esthetic results are only found in 77% of cases even when treated by experienced surgeons.[6] Thus, the assessment of the axial position of the globe is important for accurate reduction of fracture.

Clinically, enopthalmos measurement can be carried out with a noninvasive, economical, safe and simple device known as Exophthalmometer. Hertels Exophthalmometer is the commonest one being used amongst the available devices. The device can be easily mastered and can provide reliable serial documentation of globe position. The reference point is taken as the lateral orbital rim as it is less variable than other landmarks of the face as it is free of overlying soft tissues, making the placement of instrument directly on sharp bone. The measurement taken is the distance from the lateral orbital rim, which is the bony landmark to the apex cornea. Both the eyes are simultaneously measured by resting it on the intact lateral orbital rim with a mirror system visualizing the readings on millimeter scale.[7]

There are chances of occurrence of parallax errors in case the mirror is not correctly aligned with the reference cone before the reading of the position of the corneal apex is taken. To avoid interobserver variation and parallax errors, all readings on patients were taken by a single observer.[8]

The primary problem with Hertels is the difficulty to place it in patients having soft tissue edema secondary to trauma or surgery.[910] In cases of lateral orbital rim fracture, there is inaccuracy in measurement results as it is the anatomical landmark for instrument placement.

Several other exopthalmometers have been developed such as Naugle, Leudde and Yeatts Exophthalmometer using other reference points such as superior, inferior orbital rim, external auditory canal respectively. However, when there is displacement or fracture of all orbital rims or to any reference point, it becomes problematic to use the instrument. Therefore, we modified the conventional Hertel's Exophthamometer and not the reference point to use it for patients with zygomatic or orbital fractures.

There is no simple and reliable method to assess the proper reduction of zygomatic fractures. Various methods like ultrasonography, computed tomography, C-arm have been used in attempt to check proper reduction and restoration of orbital volume, but they are all associated with practical difficulties. Measurement of relative enopthalmos can be done with intraoperatively using optical 3D imaging.[11]

This modification of Hertels by attaching a spirit level to the center was done to ensure the instrument is parallel to the patient's eyes in all levels despite there is a displacement of rim in the anteroposterior direction.

CONCLUSION

Therefore our proposed modification of the instrument allows it to be used in cases when one of the lateral orbital walls is fractured or displaced due to trauma. The Modified Hertels offers practical use in the assessment of globe position in zygomatico-orbital fractures. This instrument needs further improvement in the design and further studies with a larger sample size are required to ensure its applications in the future.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.