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Journal Français d'Ophtalmologie
Volume 39, n° 8
pages 706-710 (octobre 2016)
Doi : 10.1016/j.jfo.2016.03.010
Received : 17 January 2016 ;  accepted : 18 Mars 2016
Longitudinal evaluation of central corneal thickness in congenital glaucoma
Épaisseur cornéenne centrale dans le glaucome congénital : une étude longitudinale
 

R.A. Paletta Guedes a, b, c, , A.B. Pena a, b, V.M. Paletta Guedes a, b, A. Chaoubah c
a Paletta Guedes Ophthalmological Center, Juiz de Fora, MG, Brazil 
b Santa Casa de Misericórdia Hospital, Juiz de Fora, MG, Brazil 
c Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil 

Corresponding author. Av. Barão do Rio Branco, 2337/807, Centro, 36010-905 Juiz de Fora, MG, Brazil.
Summary
Purpose

To assess the central corneal thickness in primary congenital glaucoma before and after surgical treatment and compare it with a normal population.

Methods

We conducted a longitudinal analysis of primary congenital glaucoma patients, in whom we measured central corneal thickness before and after treatment (Group 1). We compared our results with a normal population (Group 2), who underwent ophthalmological examination under anesthesia for other reasons.

Results

Mean age (months) in Group 1 (N =23) and Group 2 (N =40) at the time of the first exam was 5.5 and 9.2 (P =0.004), respectively. Mean central corneal thickness (microns) in Group 1 was: 663 before treatment and 557 after treatment (P <0.001). In Group 2, mean central corneal thickness (microns) was 551. Comparisons show statistical difference between mean values before and after treatment (P <0.001), but not between post-treatment CCT mean values in Group 1 and mean CCT values in Group 2 (P =0.627).

Conclusion

In primary congenital glaucoma, central corneal thickness values show unique peculiarities. They are higher than normal before treatment (thicker corneas), due to corneal edema caused by elevated intraocular pressure. After surgical treatment, central corneal thickness measurements decrease toward the mean values for the normal population.

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Résumé
But

Évaluer l’épaisseur cornéenne centrale (ECC) des patients avec glaucome congénital primitif (GCP) avant et après traitement chirurgical et comparer avec une population normale.

Matériels et méthodes

Une étude longitudinale a été conduite pour analyser l’ECC avant et après le traitement chirurgical dans le GCP (groupe 1). Une comparaison a été faite avec une population sans glaucome (groupe 2) et qui a été soumise à un examen ophtalmologique sous anesthésie générale pour d’autres raisons.

Résultats

L’âge moyenne du groupe 1 (n =23) et groupe 2 (n =40) au moment du premier examen a été, respectivement : 5,5 et 9,2 mois. Les valeurs moyennes de l’ECC dans le groupe 1 étaient 633 microns avant traitement et 557 après traitement. Le groupe 2 présentait 551 microns d’ECC moyenne. Les comparaisons montrent qu’il y avait une différence entre les valeurs moyennes d’ECC avant et après traitement dans le groupe 1 (p <0,001), mais pas pour les valeurs moyenne après traitement dans le groupe 1 et la moyenne du groupe 2 (p =0,627).

Conclusion

L’ECC présente des caractéristiques particulières et uniques dans l’évaluation du glaucome congénital. Au moment du diagnostic, les valeurs sont souvent très élevées, mais elles descendent vers les valeurs normales après le contrôle de la maladie.

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Keywords : Primary congenital glaucoma, Central corneal thickness, Pachymetry, Glaucoma surgery, Intraocular pressure

Mots clés : Glaucome congénital primitif, Épaisseur centrale de la cornée, Pachymétrie, Chirurgie du glaucome, Pression intraoculaire


Introduction

Globally, an estimated 19 million children below age 15 are visually impaired and 1.4 million are irreversibly blind for the rest of their lives [1]. Glaucoma is among the most frequent causes of childhood vision impairment [2]. In the United Kingdom, it is responsible for 2% of severe visual impairment and blindness in children [3].

Primary congenital glaucoma (PCG) is caused by malformation of the angle structures (isolated trabeculodysgenesis), clinically characterized by the absence of the ciliary body band in gonioscopy, due to translucent amorphous material that blocks the trabeculum [4]. This malformation results in aqueous humor drainage deficiency and consequently in elevated intraocular pressure (IOP) that damages the optic nerve head.

IOP reduction is the main target of glaucoma treatment and is recognized as the only effective way to stop the optic nerve damage and visual loss caused by the disease, but tonometry in eyes with congenital glaucoma is more susceptible to misinterpretation due to extreme corneal changes found in these patients [5].

It is well-known that central corneal thickness (CCT) and keratometry influence the IOP measurements in adults [5, 6, 7, 8]. In these patients, CCT measurement is essential for the evaluation of glaucoma, since it can lead to misinterpretation of IOP values. Thinner corneas tend to underestimate true IOP values and thicker corneas, to overestimate it. One exception to this rule is when cornea is thicker due to edema. In this particular case, IOP will be underestimated, although CCT values are higher than normal.

Conversely, influence and clinical significance of CCT in congenital glaucoma is not so clear. The literature shows mixed results for CCT in a PCG population. Some authors have found that CCT in this population is thinner when compared to a normal population [9, 10, 11, 12, 13], while others have found that it is comparable to a normal population [14, 15] and, there is even one study in which it was found to be thicker than in a normal population [16]. To our knowledge, only two studies show the longitudinal follow-up of CCT in congenital glaucoma [17, 18] and just one of these had a control group.

The aim of the present study is to evaluate the CCT of patients with PCG before and after surgical treatment and to compare it to a normal population.

Materials and methods

We conducted a retrospective analysis of records from consecutive patients who had been submitted to an ophthalmological examination under anesthesia between April 2007 and November 2012. Inclusion criteria were: children under 3 years old, ophthalmological exam for suspicious or confirmed PCG, ophthalmological exam for other causes than PCG. Exclusion criterion: absence of CCT values. In cases where both eyes of a same patient were eligible for the study, we randomized only one eye. This study was approved by the Research Ethics Committee of Santa Casa de Juiz de Fora Hospital and the tenets of the Declaration of Helsinki were followed.

We divided the patients into two groups:

Group 1 – patients diagnosed with PCG;
Group 2 – control: patients without glaucoma or other anterior segment congenital anomalies, who had been submitted to an ophthalmological exam under anesthesia for other reasons (suspicion of congenital glaucoma due to enlargement of the optic nerve cup; lachrymal drainage obstruction, etc.).

We analyzed the following variables in each group:

Group 1:
patients’ characteristics (age, race, age at onset of symptoms);
ophthalmological exam before glaucoma surgery and 1, 3, 6 and every 6 months after surgery, including:
tonometry with Tonopen® (Reichert Inc., Buffalo, NY, USA) – mean of 3 measurements with good reliability,
ultrasound pachymetry – mean of 5 measurements,
ultrasound biometry – mean of 5 measurements,
biomicroscopy using the surgical microscope,
gonioscopy,
fundus biomicroscopy;

surgical technique;
postoperative evaluation:
number of interventions necessary to control IOP,
success rate (IOP<18mmHg with or without medications and axial length growth within a normal range),
number of medications needed to control IOP,
follow-up time.


group 2:
patients’ characteristics (age, race);
ophthalmological exam, including:
tonometry with Tonopen® (Reichert Inc., Buffalo, NY, USA) – mean of 3 measurements with good reliability,
ultrasound pachymetry – mean of 5 measurements,
ultrasound biometry – mean of 5 measurements,
biomicroscopy using the surgical microscope,
gonioscopy,
fundus biomicroscopy.


Statistical analysis was performed using SPSS version 13.0 (SPSS Inc., Chicago, Il, USA), always seeking a significance level of 95%. Clinical characteristics of the study population were assessed using the mean (± standard deviation) and proportions of the variables. We compared CCT values using a parametric test (Student t test) and we tested associations between variables using the Pearson correlation test for numerical variables and Chi2 tests for categorical variables.

Results

Patients who met the inclusion and exclusion criteria comprised the study population. Twenty-three patients were included in Group 1 (PCG group) and 40 patients in Group 2 (control group). Table 1 shows comparisons between the 2 groups.

In Group 1, the mean time between the onset of symptoms and the ophthalmological exam under anesthesia was 4.4 months. We observed a reduction of all ocular parameters after surgical treatment, except for the axial length (AL), which showed no statistical significant difference in the pre- and postsurgical comparison, as shown in Table 2. Mean postoperative follow-up time in Group 1 was 37.5±18.6 months.

Table 3 demonstrates the CCT analysis in Group 1 (pre- and postoperative comparison) and in Group 2. We found that there was a statistical significant difference between the CCT values in PCG patients before the glaucoma surgery and the normal controls. After surgical treatment CCT values were comparable to those from the normal population.

In Group 1, 11 (47.8%) patients underwent 1 surgery; 6 (26.1%) patients needed 2 surgeries; and 6 (26.1%) patients needed 3 surgical interventions. The first surgical options were: trabeculotomy (78.3%); goniotomy (4.3%) and non-penetrating deep sclerectomy (17.4%). As second surgery, the surgical techniques used were trabeculotomy (50%), trabeculectomy (41.7%) and combined trabeculotomy-trabeculectomy (8.3%). When a third surgical intervention was needed, all patients were submitted to a trabeculectomy. Success rate at the end of follow-up period was 73.9% for all patients.

When we analyzed only the successful cases (17 out of the 23 patients in Group 1), we noticed that 64.7% were controlled with only 1 procedure; 23.5% with 2 procedures and 11.8% with 3 surgeries. In those who needed only one surgery (11 out of the 23 patients), trabeculotomy was performed in 7 cases (38.9% of success) and non-penetrating deep sclerectomy in 4 eyes (100% of success, since all the patients initially submitted to this procedure had the IOP under control until the end of this survey).

Among the successful cases, 70.6% were without medication at the end of the follow-up period and the remaining eyes (29.4%) were using only 1 medication to control the IOP.

Discussion

Our case series shows that there is significant difference between CCT in PCG patients and normal controls, with higher values in the first group. However, after surgical treatment and IOP reduction in PCG patients, the CCT values are comparable to those found in a normal population.

The mean age of the patients from Groups 1 and 2 was quite different (5.5 months in Group 1 and 9.2 months in Group 2, with P =0.004). This reflects the urgency to exam under anesthesia children with PCG suspicion, which is not the case for other ophthalmological conditions, such as lacrimal drainage obstruction, wherein we wait a few months for spontaneous resolution before submitting the child to exam under anesthesia. Despite this age difference, it did not interfere with the results of our study, as it was not clinically significant. The two groups were homogeneous regarding race.

IOP, CCT, AL and vertical cup-to-disc ratio were all statistically different between Groups 1 and 2 (P <0.001), which was expected due to the PCG diagnosis in Group 1. The vertical cup-to-disc ratio of 0.4 in Group 2 is somewhat unexpected in a normal population under 3 years of age; however, some of the children from the Control Group were examined under anesthesia due to a suspicion of glaucoma because of a physiological enlargement of the cup.

The short mean time between the onset of symptoms and the ophthalmological exam under anesthesia (4.4 months) can explain the high success rate with surgical treatment; it probably results from the fact that the patients have been submitted to surgery before their eyes had developed severe damage from long-lasting elevated IOP, with consequently better prognosis.

At the end of the follow-up (approximately 3 years), we have observed a reduction in the values of some of the studied parameters: IOP, CCT and vertical cup-to-disc ratio. We have also observed an interruption of the abnormal AL growth. It is well-known that IOP control directly influences the other three variables: CCT becomes thinner due to edema remission [16]; AL may decrease or the axial growth pattern may parallel the normal eye growth curve [19]; and the disc cupping often reverses, especially in younger children, such as the patients of our study. The reduction of the vertical cup-to-disc ratio after surgical PCG treatment is well documented in the literature [20].

The final mean CCT in Group 1 was similar to the mean CCT in Group 2 (P =0.627). Conversely, some studies have found thinner corneas in controlled PCG patients [9, 10, 11, 12, 13]. Therefore, we have questioned if our results were influenced by persistent corneal edema in non-successful treated patients, which could elevate the mean final CCT in Group 1. However, when we reanalyzed our results by dividing Group 1 into 2 subgroups: successful cases (eyes with IOP control) and non-successful cases (eyes without proper IOP control), the statistical analysis showed that the mean CCT of both subgroups were still comparable to that from the normal population (P =0.716 for the successful cases).

Half of the PCG cases were submitted to only one surgical procedure and different techniques were used:

angle surgeries (trabeculotomy and goniotomy);
more frequently used all over the world;
non-penetrating surgery (deep sclerectomy), which is being used by some congenital glaucoma surgeons.

The few studies published about deep sclerectomy in congenital glaucoma have shown good IOP reduction without the occurrence of serious complications commonly seen after trabeculotomy or combined trabeculotomy-trabeculectomy [21, 22]. In our case series, all eyes submitted to deep sclerectomy have achieved IOP control at the end of the study.

It is important to mention that glaucoma drainage implants were not used in our patients due to financial reasons – all surgeries were performed using the Brazilian Public Health System (Sistema Único de Saúde – SUS), which does not offer payment or reimbursement for these devices. For this reason, filtrating surgery was used in most of second procedures and in all the third ones. Glaucoma drainage implant surgery has an important role in managing refractory PCG [23].

After surgery, the majority of patients did not need any glaucoma medication. Those who needed drops to control IOP were using only one medication at the end of the study.

Important limitations of our study are its retrospective design and the small sample size. The results need further confirmation with a prospective study in a larger sample. Despite these limitations, our study has some strengths:

long-term follow-up; presence of a control group;
longitudinal evaluation of CCT;
comparisons between successful and non-successful cases after surgery.

In conclusion, we have found that mean CCT in PCG is thicker before surgery. After surgical treatment, it is comparable to the mean CCT in a normal population.

Funding

There was no funding for this study.

Disclosure of interest

The authors declare that they have no competing interest.


 Part of this study was presented as an oral communication during the 119th French Society Meeting in Paris on May 12th 2013.

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