Health & Medical Eye Health & Optical & Vision

Normal-Tension Glaucoma and Obstructive Sleep Apnea Syndrome

Normal-Tension Glaucoma and Obstructive Sleep Apnea Syndrome


This prospective study involved 24 patients with NTG (age range 53–78 years; 9 males and 15 females) who were recruited from general ophthalmology clinics. Twenty-four age and sex matched subjects without any kind of glaucoma diseases (age range 53–77 years; 9 males and 15 females) who were also similar for systemic risk factors such as diabetes mellitus (DM), hypertension (HT) or hypercholesterolaemia were selected from internal medicine clinics and taken as control group. This study followed the tenets of the Declaration of Helsinki and informed consent was obtained from all subjects. The study was approved by local ethics committee.

The diagnosis of NTG was made based on the following criteria:

  1. A cup-to-disc ratio (c/d) over 0.5 or difference of c/d between two eyes >0.2 with thinning of the neuroretinal rim.

  2. Glaucomatous visual field defects such as localized defects, paracentral scotoma, Bjerrum scotoma, nasal step, temporal sector defect, and diffuse defect which cannot be explained by any neurologic or fundus lesion.

  3. Open iridocorneal angle.

  4. IOP < 21 mmHg without treatment.

The patients were required to fulfill all 4 criteria to make the diagnosis of NTG.

All the patients in NTG group had at least 5 visual field tests and the participants in the control group had two visual field tests before the recruitment to the study. Both NTG patients and the controls and all the visual fields were reviewed by two glaucoma specialists and one neuro-ophthalmologist who were masked to the diagnosis of the subjects.

For NTG patients; mean IOP was 16.2 ± 2.4 mmHg and mean c/d ratio was 0.548 ± 0.135. The Mean deviation value and pattern standard deviation value of the patients' visual fields were found to be -5.1 ± 3.2 and 5.6 ± 2.7 decibels, respectively. Three (12.5%) of 24 NTG patients had disc haemorrhages during the diagnosis. On the other hand, mean IOP was 11.6 ± 1.8 mmHg and mean c/d ratio was 0.365 ± 0.092 for the controls. There were no field defects in the visual field tests of controls.

Participants underwent overnight PSG recordings in two sleep laboratories. Sleep was continuously recorded on a computerized system (Grass Technologies, West Warwick, Rhode Island, USA) scored in 30-sec epochs according to American Academy of Sleep Medicine (AASM) standardized criteria. Apnea during sleep was defined as cessation of airflow (90% fall in the amplitude of airflow signal compared to the baseline airflow) lasting at least 10 seconds. Hypopnea was defined as a 50% or greater fall in airflow lasting ten or more seconds associated with a 3% or greater fall in oxygen saturation from baseline. The apnea–hypopnea index (AHI) was calculated using the total number of respiratory events (apneas and hypopneas) per hour sleep. Subjects with an AHI ≥20 were regarded as having OSAS.

Means were compared by Student's t test or Mann-Whitney U test. Prevalence of OSAS in patients with NTG was compared with the matched controls by using Fisher exact test. Comparison of the clinical and polysomnographic characteristics of the patients with NTG and matched controls was performed by using the unpaired t test or Fisher exact test. SSPS version 17.0 for Windows (SSPS Inc., Chicago, Illinois, USA) was used for statistical analysis. Significance was accepted for p < 0.05.

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