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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 18  |  Issue : 3  |  Page : 170-175

Optical coherence tomography (OCT) changes after achieving target intraocular pressure


Department of Ophthalmology, Faculty of Medicine, Beni-Suef University, Beni-Suef, Egypt

Date of Submission16-Jan-2017
Date of Acceptance19-Jun-2017
Date of Web Publication17-Oct-2017

Correspondence Address:
Moustafa M Tawfeek
El Modria Street, Minia 61111
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/DJO.DJO_7_17

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  Abstract 

Purpose The aim of this study was to evaluate the ability of optical coherence tomography (OCT) to detect the changes in retinal nerve fiber layer (RNFL) after reaching target intraocular pressure (IOP) in glaucomatous patients.
Patients and methods Thirty-two (58 eyes) patients with a clinical diagnosis of primary open-angle glaucoma were assessed as regards peripapillary RNFL thickness and optic nerve head parameters by 3D-OCT for a follow-up period of 6 months. The drugs used to reach target IOP were Twinzol (dorzolamide 2%/timolol 0.5%) eye drops 5 ml and Ioprost (Latanoprost) 0.005% (50 mcg/ml) eye drops 3 ml. Eleven patients were treated with Twinzol only and reached target IOP after adding Ioprost. Eight patients were treated with Ioprost only and reached target IOP after adding Twinzol, and 13 patients had no added treatment, where four reached target IOP by Ioprost only, six reached target IOP by Twinzol only, and three reached target IOP by both drugs. OCT was done for all patients after achieving target IOP and was repeated after 6 months of medical control.
Results The mean IOP before treatment was 29.89 mmHg and decreased significantly (P<0.001) after treatment to 12.17 mmHg. There was a significant (P<0.05) difference regarding the superior RNFL thickness before and after treatment (100.31 vs. 101.15). There was also a significant (P<0.05) difference in the nasal RNFL thickness before and after treatment (73.37 vs. 74.34). The cup-to-disc area ratio (CDR) mean had decreased significantly (P<0.01) after treatment (0.51 before treatment vs. 0.47 after treatment). Vertical CDR and cup volume had the same trend (0.69 vs. 0.66 for vertical CDR and 0.42 vs. 0.39 for cup volume). There was a highly significant (P<0.01) strong positive correlation between IOP changes and rim volume (r=0.81).
Conclusion Achieving target IOP in patients with glaucoma results in a significant change in the RNFL and ganglion cell complexes layer as shown by spectral-domain OCT.

Keywords: glaucoma, intraocular pressure, optical coherence tomography


How to cite this article:
Saif MY, Abd Elkhalek MO, Tawfeek MM. Optical coherence tomography (OCT) changes after achieving target intraocular pressure. Delta J Ophthalmol 2017;18:170-5

How to cite this URL:
Saif MY, Abd Elkhalek MO, Tawfeek MM. Optical coherence tomography (OCT) changes after achieving target intraocular pressure. Delta J Ophthalmol [serial online] 2017 [cited 2020 Apr 6];18:170-5. Available from: http://www.djo.eg.net/text.asp?2017/18/3/170/216928


  Introduction Top


Glaucoma is one of the main causes of visual impairment and blindness worldwide [1]. It is a multifactorial optic neuropathy known to cause progressive loss of retinal ganglion cells and their axons, where an early diagnosis remains the key point for its management [2],[3]. Glaucoma is a group of diseases that have as a common endpoint a characteristic optic neuropathy, which is determined by both structural change and functional deficit. Although elevated intraocular pressure (IOP) is one of the primary risk factors, its presence or absence does not have a role in the definition of the disease [4].

Raised IOP (>21 mmHg) is the most important and only modifiable risk factor for glaucoma. However, some may have high eye pressure for years and never develop damage, whereas others can develop nerve damage at a relatively low pressure, and the evaluation of the retinal nerve fiber layer (RNFL), optic nerve head (ONH), and ganglion cell layer (GCL) is a crucial step in diagnosing and monitoring glaucoma [5].

Optical coherence tomography (OCT) can analyze and quantify the optic nerve, RNFL thickness, and GCL allowing broad staging of structural damage [6]. Recently, OCT provided customized scans and tailored a single scan circle to examine the RNFL thickness, and these scans can be useful to help the ophthalmologist differentiate normal from early glaucomatous peripapillary RNFL [7]. Spectral-domain optical coherence tomography (SD-OCT) system is a rapidly emerging imaging modality in diagnosing glaucomatous damage [8]. The OCT technique has a novel function that can measure the thickness of the inner three retinal layers, which are collectively known as the macular ganglion cell complex, including RNFL, GCL, and inner plexiform layer. The macular ganglion cell complex OCT evaluation is expected to target the cells directly affected by glaucoma in the area of their highest concentration [9].

The aim of this study was to assess the ability of OCT to detect changes in RNFL after reaching target IOP in glaucomatous patients.


  Patients and methods Top


This is a prospective study, including 58 eyes of 32 patients with the clinical diagnosis of primary open-angle glaucoma (POAG), controlled by medical treatment. The study was carried out in El Minia Insurance Hospital and Beni-Sueif University Hospital (Egypt) from August 2015 to August 2016. The authors assessed the peripapillary RNFL thickness after obtaining approval by hospital committee, and written informed patient consent with an explanation regarding the purpose, method, effect, and complication and ONH parameters by 3D-OCT for a follow-up duration of 6 months.

The patients were included in this study, according to the following criteria:

Inclusion criteria

The inclusion criteria were as follows:
  1. Patients with POAG.
  2. Ocular hypertension patients.


Exclusion criteria

Exclusion criteria were as follows:
  1. Diabetes mellitus.
  2. Neurological diseases.
  3. History of surgery.
  4. History of trauma.
  5. History of rheumatoid disease.


All patients were subjected to the following:
  1. Complete ophthalmic examination, including full history taking, history of treatment, and slit-lamp examination by ZEISS slit-lamp (Zeiss Medical Instruments, Germany). Uncorrected visual acuity and best-corrected visual acuity were recorded by TOPCON auto-refractometer (Topcon Medical, Topcon, Japan) and illiterate E chart. IOP was measured by Goldmann applanation tonometry, and fundus examination was done by indirect slit-lamp ophthalmoscopy using high-power convex lens (Volk 90 D), and OCT for RNFL analysis was done by Spectral-Domain 3D-OCT-2000 (Topcon Medical).


Patients had high IOP in spite of taking monotherapy or bitherapy, and achieved the target IOP after changing or adding a new medication. Monthly measurement of IOP was done to assure reaching target IOP. OCT was done for all patients after achieving the target IOP and was repeated after 6 months of medical control. The target IOP was achieved within 1 week from the beginning of treatment, according to the Saif table ([Table 1]) [10].
Table 1 Saif table showing target intraocular pressure guided by the cup-to-disc ratio [10]

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Statistical analysis

Statistical analysis of the data was performed by using the SPSS-22 software package. Categorical data parameters were presented in the form of frequency and percentage. Quantitative data were expressed in the form of mean and SD. Paired sample t-test was used to test the significance between premedical and postmedical treatment data. Probability level (P) was assumed significant if it was less than 0.05 and highly significant if the P-value was less than 0.01. The Spearman correlation coefficient was used to obtain the correlation between both readings.


  Results Top


The study included 32 (58 eyes) patients with POAG on medical treatment. They were 24 men and eight women with a mean age of 57.75±7.08 years, ranging from 48 to 78 years ([Table 2]).
Table 2 Patients’ baseline characteristics

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The mean IOP before treatment was 29.89 mmHg, ranging from 22.00 to 40.00 mmHg, and decreased after treatment to 12.17 mmHg, ranging from 8.00 to 16.00 mmHg (P<0.001) ([Table 3]).
Table 3 Intraocular pressure, retinal nerve fiber layer thicknesses, disc tomography, and macula in patients before and after medical treatment

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There were no significant differences between total, inferior, and temporal RNFL thickness before and after treatment. However, there was a significant (P<0.05) difference as regards superior RNFL thickness before and after treatment (100.31 vs. 101.15), as well as nasal RNFL thickness before and after treatment (73.37 vs. 74.34, P<0.05), as shown in [Table 3].

The cup-to-disc area ratio (CDR) mean decreased significantly (P<0.01) after treatment (0.51 before treatment vs. 0.47 after treatment). The same trend was observed in the vertical CDR and cup volume (0.69 vs. 0.66 for vertical CDR and 0.42 vs. 0.39 for cup volume). On the other hand, the rim volume and rim area increased significantly (P<0.01) after treatment (0.29 before treatment vs. 0.32 after treatment for rim volume and 1.19 vs. 1.26 mm2 for rim area), as shown in [Table 3]. There was a slight decrease (not significant) in total mean macular RNFL thickness, total macular GCL thickness, and macular region thickness as measured by central foveal thickness (CFT) after treatment ([Table 3]).

A nonsignificant weak positive correlation was found between IOP changes and total, superior, inferior, nasal, and temporal RNFL thickness before and after treatment. A similar trend was found as regards the correlation between IOP changes and CDR, vertical CDR, cup volume, and rim area. However, there was a highly significantly strong positive correlation (P<0.01) between IOP changes and rim volume (r=0.81). In addition, a significant negative correlation (P<0.05) was found between IOP changes and macular region thickness CFT (r=−0.32), whereas there was a nonsignificant weak negative correlation between IOP changes and both macular RNFL thickness and the macular GCL before and after treatment ([Table 4]).
Table 4 Correlation between retinal nerve fiber layer thickness, disc tomography, macular changes, and intraocular pressure changes before and after medical treatment

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There was a nonsignificant weak positive correlation between the percentage of IOP change and all the percentages of RNFL thickness changes before and after treatment. Highly significant (P<0.01) negative correlation was found between the percentage of IOP change and both percentage of CDR change (r=−0.36) and percentage of rim area (r=−0.50), whereas no significant correlation was found between the percentage of IOP change and the percentages of changes in cup volume. Finally, there was a significant positive correlation between percent change in rim volume and the percent change in IOP (r=0.450), and there was a significant (P<0.05) negative correlation between the percentage of IOP change and change percentage of macular RNFL thickness (r=−0.31) and macular region (r=−0.34), as shown in [Table 5].
Table 5 Correlation between percentage of change of retinal nerve fiber layer thickness, disc tomography, macula, and percentage of change of intraocular pressure before and after medical treatment

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  Discussion Top


OCT is a developed, noninvasive, and noncontact technique for imaging of the layered structure of the retina. Attempts to measure RNFL thickness were done by several investigators [11],[12].

The current results did not detect that glaucoma patients with a considerable reduction in IOP resulting after 6 months of medical treatment had any significant change in total, inferior, and temporal quadrant RNFL thickness but had a significant increase in superior and nasal quadrant RNFL thickness. In this study, no significant correlation was found between the extent of IOP reduction and any change in the RNFL OCT parameters or the percent change in the RNFL OCT parameters. These results were similar to those of Chang et al. [13], who found that IOP was lowered by medical or surgical intervention and that no significant change in the RNFL thickness was associated with the lowering of IOP, and Rebolleda et al. [14], who reported that no change in peripapillary RNFL thickness occurred 6 months following deep sclerectomy.

Other studies used different methods to evaluate the RNFL thickness, such as Sogano et al. [15], who observed, using an optic nerve Analyzer (Rodenstock, Munich, Germany), no significant change in relative nerve fiber layer height after trabeculectomy, although the changes were reported to be pressure dependent. In addition, Irak et al. [16] used a confocal scanning laser ophthalmoscopy device and found no significant change in nerve fiber layer cross-sectional area 3 months after trabeculectomy. Yamada et al. [17] showed prospectively, using scanning laser polarimetry, that the RNFL thickness in the superotemporal and inferotemporal regions of the optic disc increased significantly after trabeculectomy. However, they found no correlation between the RNFL thickness change and the percent changes in IOP [17].

In contrast to the current results, Aydin et al. [18] used a noncommercial, prototype OCT device to evaluate RNFL thickness change following trabeculectomy, and reported a significant increase in overall RNFL thickness and showed a significant correlation between RNFL thickness and extent of IOP reduction.

Regarding the correlation between the IOP change and disc tomography changes before and after medical treatment, the current study found that glaucoma patients with a considerable reduction in IOP after 6 months of medical treatment had a significant increase in rim area and rim volume, and had a significant decrease in cup volume and CDR. Furthermore, in this study, there was a significant correlation between the extent of IOP reduction and percentage change in ONH parameters.

These results are in accordance with those of Irak et al. [16], who reported an average IOP decrease (∼4 months after trabeculectomy) in 49 patients of ∼11 mmHg (∼45%) and also showed a significant decrease in the cup area, cup volume, and CDR, and a significant increase in the rim area after an IOP decrease.

In a different study, Raitta et al. [19] examined the disc topography after trabeculectomy in nine patients. The average decrease in IOP after ∼4 and 12 months was 14.9 mmHg (59%) and 13.4 mmHg (43%), respectively. They found significant decreases in cup volume and mean cup depth after 4 months and decreases in cup volume, CDR, and mean height contour after 12 months. However, no significant correlation was found between the percent change in IOP and the percent change in measured parameters, possibly because of the small sample size [19]. In addition, Shin et al. [20] found the optic disc cupping reversal (decrease of CDR, an increase of the disc rim area, and a decrease of cup volume) to be in direct proportion to the magnitude of IOP reduction in adult chronic open-angle glaucoma patients with early to moderate chronic open-angle glaucoma. Likewise, Kotecha et al. [21] reported persistent reversal of disc cupping following trabeculectomy 2 years following IOP reduction.

On the other hand, Topouzis et al. [22] found no difference in most optic disc parameters 4 months after surgery, and the cup shape also reverted to baseline values 8 months after surgery. In addition, Funk [23] could not demonstrate a significant correlation between the increase of the disc rim area and the magnitude of IOP reduction following filtration surgery in adult glaucoma patients of varying severities. The apparent lack of a significant correlation between the disc rim area and the amount of IOP reduction in Funk’s [23] study might have been because of the varying severities of glaucoma in his study patients. Some of his patients with very severe glaucomatous optic nerve damage might not have shown a demonstrable disc cupping reversal even with a large magnitude of IOP reduction. Consistent with this possibility is the observation that in glaucomatous monkey eyes the disc cupping reversal is much less in severe stages of glaucoma than in mild to moderate stages for a comparable amount of IOP reduction [24]. Therefore, a demonstrable disc cupping reversal is not expected to occur in patients with very advanced glaucoma in spite of a large magnitude of IOP reduction [24]. In addition, the mean interval between preoperative optic disc analysis and filtration surgery in Funk’s study was 5.9±9.4 weeks. Thus, some of his patients would have sustained progressive glaucomatous optic nerve damage and a further decrease of the disc rim area during the relatively long interval of uncontrolled IOP. Therefore, the increase, if any, of the disc rim area observed postoperatively in these patients would represent an underestimation.


  Conclusion Top


The early diagnosis of glaucoma and early initiation of treatment is highly important, so that further vision loss can be stopped or slowed down. RNFL, ONH, and ganglion cell complex measurement with SD-OCT could provide important information for detection and evaluation of glaucoma. SD-OCT can detect glaucomatous changes affecting the RNFL thickness, ONH parameters, and the retinal ganglion cells. There was no significant correlation between the extent of IOP reduction and any change in the RNFL OCT parameters or the percent change in the RNFL OCT parameters. However, there was a significant correlation between the extent of the IOP reduction and the percentage change in ONH parameters.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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