**Abstract**

A survey of the World Health Organization has revealed that retinal eye disease Glaucoma is the second leading cause for blindness worldwide. It is a disease which will steals the vision of the patient without any warning or symptoms. About half of the World Glaucoma Patients are estimated to be in Asia. Hence, for social and economic reasons, Glaucoma detection is necessary in preventing blindness and reducing the cost of surgical treatment of the disease. The objective of the chapter is to predict and detect Glaucoma efficiently using image processing techniques. We have developed an efficient computer-aided Glaucoma detection system to classify a fundus image as either normal or glaucomatous image based on the structural features of the fundus image such as cup-to-disc ratio (CDR), rim-to-disc ratio (RDR), superior and inferior neuroretinal rim thicknesses, vessel structure-based features, and distribution of texture features in the fundus images. An automated clinical support system is developed to assist the ophthalmologists to identify the persons who are at risk in the early stages of the disease, monitor the progression of the disease, and minimize the examination time.

**Keywords:** glaucoma, cup-to-disc ratio (CDR), rim-to-disc ratio (RDR), superior, inferior, neuroretinal rim, structure features, texture features

### **1. Introduction**

According to the survey of the World Health Organization, over the last 10 years, cataract remains the highest leading cause of blindness worldwide covering 47.9% of overall blindness. It is a progressive and painless clouding of the internal lens of the eye. Similarly, the survey declares Glaucoma as the second leading cause for blindness worldwide. About 12.3% of patients in the world are suffering from Glaucoma [1]. It is a disease which will steal the vision of the patient without any warning or symptoms. Surveys conducted in North America and Europe revealed a significant proportion of new Glaucoma patients who were previously gone undetected. The proportion estimated for Glaucoma patients in Asia and developing countries is even larger [2]. This calls for the need for early Glaucoma detection, and we can prevent blindness and reduce the surgical cost involved in treating the disease. The fundus image of the eye, Glaucoma disease, structural changes in fundus image due to Glaucoma, and its diagnosis are presented in this section.

### **1.1 Fundus image of the eyes**

The eye is the most complex organ of the human body with approximate dimension of 2.54 cm width, 2.3 cm height, and 2.54 cm deep [3]. The human eye acts like a camera [4] and processes the visual signals. **Figure 1** shows the front view of the eye fundus image consisting of the optic disc and optic cup. The optic nerves and blood vessels exit the retina from the optic disc. It is considered as one of the main features of a retinal fundus image and is located to the nasal side of the fovea. It is vertically oval, with an average dimension of horizontally 1.76 mm and vertically 1.92 mm. Inside the optic disc, there is a central depression, of variable size, called the optic cup.

The optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. The changes in the shape and color or depth of the optic disc and optic cup are the indicators of various ophthalmic pathologies especially for Glaucoma and other eye diseases. Optic disc and cup are the brightest features of the normal fundus. The disc appears to be as a bright yellow or white region in colored fundus image.

#### **1.2 Structural changes in fundus image due to glaucoma**

The structure and appearance of the optic disc can reveal the presence of Glaucoma, and they are considered as very important features to assess the damage due to Glaucoma. The optic cup concentric enlargement, decrease in rim area, and other such patterns of glaucomatous damage are most commonly found. The ratio of area of optic cup to area of the optic disc is normally considered to evaluate the disease. Due to Glaucoma, in the retina the optic cup area enlarges and progresses toward the disc. This distinction can be seen between normal and Glaucomaaffected fundus images as shown in **Figure 2(a)** and **(b)**, respectively. This cup-to-disc area ratio (CDR) is used in ophthalmology to determine the progression of Glaucoma. If the CDR value is greater than 0.3, the patient has a threat of Glaucoma. The CDR of the image in **Figure 2(b)** is nearly 0.7, and it is a prominent case of Glaucoma.

The area present between the cup and disc boundary of the eye is termed as neuroretinal rim [5] as shown in **Figure 3(a)** and **(b)** for a sample of normal and Glaucoma eye, respectively. Thinning of the neuroretinal rim is also one of the symptoms of Glaucoma. Rim-to-disc area ratio (RDR) is also an indicator

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shown in **Figure 5**.

Glaucoma eye.

**Figure 3.**

**Figure 2.**

*Efficient Computer-Aided Techniques to Detect Glaucoma*

for Glaucoma. As seen from **Figure 3**, the normal eye has more RDR than the

can also be used to detect Glaucoma more accurately [5, 6].

*Neuroretinal rim: (a) rim area in the normal eye; (b) rim area in the Glaucoma eye.*

The retinal image shall be seen as composed of inferior, superior, nasal, and temporal regions as shown in **Figure 4(a)**. Due to Glaucoma, blood vessels covered by the nasal region increase, and the inferior–superior region decreases. Hence, the ratio of the area of the sum of blood vessels in the inferior–superior region to the sum of blood vessels in the nasal-temporal region (ISNT) decreases. This feature

A study has revealed that the diameters of the retinal vessels have been seen to be significantly smaller in the glaucomatous eyes than the normal eyes [7, 8]. This reduction in vessel diameters can be continuously monitored, and the disease can be detected in early stages. Also, in the case of prominent cases of Glaucoma, there is a distortion observed in cup structure. Cup usually expands downward more toward inferior side. Therefore, disease can be detected by measuring the difference in neuroretinal rim thickness at the superior and inferior regions, which are referred as superior rim thickness and inferior rim thickness as shown in **Figure 4(b)**.

In the case of Glaucoma, thickness of the vessels around the disc goes on reducing due to lack of fresh aqueous humor. This also results in disappearance of small vessels around the disc. A normal eye contains a lot of very minute vessels like small branches of tree around the optic disc, which are absent in the Glaucoma eye as

In the normal eye, peripheral vision is present fully. In the Glaucoma-affected eye, peripheral vision goes on reducing. As an illustration, **Figure 6(a)** shows the

*DOI: http://dx.doi.org/10.5772/intechopen.89799*

*Fundus images: (a) normal eye; (b) glaucoma eye.*

**Figure 1.** *Front view of the eye fundus image.*

*Visual Impairment and Blindness - What We Know and What We Have to Know*

The eye is the most complex organ of the human body with approximate dimension of 2.54 cm width, 2.3 cm height, and 2.54 cm deep [3]. The human eye acts like a camera [4] and processes the visual signals. **Figure 1** shows the front view of the eye fundus image consisting of the optic disc and optic cup. The optic nerves and blood vessels exit the retina from the optic disc. It is considered as one of the main features of a retinal fundus image and is located to the nasal side of the fovea. It is vertically oval, with an average dimension of horizontally 1.76 mm and vertically 1.92 mm. Inside the optic disc, there is a central depression, of variable size, called

The optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. The changes in the shape and color or depth of the optic disc and optic cup are the indicators of various ophthalmic pathologies especially for Glaucoma and other eye diseases. Optic disc and cup are the brightest features of the normal fundus. The disc appears to be as a bright yellow or white region in

The structure and appearance of the optic disc can reveal the presence of Glaucoma, and they are considered as very important features to assess the damage due to Glaucoma. The optic cup concentric enlargement, decrease in rim area, and other such patterns of glaucomatous damage are most commonly found. The ratio of area of optic cup to area of the optic disc is normally considered to evaluate the disease. Due to Glaucoma, in the retina the optic cup area enlarges and progresses toward the disc. This distinction can be seen between normal and Glaucomaaffected fundus images as shown in **Figure 2(a)** and **(b)**, respectively. This cup-to-disc area ratio (CDR) is used in ophthalmology to determine the progression of Glaucoma. If the CDR value is greater than 0.3, the patient has a threat of Glaucoma. The CDR of the image in **Figure 2(b)** is nearly 0.7, and it is a prominent

The area present between the cup and disc boundary of the eye is termed as neuroretinal rim [5] as shown in **Figure 3(a)** and **(b)** for a sample of normal and Glaucoma eye, respectively. Thinning of the neuroretinal rim is also one of the symptoms of Glaucoma. Rim-to-disc area ratio (RDR) is also an indicator

**1.2 Structural changes in fundus image due to glaucoma**

**1.1 Fundus image of the eyes**

the optic cup.

colored fundus image.

case of Glaucoma.

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**Figure 1.**

*Front view of the eye fundus image.*

**Figure 2.** *Fundus images: (a) normal eye; (b) glaucoma eye.*

#### **Figure 3.** *Neuroretinal rim: (a) rim area in the normal eye; (b) rim area in the Glaucoma eye.*

for Glaucoma. As seen from **Figure 3**, the normal eye has more RDR than the Glaucoma eye.

The retinal image shall be seen as composed of inferior, superior, nasal, and temporal regions as shown in **Figure 4(a)**. Due to Glaucoma, blood vessels covered by the nasal region increase, and the inferior–superior region decreases. Hence, the ratio of the area of the sum of blood vessels in the inferior–superior region to the sum of blood vessels in the nasal-temporal region (ISNT) decreases. This feature can also be used to detect Glaucoma more accurately [5, 6].

A study has revealed that the diameters of the retinal vessels have been seen to be significantly smaller in the glaucomatous eyes than the normal eyes [7, 8]. This reduction in vessel diameters can be continuously monitored, and the disease can be detected in early stages. Also, in the case of prominent cases of Glaucoma, there is a distortion observed in cup structure. Cup usually expands downward more toward inferior side. Therefore, disease can be detected by measuring the difference in neuroretinal rim thickness at the superior and inferior regions, which are referred as superior rim thickness and inferior rim thickness as shown in **Figure 4(b)**.

In the case of Glaucoma, thickness of the vessels around the disc goes on reducing due to lack of fresh aqueous humor. This also results in disappearance of small vessels around the disc. A normal eye contains a lot of very minute vessels like small branches of tree around the optic disc, which are absent in the Glaucoma eye as shown in **Figure 5**.

In the normal eye, peripheral vision is present fully. In the Glaucoma-affected eye, peripheral vision goes on reducing. As an illustration, **Figure 6(a)** shows the

#### **Figure 4.**

*Regions of fundus image: (a) ISNT regions and vessels, (b) neuroretinal rim and superior and inferior thicknesses.*

#### **Figure 5.**

*Vessels in fundus image: (a) a normal eye as seen through the green filter; (b) a glaucoma eye in green filter.*

#### **Figure 6.**

*Vision loss due to Glaucoma: (a) normal eye vision; (b) glaucoma eye vision (courtesy: http://www.caeps.org/).*

vision of a sample picture as perceived by a normal eye, and **Figure 6(b)** shows the vision of the same picture as perceived by a Glaucoma eye.

#### **1.3 Fundus features used for glaucoma detection**

We have used the fundus features such as (i) CDR, (ii) RDR, (iii) superior rim thickness, (iv) inferior rim thickness, (v) structural features of vessels around

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**Figure 7.**

*Efficient Computer-Aided Techniques to Detect Glaucoma*

by the digital image processing techniques [9–12].

fundus eye image features for detection of Glaucoma:

Vessel structural features and Textural features.

and inferior rim thicknesses are extracted.

*Comprehensive efficient integrated glaucoma detection system.*

the disc such as maximum vessel diameter, number of vessel segments, and total number of smaller diameters of vessels, and (vi) spatial textures to detect Glaucoma

**2. Proposed comprehensive efficient integrated glaucoma detection** 

The block schematic of our proposed comprehensive efficient integrated Glaucoma detection system for Glaucoma identification using image processing

The retinal image of the eye is captured using a fundus camera. The captured eye fundus image is subjected to various image processing techniques to extract

Our proposed system extracts and uses the following three different sets of

Fundus structure based features (CDR, RDR and Neuroretinal rim thicknesses),

Structure-based features of fundus image are extracted using a template-based approach. A template aids the segmentation of the optic cup and disc from the fundus image. A template is correlated with fundus image using Pearson-r correlation for segmentation. Structure-based features such as CDR, RDR, and superior

*DOI: http://dx.doi.org/10.5772/intechopen.89799*

techniques is shown in **Figure 7**.

different features of fundus image.

**system**

*Visual Impairment and Blindness - What We Know and What We Have to Know*

*Regions of fundus image: (a) ISNT regions and vessels, (b) neuroretinal rim and superior and inferior thicknesses.*

*Vessels in fundus image: (a) a normal eye as seen through the green filter; (b) a glaucoma eye in green filter.*

*Vision loss due to Glaucoma: (a) normal eye vision; (b) glaucoma eye vision (courtesy: http://www.caeps.org/).*

vision of a sample picture as perceived by a normal eye, and **Figure 6(b)** shows the

We have used the fundus features such as (i) CDR, (ii) RDR, (iii) superior rim thickness, (iv) inferior rim thickness, (v) structural features of vessels around

vision of the same picture as perceived by a Glaucoma eye.

**1.3 Fundus features used for glaucoma detection**

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**Figure 6.**

**Figure 5.**

**Figure 4.**

the disc such as maximum vessel diameter, number of vessel segments, and total number of smaller diameters of vessels, and (vi) spatial textures to detect Glaucoma by the digital image processing techniques [9–12].
