Glaucoma characteristics evaluation in myopia – A clinical study

Introduction

Glaucoma is the leading cause of irreversible blindness among the world population,1, 2 one of the risk factors identified for this is high myopia. Patients with high myopia have a higher risk of glaucoma because of changes in optic nerve head.

Patients with high myopia will have eyeball elongation and optic nerve head tilting that will have field defects which may mimic glaucoma and treating patients with myopia with suspected Optic Nerve Head features of glaucoma is a challenge and even more challenging is the diagnosis of glaucoma in a myopic patient. In a myopic patient normal may be the Intra Ocular Pressure with the optic nerve head simulating the glaucoma features.

There is a possibility that myopic patients are associated with higher risk for glaucoma.3 Glaucoma evaluation involves many aspects like Intra Ocular Pressure levels, features of optic nerve head changes, Retinal Nerve Fibre layer and visual field changes. It is to be understood that optic disc in myopic patients might be more vulnerable to pressure changes due to their connective tissue patterns.

There is a tendency for lamina cribrosa to be deformed with increased axial length of the eyeball in myopic patients which may contribute to increased vulnerability to damage. This study was conducted to evaluate the association of glaucoma features with myopia and to create the awareness regarding the long term follow up.

Aims

To evaluate the association of glaucoma features with myopia. To create the awareness regarding the long term follow up.

Materials and Methods

Patients in the age group of 15 to 45 years who had attended our institution over a period of one year who fulfilled the inclusion and exclusion criteria were subjected for this study. Inclusion criteria were (i) unilateral or bilateral myopia patients in the age group of 15 to 45 years, (ii) myopia in the range of -3.00 D to -6.00 D, (iii) moderate and more than -6.00 D– high myopia. Patients below 15 years and above 45 years, those not having clear media and patients having retinal degeneration not related to myopia were excluded from the study.

Fifty four patients who were diagnosed to have moderate or high degree myopia were selected for this analytical study. Patients were enquired about their occupation, symptoms, spectacle usage and frequent change of spectacles. Clinically patients were subjected to visual acuity - both unaided and aided, refraction, slit lamp examination, tonometry with Goldman applanation tonometer, pachymetry, gonioscopy, fundus examination and automated perimetry. Refractive power in the range of -3.00 D to -6.00 D spherical equivalent was considered as moderate myopia and more than - 6.00 D spherical equivalent was considered as high myopia. Intra ocular pressure was measured by using standard Goldmann applanation tonometer and readings less than 21.00 mmHg was taken as normal intra ocular pressure.

The corrected intra ocular pressure was derived after measuring the central corneal thickness and using adjustment corrections to the measured intra ocular pressure.

Asymmetry of the cup disc ratio, notching in the supra temporal or infra temporal rim, localised loss of retinal nerve fibre layer and disc haemorrhage were considered as optic disc changes in glaucoma. Ophthalmoscopic features of temporal crescent, peripapillary atrophy, and optic disc tilting and tigeroid fundus are to be considered as features of myopia. Visual field charting was done taking into account necessary care to sustain adequate fixation. Visual field defects were considered glaucomatous when:

Observation and Results

Among the 54 cases, moderate myopia was seen in 30 patients and 24 patients were found to be with high myopia. The ratio between the two myopic conditions being 1.25:1

In the age group of 15 -30 years, 17 patients were having moderate myopic status while 13 were high myopes. In 31 -45 years group, 13 were moderate myopes whereas 11 were having high myopic status.

In the moderate myopic group of 30 patients 14 were males and 16 were females and in the high myopia of 24 patients, 13 were males and 11 were females.

In moderate myopia, the mean intraocular tension observed was 17.7mmHg in right eye and 17.4mm Hg in left eye. Intraocular tension measured highest in both the eyes was 21.0mmHg

In high myopia group, the mean intraocular tension recorded was 17.8mmHg in right eye and 18.20mmHg in left eye. Intraocular tension recorded highest in right eye was 23.0 mmHg and in the left eye 28.0mmHg

The mean corrected Intra Ocular Pressure recorded in the right and left eye of moderate myopic group was 18.3mmHg, the Intra Ocular Pressure recorded highest in this group was 22.0mmHg.

In high myopic group the mean corrected Intra Ocular Pressure in the right eye was 18.6mmHg and in the left eye was 18.9mmHg. The Intra Ocular Pressure measured highest in this group was 23.0mmHg in the right eye and 28mm Hg in the left eye

In the moderate myopic group, the variation between mean Intra Ocular Pressure and mean corrected Intra Ocular Pressure was 0.60mmHg in the right eye and 0.84mHg in the left eye which was considered statistically significant.(P value less than 0.001)

In high myopic group, the variation between the mean Intra Ocular Pressure and mean corrected Intra Ocular Pressure was 0.75 mm Hg in both eyes which was considered statistically significant (P value < 0.001)

Discussion

In our study group, moderate myopes constituted 55.5% and 44.5% by high myopes. In the moderate myopic group of 30 patients 31.5% belonged to 15 to 30 years of age and 24.0% represented 31 to 45years of age. Similarly 24.0% represented 15 to 30 years of age and 20.4 % belonged to 31 to 45 years of age in high myopes.

The mean IOP in high myopic group was found to be higher than seen in moderate myopic group. Similarly the mean corrected IOP seen in high myopes were observed to be higher than observed in moderate myopia. But from our study, we observed a statistically significant difference between mean IOP and mean corrected IOP in moderate myopes and high myopes.

In the moderate myopic group optic disc normal appearance was seen in 53.3% myopic fundus picture 7 in 30% and glaucomatous optic nerve head changes in 16.6 %.8

In the high myopic group 41.6% was found to have glaucomatous optic nerve head change and the most commonly observed optic nerve head changes was the asymmetry of the optic disc cup ratio.

In the study of 108 perimetric charts the most commonly observed field defect was enlarged blind spot.9 In the high myopic group of 48 perimetric charts, enlarged blind spots were seen in 27.1%, nasal step 2.1%, 6.25% with paracentral scotoma and 4.16%with arcuate scotoma.

From our study we observed a higher prevalence of glaucoma and glaucomatous suspects in high myopic group as compared with the group of moderate myopes. 10

Conclusion

There is a statistically significant difference between mean IOP and mean corrected IOP and this is also clinically significant. Hence the need for taking measurements of mean corrected IOP. This study also points to the fact that in high myopic group optic disc damage is more profuse. Enlarged blind spot was the most frequently observed field defect in high myopic group.

The number of samples may be small in our study but there is a clear indication that there is increased prevalence of glaucoma in high myopia

Source of Funding

None.

Conflicts of Interest

All contributing authors declare no conflict of interest.