Janakiraman Palani, Bachelor of Optometry
Research Optometrist, Medical Research Foundation, Sankara Nethralaya, Chennai, India
Glaucoma is a leading cause of irreversible blindness globally. The global prevalence of glaucoma for the population aged 40-80 years is 3.54%. (1) The number of people with glaucoma is expected to increase to 111.8 million in 2040 globally. (1), Glaucoma is a term describing a group of ocular disorders with multi-factorial aetiology united by a clinically characteristic intraocular pressure-associated optic neuropathy. (2) In this write-up, changes in ocular dimensions are looked at for all types of glaucoma namely, Primary open-angle glaucoma (POAG), Primary closed-angle glaucoma (PACG), Normal-tension glaucoma (NTG), Ocular hypertension (OHTN), and the suspects.
Ocular dimensional parameters considered in glaucoma are:
- Axial length
- Anterior chamber depth
- Anterior chamber volume
- Lens thickness
- Relative lens position
- Lens-Axial length factor
Past literature suggests the ocular dimension changes with different subtypes of glaucoma, starting with the axial length, which is found to be shorter in occludable angles and primary angle-closure glaucoma ranging from 21.62 mm to 22.83 mm as compared to other types of glaucoma. The corneal curvature measured with keratometry shows a steeper ‘K’ value ranging from 43.75D to 44.87D in the case of angle-closure glaucoma than other types of glaucoma. (4)(5)(7)(8) The anterior chamber depth is found to be shallow in all types of ACG ranging from 1.84 mm to 2.69 mm (4-8). Anterior chamber volume which is a unique factor found to be less than 100µl in case of ACG except for plateau iris configuration (i.e., in 91 µl in extreme narrow angles and 113 µl in case of plateau iris configuration). (6) The central corneal thickness was found to be thicker in the case of ocular hypertension as compared to other types of glaucoma (3)(4)(8) in which the value ranges from 513 to 570 microns. Lens thickness was significantly thicker in the ACG (3)(4)(5)(7)(8) which ranges from 4.23mm to 4.83mm. The lens is relatively anteriorly positioned in the case of ACG calculated using the formula given by Lowe (RLP = ACD+½ LT/ AL*10) (4)(5)(8) which ranges from 2.13 to 2.20. Lens axial-length factor was higher in the ACG (4)(5) in which the values ranged from 2.0 to 2.10.
Figure 1: Anterior Chamber dimensions in angle closure glaucoma compared with normal patients. Solid line indicates the normal values and Dotted line indicates the abnormal value.
PHOTO COURTESY: Lee, D. A., Brubaker, R. F., & Ilstrup, D. M. (1984). Anterior chamber dimensions in patients with narrow angles and angle-closure glaucoma. Archives of ophthalmology, 102(1), 46-50.
Future studies will help us to know the structures and anatomical position and change much more in detail with the use of recent advances in technology such as ultrasound biomicroscopy, anterior segment OCT and scheimpflug video imaging. It is seen that the ocular dimensions are altered from normal in the case of the ACG group than other types of glaucoma. The ACG group should be keenly looked at/observed for the structural dimensional changes over the period to prepone the need for peripheral iridotomy and further management.
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