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Change of Ocular Dimensions in Different Types of Glaucoma

by | Feb 1, 2021 | Manuscripts | 0 comments

Janakiraman Palani, Bachelor of Optometry

Research Optometrist, Medical Research Foundation, Sankara Nethralaya, Chennai, India

 

Introduction

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
  • Keratometry
  • Anterior chamber depth
  • Anterior chamber volume
  • Lens thickness
  • Pachymetry
  • 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.

 

Conclusion

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.

 

References:

  1. Tham, Y. C., Li, X., Wong, T. Y., Quigley, H. A., Aung, T., & Cheng, C. Y. (2014). Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology, 121(11), 2081-2090.
  2. Casson, R. J., Chidlow, G., Wood, J. P., Crowston, J. G., & Goldberg, I. (2012). Definition of glaucoma: clinical and experimental concepts. Clinical & experimental ophthalmology, 40(4), 341-349.
  3. Singh, R. P., Goldberg, I., Graham, S. L., Sharma, A., & Mohsin, M. (2001). Central corneal thickness, tonometry, and ocular dimensions in glaucoma and ocular hypertension. Journal of glaucoma, 10(3), 206-210.
  4. Krishnankutty, S. V., Sathish, G., Madhavan, P. K., & Narayani, V. (2019). A comparative analysis of ocular biometry in acute and chronic presentations of primary angle-closure glaucoma. Kerala Journal of Ophthalmology, 31(3), 212.
  5. Swati, R., & Shivaprasad, R. (2016). Comparative study of ocular biometry in primary angle closure suspect, primary angle closure glaucoma and normal subjects. Indian Journal of Clinical and Experimental Ophthalmology, 2(1), 9-13.
  6. 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.
  7. George, R., Paul, P. G., Baskaran, M., Ramesh, S. V., Raju, P., Arvind, H., … & Vijaya, L. (2003). Ocular biometry in occludable angles and angle closure glaucoma: a population-based survey. British Journal of Ophthalmology, 87(4), 399-402.
  8. Sihota, R., Gupta, V., Agarwal, H. C., Pandey, R. M., & Deepak, K. K. (2000). Comparison of symptomatic and asymptomatic, chronic, primary angle-closure glaucoma, open-angle glaucoma, and controls. Journal of glaucoma, 9(3), 208-213.
  9. Liu, S. A., Zhao, Z. N., Sun, N. N., Han, Y., Chen, J., & Fan, Z. G. (2018). Transitions of the understanding and definition of primary glaucoma. Chinese Medical Journal, 131(23), 2852.

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