The relationship between myopia and conjunctival scleral geometry

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Special to Ophthalmology schedules®

Myopia is the most common refractive error of the eye, affecting substantial proportions of adult populations; in a UK study, it was found to affect 49% of adults.1

The exponential increase in the prevalence of the disease is prompting an increased interest in the geometric properties of conjunctival-scleral tissue.

Generally called myopia, myopia is an ametropia characterized by an eye too long for its optical system (cornea and lens).

In recent years, the sharp increase in the prevalence of myopia in the juvenile population has generated growing concern, which has increased the need for research and development of new techniques to control axial lengthening of the eye.

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Since in vitro and post mortem studies in humans have shown that the sclera is more extensible in high myopic than in emmetropic patients, and that the weakening of the scleral structure is related to the lengthening of the eye , in vivo examination of the geometric properties of the anterior sclera in eyes with different levels of myopia may improve our understanding of variations in anterior ocular properties associated with an increase in ocular length.2-4

The risk of suffering from diseases such as glaucoma or maculopathies increases very significantly with the increase in myopia.

Therefore, it is important to understand the weakening procedure that takes place in the sclera, leading to progressive lengthening of the eye, and to see if this process also generates changes in the anterior part of the structure (covered by conjunctiva), which can be measured clinically.

In this way, geometric factors at the sclera level could predict which cases are most sensitive to scleral changes.

Considering the existing technology for the clinical evaluation of corneascleral geometry,5 as well as the comparison and validation of the main technologies applied in the clinic,6.7 profilometry of the Fourier domain (Eye Surface Profiler [ESP], Eaglet-Eye) stands out as a reasonable way to study the relationship between myopia and corneoscleral geometry.

Related: Exploring Possibilities For Myopia Prevention and Control in the United States

Nasotemporal sagittal asymmetry of height a good biomarker of myopia

Measurement with this device is minimally invasive and quickly captures all the data needed to characterize such geometry with high levels of precision.7

Nasotemporal sagittal asymmetry of height a good biomarker of myopia

We recently carried out a prospective study to analyze the relationship between the corneoscleral geometry, measured with this type of technology, and the axial length of the eye, by defining the differential aspects existing in myopic eyes and by developing models of prediction of the axial length of the eye. based on clinical data.8


Our study

A total of 64 eyes from 32 healthy participants (mean age 33) were evaluated at the Optometry Clinic at the University of Alicante, Spain, including a full anterior segment analysis, visual function analysis and an evaluation of the corneoscleral topographic profile with the ESP system.

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The study methods adhered to the principles of the Declaration of Helsinki and were approved by the ethics committee of the University of Alicante (Exp UA-2019-08-28).

A statistically significant and moderate to strong negative association was found between axial length and the difference between temporal and nasal sagittal heights for different chord lengths (from r = -0.701; P r = -0.502; P

This suggests that nasotemporal sagittal height asymmetry has potential as a biomarker of myopic changes.

It is possible that the decrease in nasotemporal asymmetry of sagittal height in myopic eyes is due to different insertion of the medial rectus muscle and the lateral rectus muscle.9 combined with the significantly lower stiffness of the sclera in such eyes.2,10,11

Specifically, there is a rearward displacement of the insertion site of the medial and lateral rectus muscles in myopic eyes,12 with rotation of the eyeball around the same nasal point and anterior to its geometric center regardless of the axial length of the eye.13

Related: Assessment of Scleral Biomechanics to Identify the Root of Accommodation

Multiple linear regression analysis showed that axial length could be predicted with acceptable levels of precision by means of a linear equation relating refractive, corneal and corneoscleral variables, although the variables involved for the prediction appear to differ in right and left eyes. .

Specifically, the following linear equations for predicting axial length (AL) were obtained:

  • Right eye (P
  • Left eye (P

The slight difference between the linear models used to predict axial length from the anterior segment parameters for the right and left eyes may be related to differences in the eyeball between the eyes:

It has been shown that the axial length asymmetry between them increases with increasing axial length.14

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These models should be considered as a preliminary approach that provides information on the potential value of anterior sclera geometry for the prediction of axial length.

Future studies should validate and refine these models in large samples including subjects of different ethnicities.


Conclusion

Analysis of the relationship between the corneoscleral geometry measured by profilometry of the Fourier domain and the axial length of the eye has shown that nasotemporal asymmetry of sagittal height may be a good biomarker of myopic changes.

Further studies are needed to clarify this question as well as to determine how these corneoscleral parameters change during the progression of myopia.

About the authors

David P. Piñero, PhD
E: [email protected]
Bataille and Molina-Martín are post-doctoral researchers in the Optics and Visual Perception Group of the Department of Optics, Pharmacology and Anatomy at the University of Alicante, Spain. Piñero is Principal Investigator and Lecturer of the same group and is responsible for the Advanced Optometry Unit of the Ophthalmology Department of the Vithas Medimar International Hospital, Alicante, Spain.

The authors have no proprietary or commercial interest in the medical devices mentioned in this manuscript.

The references
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2. McBrien NA, Jobling AI, Gentle A. Biomechanics of the sclera in myopia: extracellular and cellular factors. Optom Vis Sci. 2009; 86 (1): E23-E30. doi: 10.1097 / OPX.0b013e3181940669

3. Backhouse S, Gentle A. Scleral remodeling in myopia and its manipulation: a review of recent advances in scleral strengthening and control of myopia. Ann eye sci. 2018; 3: 1

4. Vurgese S, Panda-Jonas S, Jonas JB. Scleral thickness in human eyes. PLoS One. 2012; 7 (1): e29692. doi: 10.1371 / journal.pone.0029692

5. Battle L, Piñero DP. Characterization of the geometric properties of the sclero-conjunctival structure: a review. Int J Ophthalmol. 2020; 13: 1484-1492

6. Battle L, Molina-Martin A, Piñero DP. VScomparative analysis of two methods of clinical diagnosis of corneoscleral geometry. Eye contact lens. 2021; 47 (10): 546-551. doi: 10.1097 / ICL.00000000000000785

7. Battle L, Molina-Martin A, Piñero DP. Intrasession repeatability of corneal, limbal and scleral measurements obtained with a Fourier transform profilometer. Anterior Eye Cont lens. 2021; 44 (5): 101382. doi: 10.1016 / j.clae.2020.11.002

8. Battle L, Molina-Martín A, Piñero DP. Relationship between axial length and corneascleral topography: a preliminary study. Diagnosis (Basel). 2021; 1 (3): 542. doi: 10.3390 / diagnostics11030542

9. Haładaj R. Normal anatomy and abnormalities of the right extraocular muscles in humans: a review of recent data and findings. Biomed Res Int. December 30, 2019. DOI:10.1155 / 2019/8909162

10. McBrien NA, Gentle A. Role of the sclera in the development and pathological complications of myopia. Prog Retin Eye Res. 2003; 22: 307-338

11. McMonnies CW. An examination of the relationship between intraocular pressure, fundal stretching and myopic pathology. Clin Exp Opt. 2016; 99 (2): 113-119. doi: 10.1111 / cxo.12302

12. El-Fayoumi D, Bahgat N, Khafagy M, et al. Extraocular muscle insertion site horizontal to axial length using OCT of the anterior segment with a scanned source. Clin Ophthalmol. 2020; 14: 3583-3589

13. Clark RA, Demer JL. The effect of axial length on extraocular muscle lever. Am J Ophthalmol. 2020; 216: 186-192. doi: 10.1016 / j.ajo.2020.03.033

14. Rajan MS, Bunce C, Tuft S. Age-related interocular axial length difference and cataract. J Refractory cataract surgery. 2008; 34 (1): 76-79. doi: 10.1016 / j.jcrs.2007.08.023


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