Abstract
Purpose:
The aim of the study is to correlate between axial length of the eyeball and fundus changes and to know its importance.
Materials and Methods:
It was an observational study conducted for a duration of 1 year in patients with myopia more than 1 D and axial length more than 24 mm. A total of 100 eyes were included in the study and all underwent thorough fundus examination. The findings were documented using retinal maps and fundus camera photography. Data were analyzed for statistical significance using Chi-square or categorical data.
Results:
The study showed five posterior fundus changes and three peripheral fundus changes to be frequently associated with axial myopia. The five posterior fundus changes were optic disc crescents, Fuchs spot, lacquer cracks, posterior staphyloma, and chorioretinal atrophy. The three peripheral fundus changes were the area of white without pressure, lattice, and retinal breaks. Four of these lesions, i.e., crescents, posterior staphyloma, chorioretinal atrophy, and white without pressure, were found to be very highly significant with increasing axial length.
Conclusion:
Our study confirmed that there was a statistical significance in fundus changes with relation to axial length.
KEYWORDS: Axial Length, Myopic Fundus, Peripheral Retinal Degenerations, Correlation
INTRODUCTION
Pathological myopia, also known as degenerative myopia, is a type of myopia with degenerative changes. The axial length will be more than 26 mm or dioptric power of the eye more than −6 D. Visual disabilities due to degenerative myopia are numerous, and their incidence is related to the degree of myopia. It has been assumed that as the globe increases in size, there is thinning and stretching of the sclera resulting in fundus changes. However, the exact mechanism for fundus changes has not been clearly elucidated.[1,2,3]
With the availability of the ultrasound method, a large-scale study to statistically determine the relation between the axial length and fundus changes was possible. Many studies postulated that both axial elongation and myopic fundus changes were the phenotypic expression of genes responsible for myopia, and in some eyes, the expression was incomplete, with only fundus changes expressed, while in other eyes, both axial elongation and fundus changes were expressed.[4]
In the present study that I have undertaken, an attempt has been made to study the changes in the fundus of the high myopic eye and to correlate these changes with the axial length of the globe.
MATERIALS AND METHODS
The aims of the present study are to evaluate the fundus changes in high axial myopia and to correlate these fundus changes with the axial length of the globe.
The clinical material in this investigation consisted of patients attending the ophthalmology department for 1 year. Data were collected from 54 patients selected by purposive sampling who were diagnosed to have axial myopia unilateral or bilateral. The selection criteria were patients having a refractive status of −1 D or more with an axial length of 24 mm or more, and patients between 10 and 40 years were selected.
The exclusion criteria were patients with media opacities preventing direct ophthalmoscopic examination and other types of myopia such as index myopia, curvature myopia, or positional myopia.
A total of 100 eyes of 54 patients were included after satisfying the selection. All patients were subjected to a detailed examination after taking valid consent. The ethical clearance was obtained from the institution.
The examination was conducted in the following manner vision (unaided), improvement with a pinhole, best-corrected visual acuity (retinoscopy and subjective correction), anterior segment examination, axial length measurements, keratometry, fundus examination by direct ophthalmoscope and binocular indirect ophthalmoscope, slit-lamp biomicroscope, fundus photography, and B-Scan ultrasonography when required.
The findings were documented using retinal maps and fundus camera photography.
Instruments used were Haag-Streit 900 slit lamp, binocular indirect ophthalmoscope, Bausch and Lomb keratometer, axial length scanner, B-scan ultrasound, and fundus camera.
Data were analyzed for statistical significance using Chi-square for categorical data. The results were expressed in the form of frequency, frequency tables, and graphs.
RESULTS
The results have been arranged into two parts: posterior fundus changes and peripheral fundus changes.
Five posterior fundus changes were:
Crescent: The incidence of crescent formation demonstrated a steady rise from 10.34% in the range of axial length <24.5 mm to 100% in all eyes of the average axial length of 29 mm and above. The regression coefficient for the prevalence of crescent in eyes with increasing axial length demonstrated a high significance (P < 0.01). As the axial length increased, the tendency toward annular crescent formation increased. All crescents, regardless of position, tended to be larger in size as the axial length of the globe increased [Figure 1]
Fuchs spot: A rounded, black area of variable diameter at the macula occurred in a total of 3 eyes of 28.5 mm or more axial length. This represents an incidence of 3% in such eyes. The regression coefficient for the incidence of the Fuchs spot, in myopic eyes, showed no statistical significance in relation to the axial length [Figure 2]
Lacquer cracks: Yellow, white lines of variable orientation and diameters were seen at the posterior pole in three eyes of 27.5 mm axial length and more. Like the Fuchs spot, it has an erratic prevalence level at increased axial lengths so that a relationship with axial length could not be demonstrated [Figure 3]
Posterior staphyloma: 14% of the myopic eyes had posterior staphyloma in which the axial length was 27.5mm. They were seen more frequently in females (ratio of 2:1). They were bilateral in 4 of 10 cases (40%). The regression coefficient for the incidence of staphyloma in correlation with increasing axial length was highly significant (P < 0.01) [Figure 4]
Chorioretinal atrophy: The regression coefficient for the incidence of chorioretinal atrophy in eyes above 24 mm is found to be highly significant [P < 0.01, Figure 5].
Figure 1.
Temporal crescent
Figure 2.
Fuchs spot near the macular area
Figure 3.
Linear Grade 1 lacquer crack at the macula
Figure 4.
B-scan of posterior staphyloma
Figure 5.
Chorioretinal atrophy
Three peripheral retina findings are:
White without pressure: There were 25 eyes, which showed white without pressure in this study (25%), with eyes <24.4 mm showing a prevalence of 6.89 and rising to about 60% at the 30.5 mm axial length. The statistical significance of white without pressure with increasing axial length was found to be highly significant (P < 0.01)
Lattice degeneration: In this study, nine eyes showed areas of lattice. The prevalence was 9%. Its prevalence increased from 0 at the shortest axial length to 20% at the longer axial length of 30.5 mm. It was seen to be unilateral in 80% of the eyes, and it was seen to affect females more often in the ratio 5:4. The statistical analysis shows no significance between lattice and increasing axial length
Retinal holes: Four eyes in this study had retinal breaks. All the four retinal breaks were round holes with no operculum seen. Three of 4 eyes had holes in the inferotemporal quadrant and one eye had a hole inferiorly. There was no significant correlation between the frequency of holes and the increasing axial length of the eye.
DISCUSSION
The study showed a highly significant correlation of four lesions which included crescents, posterior staphyloma, chorioretinal atrophy, and white without pressure with increasing axial length. However, no correlation between Fuchs spot, lacquer crack, lattice, and retinal breaks with increasing axial length.
The close association of crescent formation with increasing axial diameters of the globe found in this investigation agrees with other studies, especially Curtin and Karlin. Yasuzumi et al.[5,6,7] In this study, the most common type of crescent was the temporal crescent (66%), followed by annular (21%), inferotemporal (5%), nasal (3%), inferior (1.3%), and superonasal (1.3%). This is in close agreement with the study of Curtin and Karlin,[5] who found that the more common crescent was the temporal crescent (62%), followed by annular (25%), nasal (3%), inferior (2.7%), and inferotemporal (2.2%). No sex preponderance was noted in this study (1:1). Curtin demonstrated an incidence of 5.2% in eyes >26.5 mm.
Also the study by Fried et al.,[8] showed a female-to-male ratio of 2:1. Hotchkiss and Fine[9] showed a ratio of 3:2. The correlation between Fuchs spot and increasing axial length is not as accurate with other myopic fundus changes, and no statistical significance could be demonstrated between the two. This may be due to the fact that this lesion changes in morphology with time to the extent that it can become unrecognizable as an ophthalmoscopic entity.
The incidence of lacquer crack's in this study was 3%, which is slightly lower than Curtin's study of 4.3%. The study of Klein on lacquer crack also showed a prevalence of 4.3%. The study of Curtin showed that males were more affected in the ratio of 2:1. While in the study of Klein et al.,[10] females had a slightly higher incidence. Like the pigment spot, it has an erratic prevalence level at increased axial diameters so that no statistical significance with increasing axial length could be demonstrated.
Posterior staphyloma showed a very high correlation with increasing axial length and was found in 14% of the studied eyes. Curtin and Karlin study[5] has shown the prevalence of posterior staphyloma to be 19%, while Otto recorded five staphylomas among 355 myopic eyes (16%). He found that all patients with myopia of 20 D or more demonstrated his lesion. The regression coefficient for the incidence of staphyloma with increasing axial length was highly significant.
This study shows a very highly significant correlation of increasing axial length with the incidence of chorioretinal atrophy. Other studies like Curtin have also shown a high correlation of increasing axial length with chorioretinal atrophy. In this study, 16% of all eyes above 24 mm demonstrated this lesion. Jain and Singh[11] showed a prevalence of 7.1%, while Blach RK found a prevalence of 38% in a highly myopic population. The higher prevalence observed by Blach was due to the higher number of patients in the older age group in his study. Sattler H has demonstrated that the incidence of chorioretinal atrophy increases with increasing age.
This study also shows a very highly significant correlation between increasing axial length with the incidence of white-without pressure. The incidence of white-without pressure in this study was 25%, while other studies have shown an incidence ranging from 20% to 35%. DB Karlin showed that these lesions affected 35% of the myopic population below 40 years and only 9.5% myopic population above 40 years and he postulated that this reduction was due to change tar occurring in the lesions with time.
The prevalence of lattice in this study was 9%, which is higher than the study of Karlin, who showed a prevalence of 6.1%. in case of study done by Manoj Shukla and OP Ahuja[12] they recorded a prevalence of 8.7% similar to our study. Hyams and Neumann[13] showed a prevalence of 7% in asymptomatic eyes. However our study didn't show a statistical correlation between increasing axial lengths and presence of lattice degeneration.
Retinal breaks are the other peripheral lesion seen frequently in myopes. Karlin found retinal breaks in 3% of the eyes measuring between 22 and 25 mm, and above this level, 11% of the eyes were involved. Norton et al. found 83% and Kanski found 71% of the patients with giant retinal to be myopic. This study did not show a statistical correlation between increasing axial lengths and retinal holes.
Although this study demonstrates a strong correlation between increasing axial length of the eye and some findings of pathological myopic retina (biomechanical factor), however it does not rule out the possibility of other factor's (Abiotrophic factors). One such factor could be a genetic factor. Hanan Zauberman, in his study on unilateral high myopia, suggested that genetic factors of both myopia and of fundus degeneration were expressed in one eye, only the degenerative component expressed itself in the fellow, nearly emmetropic eye. The other abiotrophic factor could be the reduction of blood flow in high myopia, as shown by Shimada. et a1.[14] in their study on retinal vessel diameter and blood velocity in high myopia using laser Doppler velocimetry. Another factor could be developmental derangement of the RPE, as shown by Takeo Iwamoto.[15]
CONCLUSION
The pathophysiology of fundus lesions is multifactorial. Both biomechanical and abiotrophic factors play an important role in the production of the different lesions found in pathological myopia. This study demonstrates the possible share of biomechanical factors acting on the myopic fundus, especially the crescent, chorioretinal atrophy, and white without pressure. This study does not demonstrate a correlation between lacquer cracks, lattices, and holes with axial length. This could be due to the effect of abiotrophic factors as an important factor in producing these lesions. Even though there was a significant correlation between posterior staphyloma and increasing axial length, the effect of biomechanics on this lesion cannot be concluded. Other studies have indicated abiotrophic factors responsible for posterior staphyloma and that the increase in axial length could be the result of the posterior staphyloma than the other way round.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
REFERENCES
- 1.Flitcroft I, He M, Jonas J, Jong M, Naidoo K, Ohno-Matsui K, et al. IMI – Defining and classifying myopia: A proposed set of standards for clinical and epidemiologic studies. Invest Opthalmol Vis Sci. 2019;60:M20–30. doi: 10.1167/iovs.18-25957. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Curtin BJ. 1st ed. Philadelphia: Harper and Row Publishers; 1985. The Myopias. [Google Scholar]
- 3.Ohno-Matsui K, Wu PC, Yamashiro K, Vutipongsatorn K, Fang Y, Cheung CM, et al. IMI pathologic myopia. Invest Ophthalmol Vis Sci. 2021;62:5. doi: 10.1167/iovs.62.5.5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Zauberman H, Merin S. Unilateral high myopia with bilateral fundus changes. Am J Ophthalmol. 1969;67:756–9. doi: 10.1016/s0002-9394(69)91004-6. [DOI] [PubMed] [Google Scholar]
- 5.Curtin BJ, Karlin DB. Axial length measurements and fundus changes of the myopic eye. Am J Ophthalmol. 1971;71:42–53. doi: 10.1016/0002-9394(71)91092-0. [DOI] [PubMed] [Google Scholar]
- 6.Karlin DB, Curtin BJ. Peripheral chorioretinal lesions and axial length of the myopic eye. Am J Ophthalmol. 1976;81:625–35. doi: 10.1016/0002-9394(76)90129-x. [DOI] [PubMed] [Google Scholar]
- 7.Yasuzumi K, Ohno-Matsui K, Yoshida T, Kojima A, Shimada N, Futagami S, et al. Peripapillary crescent enlargement in highly myopic eyes evaluated by flourescein and indocyanine green angiography. Br J Ophthalmol. 2003;87:1088–90. doi: 10.1136/bjo.87.9.1088. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Fried M, Siebert A, Meyer-Schwickerath G, A Wessing. A natural history of Fuchs' spot: a long term follow-up study. Doc Ophthalmol. 1981;28:215–21. [Google Scholar]
- 9.Hotchkiss ML, Fine SL. Pathological high myopia and choroidal neovascularization. Am J Ophthalmol. 1981;91:177. doi: 10.1016/0002-9394(81)90170-7. [DOI] [PubMed] [Google Scholar]
- 10.Klein RM, Curtin BJ. Lacquer crack lesion in pathological high myopia. Am J Ophthalmol. 1975;79:386. doi: 10.1016/0002-9394(75)90611-x. [DOI] [PubMed] [Google Scholar]
- 11.Jain IS, Singh K. A clinical study of high myopia. Orient Arch Opthalmol. 1967;5:76. [Google Scholar]
- 12.Shukla M, Ahuja OP. Peripheral retina in myopia. Indian journal of ophthalmology. 1983;31:719. [PubMed] [Google Scholar]
- 13.Hyams SW, Neumann E. Peripheral retina in myopia. With particular reference to retinal breaks. Br J Ophthalmol. 1969;53:300–6. doi: 10.1136/bjo.53.5.300. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Shimada N, Ohno-Matsui K, Harino S, Yoshida T, Yasuzumi K, Kojima A, et al. Reduction of retinal blood flow in high myopia. Graefes Arch Clin Exp Ophthalmol. 2004;242:284–8. doi: 10.1007/s00417-003-0836-0. [DOI] [PubMed] [Google Scholar]
- 15.Iwamoto T, Curtin BJ. Normal and staphylomatous sclera of high myopia. Arch Ophthalmol. 1979;97:912–5. doi: 10.1001/archopht.1979.01020010470017. [DOI] [PubMed] [Google Scholar]