Arrested Corneal Flattening and Low Astigmatism as Stable Trends Over Decades in Danish Ex-preterms

Hajer Ahmad Al-Abaiji^1,2*, Carina Slidsborg², Regitze Bangsgaard², Morten Dornonville de La Cour^1,2, Hans Callø Fledelius²

¹Department of Ophthalmology, Rigshospitalet-Glostrup, Glostrup, Denmark
²Department of Ophthalmology, Rigshospitalet-Blegdamsvej, Copenhagen, Denmark

*Correspondence author: Hajer Ahmad Al-Abaiji, Department of Ophthalmology, Rigshospitalet-Glostrup, Valdemar Hansens vej 1-23, 2600 Glostrup, Denmark; Email: [email protected]

Citation: Al-Abaiji HA, et al. Arrested Corneal Flattening and Low Astigmatism as Stable Trends Over Decades in Danish Ex-preterms. Jour Clin Med Res. 2024;5(1):1-6. http://dx.doi.org/10.46889/JCMR.2024. 5106

Copyright^© 2024 by Al-Abaiji HA, et al. All rights reserved. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Table 2: As a continuation of Table 1, refraction and corneal parameters in our most recent Danish cohort, right eye data.

Figure 1: Scatterplots including all preterms showing significant correlation between corneal curvature radius and birth weight (left plot) unlike the condition for gestational age (right plot).

Discussion

Corneal Curvature Over Time in Danish Preterm Cohort Studies

In accord with previous Danish investigations, the recent 4-year cohort of PTs demonstrated a steeper curvature as the main corneal feature, the most peaked recordings particularly being associated with early laser treatment for advanced ROP [8,9]. In most PTs, this relative corneal myopization would be balanced inter al. by the shorter axial length and refractive distribution in PTs thus differed only marginally from FTs. Small PT outlier tails seemed to represent either restricted emmetropization (high plus) or myopia of prematurity.

A general and longstanding growth restriction in ex-PTs was first suggested after the advent of ultrasonic oculometry, as introduced in our Copenhagen PT 1959-61 cohort of 10-year-old PT survivors [2]. With relatively normal refractive and visual acuity findings, the eventual effects on axial length and corneal curvature radius as main findings came unexpected. The restrictions further seemed to hold more generally and not merely based on a small section of those considered the most preterm and vulnerable. Follow-up at age 18-19 years indicated that the growth-related restrictions were permanent. Longitudinally, as a group the preterm infants in our initial cohort thus never caught up [5,6].

We first tested the new ROP classification in a regional sample born between 1982 and 1984, a period where retinal cryo-ablation therapy for advanced ROP had not yet been introduced in Denmark. Four of the 28 with observed ROP had an irreversible course and acquired bilateral blindness [7]. In the remaining 24, reversible ROP stage 2 was the most advanced finding and new trends were not disclosed at the follow-up at age 7-10 years. Only the marginal subgroup with myopia of prematurity stood out, supporting the previous observations of shorter axial length and steeper cornea. In addition to a slightly lower best corrected visual acuity, they also presented a significantly thicker lens and a shallower anterior chamber [2,3,10]. In the literature, the likewise environmental foetal alcohol syndrome has presented with a less flattened cornea, although of no obvious relevance for our data [11].

Astigmatism In the Danish Preterm Cohort Series

Besides the steeper cornea, the Danish cohort studies emphasized that astigmatism remained of low order. The childhood CA distribution thus appeared close to normal and with only a minimum contribution to the predominance of ametropia that is usually recorded in preterm follow-up series. In about 85%-cylinder values did not exceed 1 D.

Summarizing the cohort-based Danish results over time, both corneal parameters appeared uniform, so far from the variability shown in posterior segment findings. A general growth restriction was suggested, primarily manifesting as a reduced early postnatal physiological flattening of the central cornea. Allover refractive distributions came close to those of normal childhood, although with small tails of disturbed development as just mentioned. As added to the eventual astigmantism of low order, only regressed ROP after treatment of advanced disease had cases of significantly higher astigmatism and only here to suggest an impact on the apparent robustness of the cornea due to increased vulnerability in a sensitive perinatal phase of development.

Studies From Elsewhere

Swedish PT population studies over 3 decades are in keeping with the Danish childhood levels of predominantly quite low astigmatism and benign visual outcomes were also similar [12]. Further, studies from Israel, Ireland, the United Kingdom and recently also from Germany, have reported similar findings. Corneal astigmatism has generally been recorded below a cylinder value of −1 D [13-15].

In marked contrast, advanced early ROP cases from elsewhere have been reported as having high cylinder values in various childhood PT series. In particular, this held for the US cryoROP multicenter studies from 1988 and onwards, which prospectively followed threshold ROP cases (BW <1251 g), with or without cryotherapy performed neonatally [16,17]. Irrespective of intervention, a high prevalence of significant permanent astigmatism was recorded and often on line with myopia of prematurity and macular scarring. High astigmatism was also reported in Chinese studies [18,19]. Except for ethnicity (Caucasian versus Asian or mixed in the US) and the vague socio-economic concept of general health (Scandinavian welfare models), we have no valid suggestions for the differences in response as here quoted.

As indicated already, the overall corneal trends under study cannot alone be explained by elective PT minorities. This would have set other marks on the descriptive statistics. In lack of a more specific pathogenesis, the results are best explained as broadly pertaining to the PT state as such, more than to its degree. Similar suggestions found support from Fiess and coworkers based on Caucasian ex-PT adults in Germany, regarding eventual thickness of central cornea and peripapillary nerve fiber layer [20].

Conclusion

In summary, whereas corneal steepening is commonplace, corneal astigmatism has only a small place in most western PT follow-up studies. Stable corneal trends have been suggested and significant astigmatism seems to occur mainly in relation to exceptional ROP (stage 3+). As further inversely deduced from the predominating mild courses mainly encountered, corneal responses have overruled only in tougher cases. Overall, the increased eye morbidity so convincingly documented among surviving small premature individuals includes ametropias in general and still warrants ophthalmic attention during at least the preschool years.

Conflict of Interests

The authors declare that they have no conflicts of interest.

Acknowledgement

Our appreciation to Lorna O’Brien from www.authorserv.com for proofreading the manuscript.

Financial Disclosure

The corresponding author had financial support from Synoptik-Fonden for the research, the authorship and the publication of this article.

Patient Consent

Informed consent for examination and for publishing anonymized data were obtained from the parents to the participating children.

Data Availability

Delivery and perinatal data were from the National Patient Register, after approval by the Danish Data Protection Agency and the Central Committees on Health Research Ethics. The study respected the World Association Declaration of Helsinki.

Author’s Contribution

All authors took part in data acquisition, study design and final accept of the manuscript. HAA and HCF were further responsible for the analyses added to those previously published and to writing the article, the latter to include professional UK language revision.

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